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Polymers, Volume 8, Issue 8 (August 2016)

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Cover Story (view full-size image) The cover image visualizes a method to determine the strength of the proximity effect in [...] Read more.
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Open AccessCommunication
Hedgehog Buckyball: A High-Symmetry Complete Polyhedral Oligomeric Silsesquioxane (POSS)
Polymers 2016, 8(8), 315; https://doi.org/10.3390/polym8080315
Received: 19 July 2016 / Revised: 9 August 2016 / Accepted: 16 August 2016 / Published: 22 August 2016
Cited by 3 | Viewed by 1667 | PDF Full-text (3542 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this study, we report UV-MALDI-TOF MS evidence of a fullerene-like silsesquioxane, a high-symmetry polyhedral oligomeric silsesquioxane (POSS or SSO) formulated as R60-Si60O90 or T60 (T = RSiO1.5). The T60 preparation can be performed [...] Read more.
In this study, we report UV-MALDI-TOF MS evidence of a fullerene-like silsesquioxane, a high-symmetry polyhedral oligomeric silsesquioxane (POSS or SSO) formulated as R60-Si60O90 or T60 (T = RSiO1.5). The T60 preparation can be performed using a normal hydrolytic condensation of [(3-methacryloxy)propyl]trimethoxysilane (MPMS) as an example. Theoretically, four 3sp3 hybrid orbitals (each containing an unpaired electron) of a Si atom are generated before the bond formation. Then it bonds to another four atom electrons using the four generated hybrid orbitals which produced a stable configuration. This fullerene-like silsesquioxane should exhibit much more functionality, activity and selectivity and is easier to assemble than the double bonds in a fullerene. Full article
(This article belongs to the Special Issue Conjugated Polymers 2016)
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Open AccessArticle
Silica Treatments: A Fire Retardant Strategy for Hemp Fabric/Epoxy Composites
Polymers 2016, 8(8), 313; https://doi.org/10.3390/polym8080313
Received: 6 July 2016 / Revised: 30 July 2016 / Accepted: 8 August 2016 / Published: 22 August 2016
Cited by 9 | Viewed by 3163 | PDF Full-text (8668 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, for the first time, inexpensive waterglass solutions are exploited as a new, simple and ecofriendly chemical approach for promoting the formation of a silica-based coating on hemp fabrics, able to act as a thermal shield and to protect the latter [...] Read more.
In this paper, for the first time, inexpensive waterglass solutions are exploited as a new, simple and ecofriendly chemical approach for promoting the formation of a silica-based coating on hemp fabrics, able to act as a thermal shield and to protect the latter from heat sources. Fourier Transform Infrared (FTIR) and solid-state Nuclear Magnetic Resonance (NMR) analysis confirm the formation of –C–O–Si– covalent bonds between the coating and the cellulosic substrate. The proposed waterglass treatment, which is resistant to washing, seems to be very effective for improving the fire behavior of hemp fabric/epoxy composites, also in combination with ammonium polyphosphate. In particular, the exploitation of hemp surface treatment and Ammonium Polyphosphate (APP) addition to epoxy favors a remarkable decrease of the Heat Release Rate (HRR), Total Heat Release (THR), Total Smoke Release (TSR) and Specific Extinction Area (SEA) (respectively by 83%, 35%, 45% and 44%) as compared to untreated hemp/epoxy composites, favoring the formation of a very stable char, as also assessed by Thermogravimetric Analysis (TGA). Because of the low interfacial adhesion between the fabrics and the epoxy matrix, the obtained composites show low strength and stiffness; however, the energy absorbed by the material is higher when using treated hemp. The presence of APP in the epoxy matrix does not affect the mechanical behavior of the composites. Full article
(This article belongs to the Special Issue Recent Advances in Flame Retardancy of Textile Related Products)
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Open AccessArticle
Chemo-Enzymatic Synthesis of Perfluoroalkyl-Functionalized Dendronized Polymers as Cyto-Compatible Nanocarriers for Drug Delivery Applications
Polymers 2016, 8(8), 311; https://doi.org/10.3390/polym8080311
Received: 14 July 2016 / Revised: 4 August 2016 / Accepted: 9 August 2016 / Published: 18 August 2016
Cited by 5 | Viewed by 1996 | PDF Full-text (4128 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Among amphiphilic polymers with diverse skeletons, fluorinated architectures have attracted significant attention due to their unique property of segregation and self-assembly into discrete supramolecular entities. Herein, we have synthesized amphiphilic copolymers by grafting hydrophobic alkyl/perfluoroalkyl chains and hydrophilic polyglycerol [G2.0] dendrons onto a [...] Read more.
Among amphiphilic polymers with diverse skeletons, fluorinated architectures have attracted significant attention due to their unique property of segregation and self-assembly into discrete supramolecular entities. Herein, we have synthesized amphiphilic copolymers by grafting hydrophobic alkyl/perfluoroalkyl chains and hydrophilic polyglycerol [G2.0] dendrons onto a co-polymer scaffold, which itself was prepared by enzymatic polymerization of poly[ethylene glycol bis(carboxymethyl) ether]diethylester and 2-azidopropan-1,3-diol. The resulting fluorinated polymers and their alkyl chain analogs were then compared in terms of their supramolecular aggregation behavior, solubilization capacity, transport potential, and release profile using curcumin and dexamethasone drugs. The study of the release profile of encapsulated curcumin incubated with/without a hydrolase enzyme Candida antarctica lipase (CAL-B) suggested that the drug is better stabilized in perfluoroalkyl chain grafted polymeric nanostructures in the absence of enzyme for up to 12 days as compared to its alkyl chain analogs. Although both the fluorinated as well as non-fluorinated systems showed up to 90% release of curcumin in 12 days when incubated with lipase, a comparatively faster release was observed in the fluorinated polymers. Cell viability of HeLa cells up to 95% in aqueous solution of fluorinated polymers (100 μg/mL) demonstrated their excellent cyto-compatibility. Full article
(This article belongs to the Special Issue Enzymatic Polymer Synthesis)
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Open AccessReview
Stimuli-Directed Helical Chirality Inversion and Bio-Applications
Polymers 2016, 8(8), 310; https://doi.org/10.3390/polym8080310
Received: 21 July 2016 / Revised: 9 August 2016 / Accepted: 12 August 2016 / Published: 18 August 2016
Cited by 9 | Viewed by 2620 | PDF Full-text (7230 KB) | HTML Full-text | XML Full-text
Abstract
Helical structure is a sophisticated ubiquitous motif found in nature, in artificial polymers, and in supramolecular assemblies from microscopic to macroscopic points of view. Significant progress has been made in the synthesis and structural elucidation of helical polymers, nevertheless, a new direction for [...] Read more.
Helical structure is a sophisticated ubiquitous motif found in nature, in artificial polymers, and in supramolecular assemblies from microscopic to macroscopic points of view. Significant progress has been made in the synthesis and structural elucidation of helical polymers, nevertheless, a new direction for helical polymeric materials, is how to design smart systems with controllable helical chirality, and further use them to develop chiral functional materials and promote their applications in biology, biochemistry, medicine, and nanotechnology fields. This review summarizes the recent progress in the development of high-performance systems with tunable helical chirality on receiving external stimuli and discusses advances in their applications as drug delivery vesicles, sensors, molecular switches, and liquid crystals. Challenges and opportunities in this emerging area are also presented in the conclusion. Full article
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Open AccessArticle
Molecularly Imprinted Polymers Based Electrochemical Sensor for 2,4-Dichlorophenol Determination
Polymers 2016, 8(8), 309; https://doi.org/10.3390/polym8080309
Received: 30 June 2016 / Revised: 7 August 2016 / Accepted: 12 August 2016 / Published: 18 August 2016
Cited by 5 | Viewed by 1728 | PDF Full-text (2073 KB) | HTML Full-text | XML Full-text
Abstract
A molecularly imprinted polymers based electrochemical sensor was fabricated by electropolymerizing pyrrole on a Fe3O4 nanoparticle modified glassy carbon electrode. The sensor showed highly catalytic ability for the oxidation of 2,4-dichlorophenol (2,4-DCP). Square wave voltammetry was used for the determination [...] Read more.
A molecularly imprinted polymers based electrochemical sensor was fabricated by electropolymerizing pyrrole on a Fe3O4 nanoparticle modified glassy carbon electrode. The sensor showed highly catalytic ability for the oxidation of 2,4-dichlorophenol (2,4-DCP). Square wave voltammetry was used for the determination of 2,4-DCP. The oxidation peak currents were proportional to the concentrations of 2,4-DCP in the range of 0.04 to 2.0 µM, with a detection limit of 0.01 µM. The proposed sensor was successfully applied for the determination of 2,4-DCP in water samples giving satisfactory recoveries. Full article
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Open AccessArticle
A Retrofit Theory to Prevent Fatigue Crack Initiation in Aging Riveted Bridges Using Carbon Fiber-Reinforced Polymer Materials
Polymers 2016, 8(8), 308; https://doi.org/10.3390/polym8080308
Received: 8 June 2016 / Revised: 25 July 2016 / Accepted: 11 August 2016 / Published: 18 August 2016
Cited by 14 | Viewed by 2381 | PDF Full-text (5772 KB) | HTML Full-text | XML Full-text
Abstract
Most research on fatigue strengthening of steel has focused on carbon fiber-reinforced polymer (CFRP) strengthening of steel members with existing cracks. However, in many practical cases, aging steel members do not yet have existing cracks but rather are nearing the end of their [...] Read more.
Most research on fatigue strengthening of steel has focused on carbon fiber-reinforced polymer (CFRP) strengthening of steel members with existing cracks. However, in many practical cases, aging steel members do not yet have existing cracks but rather are nearing the end of their designed fatigue life. Therefore, there is a need to develop a “proactive” retrofit solution that can prevent fatigue crack initiation in aging bridge members. Such a proactive retrofit approach can be applied to bridge members that have been identified to be deficient, based on structural standards, to enhance their safety margins by extending the design service life. This paper explains a proactive retrofit design approach based on constant life diagram (CLD) methodology. The CLD approach is a method that can take into account the combined effect of alternating and mean stress magnitudes to predict the high-cycle fatigue life of a material. To validate the retrofit model, a series of new fatigue tests on steel I-beams retrofitted by the non-prestressed un-bonded CFRP plates have been conducted. Furthermore, this paper attempts to provide a better understanding of the behavior of un-bonded retrofit (UR) and bonded retrofit (BR) systems. Retrofitting the steel beams using the UR system took less than half of the time that was needed for strengthening with the BR system. The results show that the non-prestressed un-bonded ultra-high modulus (UHM) CFRP plates can be effective in preventing fatigue crack initiation in steel members. Full article
(This article belongs to the Special Issue Selected Papers from “SMAR 2015”)
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Open AccessArticle
Influence of Carbon Nanotube Coatings on Carbon Fiber by Ultrasonically Assisted Electrophoretic Deposition on Its Composite Interfacial Property
Polymers 2016, 8(8), 302; https://doi.org/10.3390/polym8080302
Received: 7 June 2016 / Revised: 5 August 2016 / Accepted: 8 August 2016 / Published: 17 August 2016
Cited by 8 | Viewed by 2436 | PDF Full-text (4497 KB) | HTML Full-text | XML Full-text
Abstract
Carbon nanotube (CNT) coatings were utilized to enhance the interfacial properties of carbon fiber (CF)/epoxy(EP) composites by ultrasonically assisted electrophoretic deposition (EPD). A characterization of the CF surface properties was done before and after coating (surface chemistry, surface morphologies, and surface energy). The [...] Read more.
Carbon nanotube (CNT) coatings were utilized to enhance the interfacial properties of carbon fiber (CF)/epoxy(EP) composites by ultrasonically assisted electrophoretic deposition (EPD). A characterization of the CF surface properties was done before and after coating (surface chemistry, surface morphologies, and surface energy). The result shows that oxygenated groups concentrations of the CF surfaces experienced significant increases from 12.11% to 24.78%. Moreover, the uniform and homogeneous CNT films were tightly attached on the surface of CF, and the surface wettability of CF is significant improved by enhanced surface free energy when introduced ultrasonic during the EPD process. In addition, the interlaminar shear strength (ILSS) and water absorption of CF/EP composite were measured. Scanning electron microscopy (SEM) revealed that the fracture mechanisms of the new interface layer formed by depositing CNTs on the CF surface contributed to the enhancement of the mechanical performance of the epoxy. This means that the efficient method to improve interfacial performance of composites has shown great commercial application potential. Full article
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Open AccessEditorial
Interdisciplinary Approaches towards Materials with Enhanced Properties for Electrical Engineering
Polymers 2016, 8(8), 307; https://doi.org/10.3390/polym8080307
Received: 1 August 2016 / Accepted: 12 August 2016 / Published: 16 August 2016
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Abstract
The internationally growing demand for electrical energy is one of the most prominent triggers stimulating research these days.[...] Full article
Open AccessArticle
Protein-Repellence PES Membranes Using Bio-grafting of Ortho-aminophenol
Polymers 2016, 8(8), 306; https://doi.org/10.3390/polym8080306
Received: 3 July 2016 / Revised: 2 August 2016 / Accepted: 8 August 2016 / Published: 15 August 2016
Cited by 1 | Viewed by 1907 | PDF Full-text (10704 KB) | HTML Full-text | XML Full-text
Abstract
Surface modification becomes an effective tool for improvement of both flux and selectivity of membrane by reducing the adsorption of the components of the fluid used onto its surface. A successful green modification of poly(ethersulfone) (PES) membranes using ortho-aminophenol (2-AP) modifier and laccase [...] Read more.
Surface modification becomes an effective tool for improvement of both flux and selectivity of membrane by reducing the adsorption of the components of the fluid used onto its surface. A successful green modification of poly(ethersulfone) (PES) membranes using ortho-aminophenol (2-AP) modifier and laccase enzyme biocatalyst under very flexible conditions is presented in this paper. The modified PES membranes were evaluated using many techniques including total color change, pure water flux, and protein repellence that were related to the gravimetric grafting yield. In addition, static water contact angle on laminated PES layers were determined. Blank and modified commercial membranes (surface and cross-section) and laminated PES layers (surface) were imaged by scanning electron microscope (SEM) and scanning probe microscope (SPM) to illustrate the formed modifying poly(2-aminophenol) layer(s). This green modification resulted in an improvement of both membrane flux and protein repellence, up to 15.4% and 81.27%, respectively, relative to the blank membrane. Full article
(This article belongs to the Special Issue Enzymatic Polymer Synthesis)
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Open AccessArticle
Study of Polymer Matrix Degradation Behavior in CFRP Short Pulsed Laser Processing
Polymers 2016, 8(8), 299; https://doi.org/10.3390/polym8080299
Received: 26 June 2016 / Revised: 26 July 2016 / Accepted: 9 August 2016 / Published: 15 August 2016
Cited by 3 | Viewed by 1788 | PDF Full-text (2884 KB) | HTML Full-text | XML Full-text
Abstract
Short pulsed laser is preferred to avoid the thermal damage in processing the heat sensitive material, such as carbon fiber reinforced plastic (CFRP). In this paper, a numerical model capturing both the material ablation and polymer matrix pyrolysis processes in pulsed laser processing [...] Read more.
Short pulsed laser is preferred to avoid the thermal damage in processing the heat sensitive material, such as carbon fiber reinforced plastic (CFRP). In this paper, a numerical model capturing both the material ablation and polymer matrix pyrolysis processes in pulsed laser processing is established. The effect of laser pulse length from ns order to μs order is studied. It was found that with shorter pulse length, ablation depth is increased and heat affected zone is remarkably reduced. Moreover the pyrolysis gas transport analysis shows that shorter pulse length results in a larger internal pressure. At pulse length in ns order, maximum pressure as high as hundreds of times atmospheric pressure in CFRP could be produced and leads to mechanical erosion of material. The predicted ablation depth of a single short laser pulse conforms well to the experiment result of the CFRP laser milling experiment. Full article
(This article belongs to the Special Issue Polymeric Fibers)
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Open AccessFeature PaperArticle
Conformational Properties of Active Semiflexible Polymers
Polymers 2016, 8(8), 304; https://doi.org/10.3390/polym8080304
Received: 29 June 2016 / Revised: 3 August 2016 / Accepted: 4 August 2016 / Published: 12 August 2016
Cited by 19 | Viewed by 2142 | PDF Full-text (1044 KB) | HTML Full-text | XML Full-text
Abstract
The conformational properties of flexible and semiflexible polymers exposed to active noise are studied theoretically. The noise may originate from the interaction of the polymer with surrounding active (Brownian) particles or from the inherent motion of the polymer itself, which may be composed [...] Read more.
The conformational properties of flexible and semiflexible polymers exposed to active noise are studied theoretically. The noise may originate from the interaction of the polymer with surrounding active (Brownian) particles or from the inherent motion of the polymer itself, which may be composed of active Brownian particles. In the latter case, the respective monomers are independently propelled in directions changing diffusively. For the description of the polymer, we adopt the continuous Gaussian semiflexible polymer model. Specifically, the finite polymer extensibility is taken into account, which turns out to be essential for the polymer conformations. Our analytical calculations predict a strong dependence of the relaxation times on the activity. In particular, semiflexible polymers exhibit a crossover from a bending elasticity-dominated dynamics to the flexible polymer dynamics with increasing activity. This leads to a significant activity-induced polymer shrinkage over a large range of self-propulsion velocities. For large activities, the polymers swell and their extension becomes comparable to the contour length. The scaling properties of the mean square end-to-end distance with respect to the polymer length and monomer activity are discussed. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessCommunication
Stabilization of Inverse Miniemulsions by Silyl-Protected Homopolymers
Polymers 2016, 8(8), 303; https://doi.org/10.3390/polym8080303
Received: 24 May 2016 / Revised: 1 August 2016 / Accepted: 2 August 2016 / Published: 12 August 2016
Cited by 1 | Viewed by 1649 | PDF Full-text (3328 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Inverse (water-in-oil) miniemulsions are an important method to encapsulate hydrophilic payloads such as oligonucleotides or peptides. However, the stabilization of inverse miniemulsions usually requires block copolymers that are difficult to synthesize and/or cannot be easily removed after transfer from a hydrophobic continuous phase [...] Read more.
Inverse (water-in-oil) miniemulsions are an important method to encapsulate hydrophilic payloads such as oligonucleotides or peptides. However, the stabilization of inverse miniemulsions usually requires block copolymers that are difficult to synthesize and/or cannot be easily removed after transfer from a hydrophobic continuous phase to an aqueous continuous phase. We describe here a new strategy for the synthesis of a surfactant for inverse miniemulsions by radical addition–fragmentation chain transfer (RAFT) polymerization, which consists in a homopolymer with triisopropylsilyl protecting groups. The protecting groups ensure the efficient stabilization of the inverse (water-in-oil, w/o) miniemulsions. Nanocapsules can be formed and the protecting group can be subsequently cleaved for the re-dispersion of nanocapsules in an aqueous medium with a minimal amount of additional surfactant. Full article
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Open AccessArticle
Well-Defined Polypropylene/Polypropylene-Grafted Silica Nanocomposites: Roles of Number and Molecular Weight of Grafted Chains on Mechanistic Reinforcement
Polymers 2016, 8(8), 300; https://doi.org/10.3390/polym8080300
Received: 4 June 2016 / Revised: 22 July 2016 / Accepted: 9 August 2016 / Published: 12 August 2016
Cited by 10 | Viewed by 2196 | PDF Full-text (2911 KB) | HTML Full-text | XML Full-text
Abstract
Grafting terminally functionalized polypropylene (PP) to nanofillers provides well-defined PP-based nanocomposites plausibly featured with a physical cross-linkage structure. In this paper, a series of PP-grafted silica nanoparticles (PP-g-SiO2) were synthesized by varying the number of grafted chains per silica [...] Read more.
Grafting terminally functionalized polypropylene (PP) to nanofillers provides well-defined PP-based nanocomposites plausibly featured with a physical cross-linkage structure. In this paper, a series of PP-grafted silica nanoparticles (PP-g-SiO2) were synthesized by varying the number of grafted chains per silica particle, and influences of the number and the molecular weight of grafted chains were studied on physical properties of PP/PP-g-SiO2 nanocomposites. We found that only 20–30 chain/particle was sufficient to exploit benefits of the PP grafting for the nanoparticle dispersion, the nucleation, and the Young’s modulus. Meanwhile, the yield strength was sensitive to both of the number and the molecular weight of grafted PP: Grafting longer chains at a higher density led to greater reinforcement. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2016)
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Open AccessReview
Fiber Reinforced Polymer Strengthening of Structures by Near-Surface Mounting Method
Polymers 2016, 8(8), 298; https://doi.org/10.3390/polym8080298
Received: 17 June 2016 / Revised: 26 July 2016 / Accepted: 3 August 2016 / Published: 11 August 2016
Cited by 8 | Viewed by 2043 | PDF Full-text (705 KB) | HTML Full-text | XML Full-text
Abstract
This paper provides a critical review of recent studies on strengthening of reinforced concrete and unreinforced masonry (URM) structures by fiber reinforced polymers (FRP) through near-surface mounting (NSM) method. The use of NSM-FRP has been on the rise, mainly due to composite materials’ [...] Read more.
This paper provides a critical review of recent studies on strengthening of reinforced concrete and unreinforced masonry (URM) structures by fiber reinforced polymers (FRP) through near-surface mounting (NSM) method. The use of NSM-FRP has been on the rise, mainly due to composite materials’ high strength and stiffness, non-corrosive nature and ease of installation. Experimental investigations presented in this review have confirmed the benefits associated with NSM-FRP for flexural and shear strengthening of RC and URM structures. The use of prestressing and anchorage systems to further improve NSM-FRP strain utilization and changes in failure modes has also been presented. Bond behavior of NSM-FRP-concrete or masonry interface, which is a key factor in increasing the load capacity of RC and URM structures has been briefly explored. Presented studies related to the effect of temperature on the bond performance of NSM-FRP strengthened systems with various insulations and adhesive types, show better performance than externally bonded reinforcement (EBR) FRP retrofitting. In summary, the presented literature review provides an insight into the ongoing research on the use of NSM-FRP for strengthening of structural members and the trends for future research in this area. Full article
(This article belongs to the Special Issue Selected Papers from “SMAR 2015”)
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Open AccessArticle
Effect of Argon Plasma Treatment on Tribological Properties of UHMWPE/MWCNT Nanocomposites
Polymers 2016, 8(8), 295; https://doi.org/10.3390/polym8080295
Received: 13 June 2016 / Revised: 25 June 2016 / Accepted: 30 June 2016 / Published: 11 August 2016
Cited by 10 | Viewed by 2026 | PDF Full-text (5536 KB) | HTML Full-text | XML Full-text
Abstract
Ultra-high molecular weight polyethylene (UHMWPE) is widely used in artificial joints in the replacement of knee, hip and shoulder that has been impaired as a result of arthritis or other degenerative joint diseases. The UHMWPE made plastic cup is placed in the joint [...] Read more.
Ultra-high molecular weight polyethylene (UHMWPE) is widely used in artificial joints in the replacement of knee, hip and shoulder that has been impaired as a result of arthritis or other degenerative joint diseases. The UHMWPE made plastic cup is placed in the joint socket in contact with a metal or ceramic ball affixed to a metal stem. Effective reinforcement of multi-walled carbon nanotubes (MWCNTs) in UHMWPE results in improved mechanical and tribological properties. The hydrophobic nature of the nanocomposites surface results in lesser contact with biological fluids during the physiological interaction. In this project, we investigate the UHMWPE/MWCNTs nanocomposites reinforced with MWCNTs at different concentrations. The samples were treated with cold argon plasma at different exposure times. The water contact angles for 60 min plasma-treated nanocomposites with 0.0, 0.5, 1.0, 1.5, and 2.0 wt % MWCNTs were found to be 55.65°, 52.51°, 48.01°, 43.72°, and 37.18° respectively. Increasing the treatment time of nanocomposites has shown transformation from a hydrophobic to a hydrophilic nature due to carboxyl groups being bonded on the surface for treated nanocomposites. Wear analysis was performed under dry, and also under biological lubrication, conditions of all treated samples. The wear factor of untreated pure UHMWPE sample was reduced by 68% and 80%, under dry and lubricated conditions, respectively, as compared to 2 wt % 60 min-treated sample. The kinetic friction co-efficient was also noted under both conditions. The hardness of nanocomposites increased with both MWCNTs loading and plasma treatment time. Similarly, the surface roughness of the nanocomposites was reduced. Full article
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Open AccessFeature PaperArticle
Spatio-Temporal Proximity Characteristics in 3D μ-Printing via Multi-Photon Absorption
Polymers 2016, 8(8), 297; https://doi.org/10.3390/polym8080297
Received: 15 June 2016 / Revised: 29 July 2016 / Accepted: 3 August 2016 / Published: 10 August 2016
Cited by 7 | Viewed by 1913 | PDF Full-text (2374 KB) | HTML Full-text | XML Full-text
Abstract
One of the major challenges in high-resolution μ-printing is the cross-talk between features written in close proximity—the proximity effect. This effect prevents, e.g., gratings with periods below a few hundred nanometers. Surprisingly, the dependence of this effect on space and time has not [...] Read more.
One of the major challenges in high-resolution μ-printing is the cross-talk between features written in close proximity—the proximity effect. This effect prevents, e.g., gratings with periods below a few hundred nanometers. Surprisingly, the dependence of this effect on space and time has not thoroughly been investigated. Here, we present a spatial-light-modulator based method to dynamically measure the strength of the proximity effect on length and timescales typical to μ-printing. The proximity strength is compared in various photo resists. The results indicate that molecular diffusion strongly contributes to the proximity effect. Full article
(This article belongs to the Special Issue Three-Dimensional Structures: Fabrication and Application)
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Open AccessFeature PaperReview
Semiflexible Polymers in the Bulk and Confined by Planar Walls
Polymers 2016, 8(8), 296; https://doi.org/10.3390/polym8080296
Received: 23 June 2016 / Revised: 27 July 2016 / Accepted: 29 July 2016 / Published: 10 August 2016
Cited by 9 | Viewed by 1582 | PDF Full-text (1771 KB) | HTML Full-text | XML Full-text
Abstract
Semiflexible polymers in solution under good solvent conditions can undergo an isotropic-nematic transition. This transition is reminiscent of the well-known entropically-driven transition of hard rods described by Onsager’s theory, but the flexibility of the macromolecules causes specific differences in behavior, such as anomalous [...] Read more.
Semiflexible polymers in solution under good solvent conditions can undergo an isotropic-nematic transition. This transition is reminiscent of the well-known entropically-driven transition of hard rods described by Onsager’s theory, but the flexibility of the macromolecules causes specific differences in behavior, such as anomalous long wavelength fluctuations in the ordered phase, which can be understood by the concept of the deflection length. A brief review of the recent progress in the understanding of these problems is given, summarizing results obtained by large-scale molecular dynamics simulations and density functional theory. These results include also the interaction of semiflexible polymers with hard walls and the wall-induced nematic order, which can give rise to capillary nematization in thin film geometry. Various earlier theoretical approaches to these problems are briefly mentioned, and an outlook on the status of experiments is given. It is argued that in many cases of interest, it is not possible to describe the scaled densities at the isotropic-nematic transition as functions of the ratio of the contour length and the persistence length alone, but the dependence on the ratio of chain diameter and persistence length also needs to be considered. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessArticle
Optimized Synthesis According to One-Step Process of a Biobased Thermoplastic Polyacetal Derived from Isosorbide
Polymers 2016, 8(8), 294; https://doi.org/10.3390/polym8080294
Received: 7 June 2016 / Revised: 29 July 2016 / Accepted: 4 August 2016 / Published: 10 August 2016
Cited by 3 | Viewed by 2444 | PDF Full-text (6759 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes both the synthesis and characterization of a biobased and non-aromatic polyacetal produced from the reaction between isosorbide and methylene chloride. The reaction was conducted in an aprotic dipolar and harmless solvent using a one-step, fast and economical procedure. The chemical [...] Read more.
This paper describes both the synthesis and characterization of a biobased and non-aromatic polyacetal produced from the reaction between isosorbide and methylene chloride. The reaction was conducted in an aprotic dipolar and harmless solvent using a one-step, fast and economical procedure. The chemical composition of this polymer was investigated using Nuclear Magnetic Resonance and Fourier Transform Infra-Red spectroscopies. The molecular weights were examined by size exclusion chromatography and MALDI-TOF spectrometry. The synthesis conditions (concentration, mixing speed, solvent nature, stoichiometry, addition mode of one reactan) were found to strongly influence both polymer architecture and reaction yield. Under moderated stirring conditions, the polyacetal was characterized by a larger amount of macro-cycles. Inversely, under higher intensity mixing and with an excess of methylene chloride, it was mainly composed of linear chains. In this latter case, the polymeric material presented an amorphous morphology with a glass transition temperature (Tg) close to 55 °C. Its degradation temperature was evaluated to be close to 215 °C using thermogravimetry according to multi-ramp methodology. The chemical approach and the physicochemical properties are valuable in comparison with that characteristic of other isosorbide-based polyacetals. Full article
(This article belongs to the Special Issue Renewable Polymeric Adhesives)
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Open AccessFeature PaperArticle
Flammability of Cellulose-Based Fibers and the Effect of Structure of Phosphorus Compounds on Their Flame Retardancy
Polymers 2016, 8(8), 293; https://doi.org/10.3390/polym8080293
Received: 30 June 2016 / Revised: 3 August 2016 / Accepted: 4 August 2016 / Published: 10 August 2016
Cited by 7 | Viewed by 2590 | PDF Full-text (1090 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Cellulose fibers are promoted for use in various textile applications due their sustainable nature. Cellulose-based fibers vary considerably in their mechanical and flammability properties depending on their chemical composition. The chemical composition of a cellulose-based fiber is further dependent on their source (i.e., [...] Read more.
Cellulose fibers are promoted for use in various textile applications due their sustainable nature. Cellulose-based fibers vary considerably in their mechanical and flammability properties depending on their chemical composition. The chemical composition of a cellulose-based fiber is further dependent on their source (i.e., seed, leaf, cane, fruit, wood, bast, and grass). Being organic in nature, cellulose fibers, and their products thereof, pose considerable fire risk. In this work we have compared the flammability properties of cellulose fibers obtained from two different sources (i.e., cotton and peat). Compared to cotton cellulose textiles, peat-based cellulose textiles burn longer with a prominent afterglow which can be attributed to the presence of lignin in its structure. A series of phosphoramidates were synthesized and applied on both cellulose textiles. From thermogravimetric and pyrolysis combustion flow analysis of the treated cellulose, we were able to relate the flame retardant efficacy of the synthesized phosphorus compounds to their chemical structure. The phosphoramidates with methyl phosphoester groups exhibited higher condensed phase flame retardant effects on both types of cellulose textiles investigated in this study. In addition, the bis-phosphoramidates exhibited higher flame retardant efficacy compared to the mono-phosphoramidates. Full article
(This article belongs to the Special Issue Recent Advances in Flame Retardancy of Textile Related Products)
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Open AccessArticle
A Bio Polymeric Adhesive Produced by Photo Cross-Linkable Technique
Polymers 2016, 8(8), 292; https://doi.org/10.3390/polym8080292
Received: 22 May 2016 / Revised: 23 July 2016 / Accepted: 27 July 2016 / Published: 10 August 2016
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Abstract
The advantages of photo polymerization methods compared to thermal techniques are: rapid cure reactions, low energy demands, solvent free requirements and room temperature use. In order to form a macromer, polycaprolactone (PCL) was cross-linked via ultraviolet power with 2-isocyanatoethyl methacrylate. Different methods of [...] Read more.
The advantages of photo polymerization methods compared to thermal techniques are: rapid cure reactions, low energy demands, solvent free requirements and room temperature use. In order to form a macromer, polycaprolactone (PCL) was cross-linked via ultraviolet power with 2-isocyanatoethyl methacrylate. Different methods of characterization were carried out: estimation of swelling capacity, adhesive capacity (using aminated substrates), surface energy (by contact angle), and attenuated total reflectance Fourier transform infrared. In addition to these experiments, we carried out dynamical mechanical thermal analysis, thermogravimetry and thermorphology characterizations of PCL. Thus, it has been concluded that the prepared macromer could be transformed into membranes that were effective as a medical adhesive. The degree of cross linking has been estimated using two different techniques: swelling of the samples and photo cross linking of the samples with different periods of irradiation at relatively high UV-power (600 mW/cm2). Full article
(This article belongs to the Special Issue Renewable Polymeric Adhesives)
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Open AccessArticle
Moisture Absorption/Desorption Effects on Flexural Property of Glass-Fiber-Reinforced Polyester Laminates: Three-Point Bending Test and Coupled Hygro-Mechanical Finite Element Analysis
Polymers 2016, 8(8), 290; https://doi.org/10.3390/polym8080290
Received: 30 May 2016 / Revised: 20 July 2016 / Accepted: 3 August 2016 / Published: 10 August 2016
Cited by 4 | Viewed by 2407 | PDF Full-text (5580 KB) | HTML Full-text | XML Full-text
Abstract
Influence of moisture absorption/desorption on the flexural properties of Glass-fibre-reinforced polymer (GFRP) laminates was experimentally investigated under hot/wet aging environments. To characterize mechanical degradation, three-point bending tests were performed following the ASTM test standard (ASTM D790-10A). The flexural properties of dry (0% M [...] Read more.
Influence of moisture absorption/desorption on the flexural properties of Glass-fibre-reinforced polymer (GFRP) laminates was experimentally investigated under hot/wet aging environments. To characterize mechanical degradation, three-point bending tests were performed following the ASTM test standard (ASTM D790-10A). The flexural properties of dry (0% Mt/M), moisture unsaturated (30% Mt/M and 50% Mt/M) and moisture saturated (100% Mt/M) specimens at both 20 and 40 °C test temperatures were compared. One cycle of moisture absorption-desorption process was considered in this study to investigate the mechanical degradation scale and the permanent damage of GFRP laminates induced by moisture diffusion. Experimental results confirm that the combination of moisture and temperature effects sincerely deteriorates the flexural properties of GFRP laminates, on both strength and stiffness. Furthermore, the reducing percentage of flexural strength is found much larger than that of E-modulus. Unrecoverable losses of E-modulus (15.0%) and flexural strength (16.4%) for the GFRP laminates experiencing one cycle of moisture absorption/desorption process are evident at the test temperature of 40 °C, but not for the case of 20 °C test temperature. Moreover, a coupled hygro-mechanical Finite Element (FE) model was developed to characterize the mechanical behaviors of GFRP laminates at different moisture absorption/desorption stages, and the modeling method was subsequently validated with flexural test results. Full article
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Open AccessArticle
The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods
Polymers 2016, 8(8), 291; https://doi.org/10.3390/polym8080291
Received: 31 May 2016 / Revised: 1 August 2016 / Accepted: 2 August 2016 / Published: 9 August 2016
Cited by 4 | Viewed by 1972 | PDF Full-text (993 KB) | HTML Full-text | XML Full-text
Abstract
The complete orientational ordering tensor of quasi-ideal colloidal rods is obtained as a function of shear rate by performing rheo-SANS (rheology with small angle neutron scattering) measurements on isotropic fd-virus suspensions in the two relevant scattering planes, the flow-gradient (1-2) and the flow-vorticity [...] Read more.
The complete orientational ordering tensor of quasi-ideal colloidal rods is obtained as a function of shear rate by performing rheo-SANS (rheology with small angle neutron scattering) measurements on isotropic fd-virus suspensions in the two relevant scattering planes, the flow-gradient (1-2) and the flow-vorticity (1-3) plane. Microscopic ordering can be identified as the origin of the observed shear thinning. A qualitative description of the rheological response by Smoluchowski, as well as Doi–Edwards–Kuzuu theory is possible, as we obtain a master curve for different concentrations, scaling the shear rate with the apparent collective rotational diffusion coefficient. However, the observation suggests that the interdependence of ordering and shear thinning at small shear rates is stronger than predicted. The extracted zero-shear viscosity matches the concentration dependence of the self-diffusion of rods in semi-dilute solutions, while the director tilts close towards the flow direction already at very low shear rates. In contrast, we observe a smaller dependence on the shear rate in the overall ordering at high shear rates, as well as an ever-increasing biaxiality. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessFeature PaperArticle
Flame Retardant Polyamide Fibres: The Challenge of Minimising Flame Retardant Additive Contents with Added Nanoclays
Polymers 2016, 8(8), 288; https://doi.org/10.3390/polym8080288
Received: 21 June 2016 / Revised: 26 July 2016 / Accepted: 2 August 2016 / Published: 9 August 2016
Cited by 12 | Viewed by 2671 | PDF Full-text (1972 KB) | HTML Full-text | XML Full-text
Abstract
This work shows that halogen-free, flame retarded polyamide 6 (PA6), fabrics may be produced in which component fibres still have acceptable tensile properties and low levels (preferably ≤10 wt %) of additives by incorporating a nanoclay along with two types of flame retardant [...] Read more.
This work shows that halogen-free, flame retarded polyamide 6 (PA6), fabrics may be produced in which component fibres still have acceptable tensile properties and low levels (preferably ≤10 wt %) of additives by incorporating a nanoclay along with two types of flame retardant formulations. The latter include (i) aluminium diethyl phosphinate (AlPi) at 10 wt %, known to work principally in the vapour phase and (ii) ammonium sulphamate (AS)/dipentaerythritol (DP) system present at 2.5 and 1 wt % respectively, believed to be condense phase active. The nanoclay chosen is an organically modified montmorillonite clay, Cloisite 25A. The effect of each additive system is analysed in terms of its ability to maximise both filament tensile properties relative to 100% PA6 and flame retardant behaviour of knitted fabrics in a vertical orientation. None of the AlPi-containing formulations achieved self-extinguishability, although the presence of nanoclay promoted lower burning and melt dripping rates. The AS/DP-containing formulations with total flame retardant levels of 5.5 wt % or less showed far superior properties and with nanoclay, showed fabric extinction times ≤ 39 s and reduced melt dripping. The tensile and flammability results, supported by thermogravimetric analysis, have been interpreted in terms of the mechanism of action of each flame retardant/nanoclay type. Full article
(This article belongs to the Special Issue Recent Advances in Flame Retardancy of Textile Related Products)
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Open AccessFeature PaperArticle
Key Role of Reinforcing Structures in the Flame Retardant Performance of Self-Reinforced Polypropylene Composites
Polymers 2016, 8(8), 289; https://doi.org/10.3390/polym8080289
Received: 30 June 2016 / Revised: 30 July 2016 / Accepted: 3 August 2016 / Published: 8 August 2016
Cited by 5 | Viewed by 2233 | PDF Full-text (2043 KB) | HTML Full-text | XML Full-text
Abstract
The flame retardant synergism between highly stretched polymer fibres and intumescent flame retardant systems was investigated in self-reinforced polypropylene composites. It was found that the structure of reinforcement, such as degree of molecular orientation, fibre alignment and weave type, has a particular effect [...] Read more.
The flame retardant synergism between highly stretched polymer fibres and intumescent flame retardant systems was investigated in self-reinforced polypropylene composites. It was found that the structure of reinforcement, such as degree of molecular orientation, fibre alignment and weave type, has a particular effect on the fire performance of the intumescent system. As little as 7.2 wt % additive content, one third of the amount needed in non-reinforced polypropylene matrix, was sufficient to reach a UL-94 V-0 rating. The best result was found in self-reinforced polypropylene composites reinforced with unidirectional fibres. In addition to the fire retardant performance, the mechanical properties were also evaluated. The maximum was found at optimal consolidation temperature, while the flame retardant additive in the matrix did not influence the mechanical performance up to the investigated 13 wt % concentration. Full article
(This article belongs to the Special Issue Recent Advances in Flame Retardancy of Textile Related Products)
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Open AccessArticle
Novel Electrospun Polylactic Acid Nanocomposite Fiber Mats with Hybrid Graphene Oxide and Nanohydroxyapatite Reinforcements Having Enhanced Biocompatibility
Polymers 2016, 8(8), 287; https://doi.org/10.3390/polym8080287
Received: 2 June 2016 / Revised: 28 July 2016 / Accepted: 3 August 2016 / Published: 8 August 2016
Cited by 23 | Viewed by 2566 | PDF Full-text (8310 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Graphene oxide (GO) and a nanohydroxyapatite rod (nHA) of good biocompatibility were incorporated into polylactic acid (PLA) through electrospinning to form nanocomposite fiber scaffolds for bone tissue engineering applications. The preparation, morphological, mechanical and thermal properties, as well as biocompatibility of electrospun PLA [...] Read more.
Graphene oxide (GO) and a nanohydroxyapatite rod (nHA) of good biocompatibility were incorporated into polylactic acid (PLA) through electrospinning to form nanocomposite fiber scaffolds for bone tissue engineering applications. The preparation, morphological, mechanical and thermal properties, as well as biocompatibility of electrospun PLA scaffolds reinforced with GO and/or nHA were investigated. Electron microscopic examination and image analysis showed that GO and nHA nanofillers refine the diameter of electrospun PLA fibers. Differential scanning calorimetric tests showed that nHA facilitates the crystallization process of PLA, thereby acting as a nucleating site for the PLA molecules. Tensile test results indicated that the tensile strength and elastic modulus of the electrospun PLA mat can be increased by adding 15 wt % nHA. The hybrid nanocomposite scaffold with 15 wt % nHA and 1 wt % GO fillers exhibited higher tensile strength amongst the specimens investigated. Furthermore, nHA and GO nanofillers enhanced the water uptake of PLA. Cell cultivation, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and alkaline phosphatase tests demonstrated that all of the nanocomposite scaffolds exhibit higher biocompatibility than the pure PLA mat, particularly for the scaffold with 15 wt % nHA and 1 wt % GO. Therefore, the novel electrospun PLA nanocomposite scaffold with 15 wt % nHA and 1 wt % GO possessing a high tensile strength and modulus, as well as excellent cell proliferation is a potential biomaterial for bone tissue engineering applications. Full article
(This article belongs to the Special Issue Biodegradable Polymers)
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Open AccessFeature PaperReview
Semiflexible Chains at Surfaces: Worm-Like Chains and beyond
Polymers 2016, 8(8), 286; https://doi.org/10.3390/polym8080286
Received: 7 June 2016 / Revised: 29 July 2016 / Accepted: 29 July 2016 / Published: 8 August 2016
Cited by 11 | Viewed by 2200 | PDF Full-text (8244 KB) | HTML Full-text | XML Full-text
Abstract
We give an extended review of recent numerical and analytical studies on semiflexible chains near surfaces undertaken at Institut Charles Sadron (sometimes in collaboration) with a focus on static properties. The statistical physics of thin confined layers, strict two-dimensional (2D) layers and adsorption [...] Read more.
We give an extended review of recent numerical and analytical studies on semiflexible chains near surfaces undertaken at Institut Charles Sadron (sometimes in collaboration) with a focus on static properties. The statistical physics of thin confined layers, strict two-dimensional (2D) layers and adsorption layers (both at equilibrium with the dilute bath and from irreversible chemisorption) are discussed for the well-known worm-like-chain (WLC) model. There is mounting evidence that biofilaments (except stable d-DNA) are not fully described by the WLC model. A number of augmented models, like the (super) helical WLC model, the polymorphic model of microtubules (MT) and a model with (strongly) nonlinear flexural elasticity are presented, and some aspects of their surface behavior are analyzed. In many cases, we use approaches different from those in our previous work, give additional results and try to adopt a more general point of view with the hope to shed some light on this complex field. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessArticle
Enhancing the Adhesive Strength of a Plywood Adhesive Developed from Hydrolyzed Specified Risk Materials
Polymers 2016, 8(8), 285; https://doi.org/10.3390/polym8080285
Received: 12 July 2016 / Revised: 29 July 2016 / Accepted: 1 August 2016 / Published: 8 August 2016
Cited by 9 | Viewed by 2131 | PDF Full-text (1285 KB) | HTML Full-text | XML Full-text
Abstract
The current production of wood composites relies mostly on formaldehyde-based adhesives such as urea formaldehyde (UF) and phenol formaldehyde (PF) resins. As these resins are produced from non-renewable resources, and there are some ongoing issues with possible health hazard due to formaldehyde emission [...] Read more.
The current production of wood composites relies mostly on formaldehyde-based adhesives such as urea formaldehyde (UF) and phenol formaldehyde (PF) resins. As these resins are produced from non-renewable resources, and there are some ongoing issues with possible health hazard due to formaldehyde emission from such products, the purpose of this research was to develop a formaldehyde-free plywood adhesive utilizing waste protein as a renewable feedstock. The feedstock for this work was specified risk material (SRM), which is currently being disposed of either by incineration or by landfilling. In this report, we describe a technology for utilization of SRM for the development of an environmentally friendly plywood adhesive. SRM was thermally hydrolyzed using a Canadian government-approved protocol, and the peptides were recovered from the hydrolyzate. The recovered peptides were chemically crosslinked with polyamidoamine-epichlorohydrin (PAE) resin to develop an adhesive system for bonding of plywood specimens. The effects of crosslinking time, peptides/crosslinking agent ratio, and temperature of hot pressing of plywood specimens on the strength of formulated adhesives were investigated. Formulations containing as much as 78% (wt/wt) peptides met the ASTM (American Society for Testing and Materials) specifications of minimum dry and soaked shear strength requirement for UF resin type adhesives. Under the optimum conditions tested, the peptides–PAE resin-based formulations resulted in plywood specimens having comparable dry as well as soaked shear strength to that of commercial PF resin. Full article
(This article belongs to the Special Issue Renewable Polymeric Adhesives)
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Open AccessArticle
Finsler Geometry Modeling of Phase Separation in Multi-Component Membranes
Polymers 2016, 8(8), 284; https://doi.org/10.3390/polym8080284
Received: 15 May 2016 / Revised: 22 July 2016 / Accepted: 25 July 2016 / Published: 4 August 2016
Cited by 5 | Viewed by 1749 | PDF Full-text (2157 KB) | HTML Full-text | XML Full-text
Abstract
A Finsler geometric surface model is studied as a coarse-grained model for membranes of three components, such as zwitterionic phospholipid (DOPC), lipid (DPPC) and an organic molecule (cholesterol). To understand the phase separation of liquid-ordered (DPPC rich) Lo and liquid-disordered (DOPC rich) [...] Read more.
A Finsler geometric surface model is studied as a coarse-grained model for membranes of three components, such as zwitterionic phospholipid (DOPC), lipid (DPPC) and an organic molecule (cholesterol). To understand the phase separation of liquid-ordered (DPPC rich) L o and liquid-disordered (DOPC rich) L d , we introduce a binary variable σ ( = ± 1 ) into the triangulated surface model. We numerically determine that two circular and stripe domains appear on the surface. The dependence of the morphological change on the area fraction of L o is consistent with existing experimental results. This provides us with a clear understanding of the origin of the line tension energy, which has been used to understand these morphological changes in three-component membranes. In addition to these two circular and stripe domains, a raft-like domain and budding domain are also observed, and the several corresponding phase diagrams are obtained. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessArticle
Microscopic Dynamics and Topology of Polymer Rings Immersed in a Host Matrix of Longer Linear Polymers: Results from a Detailed Molecular Dynamics Simulation Study and Comparison with Experimental Data
Polymers 2016, 8(8), 283; https://doi.org/10.3390/polym8080283
Received: 15 June 2016 / Revised: 21 July 2016 / Accepted: 27 July 2016 / Published: 4 August 2016
Cited by 10 | Viewed by 2012 | PDF Full-text (7678 KB) | HTML Full-text | XML Full-text
Abstract
We have performed molecular dynamics (MD) simulations of melt systems consisting of a small number of long ring poly(ethylene oxide) (PEO) probes immersed in a host matrix of linear PEO chains and have studied their microscopic dynamics and topology as a function of [...] Read more.
We have performed molecular dynamics (MD) simulations of melt systems consisting of a small number of long ring poly(ethylene oxide) (PEO) probes immersed in a host matrix of linear PEO chains and have studied their microscopic dynamics and topology as a function of the molecular length of the host linear chains. Consistent with a recent neutron spin echo spectroscopy study (Goossen et al., Phys. Rev. Lett. 2015, 115, 148302), we have observed that the segmental dynamics of the probe ring molecules is controlled by the length of the host linear chains. In matrices of short, unentangled linear chains, the ring probes exhibit a Rouse-like dynamics, and the spectra of their dynamic structure factor resemble those in their own melt. In striking contrast, in matrices of long, entangled linear chains, their dynamics is drastically altered. The corresponding dynamic structure factor spectra exhibit a steep initial decay up to times on the order of the entanglement time τe of linear PEO at the same temperature but then they become practically time-independent approaching plateau values. The plateau values are different for different wavevectors; they also depend on the length of the host linear chains. Our results are supported by a geometric analysis of topological interactions, which reveals significant threading of all ring molecules by the linear chains. In most cases, each ring is simultaneously threaded by several linear chains. As a result, its dynamics at times longer than a few τe should be completely dictated by the release of the topological restrictions imposed by these threadings (interpenetrations). Our topological analysis did not indicate any effect of the few ring probes on the statistical properties of the network of primitive paths of the host linear chains. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessArticle
Enhanced Anti-Ultraviolet and Thermal Stability of a Pesticide via Modification of a Volatile Organic Compound (VOC)-Free Vinyl-Silsesquioxane in Desert Areas
Polymers 2016, 8(8), 282; https://doi.org/10.3390/polym8080282
Received: 13 June 2016 / Revised: 25 July 2016 / Accepted: 28 July 2016 / Published: 4 August 2016
Cited by 1 | Viewed by 1861 | PDF Full-text (1516 KB) | HTML Full-text | XML Full-text
Abstract
Due to the effect of severe environmental conditions, such as intense heat, blowing sand, and ultraviolet light, conventional pesticide applications have repeatedly failed to adequately control mosquito and sandfly populations in desert areas. In this study, a vinyl silsesquioxane (VS) was added to [...] Read more.
Due to the effect of severe environmental conditions, such as intense heat, blowing sand, and ultraviolet light, conventional pesticide applications have repeatedly failed to adequately control mosquito and sandfly populations in desert areas. In this study, a vinyl silsesquioxane (VS) was added to a pesticide (citral) to enhance residual, thermal and anti-ultraviolet properties via three double-bond reactions in the presence of an initiator: (1) the connection of VS and citral, (2) a radical self-polymerization of VS and (3) a radical self-polymerization of citral. VS-citral, the expected and main product of the copolymerization of VS and citral, was characterized using standard spectrum techniques. The molecular consequences of the free radical polymerization were analyzed by MALDITOF spectrometry. Anti-ultraviolet and thermal stability properties of the VS-citral system were tested using scanning spectrophotometry (SSP) and thermogravimetric analysis (TGA). The repellency of VS-citral decreased over time, from 97.63% at 0 h to 72.98% at 1 h and 60.0% at 2 h, as did the repellency of citral, from 89.56% at 0 h to 62.73% at 1 h and 50.95% at 2 h. Full article
(This article belongs to the Special Issue Hybrid Polymeric Materials)
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