Theory of the epitaxial crystallization of polymers on alkali halide substrates. III. Solvation effects

Abstract

The role of solvent in the initial nucleation of a single chain segment in the epitaxial crystallization of polyethylene (PE), from solution, upon an NaCl substrate, has been interpreted in terms of molecular energetics. Consideration of polymer-solvent, solvent-solvent, and solvent-substrate interaction energies, in addition to the assumption that the solvation energy of a helical polymer is linearly related to the volume of overlap between an adsorbed cylindrical monolayer of solvent molecules and the substrate surface, has placed our theoretical understanding of environmental effects in proper perspective. A conceptually similar hydration shell theory has been successfully employed by Hopfinger2 in understanding solvation effects in molecules of biological interest. Computer simulation modeling of the interfacial energetics indicates an energy of activation, for epitaxial nucleation, that is characteristic of a given polymer-solvent-substrate combination. This activation barrier is related to the relative abilities of the solvent molecules to (a) initially dissolve the polymer, and (b) subsequently become deadsorbed from the polymer molecule and permit its nucleation upon the substrate surface. The results of applying this model to the solvents benzene, toluene, and o-xylene are reported.

Modeling of polymer epitaxial crystallization: β-poly(vinylidene fluoride) on (111) calcium difluoride

“…The global energy minimum values for these two orientations are very similar, although the value for orientation 2 is slightly lower by 2.0 (kcal/mol)/10 repeat units. The total Figure 6. Energy contours in (kcal/mol)/10 PVF2 repeat units above the absolute minimum for orientation 2 with (x, y, µ, ) = (0.6, 0, 90°, 90°).…”

“…/r12 = 5Ah^°+ 60exp(2irikvr) (6) In these expressions A is the area of the substrate unit cell, h is the height of the polymer atom above the substrate surface, kA is an arbitrary vector in the reciprocal lattice of the substrate, r is the component of the position vector of the polymer atom in the space of the substrate lattice, and K2 and K5 represent second-and fifth-order modified Bessel functions of the second kind, respectively. The sums are taken over all values of kh and are truncated when the relative contribution of the last term to the sum is negligible.…”