On the dynamics and structure of charge-stabilized suspensions

Assembly of supramolecular polymers in ultrathin films

A brief examination of some issues of current interest in polymer physical chemistry is provided. Emphasis is placed on topics for which the interplay of theory and experiment has been particularly...

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Physical chemistry of polymers: Entropy, interactions, and dynamics

We report ab initio investigations of the adsorption of atomic hydrogen on the (100) surfaces of Rh and Pd in the local-density-functional and generalized-gradient approximations. Our calculations have been performed using a plane-wave basis, using optimized ultrasoft pseudopotentials for describing the electron - ion interactions. Detailed results are reported for the adsorption energies, the stabilities of various adsorption geometries, and the adsorption-induced changes in the surface relaxations and in the work-functions. We find that the adsorption of a monolayer of hydrogen changes the inward relaxation of the top layer of the substrate into an outward relaxation. However, the change of the substrate relaxation has only a very small influence on the adsorption energy and geometry. For both metals the stable adsorption sites are the fourfold hollows. The site preference has its origin in a maximum gain of covalent bonding energy resulting from the overlap of the hydrogen s and the metal orbitals and from a minimal Pauli repulsion. Non-local exchange - correlation corrections have only a small influence on the atomic adsorption process and on the relaxation of the substrate, but influence the adsorption energy through corrections to the binding energy of the hydrogen molecule. Relativistic effects, however, turn out to be quite important.

https://iopscience.iop.org/article/10.1088/0953-8984/8/41/012/pdf

Hydrogen adsorption on the (100) surfaces of rhodium and palladium: the influence of non-local exchange - correlation interactions

Effect of shear flow on multi-component polymer mixtures

The area of "polymer mixtures," or the so-called "polymer blends," has interested many scientists since the 1960s. This is evident by the develop­ ment of the Flory-Huggins equation ( 1), which is a mean-field description of the free energy of mixing of flexible polymers. In early 1970, de Gennes (2-4) developed the Random-Phase-Approximation calculation (RPA) for polymer mixtures. This theory provided a quantitative description of the static structure factor, Seq), of a polymer mixture and related the con­ centration fluctuation to the single-chain structure factor (i.e. the Debye function) and the binary interaction parameter, X, between monomer pairs. Herkt-Maetzky & Schelten (5) have utilized this theory and the small angle neutron scattering technique to demonstrate the possibility of obtaining the correlation length, �, the generalized susceptibility Seq = 0), and the spinodal temperature of a polymer blend. Meanwhile, the linearized spinodal decomposition (SD) theory of Cahn-Hilliard-Cook (CRC) (6-7) has been extended to include the polymeric nature of long-chain molecules by de Gennes (8), Pincus (9), and Binder (4). Many experimental inves­ tigations have been reported since then ( 10-36).

Phase Decomposition in Polymers

The question of nonlinear stability of stationary reactor systems is investigated by two methods. The first method is analytic and sets the theory of nonlinear stability on a firm mathematical basi...

A Study of Nonlinear Reactor Dynamics

Dynamic light scattering has been used to investigate the diffusional dynamics in very dilute polystyrene/poly(propylene oxide), PS/PPO, polymer blends. Compared to previous investigations in the field, this system is more suitable for this type of investigation due to the significant refractive index difference between the two components and the fact that the matrix (PPO) dynamics do not interfere with the measurements. The tracer diffusion coefficient of PS thus obtained in the limit of infinite dilution scales as N−0.8±0.04PS with the PS degree of polymerization, i.e., behavior intermediate between the limits of nondraining Zimm and free‐draining Rouse behavior. The effect of the addition of a third component even at tracer concentrations on the diffusion dynamics was investigated both experimentally and theoretically in the framework of the dynamic random phase approximation. Similarities and differences between theory and experiment were found that are rather due to a modification of hydrodynamic int...

/pdf/interdiffusion-in-dilute-polymer-mixtures-a-subtle-1w44evdtjo.pdf

Interdiffusion in dilute polymer mixtures. A subtle concentration effect

It is shown that the two exponential modes in the dynamic scattering intensity obtained by scattering experiments from ternary polymer mixtures cannot, in general, be identified with the interdiffusion and cooperative diffusion processes, contrary to recent suggestions in the literature. Conditions under which such an identification is possible are obtained. General expressions for the interdiffusion and cooperative diffusion coefficients associated with a given pair of components a and b in a ternary, or, in general, multicomponent polymer mixture are obtained in terms of the partial mobilities μαβ and partial scattering functions S αβ(q) of the a and b polymers. In the framework of the random phase approximation, a new expression of the interdiffusion coefficient in an incompressible ternary mixture of a and b homopolymers in a matrix of c homopolymers is found in terms of the tracer diffusion coefficients of the three species. It is shown that the results of the controversional “fast mode” and “slow mode” theories are obtained from this new expression as two limiting cases.

A. Z. Akcasu

Papers

Phase Decomposition in Polymers

A Study of Nonlinear Reactor Dynamics

Interdiffusion in dilute polymer mixtures. A subtle concentration effect

Interdiffusion in polymer mixtures

Local stability in reactors with a linear feedback