We describe a detailed study of the conformational properties of a very long polymer chain in the presence of small colloidal particles. The polymer chain is modeled by a random self-avoiding walk (SAW) on the cubic lattice. The properties of interest include the conformational entropy, segment distributions in the coil, and dimensions of the coiled chain attached to a particle. The conformational entropy of a coil perturbed by a nonadsorbing particle and by a particle attached to the chain end is calculated. The influence of the particle size on the minimum adsorption energy per surface unit of the particle, needed to outweigh the conformational entropy effect, is examined. The conformations of the free coil and the coil distorted by the irreversible adsorption of a particle are studied. On the basis of the results obtained, the possible structures of the particle-plus-polymer aggregates are discussed.

A simple and inexpensive experiment for verifying the Schulze-Hardy rule.

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A linear chain on a simple cubic lattice was simulated by the Metropolis Monte Carlo method using a combination of local and non-local chain modifications. Kink-jump, crankshaft, reptation and end-segment moves were used for local changes of the chain conformation, while for non-local chain rearrangements the "cut-and-paste" algorithm was employed. The statistics of local micromodifications was examined. An approximate method for estimating the conformational entropy of a polymer chain, based on the efficiency of the kink-jump motion respecting chain continuity and excluded volume constraints, was proposed. The method was tested by calculating the conformational entropy of the undisturbed chain, the chain under tension and in different solvent conditions (athermal, theta and poor) and also of the chain confined in a slit. The results of these test calculations are qualitatively consistent with expectations. Moreover, the obtained values of the conformational entropy of self avoiding chain with ends fixed over different separations, agree very well with the available literature data.FigureVisualization of the neighborhood of two local chain microconformations containing a bead (indicated by the arrow) which a) can and b) cannot be moved by the kink-jump. In red there are marked the possible trajectories of chain fragment which can block the adjacent site

The purpose of the experiment described is to acquaint the students with the problems of colloid stability. For more advanced students, the experiment can be extended to verify the Schulze-Hardy rule.

Morphology and thermodynamics of a microdroplet deposited on a grooved inhomogeneous surface with triangular cross section of the grooves were studied by computer simulations with the use of Surface Evolver program. With increasing volume of the droplet, it initially spreads along the series of grooves assuming the filament-like morphology. After reaching a certain volume, the surface wetted by the droplet is reduced and the droplet assumes the bulge morphology or spreads over the surface bordering on the groove initially occupied (it can be either a neighboring groove or a flat surface). The character of the process is determined by the geometry of the edge of the inhomogeneity studied. The effect described also depends on the number of grooves G and the Young contact angle θY. The change in the shape of the droplet becomes more pronounced with decreasing θY and G. Above a certain number of grooves, in the range of contact angles studied (e.g., G > 6 if θY = 70° and G > 4 if θY = 75°), no morphological transition of the droplet was observed.