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In this paper, Brownian dynamics simulation (BDS) studies are executed to demonstrate the distinctive influences of the extent of confinement on the collapsing mechanism and kinetics of a flexible hydrophobic polymer chain in a poor solvent. The collapsing behavior is quantified by the time of collapse, which below a critical dimension of the confinement (hc), encounters a drastic reduction with a further strengthening in the degree of confinement. For dimensions greater than this critical one, the collapse occurs through the well-known hydrodynamic interaction (HI) controlled multiple-globule-mediated mechanisms. However, for channel dimensions less than this critical one, the collapse mechanism is drastically altered. Under such circumstances, the collapse gets predominantly controlled by the confinement effects (with negligible contribution of the HIs) and occurs via the formation of a single central globule. This central globule rapidly engulfs the noncondensed polymer segments, and in the process largely hastens up the collapsing event. Under such circumstances, the collapse time is found to decrease linearly with decrements in the channel height. On the contrary, for channel heights greater than hc, the multiple-globule-mediated collapse is characterized by a collapse time that shows an exponential dependence on the channel height, rapidly attaining a state in which the confinement effect becomes inconsequential and HIs dictate the entire collapsing behavior. We further propose detailed arguments based on physical reasoning as well as free energy estimations to conclusively support the qualitative and quantitative nature of influences of the confinement on the polymer collapse. [ABSTRACT FROM AUTHOR]

We propose a simulation method for infinitely dilute polymer solutions. In this method, an effective Hamiltonian of the solvated polymer chain is introduced to eliminate the degree of freedom of the solvent particle. The effective Hamiltonian is coupled with the density-functional theory (DFT) that we have developed for a polymer-solvent pair correlation function. All the equations proposed in this paper are derived from the first principle. This simulation method was applied to polymer chains in supercritical solvents. We observed anomalous behaviors of polymer chains near the liquid-vapor critical point: both solvophilic and solvophobic polymers expand significantly near the critical point; this is in contrast to the behavior of polymer chains in vacuum. This expansion can be interpreted as a cooperative phenomenon, which enhances the large long-wavelength density fluctuation of the solvent. [ABSTRACT FROM AUTHOR]

In this paper, we present computer simulation results concerning interdiffusion of fully compatible components in symmetric binary (AB) polymer mixtures in solutions. The simulation is performed in two dimensions using the algorithm based on the dynamic lattice liquid model. The solvent molecules are taken into account explicitly. The evolution of the concentration profiles in time at an interface is studied for chain lengths N=2,4,8,16 for three polymer concentrations [lowercase_phi_synonym]=0.1,0.5,0.9. The tracer diffusion coefficients for polymer chains and for the solvent are obtained by monitoring the mean square displacements of their center of mass. The relationships between coefficients of interdiffusion and self-diffusion are tested. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper describes the behavior of charged, polymer brushes in electrolyte solutions of varying solvent quality. The brush height, d, dependence on the chain length, L (=Nl, where l is the Kuhn length), the grafting density s, and solvent conditions is determined. We consider a monomer-monomer potential consisting of three components: (1) a long-ranged, screened Coulombic component of strength νsline;/l (l is the Kuhn length) and range κ[SUP-1]; (2) a short-ranged, two-body component of strength &wsline;l; and (3) a short-ranged, three-body component of strength νsline;l(3). In particular, we examine the transition from a stretched state to a collapsed state in a poor solvent (&wsline;<0) as the solvent quality is decreased. Using dimensional analysis, Monte Carlo methods, and a variational technique, a first order transition is observed as predicted by the scaling arguments of Ross et al. and Borisov et al. for high charge/grafting densities. Using a variational procedure, we derive an analytical expression for the brush size and determine, quantitatively, the critical conditions for a first order transition in terms of key dimensionless variables, νN[SUP&frac52;]), κlN[SUP½], wN[SUP&frac32;], and uN[SUP2] (where v= 2π&ssgma;l[SUP2]νsline;, w = σl[SUP2]&wsline;, and u = σ[SUP2]l[SUP4]νsline;). [ABSTRACT FROM AUTHOR]

We consider a lattice model of a semiflexible homopolymer chain in a bad solvent. Beside the temperature T, this model is described by (i) a curvature energy εh, representing the stiffness of the chain; (ii) a nearest-neighbor attractive energy εv, representing the solvent; and (iii) the monomer density ρ=N/Ω, where N and Ω denote, respectively, the number of monomers and the number of lattice sites. This model is a simplified view of the protein folding problem, which encompasses the geometrical competition between secondary structures (the curvature term modelling helix formation) and the global compactness (modeled here by the attractive energy), but contains no side chain information. By allowing the monomer density ρ to depart from unity one has made a first (albeit naive) step to include the role of the water. In previous analytical studies, we considered only the (fully compact) case ρ=1, and found a first order freezing transition towards a crystalline ground state (also called the native state in the protein literature). In this paper, we extend this calculation to the description of both compact and noncompact phases. The analysis is done first at a mean-field level. We then find that the transition from the high temperature swollen coil state to the crystalline ground state is a two-step process for which (i) there is first a θ collapse transition towards a compact ‘‘liquid’’ globule, and (ii) at low temperature, this ‘‘liquid’’ globule undergoes a discontinuous freezing transition. The mean-field value of the θ collapse temperature is found to be independent of the curvature energy εh. This mean-field analysis is improved by a variational bound, which confirms the independence of the θ collapse temperature with respect to εh. This result is confirmed by a Monte Carlo simulation, although with a much lower value of the θ... [ABSTRACT FROM AUTHOR]

The chemical potential of lattice polymers is calculated in two alternative ways: by the Widom insertion method using the Rosenbluth and Rosenbluth sampling technique and by the modified Widom method, based on the insertion of one segment to an existing polymer chain. In the first part of this paper we present a detailed derivation of the modified Widom technique for lattice systems. We then proceed to calculate the chemical potential for chains of up to 50-mers in monomeric and polymeric solvents. We observe marked odd-even effects on the chemical potential. The density dependence of the chemical potential is found to vary with chain length. For most temperatures and densities studied the chemical potential of chain molecules in a fixed environment becomes linear in chain length for molecules longer than 10–20 segments. The results are compared to the classical lattice theories, which are found to be best at high densities, as expected based on previous investigations. [ABSTRACT FROM AUTHOR]

In many types of computer simulation, a ring polymer of length l in a particular solvent is represented as a polygon of N sides of length lp, where N≊l/lp, and lp is the persistence length. There are many established methods to make such polygons, including kink-jump, bead-spring, and dimerization. This paper introduces a very efficient and easy-to-program method, called vector shuffling, which is useful for generating such polygons in the important special case where the quality of the solvent is good, and the polymer is said to be under θ conditions. [ABSTRACT FROM AUTHOR]

The statistics of a polymer solvent in a network are investigated. We find that, without any explicit nematic interaction, the free chains are coupled to the orientation of the network via the excluded volume interaction. Because their conformations are dominated by screening, the minimum in the free energy of the solvent chains is found by following the network. This first paper considers a rigid network frozen from an earlier equilibrium configuration. In the limiting case of the melt the change in the scattering function is ΔS(k)=12VcscN(cS+cN)-1 l-2[(E·k)-2-k-2], where cS and cN are the concentrations of solvent and network, l is the Kuhn length, and E is the strain tensor. In the case of a swollen network, the full scattering pattern may assume the ‘‘lozenge’’ appearance noticed by several workers. [ABSTRACT FROM AUTHOR]