ROLE OF BLOCK SIZE ASYMMETRY ON THE ADSORBED AMOUNT OF POLYSTYRENE-B-POLY(ETHYLENE OXIDE) ON MICA SURFACES FROM TOLUENE

Surface force and IR data on polystyrene-b-poly(ethylene oxide) block copolymers adsorbed on mica from toluene are presented. The copolymers were selected to have a wide range of asymmetry radius ratio (beta = R(F,PS)/R(F,PEO)3/5 as defined by Marques and Joanny. The extended length L of the block copolymers has been measured with the surface force apparatus and shown to scale as L approximately N(PS)N(PEO)1/3 for moderately asymmetric copolymers (1 much less than beta < N(PEO)1/2). Deviations are observed when the nonadsorbing block is either much larger than the anchor block or approximately the same size. A general method using infrared spectroscopy has been developed which can measure the quantity of adsorbed polymers on mica. The Alexander-de Gennes scaling law for the surface density, L approximately N(B)sigma-1/3, has been found to be roughly obeyed over a wide range of copolymer molecular weights and radius ratio beta. The Marques and Joanny scaling laws for sigma, sigma approximately 1/N(A), describe well the behavior of the moderately asymmetric materials. However, their model does not appear to predict the proper surface density for material at the crossover point between the 3D and 2D regimes, near beta almost-equal-to N(A)1/2.