Polymer Chains In Solvent Research Articles

Coil-globule transition in two-dimensional polymer chains in an explicit solvent.

The structure of two-dimensional polymer chains in a solvent at different temperatures is still far from being fully understood. Computer simulations of high-density macromolecular systems require the use of appropriate algorithms, and therefore the simulations were carried out using the Cooperative Motion Algorithm. The polymer model studied was exactly two-dimensional, coarse-grained and based on a triangular lattice. The theta temperature and temperature of coil-to-globule transition, and critical exponents were determined. The differences between the structure of such a disk and that of a chain in a dense polymer liquid were shown.

Solvation and diffusion of poly(vinyl alcohol) chains in a hydrated inorganic ionic liquid.

While the behavior of polyelectrolyte chains in aqueous salt solutions has been extensively studied, little is known about polar polymer chains in solvents with extremely high concentrations of inorganic ions, such as those found in ionic liquids (ILs). Here, we report on expansion, solvation and diffusion of poly(vinyl alcohol), PVA, chains in dilute solutions of a hydrated inorganic IL phase change material (PCM), lithium nitrate trihydrate (LNH). This solvent has an extremely high concentration of inorganic ions (≈18 M) with a low concentration of water molecules largely forming solvation shells of Li+ and NO3- ions, as shown using ATR-FTIR spectroscopy. Diffusion and hydrodynamic size of PVA chains of different molecular weights in this unusual solvent were studied using fluorescence correlation spectroscopy (FCS). A higher scaling exponent obtained from the molecular weight dependences of the diffusion coefficients of PVA chains as well as a lower overlap concentration (c*) of PVA in LNH solutions as measured by FCS suggest an expansion of the polymer coils in this solvent. We argue that enhanced solubility of PVA in LNH solutions is likely a result of increased rigidification of polymer chains due to the binding of solvated Li+ ions, which is demonstrated using 7Li NMR spectroscopy. We believe that an understanding of solvation and ion-binding capability can offer crucial insight into designing polymer-based shape stabilization matrices for inorganic PCMs.

The properties of a single polymer chain in solvent confined in a slit: A molecular dynamics simulation

A single polymer chain in solvent confined in a slit formed by two parallel plates is studied by using molecular dynamics simulation method. The square radii of gyration and diffusion behaviors of polymers are greatly affected by the distance between the two plates, but they do not follow the same way. The chain size decays drastically with increasing h (h is the distance between two plates), until a basin occurs, and a universal h/〈Rg〉0 dependence for polymer chains with different degrees of polymerization can be obtained. While, for the chain’s diffusion coefficient, it decays monotonously and there is no such basin-like behavior. Furthermore, we studied the radial distribution function of confined polymer chains to explain the reason why there is a difference for the decay behaviors between dynamic properties and static properties. Besides, we also give the degree of confinement dependence of the static scaling exponent for a single polymer chain. Our work provides an efficient way to estimate the dynamics and static properties of confined polymer chains, and also helps us to understand the behavior of polymer chains under confinement.

Colloidal and electrophoretic behavior of polymer particulates in suspension

The behavior of individual polymer chains in solvent has been reported in the literature and formed the basis of polymer dynamic understanding [S.R. Quake, H. Babcock and S. Chu, Nature 388 (1997) 151, T.T. Perkins, D.E. Smith and S. Chu, Science 276 (1997) 2016.]. However, thus far, the behavior of isolated particulate polymer or block polymer/copolymers in suspension has not been investigated. In the present work, it is found that classical colloidal theories that describe the particle behavior in suspension can be applied to polymer particulates/blocks. This, in turn, suggests many possibilities in materials processing including co-processing of composites via particulate or powder route to formulate complex microstructures. A polymeric material, polyetheretherketone (PEEK), was used to examine the colloidal behavior of polymer particulates in the present work. Zeta potential of the particulate suspension was measured and the electrostatic interaction of the particulates was examined by DLVO theory. The electrosteric effect between the charged particulates in suspension was also studied. Based on the findings, an optimum condition for a dispersed stable suspension was identified and applied to the electrophoretic deposition of PEEK particulates.

Computer simulation of aqueous block copolymer assemblies: Length scales and methods

AbstractAtomistic, coarse‐grain, and mesoscopic computer simulation methods applied recently to the study of block copolymer assemblies in solution are reviewed. At the atomic level, particle‐based simulations have provided insight into specific interactions such as hydrogen bonding between polymer and water. Coarse‐grain models have given a generalized view of the conformations of polymer chains in solvents of different qualities by grouping clusters of atoms into effective interaction sites. Mesoscopic self‐consistent field theory allows for the study of the phase diagram of block copolymers in water using a mean‐field continuum description. Advances in and results with these methodologies are presented along with present challenges. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1907–1918, 2006

Simulation of Phase Transitions of Single Polymer Chains: Recent Advances

AbstractSummary:The behaviour of a flexible polymer chain in solvents of variable quality in dilute solution is discussed both in the bulk and in the presence of an adsorbing wall. Monte Carlo simulations of coarse‐grained bead‐spring models and of the bond fluctuation model are presented and interpreted in terms of phenomenological theories and scaling concepts. Particular attention is paid to the behaviour of the polymer chain when the temperature of the polymer solution gets lower than the Theta temperature. It is argued that the adsorption transition line at the Theta temperature splits into lines of wetting and drying transitions of polymer globules attached to the wall. In addition, it is shown that the coil‐globule transition is followed by a second transition, which in the bond fluctuation model is a crystallization into a regular lattice structure. Performing a finite size scaling analysis on the two transitions it is shown that (for the chosen model) both transitions coincide in the thermodynamic limit, corresponding to a direct collapse of the random coil into the crystal without intermediate coil‐globule transition. The implications of this result for the standard mean field or tricritical theory of the coil‐globule transition based on a truncated virial expansion are discussed.

Computer Simulation of Polymer Diffusion Under External Electric Field

Molecular dynamics simulations were carried out to investigate the diffusion of polymer chains in solvent under an external electric field. Polyethylene-like polymer and methyl chloride molecule were chosen as solute and solvent. The external DC electric field strength was varied from 10 to 50 (4.3×108 V/m). Both polar and non-polar polymer chains in polar and non-polar solvents were investigated. The simulation shows that the center of mass diffusion coefficient of polymer is sensitive to the polarities of polymer and solvent, field strength, polymer concentration and the density of the system. Various factors that affect the diffusion constant of the polymer are discussed. The present simulation is consistent with the results from light scattering experiments.