Surface morphology and molecular chemical structure of poly(n-butyl methacrylate)/polystyrene blend studied by atomic force microscopy (AFM) and sum frequency generation (SFG) vibrational spectroscopy

Sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM) have been applied to study the poly(n-butyl methacrylate) (PBMA)/polystyrene (PS) blend surfaces. SFG showed that PBMA tended to segregate to the blend surfaces because of its lower surface tension. The phenyl groups on the pure PS surface orientated closely to the surface normal with a narrow angle distribution. Presence of PBMA dramatically affected the orientation angle of the phenyl groups on the blend surface. For example, on the surface of the blend with only 4 wt % PBMA in the bulk, the phenyl groups would tilt more toward the surface, but they did not completely lie down on the surface. Because of the larger orientation angle of the phenyl groups versus the surface normal, no ppp signal of PS could be detected on the PBMA/PS blend surfaces with our experimental geometry. AFM results showed that pure PS and PBMA surfaces were flat, but domain structures existed on the polymer blend surfaces. Selective solvent cyclohexane has been used to identify species on the PBMA/PS blend surface. Annealing and solvent effects on the blend surface morphology have also been investigated.