CONFORMATIONAL TRANSITIONS OF END-ADSORBED TRIBLOCK COPOLYMERS IN A NONSELECTIVE SOLVENT

Conformational dynamics of triblock copolymers end-adsorbed onto a sur face from a nonselective solvent have been studied by a Monte Carlo la ttice simulation technique. The triblock copolymers are A(NA)B(NB)A(NA ) With N-A = 10 and N-B = 5, 10, 20 and 40, at surface interaction par ameters epsilon = -0.5 and -1.0. A is the adsorbing block and B is the nonadsorbing block. The number of chains in the periodic box is varie d over the range 100 less than or equal to n less than or equal to 500 . The triblock copolymer can exist in three states: loop (L), tail (T) and free (F) chain. Fractions of those conformations at different sys tem parameters (n, N-B and epsilon) and the associated lifetimes are c alculated from the simulations. A kinetic scheme is constructed and th e corresponding transition rate matrix is used in the master formalism equation, the solution of which yields the dynamic modes of the syste m. A correlation function is defined to produce a single overall view of the rate of transitions between different conformational states. Th e degree of surface interaction has strong influence on the rate of tr ansitions between the states, in particular, longer average lifetimes and a wider distribution of lifetimes of the loop conformation contrib ute to the slower decay of the correlation curves. At high surface ads orption, larger N-B decrease the rate of all transitions at all values of a. A weak dependence on n is observed for all sizes of N-B at both surface energies.