SOLITONS IN CRYSTALLINE POLYETHYLENE - A CHAIN SURROUNDED BY IMMOVABLE NEIGHBORS

A numerical solution to the problem of existence and stability of topo logical solitons in a polyethylene chain surrounded by immovable neigh boring chains is obtained. In the framework of a realistic model that takes into account deformations of valence bonds, valence and torsiona l angles, as well as intermolecular interactions, three types of solit ons describing local topological defects in the crystal are found. The y correspond, respectively, to (i) stretching or compression of the zi gzag backbone by one Lattice spacing, (ii) stretching or compression o ver half-lattice spacing together with twisting by 180 degrees, and (i ii) pure twisting by 360 degrees. The existence of such solitons is ca used by specific topology of the polyethylene crystal. For each of the se solitons the velocity spectrum is found in die subsonic region. Mol ecular-dynamics modeling leads to conclusion about their stability in the whole interval of admissible velocities. The influence of temperat ure is also taken into account. It is shown that thermal vibrations ca n result only in the formation of the second type of solitons. These s olitons are created as kink-antikink pairs that can move along the cha in as Brownian particles. The abrupt increase of the soliton density i s shown to occur near the crystal melting point. [S0163-1829(98)04338- 0].