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Polymers, Volume 6, Issue 6 (June 2014), Pages 1655-1876

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Research

Jump to: Review

Open AccessArticle A Coarse-Grained DNA Model Parameterized from Atomistic Simulations by Inverse Monte Carlo
Polymers 2014, 6(6), 1655-1675; doi:10.3390/polym6061655
Received: 15 April 2014 / Revised: 15 May 2014 / Accepted: 18 May 2014 / Published: 30 May 2014
Cited by 14 | PDF Full-text (815 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Computer modeling of very large biomolecular systems, such as long DNA polyelectrolytes or protein-DNA complex-like chromatin cannot reach all-atom resolution in a foreseeable future and this necessitates the development of coarse-grained (CG) approximations. DNA is both highly charged and mechanically rigid semi-flexible [...] Read more.
Computer modeling of very large biomolecular systems, such as long DNA polyelectrolytes or protein-DNA complex-like chromatin cannot reach all-atom resolution in a foreseeable future and this necessitates the development of coarse-grained (CG) approximations. DNA is both highly charged and mechanically rigid semi-flexible polymer and adequate DNA modeling requires a correct description of both its structural stiffness and salt-dependent electrostatic forces. Here, we present a novel CG model of DNA that approximates the DNA polymer as a chain of 5-bead units. Each unit represents two DNA base pairs with one central bead for bases and pentose moieties and four others for phosphate groups. Charges, intra- and inter-molecular force field potentials for the CG DNA model were calculated using the inverse Monte Carlo method from all atom molecular dynamic (MD) simulations of 22 bp DNA oligonucleotides. The CG model was tested by performing dielectric continuum Langevin MD simulations of a 200 bp double helix DNA in solutions of monovalent salt with explicit ions. Excellent agreement with experimental data was obtained for the dependence of the DNA persistent length on salt concentration in the range 0.1–100 mM. The new CG DNA model is suitable for modeling various biomolecular systems with adequate description of electrostatic and mechanical properties. Full article
(This article belongs to the Special Issue Polyelectrolytes 2014)
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Open AccessArticle Laccase Functionalization of Flax and Coconut Fibers
Polymers 2014, 6(6), 1676-1684; doi:10.3390/polym6061676
Received: 25 March 2014 / Revised: 20 May 2014 / Accepted: 26 May 2014 / Published: 30 May 2014
Cited by 1 | PDF Full-text (209 KB) | HTML Full-text | XML Full-text
Abstract
Natural fibers have gained much attention as reinforcing components in composite materials. Despite several interesting characteristics like low cost, low density, high specific properties and biodegradability they show poor compatibility with the polymer matrix. We have shown that it is possible to [...] Read more.
Natural fibers have gained much attention as reinforcing components in composite materials. Despite several interesting characteristics like low cost, low density, high specific properties and biodegradability they show poor compatibility with the polymer matrix. We have shown that it is possible to use a laccase from Trametes hirsuta as a biocatalyst to attach different types of functional phenolic molecules onto the fibers. A 5% incorporation of the functional molecules was achieved as measured via X-ray photoelectron spectroscopy (XPS) in flax although it was lower in coconut fibers. In combination with different mediators it was possible to broaden the activation scope and graft hydrophobic molecules like dimer fatty amines. Among the different mediators tested 1-hydroxybenzotriazole (HBT), 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO) and 2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), TEMPO were the most effective achieving a 10% increase in carbon as measured by XPS. Full article
Open AccessArticle The Effects of Loading Rate and Duration on the Axial Behavior of Low-Strength and Medium-Strength Noncircular Concrete Members Confined by Fiber-Reinforced Polymer Sheets
Polymers 2014, 6(6), 1685-1704; doi:10.3390/polym6061685
Received: 8 May 2014 / Revised: 28 May 2014 / Accepted: 29 May 2014 / Published: 6 June 2014
Cited by 2 | PDF Full-text (1629 KB) | HTML Full-text | XML Full-text
Abstract
In this study, 36 concrete specimens with square cross-sections and different concrete qualities were tested either under uniaxial compression at different loading rates or subjected to sustained uniaxial stresses after externally jacketing with carbon fiber-reinforced polymer (CFRP) sheets. The main test parameters [...] Read more.
In this study, 36 concrete specimens with square cross-sections and different concrete qualities were tested either under uniaxial compression at different loading rates or subjected to sustained uniaxial stresses after externally jacketing with carbon fiber-reinforced polymer (CFRP) sheets. The main test parameters were the loading rate and the applied sustained stress level. Among these parameters, the loading rate varied in the range of 0.0002 and 0.04 strain/min. In the case of short-term creep tests under sustained loads, three stress levels (between 0.73 f'cc and 0.90 f'cc or 2.76 f'cc and 3.37 f'cc) for low-strength and four stress levels (between 0.69 f'cc and 0.92 f'cc or 0.89 f'co and 1.20 f'co) for medium-strength prisms were applied. The test results showed that the stress-strain behavior of CFRP-confined concrete was affected by the change in loading rate, and external CFRP confinement enhanced the creep performance of concrete significantly. For low-strength concrete specimens, higher strain rates did not bring higher strength values; however, an increase in strength was obvious for medium-strength prisms. On the other hand, for both concrete qualities, the specimens loaded at slower strain rates exhibited better deformability. None of the specimens of the medium-strength concrete failed during the short-term creep tests; however, three of the low-strength concrete prisms failed during the tests. The results of residual strength tests showed that sustained loading did not cause a strength or ultimate deformation capacity loss, but affected the residual strain capacities. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)
Open AccessArticle The Effect of CFRP Length on the Failure Mode of Strengthened Concrete Beams
Polymers 2014, 6(6), 1705-1726; doi:10.3390/polym6061705
Received: 9 April 2014 / Revised: 30 May 2014 / Accepted: 3 June 2014 / Published: 10 June 2014
Cited by 1 | PDF Full-text (1346 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports the effects of carbon fiber-reinforced polymer (CFRP) length on the failure process, pattern and crack propagation for a strengthened concrete beam with an initial notch. The experiments measuring load-bearing capacity for concrete beams with various CFRP lengths have been [...] Read more.
This paper reports the effects of carbon fiber-reinforced polymer (CFRP) length on the failure process, pattern and crack propagation for a strengthened concrete beam with an initial notch. The experiments measuring load-bearing capacity for concrete beams with various CFRP lengths have been performed, wherein the crack opening displacements (COD) at the initial notch are also measured. The application of CFRP can significantly improve the load-bearing capacity, and the failure modes seem different with various CFRP lengths. The stress profiles in the concrete material around the crack tip, at the end of CFRP and at the interface between the concrete and CFRP are then calculated using the finite element method. The experiment measurements are validated by theoretical derivation and also support the finite element analysis. The results show that CFRP can significantly increase the ultimate load of the beam, while such an increase stops as the length reaches 0.15 m. It is also concluded that the CFRP length can influence the stress distribution at three critical stress regions for strengthened concrete beams. However, the optimum CFRP lengths vary with different critical stress regions. For the region around the crack tip, it is 0.15 m; for the region at the interface it is 0.25 m, and for the region at the end of CFRP, it is 0.30 m. In conclusion, the optimum CFRP length in this work is 0.30 m, at which CFRP strengthening is fully functioning, which thus provides a good reference for the retrofitting of buildings. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)
Open AccessArticle The Effect of Salt on the Complex Coacervation of Vinyl Polyelectrolytes
Polymers 2014, 6(6), 1756-1772; doi:10.3390/polym6061756
Received: 5 May 2014 / Revised: 3 June 2014 / Accepted: 4 June 2014 / Published: 16 June 2014
Cited by 25 | PDF Full-text (1785 KB) | HTML Full-text | XML Full-text
Abstract
Complex coacervation is an electrostatically-driven phase separation phenomenon that is utilized in a wide range of everyday applications and is of great interest for the creation of self-assembled materials. Here, we utilized turbidity to characterize the effect of salt type on coacervate [...] Read more.
Complex coacervation is an electrostatically-driven phase separation phenomenon that is utilized in a wide range of everyday applications and is of great interest for the creation of self-assembled materials. Here, we utilized turbidity to characterize the effect of salt type on coacervate formation using two vinyl polyelectrolytes, poly(acrylic acid sodium salt) (pAA) and poly(allylamine hydrochloride) (pAH), as simple models for industrial and biological coacervates. We confirmed the dominant role of salt valence on the extent of coacervate formation, while demonstrating the presence of significant secondary effects, which can be described by Hofmeister-like behavior. These results revealed the importance of ion-specific interactions, which are crucial for the informed design of coacervate-based materials for use in complex ionic environments, and can enable more detailed theoretical investigations on the role of subtle electrostatic and thermodynamic effects in complex coacervation. Full article
(This article belongs to the Special Issue Polyelectrolytes 2014)
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Open AccessArticle Long-Term Flexural Behaviors of GFRP Reinforced Concrete Beams Exposed to Accelerated Aging Exposure Conditions
Polymers 2014, 6(6), 1773-1793; doi:10.3390/polym6061773
Received: 19 April 2014 / Revised: 3 June 2014 / Accepted: 5 June 2014 / Published: 16 June 2014
Cited by 4 | PDF Full-text (1528 KB) | HTML Full-text | XML Full-text
Abstract
This study investigates the impact of accelerated aging conditions on the long-term flexural behavior and ductility of reinforced concrete (RC) members with glass fiber-reinforced polymer (GFRP) bars (RC-GFRP specimen) and steel bars (RC-steel specimen). A total of thirty six specimens were designed [...] Read more.
This study investigates the impact of accelerated aging conditions on the long-term flexural behavior and ductility of reinforced concrete (RC) members with glass fiber-reinforced polymer (GFRP) bars (RC-GFRP specimen) and steel bars (RC-steel specimen). A total of thirty six specimens were designed with different amounts of reinforcement with three types of reinforcing bars (i.e., helically wrapped GFRP, sand-coated surface GFRP and steel). Eighteen specimens were subjected to sustained loads and accelerated aging conditions (i.e., 47 °C and 80% relative humidity) in a chamber. The flexural behavior of specimens under 300-day exposure was compared to that of the companion specimens without experiencing accelerated aging conditions. Results indicate that the accelerated aging conditions reduced flexural capacity in not only RC-steel, but also RC-GFRP specimens, with different rates of reduction. Different types of GFRP reinforcement exhibited different rates of degradation of the flexural capacity when embedded in concrete under the same exposure conditions. Several existing models were compared with experimental results for predicting the deflection and deformability index for specimens. Bischoff and Gross’s model exhibited an excellent prediction of the time-dependent deflections. Except for the deformability index proposed by Jaeger, there was no general trend related to the aging duration. This study recommends the need for further investigation on the prediction of the deformability index. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)
Open AccessArticle Fabrication and Characterization of Inorganic Silver and Palladium Nanostructures within Hexagonal Cylindrical Channels of Mesoporous Carbon
Polymers 2014, 6(6), 1794-1809; doi:10.3390/polym6061794
Received: 17 February 2014 / Revised: 6 June 2014 / Accepted: 10 June 2014 / Published: 17 June 2014
Cited by 1 | PDF Full-text (1345 KB) | HTML Full-text | XML Full-text
Abstract
In this study, we prepared a mesoporous carbon with hexagonally packed mesopores through evaporation-induced self-assembly (EISA)—with the diblock copolymer poly(ethylene oxide-b-ε-caprolactone) (PEO-b-PCL) as the template (EO114CL84), phenolic resin as the carbon precursor, hexamethylenetetramine (HMTA) [...] Read more.
In this study, we prepared a mesoporous carbon with hexagonally packed mesopores through evaporation-induced self-assembly (EISA)—with the diblock copolymer poly(ethylene oxide-b-ε-caprolactone) (PEO-b-PCL) as the template (EO114CL84), phenolic resin as the carbon precursor, hexamethylenetetramine (HMTA) as the curing agent, and star octakis-PEO-functionalized polyhedral oligomeric silsesquioxane (PEO–POSS) as the structure modifier—and subsequent carbonization. We then took the cylindrical mesoporous carbon as a loading matrix, with AgNO3 and Pd(NO3)2 as metal precursors, to fabricate Ag nanowire/mesoporous carbon and Pd nanoparticle/mesoporous carbon nanocomposites, respectively, through an incipient wetness impregnation method and subsequent reduction under H2. We used transmission electron microscopy, electron diffraction, small-angle X-ray scattering, N2 isotherm sorption experiment, Raman spectroscopy, and power X-ray diffraction to investigate the textural properties of these nanometal/carbon nanocomposites. Most notably, the Raman spectra of the cylindrical mesoporous carbon, Ag/mesoporous carbon, and Pd/mesoporous carbon revealed interesting phenomena in terms of the ratios of the intensities of the D and G bands (ID/IG), the absolute scattering intensities, and the positions of the D bands. Full article
(This article belongs to the Special Issue Polymer-Inorganic Hybrids and Their Applications 2014)
Open AccessArticle Thymine- and Adenine-Functionalized Polystyrene Form Self-Assembled Structures through Multiple Complementary Hydrogen Bonds
Polymers 2014, 6(6), 1827-1845; doi:10.3390/polym6061827
Received: 22 May 2014 / Revised: 6 June 2014 / Accepted: 9 June 2014 / Published: 18 June 2014
Cited by 4 | PDF Full-text (3120 KB) | HTML Full-text | XML Full-text
Abstract
In this study, we investigated the self-assembly of two homopolymers of the same molecular weight, but containing complementary nucleobases. After employing nitroxide-mediated radical polymerization to synthesize poly(vinylbenzyl chloride), we converted the polymer into poly(vinylbenzyl azide) through a reaction with NaN3 and [...] Read more.
In this study, we investigated the self-assembly of two homopolymers of the same molecular weight, but containing complementary nucleobases. After employing nitroxide-mediated radical polymerization to synthesize poly(vinylbenzyl chloride), we converted the polymer into poly(vinylbenzyl azide) through a reaction with NaN3 and then performed click chemistry with propargyl thymine and propargyl adenine to yield the homopolymers, poly(vinylbenzyl triazolylmethyl methylthymine) (PVBT) and poly(vinylbenzyl triazolylmethyl methyladenine) (PVBA), respectively. This PVBT/PVBA blend system exhibited a single glass transition temperature over the entire range of compositions, indicative of a miscible phase arising from the formation of multiple strong complementary hydrogen bonds between the thymine and adenine groups of PVBT and PVBA, respectively; Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy confirmed the presence of these noncovalent interactions. In addition, dynamic rheology, dynamic light scattering and transmission electron microscopy provided evidence for the formation of supramolecular network structures in these binary PVBT/PVBA blend systems. Full article
(This article belongs to the Special Issue Polymer Colloids)
Open AccessArticle Effects of Additives on the Morphology and Performance of PPTA/PVDF in Situ Blend UF Membrane
Polymers 2014, 6(6), 1846-1861; doi:10.3390/polym6061846
Received: 22 April 2014 / Revised: 13 June 2014 / Accepted: 16 June 2014 / Published: 20 June 2014
Cited by 4 | PDF Full-text (3053 KB) | HTML Full-text | XML Full-text
Abstract
Poly(p-phenylene terephtalamide) (PPTA), a high-performance polymer with high modulus and good hydrophilicity, is often used as a reinforced material. However, due to its high crystallity, micro-phase separation often occurs in the blends. In this paper, PPTA/poly(vinylidene fluoride) (PVDF) compatible blend [...] Read more.
Poly(p-phenylene terephtalamide) (PPTA), a high-performance polymer with high modulus and good hydrophilicity, is often used as a reinforced material. However, due to its high crystallity, micro-phase separation often occurs in the blends. In this paper, PPTA/poly(vinylidene fluoride) (PVDF) compatible blend solution was synthesized by in situ polycondensation. Blend ultra-filtration membrane was prepared through the immersion phase inversion process. In order to obtain desired pore structure, the effects of different additives including hydrophilic polymer (polyethylene glycol (PEG)), inorganic salt (lithium chloride (LiCl)) and the surfactant (Tween-80) on the morphology and performance of PPTA/PVDF blend membranes were studied. The membrane formation process was investigated through ternary phase diagram (thermodynamics) and viscosities (kinetics) analysis. It was found that, with the increasing of LiCl content, a porous membrane structure with long finger-like pores was formed due to the accelerated demixing process which resulted in the increase of porosity and pore diameter as well as the enhancement of water flux and the decline of PEG rejection. When Tween content increased to over 3 wt%, dynamic viscosity became the main factor resulting in a decreased phase separation rate. The transfer of PEG and LiCl molecules onto membrane surface increased the surface hydrophilicity. The effect of Tween content on membrane hydrophilicity was also correlated with the compatibility of blend components. Full article
(This article belongs to the Special Issue Polymer Blends)
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Open AccessArticle Mechanical Behavior of BFRP-Steel Composite Plate under Axial Tension
Polymers 2014, 6(6), 1862-1876; doi:10.3390/polym6061862
Received: 8 April 2014 / Revised: 28 May 2014 / Accepted: 12 June 2014 / Published: 23 June 2014
Cited by 2 | PDF Full-text (749 KB) | HTML Full-text | XML Full-text
Abstract
Combining the advantages of basalt fiber-reinforced polymer (BFRP) material and steel material, a novel BFRP-steel composite plate (BSP) is proposed, where a steel plate is sandwiched between two outer BFRP laminates. The main purpose of this research is to investigate the mechanical [...] Read more.
Combining the advantages of basalt fiber-reinforced polymer (BFRP) material and steel material, a novel BFRP-steel composite plate (BSP) is proposed, where a steel plate is sandwiched between two outer BFRP laminates. The main purpose of this research is to investigate the mechanical behavior of the proposed BSP under uniaxial tension and cyclic tension. Four groups of BSP specimens with four different BFRP layers and one control group of steel plate specimens were prepared. A uniaxial tensile test and a cyclic tensile test were conducted to determine the initial elastic modulus, postyield stiffness, yield strength, ultimate bearing capacity and residual deformation. Test results indicated that the stress-strain curve of the BSP specimen was bilinear prior to the fracture of the outer BFRP, and the BSP specimen had stable postyield stiffness and small residual deformation after the yielding of the inner steel plate. The postyield modulus of BSP specimens increased almost linearly with the increasing number of outer BFRP layers, as well as the ultimate bearing capacity. Moreover, the predicted results from the selected models under both monotonic tension and cyclic tension were in good agreement with the experimental data. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)
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Review

Jump to: Research

Open AccessReview Low Molecular Weight Chitosan (LMWC)-based Polyplexes for pDNA Delivery: From Bench to Bedside
Polymers 2014, 6(6), 1727-1755; doi:10.3390/polym6061727
Received: 14 February 2014 / Revised: 21 May 2014 / Accepted: 26 May 2014 / Published: 16 June 2014
Cited by 8 | PDF Full-text (2212 KB) | HTML Full-text | XML Full-text
Abstract
Non-viral gene delivery vectors are emerging as a safer alternative to viral vectors. Among natural polymers, chitosan (Ch) is the most studied one, and low molecular weight Ch, specifically, presents a wide range of advantages for non-viral pDNA delivery. It is crucial [...] Read more.
Non-viral gene delivery vectors are emerging as a safer alternative to viral vectors. Among natural polymers, chitosan (Ch) is the most studied one, and low molecular weight Ch, specifically, presents a wide range of advantages for non-viral pDNA delivery. It is crucial to determine the best process for the formation of Low Molecular Weight Chitosan (LMWC)-pDNA complexes and to characterize their physicochemical properties to better understand their behavior once the polyplexes are administered. The transfection efficiency of Ch based polyplexes is relatively low. Therefore, it is essential to understand all the transfection process, including the cellular uptake, endosomal escape and nuclear import, together with the parameters involved in the process to improve the design and development of the non-viral vectors. The aim of this review is to describe the formation and characterization of LMWC based polyplexes, the in vitro transfection process and finally, the in vivo applications of LMWC based polyplexes for gene therapy purposes. Full article
(This article belongs to the Special Issue Natural Polymers 2014)
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Open AccessReview A Critical Review of Research on Reuse of Mechanically Recycled FRP Production and End-of-Life Waste for Construction
Polymers 2014, 6(6), 1810-1826; doi:10.3390/polym6061810
Received: 25 April 2014 / Revised: 28 May 2014 / Accepted: 4 June 2014 / Published: 17 June 2014
Cited by 5 | PDF Full-text (1464 KB) | HTML Full-text | XML Full-text
Abstract
For the last three decades, fiber reinforced polymer (FRP) composite materials have been widely used in major engineering industries. Managing FRP waste is becoming an important issue due to the growth in the production of FRP composite materials. In this article, the [...] Read more.
For the last three decades, fiber reinforced polymer (FRP) composite materials have been widely used in major engineering industries. Managing FRP waste is becoming an important issue due to the growth in the production of FRP composite materials. In this article, the issue of FRP waste management is discussed and the commonly used methods for the handling of FRP waste are reviewed. One potentially viable use of FRP waste is in the partial replacement of fillers or aggregates in cementitious materials (particularly portland cement mortar and concrete). A number of important prior investigations performed on the use of FRP waste in concrete and mortar are reviewed. The results from most of those investigations suggest that FRP aggregates significantly reduce the strength of cementitious materials with little significant effect on durability. Recommendations for future research in this area are provided for producing stronger mortars and concretes incorporating FRP production and end-of-life waste. Full article
(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)

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