Open AccessArticle
Dynamics of DNA Squeezed Inside a Nanochannel via a Sliding Gasket
Polymers 2016, 8(10), 352; doi:10.3390/polym8100352 -
Abstract
We use Brownian dynamics (BD) simulation of a coarse-grained (CG) bead-spring model of DNA to study the nonequilibrim dynamics of a single DNA molecule confined inside a rectangular nanochannel being squeezed with a sliding gasket piston or “nanodozer”. From our simulations we [...] Read more.
We use Brownian dynamics (BD) simulation of a coarse-grained (CG) bead-spring model of DNA to study the nonequilibrim dynamics of a single DNA molecule confined inside a rectangular nanochannel being squeezed with a sliding gasket piston or “nanodozer”. From our simulations we extract the nonequilibrim density profile c(x,t) of the squeezed molecule along the channel axis (x-coordinate) and then analyze the non-equilibrium profile using a recently introduced phenomenological Nonlinear Partial Differential Equation (NPDE) model. Since the NPDE approach also fits the experimental results well and is numerically efficient to implement, the combined BD + NPDE methods can be a powerful approach to analyze details of the confined molecular dynamics. In particular, the overall excellent agreement between the two complementary sets of data provides a strategy for carrying out large scale simulation on semi-flexible biopolymers in confinement at biologically relevant length scales. Full article
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Open AccessArticle
Study of Non-Isothermal Crystallization of Polydioxanone and Analysis of Morphological Changes Occurring during Heating and Cooling Processes
Polymers 2016, 8(10), 351; doi:10.3390/polym8100351 -
Abstract
Non-isothermal crystallization kinetics of polydioxanone (PDO), a polymer with well-established applications as bioabsorbable monofilar suture, was investigated by Avrami, Mo, and isoconversional methodologies. Results showed Avrami exponents appearing in a relatively narrow range (i.e., between 3.76 and 2.77), which suggested a three-dimensional [...] Read more.
Non-isothermal crystallization kinetics of polydioxanone (PDO), a polymer with well-established applications as bioabsorbable monofilar suture, was investigated by Avrami, Mo, and isoconversional methodologies. Results showed Avrami exponents appearing in a relatively narrow range (i.e., between 3.76 and 2.77), which suggested a three-dimensional spherulitic growth and instantaneous nucleation at high cooling rates. The nucleation mechanism changed to sporadic at low rates, with both crystallization processes being detected in the differential scanning calorimetry (DSC) cooling traces. Formation of crystals was hindered as the material crystallized because of a decrease in the motion of molecular chains. Two secondary nucleation constants were derived from calorimetric data by applying the methodology proposed by Vyazovkin and Sbirrazzuoli through the estimation of effective activation energies. In fact, typical non-isothermal crystallization analysis based on the determination of crystal growth by optical microscopy allowed secondary nucleation constants of 3.07 × 105 K2 and 1.42 × 105 K2 to be estimated. Microstructure of sutures was characterized by a stacking of lamellae perpendicularly oriented to the fiber axis and the presence of interlamellar and interfibrillar amorphous regions. The latter became enhanced during heating treatments due to loss of partial chain orientation and decrease of electronic density. Degradation under various pH media revealed different macroscopic morphologies and even a distinct evolution of lamellar microstructure during subsequent heating treatments. Full article
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Open AccessArticle
Microstructure of Sheared Entangled Solutions of Semiflexible Polymers
Polymers 2016, 8(10), 353; doi:10.3390/polym8100353 -
Abstract
We study the influence of finite shear deformations on the microstructure and rheology of solutions of entangled semiflexible polymers theoretically and by numerical simulations and experiments with filamentous actin. Based on the tube model of semiflexible polymers, we predict that large finite [...] Read more.
We study the influence of finite shear deformations on the microstructure and rheology of solutions of entangled semiflexible polymers theoretically and by numerical simulations and experiments with filamentous actin. Based on the tube model of semiflexible polymers, we predict that large finite shear deformations strongly affect the average tube width and curvature, thereby exciting considerable restoring stresses. In contrast, the associated shear alignment is moderate, with little impact on the average tube parameters, and thus expected to be long-lived and detectable after cessation of shear. Similarly, topologically preserved hairpin configurations are predicted to leave a long-lived fingerprint in the shape of the distributions of tube widths and curvatures. Our numerical and experimental data support the theory. Full article
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Open AccessArticle
Influence of Polyelectrolyte Multilayer Properties on Bacterial Adhesion Capacity
Polymers 2016, 8(10), 345; doi:10.3390/polym8100345 -
Abstract
Bacterial adhesion can be controlled by different material surface properties, such as surface charge, on which we concentrate in our study. We use a silica surface on which poly(allylamine hydrochloride)/sodium poly(4-styrenesulfonate) (PAH/PSS) polyelectrolyte multilayers were formed. The corresponding surface roughness and hydrophobicity [...] Read more.
Bacterial adhesion can be controlled by different material surface properties, such as surface charge, on which we concentrate in our study. We use a silica surface on which poly(allylamine hydrochloride)/sodium poly(4-styrenesulfonate) (PAH/PSS) polyelectrolyte multilayers were formed. The corresponding surface roughness and hydrophobicity were determined by atomic force microscopy and tensiometry. The surface charge was examined by the zeta potential measurements of silica particles covered with polyelectrolyte multilayers, whereby ionic strength and polyelectrolyte concentrations significantly influenced the build-up process. For adhesion experiments, we used the bacterium Pseudomonas aeruginosa. The extent of adhered bacteria on the surface was determined by scanning electron microscopy. The results showed that the extent of adhered bacteria mostly depends on the type of terminating polyelectrolyte layer, since relatively low differences in surface roughness and hydrophobicity were obtained. In the case of polyelectrolyte multilayers terminating with a positively charged layer, bacterial adhesion was more pronounced than in the case when the polyelectrolyte layer was negatively charged. Full article
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Open AccessArticle
Comparative Analysis of the Thermal Insulation of Traditional and Newly Designed Protective Clothing for Foundry Workers
Polymers 2016, 8(10), 348; doi:10.3390/polym8100348 -
Abstract
An objective of the undertaken research was checking the applicability of aluminized basalt fabrics for the production of clothing for foundry workers. The results of flammability, the resistance to contact, convective and radiation heat, as well as the resistance to big molten [...] Read more.
An objective of the undertaken research was checking the applicability of aluminized basalt fabrics for the production of clothing for foundry workers. The results of flammability, the resistance to contact, convective and radiation heat, as well as the resistance to big molten metal splashes confirmed the thesis of applicability of the packages with the use of aluminized basalt fabric content for the assumed purpose; therefore, such protective clothing was produced. Thermal comfort of foundry workers is very important and related to many factors, i.e., the structure of the protective clothing package, the number of layers, their thickness, the distance between the body and appropriate underwear. In the paper, a comparison of the results of thermal insulation measurement of two kinds of protective clothing is presented: the traditional one made of aluminized glass fabrics and the new one made of aluminized basalt fabrics. Measurements of clothing thermal insulation were conducted using a thermal manikin dressed in the protective clothing and three kinds of underwear products covering the upper and lower part of the manikin. Full article
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Open AccessArticle
Role of Bending Energy and Knot Chirality in Knot Distribution and Their Effective Interaction along Stretched Semiflexible Polymers
Polymers 2016, 8(10), 347; doi:10.3390/polym8100347 -
Abstract
Knots appear frequently in semiflexible (bio)polymers, including double-stranded DNA, and their presence can affect the polymer’s physical and functional properties. In particular, it is possible and indeed often the case that multiple knots appear on a single chain, with effects which have [...] Read more.
Knots appear frequently in semiflexible (bio)polymers, including double-stranded DNA, and their presence can affect the polymer’s physical and functional properties. In particular, it is possible and indeed often the case that multiple knots appear on a single chain, with effects which have only come under scrutiny in the last few years. In this manuscript, we study the interaction of two knots on a stretched semiflexible polymer, expanding some recent results on the topic. Specifically, we consider an idealization of a typical optical tweezers experiment and show how the bending rigidity of the chain—And consequently its persistence length—Influences the distribution of the entanglements; possibly more importantly, we observe and report how the relative chirality of the otherwise identical knots substantially modifies their interaction. We analyze the free energy of the chain and extract the effective interactions between embedded knots, rationalizing some of their pertinent features by means of simple effective models. We believe the salient aspect of the knot–knot interactions emerging from our study will be present in a large number of semiflexible polymers under tension, with important consequences for the characterization and manipulation of these systems—Be they artificial or biologica in origin—And for their technological application. Full article
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Open AccessArticle
A New Flexible Soy-Based Adhesive Enhanced with Neopentyl Glycol Diglycidyl Ether: Properties and Application
Polymers 2016, 8(9), 346; doi:10.3390/polym8090346 -
Abstract
Soy-based adhesives inherently possess low water resistance and brittleness, which limit their application on plywood fabrication. This investigation involves using a long chain cross-linker, neopentyl glycol diglycidyl ether (NGDE), to produce an intrinsic toughening effect to reduce the brittleness and improve the [...] Read more.
Soy-based adhesives inherently possess low water resistance and brittleness, which limit their application on plywood fabrication. This investigation involves using a long chain cross-linker, neopentyl glycol diglycidyl ether (NGDE), to produce an intrinsic toughening effect to reduce the brittleness and improve the water resistance of a soybean meal–based adhesive. The solids content, viscosity, functional groups, fracture surface micrographs, and thermal stability of the adhesives were measured. Three-layer plywood was fabricated using the resultant adhesive, and the tensile shear strength of the plywood was measured. All adhesive properties were compared with a soybean meal/polyamidoamine-epichlorohydrin (PAE) adhesive and commercial melamine urea formaldehyde resin. The results showed that adding 6 g NGDE improved the water resistance of the soybean meal-based adhesive by 12.5%. This improvement is attributed to the following reasons: (1) a dense cross-linked network is formed by the chemical reaction between NGDE and protein molecules; (2) the toughness of the adhesive increases and a smooth and homogeneous fracture surface is created, which effectively prevents moisture intrusion; (3) the addition of NGDE increases the thermostability of the cured adhesive. The tensile shear strength of the plywood bonded with the soybean meal-based adhesive with 6 g NGDE was 286.2% higher than that without NGDE and attained 1.12 MPa, which was attributed to the reduction in the adhesive’s viscosity, and the improvement in the water resistance and toughness of the adhesive. The tensile shear strength of the plywood bonded with 6 g NGDE was 19.1% higher than that with 6 g PAE and was similar to the MUF resin, which validated the novel adhesive being suitable for use as an industrial plywood adhesive. Full article
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Open AccessArticle
Nanoindentation Investigation of Temperature Effects on the Mechanical Properties of Nafion® 117
Polymers 2016, 8(9), 344; doi:10.3390/polym8090344 -
Abstract
Operating temperature can be a limiting factor in reliable applications of Proton Exchange Membrane (PEM) fuel cells. Nanoindentation tests were performed on perfluorosulfonic acid (PFSA) membranes (Nafion® 117) in order to study the influence of the temperature condition on their mechanical [...] Read more.
Operating temperature can be a limiting factor in reliable applications of Proton Exchange Membrane (PEM) fuel cells. Nanoindentation tests were performed on perfluorosulfonic acid (PFSA) membranes (Nafion® 117) in order to study the influence of the temperature condition on their mechanical properties. The hardness and reduced modulus of Nafion® 117 were measured within a certain temperature range, from 10 to 70 °C. The results indicate that both hardness and elastic modulus show non-monotonic transition with the increase of the test temperature, with reaching peak values of 0.143 and 0.833 GPa at 45 °C. It also found that the membranes have a shape memory effect and a temperature dependent shape recovery ratio. Full article
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Open AccessArticle
Microwave-Assisted Hydrothermal Synthesis of Cellulose/Hydroxyapatite Nanocomposites
Polymers 2016, 8(9), 316; doi:10.3390/polym8090316 -
Abstract
In this paper, we report a facile, rapid, and green strategy for the synthesis of cellulose/hydroxyapatite (HA) nanocomposites using an inorganic phosphorus source (sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O)), or organic phosphorus sources (adenosine 5′-triphosphate disodium salt [...] Read more.
In this paper, we report a facile, rapid, and green strategy for the synthesis of cellulose/hydroxyapatite (HA) nanocomposites using an inorganic phosphorus source (sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O)), or organic phosphorus sources (adenosine 5′-triphosphate disodium salt (ATP), creatine phosphate disodium salt tetrahydrate (CP), or D-fructose 1,6-bisphosphate trisodium salt octahydrate (FBP)) through the microwave-assisted hydrothermal method. The effects of the phosphorus sources, heating time, and heating temperature on the phase, size, and morphology of the products were systematically investigated. The experimental results revealed that the phosphate sources played a critical role on the phase, size, and morphology of the minerals in the nanocomposites. For example, the pure HA was obtained by using NaH2PO4·2H2O as phosphorus source, while all the ATP, CP, and FBP led to the byproduct, calcite. The HA nanostructures with various morphologies (including nanorods, pseudo-cubic, pseudo-spherical, and nano-spherical particles) were obtained by varying the phosphorus sources or adjusting the reaction parameters. In addition, this strategy is surfactant-free, avoiding the post-treatment procedure and cost for the surfactant removal from the product. We believe that this work can be a guidance for the green synthesis of cellulose/HA nanocomposites in the future. Full article
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Open AccessArticle
Particle-Based Modeling of Living Actin Filaments in an Optical Trap
Polymers 2016, 8(9), 343; doi:10.3390/polym8090343 -
Abstract
We report a coarse-grained molecular dynamics simulation study of a bundle of parallel actin filaments under supercritical conditions pressing against a loaded mobile wall using a particle-based approach where each particle represents an actin unit. The filaments are grafted to a fixed [...] Read more.
We report a coarse-grained molecular dynamics simulation study of a bundle of parallel actin filaments under supercritical conditions pressing against a loaded mobile wall using a particle-based approach where each particle represents an actin unit. The filaments are grafted to a fixed wall at one end and are reactive at the other end, where they can perform single monomer (de)polymerization steps and push on a mobile obstacle. We simulate a reactive grand canonical ensemble in a box of fixed transverse area A, with a fixed number of grafted filaments Nf, at temperature T and monomer chemical potential μ1. For a single filament case (Nf=1) and for a bundle of Nf=8 filaments, we analyze the structural and dynamical properties at equilibrium where the external load compensates the average force exerted by the bundle. The dynamics of the bundle-moving-wall unit are characteristic of an over-damped Brownian oscillator in agreement with recent in vitro experiments by an optical trap setup. We analyze the influence of the pressing wall on the kinetic rates of (de)polymerization events for the filaments. Both static and dynamic results compare reasonably well with recent theoretical treatments of the same system. Thus, we consider the proposed model as a good tool to investigate the properties of a bundle of living filaments. Full article
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Open AccessArticle
Tailoring the Static and Dynamic Mechanical Properties of Tri-Block Copolymers through Molecular Dynamics Simulation
Polymers 2016, 8(9), 335; doi:10.3390/polym8090335 -
Abstract
Although the research of the self-assembly of tri-block copolymers has been carried out widely, little attention has been paid to study the mechanical properties and to establish its structure-property relation, which is of utmost significance for its practical applications. Here, we adopt [...] Read more.
Although the research of the self-assembly of tri-block copolymers has been carried out widely, little attention has been paid to study the mechanical properties and to establish its structure-property relation, which is of utmost significance for its practical applications. Here, we adopt molecular dynamics simulation to study the static and dynamic mechanical properties of the ABA tri-block copolymer, by systematically varying the morphology, the interaction strength between A-A blocks, the temperature, the dynamic shear amplitude and frequency. In our simulation, we set the self-assembled structure formed by A-blocks to be in the glassy state, with the B-blocks in the rubbery state. With the increase of the content of A-blocks, the spherical, cylindrical and lamellar domains are formed, respectively, exhibiting a gradual increase of the stress-strain behavior. During the self-assembly process, the stress-strain curve is as well enhanced. The increase of the interaction strength between A-A blocks improves the stress-strain behavior and reduces the dynamic hysteresis loss. Since the cylindrical domains are randomly dispersed, the stress-strain behavior exhibits the isotropic mechanical property; while for the lamellar domains, the mechanical property seems to be better along the direction perpendicular to than parallel to the lamellar direction. In addition, we observe that with the increase of the dynamic shear amplitude and frequency, the self-assembled domains become broken up, resulting in the decrease of the storage modulus and the increase of the hysteresis loss, which holds the same conclusion for the increase of the temperature. Our work provides some valuable guidance to tune the static and dynamic mechanical properties of ABA tri-block copolymer in the field of various applications. Full article
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Open AccessArticle
Factors for Consideration in an Open-Flame Test for Assessing Fire Blocking Performance of Barrier Fabrics
Polymers 2016, 8(9), 342; doi:10.3390/polym8090342 -
Abstract
The main objective of the work reported here is to assess factors that could affect the outcome of a proposed open flame test for barrier fabrics (BF-open flame test). The BF-open flame test characterizes barrier effectiveness by monitoring the ignition of a [...] Read more.
The main objective of the work reported here is to assess factors that could affect the outcome of a proposed open flame test for barrier fabrics (BF-open flame test). The BF-open flame test characterizes barrier effectiveness by monitoring the ignition of a flexible polyurethane foam (FPUF) layer placed in contact with the upper side of the barrier fabric, exposed to a burner flame from below. Particular attention is given to the factors that influence the ignitibility of the FPUF, including thermal resistance, permeability, and structural integrity of the barrier fabrics (BFs). A number of barrier fabrics, displaying a wide range of the properties, are tested with the BF-open flame test. Visual observations of the FPUF burning behavior and BF char patterns, in addition to heat flux measurements on the unexposed side of the barrier fabrics, are used to assess the protective performance of the BF specimen under the open flame test conditions. The temperature and heat transfer measurements on the unexposed side of the BF and subsequent ranking of BFs for their thermal protective performance suggest that the BF-open flame test does not differentiate barrier fabrics based on their heat transfer properties. A similar conclusion is reached with regard to BF permeability characterized at room temperature. However, the outcome of this BF-open flame test is found to be heavily influenced by the structural integrity of thermally degraded BF. The BF-open flame test, in its current form, only ignited FPUF when structural failure of the barrier was observed. Full article
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Open AccessArticle
Modification of Thermal and Mechanical Properties of PEG-PPG-PEG Copolymer (F127) with MA-POSS
Polymers 2016, 8(9), 341; doi:10.3390/polym8090341 -
Abstract
Pluronic F127 exhibits thermogelling behaviour at 20–30 °C via a micelle packing mechanism. Disruption of the micelle packing increases the sol-gel temperature, but results in the decrease of modulus. Herein, we reported a method to modify F127 with polyhedral oligosilsesquioxane (POSS) to [...] Read more.
Pluronic F127 exhibits thermogelling behaviour at 20–30 °C via a micelle packing mechanism. Disruption of the micelle packing increases the sol-gel temperature, but results in the decrease of modulus. Herein, we reported a method to modify F127 with polyhedral oligosilsesquioxane (POSS) to impart a higher gelling temperature without yielding the property and strength of the thermogel. The thermal degradation temperature was enhanced to 15 °C after POSS incorporation and the gelling temperature shifted 10 °C higher, without sacrificing the modulus of the gel. Rheological studies supported the claim that the gel property was reinforced after POSS incorporation. F127-POSS copolymer matrix stored more energy from POSS reinforcement, which saw larger Lissajous curve areas before the collapse of the microstructure for the same amount of stress applied. These results indicated that modification with POSS would raise the sol-gel transition temperature without sacrificing the modulus of the gel. Full article
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Open AccessArticle
Organosolv Lignin-Based Wood Adhesive. Influence of the Lignin Extraction Conditions on the Adhesive Performance
Polymers 2016, 8(9), 340; doi:10.3390/polym8090340 -
Abstract
Ethanol organosolv alfa grass lignins were extracted in the presence of sulfuric acid or Lewis acids (Sc(OTf)3, FeCl3) as catalysts and subjected to a comprehensive structural characterization by solid state 13C NMR, GPC, MALDI-TOF, and ASAP-MS/MS. The [...] Read more.
Ethanol organosolv alfa grass lignins were extracted in the presence of sulfuric acid or Lewis acids (Sc(OTf)3, FeCl3) as catalysts and subjected to a comprehensive structural characterization by solid state 13C NMR, GPC, MALDI-TOF, and ASAP-MS/MS. The impact of the severity of the treatment and of the nature of the acid catalyst on the recovered lignin structure was investigated. The lignins isolated at high severity were highly recondensed and partly composed of regular structures composed of furan-like rings. The alfa (Stipa tenacissima L.) organosolv lignins were used for the preparation of formaldehyde-free adhesives which were characterized by TMA and used for the preparation of particleboard without any addition of synthetic resin. It has been demonstrated for the first time that: (1) the addition of 10% to 30% of organosolv alfa lignin in a tannin-based adhesive improved the adhesive performance; and (2) the conditions of the lignin extraction strongly impact the lignin-based adhesive performances. The highly recondensed lignin extracted with sulfuric acid as a catalyst allowed the production of resins with improved performances. Formulations composed of 50% glyoxalated alfa lignin and 50% of Aleppo Pine tannins yielded good internal bond strength results for the panels (IB = 0.45 MPa) and satisfied relevant international standard specifications for interior-grade panels. Full article
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Open AccessReview
Scattering and Gaussian Fluctuation Theory for Semiflexible Polymers
Polymers 2016, 8(9), 301; doi:10.3390/polym8090301 -
Abstract
The worm-like chain is one of the best theoretical models of the semiflexible polymer. The structure factor, which can be obtained by scattering experiment, characterizes the density correlation in different length scales. In the present review, the numerical method to compute the [...] Read more.
The worm-like chain is one of the best theoretical models of the semiflexible polymer. The structure factor, which can be obtained by scattering experiment, characterizes the density correlation in different length scales. In the present review, the numerical method to compute the static structure factor of the worm-like chain model and its general properties are demonstrated. Especially, the chain length and persistence length involved multi-scale nature of the worm-like chain model are well discussed. Using the numerical structure factor, Gaussian fluctuation theory of the worm-like chain model can be developed, which is a powerful tool to analyze the structure stability and to predict the spinodal line of the system. The microphase separation of the worm-like diblock copolymer is considered as an example to demonstrate the usage of Gaussian fluctuation theory. Full article
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Open AccessArticle
Preparation of a Novel Chitosan Based Biopolymer Dye and Application in Wood Dyeing
Polymers 2016, 8(9), 338; doi:10.3390/polym8090338 -
Abstract
A novel chitosan-based biopolymer dye possessing antibacterial properties was synthesized by reaction of O-carboxymethyl chitosan and Acid Red GR. The synthesized materials were characterized by Fourier transform infrared spectroscopy (FTIR), degree of substitution (DS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TG), [...] Read more.
A novel chitosan-based biopolymer dye possessing antibacterial properties was synthesized by reaction of O-carboxymethyl chitosan and Acid Red GR. The synthesized materials were characterized by Fourier transform infrared spectroscopy (FTIR), degree of substitution (DS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TG), X-ray diffraction (XRD), water solubility test, antibacterial property test, and dyeing performance, including dye uptake, color difference, and fastness. Results showed that the synthesized dye was combined by –NH3+ of O-carboxymethyl chitosan and the sulfonic group of Acid Red GR. According to the comprehensive analysis of XRD and water solubility, the introduction of the carboxymethyl group and acid dye molecule changed the structure of the chitosan from compact to loose, which improved the synthesized dye’s water solubility. However, the thermal stability of the synthesized dye was decreased. The antibacterial property of the poplar wood dyed with the synthesized dye was enhanced and its antibacterial rate, specifically against Staphylococcus aureus and Escherichia coli, also increased to a rate of more than 99%. However, the dye uptake of the synthesized dye was lower than that of the original dye. Despite this, though, the dyeing effect of the synthesized dye demonstrated better water-fastness, and light-fastness than the original dye. Therefore, the novel chitosan-based biopolymer dye can be a promising product for wood dyeing. Full article
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Open AccessArticle
Stretching a Semiflexible Polymer in a Tube
Polymers 2016, 8(9), 328; doi:10.3390/polym8090328 -
Abstract
How the statistical behavior of semiflexible polymer chains may be affected by force stretching and tube confinement is a classical unsolved problem in polymer physics. Based on the Odijk deflection theory and normal mode decomposition in terms of Fourier expansion, we have [...] Read more.
How the statistical behavior of semiflexible polymer chains may be affected by force stretching and tube confinement is a classical unsolved problem in polymer physics. Based on the Odijk deflection theory and normal mode decomposition in terms of Fourier expansion, we have derived a new compact formula for the extension of a wormlike chain of finite length strongly confined in a tube and simultaneously stretched by an external force. We have also suggested a new deflection length, which together with the force-extension relation is valid for a very extended range of the tube-diameter/persistence-length ratio comparing to the classic Odijk theory. The newly derived formula has no adjustable fitting parameters for the whole deflection regime; in contrast, the classic Odijk length needs different prefactors to fit the free energy and average extension, respectively. Brownian dynamics simulations based on the Generalized Bead-Rod (GBR) model were extensively performed, which justified the theoretical predictions. Full article
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Open AccessArticle
Model-Assisted Control of Flow Front in Resin Transfer Molding Based on Real-Time Estimation of Permeability/Porosity Ratio
Polymers 2016, 8(9), 337; doi:10.3390/polym8090337 -
Abstract
Resin transfer molding (RTM) is a popular manufacturing technique that produces fiber reinforced polymer (FRP) composites. In this paper, a model-assisted flow front control system is developed based on real-time estimation of permeability/porosity ratio using the information acquired by a visualization system. [...] Read more.
Resin transfer molding (RTM) is a popular manufacturing technique that produces fiber reinforced polymer (FRP) composites. In this paper, a model-assisted flow front control system is developed based on real-time estimation of permeability/porosity ratio using the information acquired by a visualization system. In the proposed control system, a radial basis function (RBF) network meta-model is utilized to predict the position of the future flow front by inputting the injection pressure, the current position of flow front, and the estimated ratio. By conducting optimization based on the meta-model, the value of injection pressure to be implemented at each step is obtained. Moreover, a cascade control structure is established to further improve the control performance. Experiments show that the developed system successfully enhances the performance of flow front control in RTM. Especially, the cascade structure makes the control system robust to model mismatch. Full article
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Open AccessReview
DNA as a Model for Probing Polymer Entanglements: Circular Polymers and Non-Classical Dynamics
Polymers 2016, 8(9), 336; doi:10.3390/polym8090336 -
Abstract
Double-stranded DNA offers a robust platform for investigating fundamental questions regarding the dynamics of entangled polymer solutions. The exceptional monodispersity and multiple naturally occurring topologies of DNA, as well as a wide range of tunable lengths and concentrations that encompass the entanglement [...] Read more.
Double-stranded DNA offers a robust platform for investigating fundamental questions regarding the dynamics of entangled polymer solutions. The exceptional monodispersity and multiple naturally occurring topologies of DNA, as well as a wide range of tunable lengths and concentrations that encompass the entanglement regime, enable direct testing of molecular-level entanglement theories and corresponding scaling laws. DNA is also amenable to a wide range of techniques from passive to nonlinear measurements and from single-molecule to bulk macroscopic experiments. Over the past two decades, researchers have developed methods to directly visualize and manipulate single entangled DNA molecules in steady-state and stressed conditions using fluorescence microscopy, particle tracking and optical tweezers. Developments in microfluidics, microrheology and bulk rheology have also enabled characterization of the viscoelastic response of entangled DNA from molecular levels to macroscopic scales and over timescales that span from linear to nonlinear regimes. Experiments using DNA have uniquely elucidated the debated entanglement properties of circular polymers and blends of linear and circular polymers. Experiments have also revealed important lengthscale and timescale dependent entanglement dynamics not predicted by classical tube models, both validating and refuting new proposed extensions and alternatives to tube theory and motivating further theoretical work to describe the rich dynamics exhibited in entangled polymer systems. Full article
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Open AccessArticle
The Semiflexible Polymer Translocation into Laterally Unbounded Region between Two Parallel Flat Membranes
Polymers 2016, 8(9), 332; doi:10.3390/polym8090332 -
Abstract
Using the dynamic Monte Carlo method, we investigate dynamics of semiflexible polymer translocation through a nanopore into laterally unbounded region between two parallel flat membranes with separation R in presence of an electric field inside the pore. The average translocation time τ [...] Read more.
Using the dynamic Monte Carlo method, we investigate dynamics of semiflexible polymer translocation through a nanopore into laterally unbounded region between two parallel flat membranes with separation R in presence of an electric field inside the pore. The average translocation time τ initially decreases rapidly with increase of R in the range of R < 10 and then almost keeps constant for R ≥ 10, and the decline range increases with increase of dimensionless bending stiffness κ. We mainly study the effect of chain length N, κ and electric field strength E on the translocation process for R = 5. The translocation dynamics is significantly altered in comparison to an unconfined environment. We find τ ~ Nα, where the exponent α increases with increase of E for small κ. α initially increases slowly with increase of E and then keeps constant for moderate κ. α decreases with increase of E for large κ. However, α decreases with increase of κ under various E. In addition, we find τ ~ κβ. β decreases with increase of N under various E. These behaviors are interpreted in terms of the probability distribution of translocation time and the waiting time of an individual monomer segment passing through the pore during translocation. Full article
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