RESUMO
The conformational behavior of a single diblock copolymer chain with comb blocks is studied by computer simulation. The comb blocks have equal lengths of the backbones and side chains and differ only by the degree of grafting of the side chains. The collapse behavior is studied for two cases: (i) comb diblock copolymer with attracting backbones of the blocks and swollen side chains and (ii) comb diblock copolymer with attracting monomer units of the side chains of the blocks and swollen backbones. In both cases the conformation of a globule with a tail is observed when one of the block collapses while the other stays swollen. At high attraction micellar-type globules are formed. The core of the micelle consists of attracting monomeric units and the soluble segments (side chains or backbones) comprise the corona. It is shown that separation of monomeric units belonging to different blocks can take place both in the core and in the corona regions of the micelle.
RESUMO
Micellization in dilute solutions of diblock copolymers with a polyelectrolyte and a hydrophilic nonionic blocks and oppositely charged polyions is studied using mean-field theory. In aqueous solutions the micelle core consists of the polyelectrolyte complex (PEC) while the corona is formed by hydrophilic blocks of the block copolymers. Describing PEC as a globule in the framework of the Lifshitz [Zh. Eksp. Teor. Fiz. 55, 2408 (1968)] globule theory we calculate the surface tension of the micellar core/solvent interface as a function of the polyion degree of ionization, solvent quality, and concentration of low-molecular-mass salt. The equilibrium aggregation number of starlike micelles formed by block copolymers and homopolymers of opposite charge at stoichiometric mixture compositions is found as a function of the system parameters. It is shown that micelles disintegrate upon addition of salt.
RESUMO
We study a Fock-space operator technique for describing the stochastic kinetics of a spin-facilitated kinetic Ising model. We focus in particular on the diffusion (fast Kawasaki exchange) limit in which the kinetics can be described by a single mean field evolution equation. We derive some general criteria for the approximative validity of mean field theory for the case of a nondiverging diffusion coefficient of the local spin states.
RESUMO
We study the diffusion of classical particles in channels with varying boundaries. The problem is characterized by the Neumann boundary condition (zero normal current) in contrast to the Dirichlet boundary condition (zero function) for "quantum confinement" problems. Eliminating transverse modes, we derive an effective diffusion equation that describes particle propagation in the space of reduced dimension in the presence of a frozen drift field. The latter stems from boundary variations of the original boundary problem. Boundary variations may thus result in an appreciable change of the particle transport and, in particular, in a nonlinear response to an external field. We show also that there is a difference between the nonlinear responses of open and closed channels.
RESUMO
The partition function of a semiflexible chain molecule with harmonically confined transverse fluctuations is calculated. Equilibrium properties exhibit qualitative differences between the weak and the strong confinement behavior. The relaxation times of undulations perpendicular to the chain molecule contour are calculated on the basis of a Langevin equation approach. With increasing confinement a decrease of the relaxation times is found. As a consequence the mean square displacement of monomers and the dynamic structure factor are strongly influenced by the confinement. The comparison of the calculated mean square displacement with diffusing wave spectroscopy measurements of actin filaments exhibits good agreement.
