A method for carrying out 'Monte Carlo' calculations on chains is described. Close agreement between the present results and those of Wall et al. for chains on a two-choice, plane hexagonal lattice establishes the reliability of the present method. The calculations are extended to the chains whose segments interact in accord with a Lennard-Jones potential.

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Molecular dynamics simulations of passivated and bare gold nanoparticles immersed in ethane have been performed in the reduced temperature (T r ) T/T c ) range 0.95-1.05 along the critical isochore of the solvent. The effects of temperature and passivation on the radial distribution of the solvent molecules about the center of mass of the metal core and on the degree of solvation (ϑ) have been investigated. The results show that the solvation of the 38-atom bare particle is qualitatiVely different from that of the passivated particle: the degree of solvation of the bare particle is positiVe, whereas it is negatiVe for the passivated particle. This difference in the solvation propensity of the particle in the presence and absence of the passivating layer is attributed to the different forces controlling the solvation process in the two cases. It is found that the degree of solvation of the 8-atom-core passivated particle is greater than that of the 38-atom-core passivated particle, due essentially to different configurational structures assumed by the passivating layers of the smaller and the larger particle. For the bare particle, the degree of solvation as a function of temperature passes through a maximum, a manifestation of the enhancement effect produced in the clustering of the solvent molecules around the solute as the system moves toward the critical point. The initial, minimum-energy configuration of the particle cores underwent appreciable changes as the system approached the equilibrium state in the simulations.

In seeking validation of Dissipative Particle Dynamics (DPD) for the mesoscopic modeling of multiphase fluid-fluid systems in external fields, simulations of a pendant drop and a drop in simple shear flow have been performed. The shape profile of the simulated pendant drop was found to be in perfect agreement with that computed by solving the Laplace equation. At increased values of the gravitational force (g), the drop underwent considerable elongation, developing a "neck" between the solid support and its bulk part. Further increases in g resulted in thinning of the neck, which ruptured as g exceeded a certain value, leading to the detachment of the drop. This picture of the detachment process is consistent with the experimental observations published in the literature. Also, the simulations reproduced the drop volume experiment quantitatively. For the drop in shear flow, the degree of deformation was found to be a linear function of the capillary number (Ca) in the region Ca e 0.11, in good agreement with Taylor's theory; this is despite the fact that the hydrodynamic regime in the simulations (Re ∼ 1-10) is quite different from that assumed in the theory (Re , 1). At increased shear rates the results showed positive departure from linearity, in agreement with theory and experiment. Further increases in Ca resulted in the drop assuming a dumbbell like shape, the middle part of the "dumbbell" gradually stretching to form a thin neck. The rupture of the neck was occasioned by the instabilities manifested in the form of stochastic oscillations which magnified as the critical point was reached. The time evolution of the shape of the drop as it underwent the breakup process in our simulations bears remarkable similarity to the experimental observations of Torza et al. The critical value of the capillary number obtained in the simulations is in reasonable agreement with the experimental figure.