pinecone/core-2020-05-10-deduplication huggingface dataset:
Reversible Gel Formation of Triblock Copolymers Studied by Molecular
  Dynamics Simulation

Molecular dynamics simulations have been employed to study the formation of a
physical (thermoreversible) gel by amphiphilic A-B-A triblock copolymers in
aqueous solution. In order to mimic the structure of hydrogel-forming
polypeptides employed in experiments [W.A. Petka et al., Science 281, 389
(1998)], the endblocks of the polymer chains are modeled as hydrophobic rods
representing the alpha-helical part of the polypeptides whereas the central
B-block is hydrophilic and semi-flexible. We have determined structural
properties, such as the hydrophobic cluster-size distribution function, the
geometric percolation point and pair correlation functions, and related these
to the dynamical properties of the system. Upon decrease of the temperature, a
network structure is formed in which bundles of endblocks act as network
junctions. Both at short and medium distances an increased ordering is
observed, as characterized by the pair correlation function. Micelle formation
and the corresponding onset of geometric percolation induce a strong change in
dynamical quantities, e.g., in the diffusion constant and the viscosity, and
causes the system to deviate from the Stokes-Einstein relation. The dynamical
properties show a temperature dependence that is strongly reminiscent of the
behavior of glass-forming liquids. The appearance of a plateau in the stress
autocorrelation function suggests that the system starts to exhibit a
solid-like response to applied stress once the network structure has been
formed, although the actual sol-gel transition occurs only at a considerably
lower temperature.Comment: Submitted to J. Polymer Science Part B: Polymer Physic
Investigating Interactions of Biomembranes and Alcohols: A Multiscale
  Approach

We study the interaction of lipid bilayers with short chain alcohols using
molecular dynamics on different length scales. We use detailed atomistic
modeling and modeling on the length scale where an alcohol is just an
amphiphilic dimer. Our strategy is to calibrate a coarse--grained model against
the detailed model at selected state points at low alcohol concentration and
then perform a wider range of simulations using the coarse--grained model. We
get semiquantitative agreement with experiment for the major observables such
as order parameter and area per molecule. We find a linear increase of area per
molecule with alcohol concentration. The alcohol molecules in both system
descriptions are in close contact with the glycerol backbone. Butanol molecules
can enter the bilayer to some extent in contrast to the behavior of shorter
alcohols. At very high alcohol concentrations we find clearly increased
interdigitation between leaflets.Comment: 14 pages, 6 figure
Evaluation of piezoelectric PVDF polymers for use in space environments. II. Effects of atomic oxygen and vacuum UV exposure

The effects of atomic oxygen (AO) and vacuum UV radiation simulating\ud
low Earth orbit conditions on two commercially available piezoelectric polymer films,\ud
poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-trifluoroethylene)\ud
P(VDF-TrFE), have been studied. Surface erosion and pattern development are significant\ud
for both polymers. Erosion yields were determined as 2.8 � 10�24 cm3/atom\ud
for PVDF and 2.5 � 10�24 cm3/atom for P(VDF-TrFE). The piezoelectric properties of the residual material of both polymers were largely unchanged after exposure, although a slight shift in the Curie transition of the P(VDF-TrFE) was observed. A lightly cross-linked network was formed in the copolymer presumably because of penetrating vacuum ultraviolet (VUV) radiation, while the homopolymer remained\ud
uncross-linked. These differences were attributed to varying degrees of crystallinity and potentially greater absorption, and hence damage, of VUV radiation in P(VDFTrFE)\ud
compared with PVDF
Understanding the effect of skin formation on the removal of solvents from semicrystalline polymers

The effect of glassy skin formation on the drying of semicrystalline polymers was investigated with a comprehensive mathematical model developed for multicomponent systems. Polymers with high glass-transition temperatures can become rubbery at room temperature under the influence of solvents. As the solvents are removed from the polymer, a glassy skin can form and continue to develop. The model takes into account the effects of diffusion-induced polymer crystallization as well as glassy-rubbery transitions on the overall solvent content and polymer crystallinity. A Vrentas-Duda free-volume-based diffusion scheme and crystallization kinetics were used in our model. The polymer-solvent system chosen was a poly(vinyl alcohol) (PVA)-water-methanol system. The drying kinetics of PVA films were obtained by gravimetric methods with swollen films with known water/methanol concentrations. The overall drying behaviors of the polymer system determined by our model and experimental methods were compared and found to match well.National Science Foundationfor: NSF-CTS010716
Coarse Graining in Block Copolymer Films

We present few ordering mechanisms in block copolymer melts in the
coarse-graining approach. For chemically homogeneous or modulated confining
surfaces, the surface ordering is investigated above and below the
order-disorder temperature. In some cases the copolymer deformation near the
surface is similar to the copolymer morphology in bulk grain boundaries. Block
copolymers in contact with rough surfaces are considered as well, and the
transition from lamellae parallel to perpendicular to the surface is
investigated as a function of surface roughness. Finally, we describe how
external electric fields can be used to align block copolymer meso-phases in a
desired direction, or to induce an order-order phase transition, and dwell on
the role of mobile dissociated ions on the transition.Comment: Review for special edition of Journal of Polymer Science part
  B:Polymer Physic
Crystallization of poly(vinyl alcohol) during solvent removal: Infrared characterization and mathematical modeling

Crystallization of semicrystalline polymer films during drying has a significant effect on the rate of solvent removal. Understanding and controlling the crystallization kinetics is important in controlling residual solvent levels and drying kinetics. The degree of crystallinity of the poly(vinyl alcohol) films during multicomponent drying was investigated using Fourier transform infrared spectroscopy (FTIR). The 1141 cm-1 band is sensitive to the degree of crystallinity of the polymer and the growth of intensity of this band was monitored as drying progressed. The results from the FTIR studies were comparable to the results obtained from differential scanning calorimetry. Studies were conducted to test the effect of initial solvent composition (water-methanol mixture), drying temperature, and polymer molecular weight on the rate of crystallization and the final crystallinity of the films. An increase in initial methanol composition increased the crystallization rate but did not affect the final degree of crystallinity. An increase in drying temperature and decrease in polymer molecular weight increased the rate of crystallization as well as the final degree of crystallinity. Based on the experimental data, rate constants for crystallization kinetics were extracted from our previously developed model based on free volume theory. The experimental data and the simulation results showed good agreement. The ability of the free volume theory to illustrate the crystallization behavior validated the model and improved its capability.National Science Foundation NSF-CTS010716
The Effect of Nanoparticle Shape on Polymer-Nanocomposite Rheology and
  Tensile Strength

Nanoparticles can influence the properties of polymer materials by a variety
of mechanisms. With fullerene, carbon nanotube, and clay or graphene sheet
nanocomposites in mind, we investigate how particle shape influences the melt
shear viscosity $\eta$ and the tensile strength $\tau$, which we determine via
molecular dynamics simulations. Our simulations of compact (icosahedral), tube
or rod-like, and sheet-like model nanoparticles indicate an order of magnitude
increase in the viscosity $\eta$ relative to the pure melt. This finding
evidently can not be explained by continuum hydrodynamics and we provide
evidence that the $\eta$ increase in our model nanocomposites has its origin in
chain bridging between the nanoparticles. We find that this increase is the
largest for the rod-like nanoparticles and least for the sheet-like
nanoparticles. Curiously, the enhancements of $\eta$ and $\tau$ exhibit {\it
opposite trends} with increasing chain length $N$ and with particle shape
anisotropy. Evidently, the concept of bridging chains alone cannot account for
the increase in $\tau$ and we suggest that the deformability or flexibility of
the sheet nanoparticles contributes to nanocomposite strength and toughness by
reducing the relative value of the Poisson ratio of the composite. Our
simulations point to a substantial contribution of nanoparticle shape to both
mechanical and processing properties of polymer nanocomposites
Solubility and diffusivity of methylmethacrylate and butylacrylate monomers in a MMA-BA copolymer

Mutual diffusion coefficients and sorption isotherms of methyl methacrylate (MMA) and butyl acrylate (BA) monomers in methyl methacrylate-butyl acrylate copolymer (MMA-BA) have been measured by gravimetric sorption. MMA is found to have higher solubility and diffusion rates in the copolymer than BA. Sorption data for MMA were interpreted using classical Flory-Huggins thermodynamic theory with a constant interaction parameter (χ). A modified version of this theory has been applied to correlate the sorption data of BA, which exhibit a temperature and concentration-dependent χ parameter. For MMA, the isotherm data reveal enhanced polymer-solvent interactions with increasing temperature, while for BA the data indicate a drive toward phase separation with increasing temperature. Despite the difference in thermodynamic behavior, both monomers are found to exhibit Fickian diffusion and the diffusivity data are correlated reasonably well with the Vrentas-Duda free volume theory. Some deviation between the free-volume correlation and the experimental data is observed at the lowest temperature and BA concentration examined.TÜBİTAK and İYT
Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

Syndiotactic polystyrene (sPS) was solidified from the melt under drastic conditions according to a continuous cooling transformation methodology developed by the authors, which covered a cooling rate range spanning from approximately 0.03 to 3000 °C/s. The samples produced, structurally homogeneous across both their thickness and surface, were analyzed by macroscopic methods, such as density, wide-angle X-ray diffraction (WAXD), and microhardness (MH) measurements. The density was strictly related to the phase content, as confirmed by WAXD deconvolution. The peculiar behavior encountered (the density first decreasing and then increasing with the cooling rate) was attributed to the singularity of the phases formed in sPS; that is, one of the crystalline phases (α) was less dense than the amorphous phase, and the latter, in turn, was less dense than the other crystalline phase (β). With an increasing cooling rate, the thermodynamically stable phase (β) disappeared first, and it was followed by the α phase. On the other hand, the MH values remarkably depended on the amount of the β phase, the α-phase content influencing the mechanical properties only to a minor extent. The behavior of the crystallization kinetics was described through a modified multiphase Kolmogoroff–Avrami–Evans model for nonisothermal crystallization
Field-Theoretic Simulations of Polyelectrolyte Complexation

We briefly discuss our recent field-theoretic study of polyelectrolyte
complexation, which occurs in solutions of two oppositely charged
polyelectrolytes. Charged systems require theoretical methods beyond the
mean-field (or self-consistent field) approximation; indeed, mean-field theory
is qualitatively incorrect for such polyelectrolyte solutions. Both analytical
(one-loop) and numerical (complex Langevin) methods to account for charge
correlations are discussed. In particular, the first application of
field-theoretic simulations to polyelectrolyte systems is reported. The
polyelectrolyte charge-charge correlation length and a phase diagram are
provided; effects of charge redistribution are qualitatively explored.Comment: 7 pages, 3 figures, 3 equations, LaTeX; accepted to Journal of
  Polymer Science B: Polymer Physics; v2: a revised and expanded version, 6
  paragraphs of text and about 20 references adde
Initial Stage of Fiber Structure Development in the Continuous Drawing of Poly(ethylene terephthalate)

This is a preprint of an article published in Journal of Polymer Science: Part B: Polymer Physics. 46(19): 2126-2142 (2008).The initial stage of fiber structure development in the continuous neckdrawing of amorphous poly(ethylene terephthalate) fibers was analyzed by in situ wide-angle X-ray diffraction, small-angle X-ray scattering, and fiber temperature measurements. The time error of the measurements (\600 ls) was obtained by synchrotron X-ray source and laser irradiation heating. A highly ordered fibrillar-shaped two-dimensional (smectic-like) structure was found to be formed less than 1 ms after necking. By analyzing its (0010) and (0020) diffractions, the length of the structure 60–70 nm were obtained. A three-dimensionally ordered triclinic crystal began to form with the vanishing of the structure around 1 ms after necking. The amount and size of the crystal were almost saturated within several milliseconds of necking, during which time a mainly exothermic heat of crystallization was also observed
Equations of state for polyamide-6 and its nanocomposites. 1. Fundamentals and the matrix

The pressure-volume-temperature (PVT) surface of polyamide-6 (PA-6) was determined in the range of temperature T = 300\u2013600 K and pressure P = 0.1\u2013190 MPa. The data were analyzed separately for the molten and the noncrystalline phase using the Simha-Somcynsky (S-S) equation of state (eos) based on the cell-hole theory. At Tg(P) \u2264 T \u2264 Tm(P), the \u2018\u2018solid\u2019\u2019 state comprises liquid phase with crystals dispersed in it. The PVT behavior of the latter phase was described using Midha-Nanda-Simha- Jain (MNSJ) eos based on the cell theory. The data fitting to these two theories yielded two sets of the Lennard-Jones interaction parameters: e*(S-S) = 34.0 \ub1 0.3 and e*(MNSJ) = 22.8 \ub1 0.3 kJ/mol, whereas v*(S-S) = 32.00 \ub1 0.1 and v*(MNSJ) = 27.9 \ub1 0.2 mL/mol. The raw PVT data were numerically differentiated to obtain the thermal expansion and compressibility coefficients, \u3b1 and \u39a, respectively. At constant P, j followed the same dependence on both sides of the melting zone near Tm. By contrast, \u3b1 = \u3b1(T) dependencies were dramatically different for the solid and molten phase; at T < Tm, \u3b1 linearly increased with increasing T, then within the melting zone, its value step-wise decreased, to slowly increase at higher temperatures.NRC publication: Ye
Thermal curing behavior of MWCNT modified vinyl ester-Polyester resin suspensions prepared with 3-roll milling technique

This study aims to investigate the curing behavior of a vinyl ester-polyester resin suspensions containing 0.3 wt % of multiwalled carbon nanotubes with and without amine functional groups (MWCNTs and MWCNT-NH2). For this purpose, various analytical techniques, including Differential Scanning Calorimetry (DSC), Fourier infrared spectroscopy (FTIR), Raman Spectroscopy, and Thermo Gravimetric Analyzer (TGA) were conducted. The resin suspensions with carbon nanotubes (CNTs) were prepared via 3-roll milling technique. DSC measurements showed that resin suspensions containing CNTs exhibited higher heat of cure (Q), besides lower activation energy (Ea) when compared with neat resin. For the sake of simplicity of interpretation, FTIR investigations were performed on neat vinyl ester resin suspensions containing the same amount of CNTs as resin. As a result, the individual fractional conversion rates of styrene and vinyl ester were interestingly found to be altered dependent on MWCNTs and MWCNT-NH2. The findings obtained from RS measurements of the cured samples are highly proportional to those obtained from FTIR measurements. TGA measurements revealed that CNT modified nanocomposites have higher activation energy of degradation (Ed) compared with the cured polymer. The findings obtained revealed that CNTs with and without amine functional groups alter overall thermal curing response of the surrounding matrix resin, which may probably impart distinctive characteristics to mechanical behavior of the corresponding nanocomposites achieved
Investigation by combined solid-state NMR and SAXS methods of the morphology and domain size in polystyrene-b-polyethylene oxide-b-polystyrene triblock copolymers

The microphase structure of a series of polystyrene-b-polyethylene oxide-b-polystyrene (SEOS) triblock copolymers with different compositions and molecular weights has been studied by solid-state NMR, DSC, wide and small angle X-ray scattering (WAXS and SAXS). WAXS and DSC measurements were used to detect the presence of crystalline domains of polyethylene-oxide (PEO) blocks at room temperature as a function of the copolymer chemical composition. Furthermore, DSC experiments allowed the determination of the melting temperatures of the crystalline part of the PEO blocks. SAXS measurements, performed above and below the melting temperature of the PEO blocks, revealed the formation of periodic structures, but the absence or the weakness of high order reflections peaks did not allow a clear assessment of the morphological structure of the copolymers. This information was inferred by combining the results obtained by SAXS and 1H NMR spin diffusion experiments, which also provided an estimation of the size of the dispersed phases of the nanostructured copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 55–64, 2010FAPES
Nanostructure and mechanical properties studied during dynamical straining of microfibrillar reinforced HDPE/PA blends

Oriented polymer blends based on high-density polyethylene (HDPE) are strained until failure. Twodimensional
(2D) small-angle X-ray scattering patterns monitor the nanostructure evolution. Data evaluation methods
for high-precision determination of macroscopic mechanical and nanoscopic structure parameters are presented. The
hardest materials exhibit a very inhomogeneous nanodomain structure. During straining their domains appear to be
wedged together and inhibit transverse contraction on the nanometer scale. Further components are polyamides (PA6,
PA12) (20–30%) and as compatibilizer Yparex® 8102 (YP) (0–10%). Some HDPE/PA6 blends are additionally loaded
with nanoclays (Nanomer® or Cloisite®). Blending of HDPE with PA12 causes no synergistic effect. In the absence
of nanoclay, PA6 and HDPE form a heterogeneous nanostructure with high Young’s modulus. After addition of YP a
more homogeneous scaffold structure is observed in which some of the PA6 microfibrils and HDPE crystallites appear
to be rigidly connected, but the modulus has decreased. Both kinds of nanoclay induce a transition from a structure
without transverse correlation among the microfibrils into a macrolattice with 3D correlations among HDPE domains
from neighboring microfibrils. For extensions between 0.7% and 3.5% the scattering entities with 3D correlation exhibit
transverse elongation instead of transverse contraction. The process is interpreted as overcoming a correlation barrier
executed by the crystallites in an evasion-upon-approaching mechanism. During continued straining the 3D correlation
is reduced or removed.SFRH/BSAB/812/200
PVT properties of linear and dendritic polymers

The aim of this article is to examine the limits of applicability of the Simha-Somcynsky (S-S) equation of state (EOS) by comparing the pressure-volume-temperature (PVT) data and the derivatives (compressibility, j, and thermal expansion coefficient, a) of anionic linear polystyrene (PS) with poly(benzyl ether) dendrimers (PBED). Fitting the PVT of PBED data to the S-S EOS was similarly satisfactory as that of PS and the computed Lennard-Jones (L-J) interaction parameters showed similar errors of ca. 1%. Next, the experimental derivatives, a and j of PS and PBED were compared with these functions computed from the S-S EOS\ue2\u20ac\u201dgood agreement was obtained for a at ambient pressure, P, indicating validity of the S-S theory at least up to the first derivative. While the predicted j \uc2\ubc j(P) dependence for PS and a linear PBED homologue was correct, for dendrimers the compressibility was higher at low pressure and it was lower at high P than theory predicts. Also the extracted values of the L-J repulsion volume,v, between a segment pair was smaller than expected. The specific architecture of dendrimer molecules is responsible for this behavior, since their 3D configuration is significantly different from the S-S model with uniform segmental density and oxygen bonds in the main and side chains add flexibility.Peer reviewed: YesNRC publication: Ye
Single-Phase Flow of Non-Newtonian Fluids in Porous Media

The study of flow of non-Newtonian fluids in porous media is very important
and serves a wide variety of practical applications in processes such as
enhanced oil recovery from underground reservoirs, filtration of polymer
solutions and soil remediation through the removal of liquid pollutants. These
fluids occur in diverse natural and synthetic forms and can be regarded as the
rule rather than the exception. They show very complex strain and time
dependent behavior and may have initial yield-stress. Their common feature is
that they do not obey the simple Newtonian relation of proportionality between
stress and rate of deformation. Non-Newtonian fluids are generally classified
into three main categories: time-independent whose strain rate solely depends
on the instantaneous stress, time-dependent whose strain rate is a function of
both magnitude and duration of the applied stress and viscoelastic which shows
partial elastic recovery on removal of the deforming stress and usually
demonstrates both time and strain dependency. In this article the key aspects
of these fluids are reviewed with particular emphasis on single-phase flow
through porous media. The four main approaches for describing the flow in
porous media are examined and assessed. These are: continuum models, bundle of
tubes models, numerical methods and pore-scale network modeling.Comment: 94 pages, 12 figures, 1 tabl
A “self-pinning” adhesive based on responsive surface wrinkles

Surface wrinkles are interesting since they form spontaneously into well-defined patterns. The mechanism of formation is well-studied and is associated with the development of a critical compressive stress that induces the elastic instability. In this work, we demonstrate surface wrinkles that dynamically change in response to a stimulus can improve interfacial adhesion with a hydrogel surface through the dynamic evolution of the wrinkle morphology. We observe that this control is related to the local pinning of the crack separation pathway facilitated by the surface wrinkles during debonding, which is dependent on the contact time with the hydrogel.available in PMC 2012 January 1.National Science Foundation (U.S.) (NIRT grant 0609182)National Science Foundation (U.S.) (NIH grant DE013023)Center for Integration of Medicine and Innovative Technology (U.S. Army grant W81XWH-07-2-0011)Center for Integration of Medicine and Innovative Technology (NIH GM086433)University of Massachusetts (System)Massachusetts Technology Transfer CenterAmerican Heart Association (Grant 0835601D