Conformational transitions of end-adsorbed triblock copolymers in a nonselective solvent

Conformational dynamics of triblock copolymers end-adsorbed onto a surface from a nonselective solvent have been studied by a Monte Carlo lattice 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 parameters 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 varied 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 system parameters (n, N-B and epsilon) and the associated lifetimes are calculated from the simulations. A kinetic scheme is constructed and the corresponding transition rate matrix is used in the master formalism equation, the solution of which yields the dynamic modes of the system. A correlation function is defined to produce a single overall view of the rate of transitions between different conformational states. The degree of surface interaction has strong influence on the rate of transitions between the states, in particular, longer average lifetimes and a wider distribution of lifetimes of the loop conformation contribute to the slower decay of the correlation curves. At high surface adsorption, 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.