Search results for "dynamics"

Combined main chain/side chain polymers. A new class of liquid crystalline polymers with unusual structural, thermodynamic and dynamic properties

1990

Abstract Combined main chain/side chain polymers carry rigid rod-like mesogenic units both in the side chain and along the chain backbone. The properties of such combined systems are expected to be controlled by the competition of the interactions between the mesogenic units in the side and main chains as well as the tendency of the chain backbones to maximize their entropy. The thermodynamic, structural and dynamic properties of such combined main chain/side chain liquid-crystalline polymers were investigated for various chain architectures. The combined systems were found to display properties corresponding in many cases to a favourable superposition of properties characteristic of both m…

Elastic Properties of Liquid Crystal Elastomer Balloons

2001

We introduce a method to measure elastic properties of smectic liquid crystalline elastomers. Freely suspended smectic polymer films containing photoreactive groups are inflated to spherical bubbles and crosslinked by UV light irradiation. After crosslinking, the balloon volume is varied and elastic properties of the material are determined from the relation between radius and inner excess pressure. The influence of the network topology on the elastic behaviour is discussed.

Disentangling the Role of Chain Conformation on the Mechanics of Polymer Tethered Particle Materials

2019

[Image: see text] The linear elastic properties of isotropic materials of polymer tethered nanoparticles (NPs) are evaluated using noncontact Brillouin light spectroscopy. While the mechanical properties of dense brush materials follow predicted trends with NP composition, a surprising increase in elastic moduli is observed in the case of sparsely grafted particle systems at approximately equal NP filling ratio. Complementary molecular dynamics simulations reveal that the stiffening is caused by the coil-like conformations of the grafted chains, which lead to stronger polymer–polymer interactions compared to densely grafted NPs with short chains. Our results point to novel opportunities to …

Structured Nanoparticles from the Self-Assembly of Polymer Blends through Rapid Solvent Exchange

2017

Molecular dynamics simulations were performed to study systematically the rapid mixing of a polymer blend in solution with a miscible nonsolvent. In agreement with experiments, we observe that polymers self-assemble into complex nanoparticles, such as Janus and core-shell particles, when the good solvent is displaced by the poor solvent. The emerging structures can be predicted on the basis of the surface tensions between the polymers as well as between the polymers and the surrounding liquid. Furthermore, the size of the nanoparticles can be independently tuned through the mixing rate and the polymer concentration in the feed stream; meanwhile, the composition of the nanoparticles can be c…

Interfacial Tensions from Drop Retraction versus Pendant Drop Data and Polydispersity Effects

2004

Interfacial tensions sigma were measured by means of both methods for the following polymer pair: polyisobutylene (PIB 3) plus poly(dimethylsiloxane) (PDMS 152) and poly(dimethyl-co-methylphenylsiloxane) (CoP26*) plus PDMS 48. The numbers after the abbreviation state the molar masses in kilograms; the homopolymers exhibit polydispersities on the order of 2. The reliability of the method of drop retraction is backed up by systematic measurements, which demonstrate that it is possible to study the time evolution of sigma. Because of the free choice of the phases (drop or matrix) and the possibility to vary the overall composition of the system in a wide range, drop retraction yields more info…

Pearl-necklace structures of molecular brushes with rigid backbone under poor solvent conditions: A simulation study

2010

Bottle-brush polymers, where flexible side chains containing N=20 to 50 effective monomers are grafted to a rigid backbone, are studied by molecular dynamics simulations, varying the grafting density σ and the solvent quality. Whereas for poor solvents and large enough σ the molecular brush is a cylindrical object, homogeneous in axial direction, for intermediate values of σ an axially inhomogeneous structure of "pearl-necklace" type is formed. The "pearls," however, have a strongly nonspherical ellipsoidal shape, due to the fact that several side chains cluster together in one pearl, qualitatively consistent with predictions of Sheiko et al. [Eur. Phys. J. E 13, 125 (2004)] We analyze the …

Multi-scale simulations of polymeric nanoparticle aggregation during rapid solvent exchange.

2018

Using a multi-scale approach which combines both molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations, we study a simple and scalable method for fabricating charge-stabilized nanoparticles through a rapid solvent exchange, i.e., Flash NanoPrecipitation (FNP). This multi-scale approach is based on microscopic information from MD simulations and uses a KMC algorithm to access macroscopic length- and time scales, which allows direct comparison with experiments and quantitative predictions. We find good agreement of our simulation results with the experiments. In addition, the model allows us to understand the aggregation mechanism on both microscopic and macroscopic levels and det…

Molecular Simulation of Polymer Melts and Blends: Methods, Phase Behavior, Interfaces, and Surfaces

2016

Penetrant diffusion in frozen polymer matrices: A finite-size scaling study of free volume percolation

1996

The diffusion of penetrant particles in frozen polymer matrices is investigated by means of Monte Carlo simulations of the bond fluctuation model. By applying finite-size scaling to data obtained from very large systems it is demonstrated that the diffusion process takes place on a percolating free volume cluster describable by a correlated site percolation model which falls into the same universality class as random percolation. The diverging correlation length entails a pronounced dependence of the diffusion constant on the size of the simulated system. It is shown that this dependence is appreciable for a wide range of parameters around the transition. \textcopyright{} 1996 The American …

Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer

2003

The effects of the physical aging on the vibrational density of states (VDOS) of a polymeric glass is studied. The VDOS of a poly(methyl methacrylate) glass at low-energy (<15 meV), was determined from inelastic neutron scattering at low-temperature for two different physical thermodynamical states. One sample was annealed during a long time at temperature lower than Tg, and another was quenched from a temperature higher than Tg. It was found that the VDOS around the boson peak, relatively to the one at higher energy, decreases with the annealing at lower temperature than Tg, i.e., with the physical aging.