ABSTRACT:The aggregation structure of proton-, monocarboxyl-, and dicarboxyl terminated polystyrene (PS) ultrathin films spin-coated onto different substrate surfaces was investigated on the basis of atomic force microscopy (AFM). In the case of the monocarboxyl-and dicarboxyl-terminated PS ultrathin films spin-coated onto Si-wafer, the dewetting occurred after annealing above their bulk glass transition temperatures. In contrast, those (monocarboxyl and dicarboxyl-terminated PS ultrathin films spin-coated) onto aminosilane-treatcd Si-wafer did not dewet even after annealing above the bulk T., owing to the specific interaction between -COOH and -NH 2 groups of aminosilane onto the Si-wafer.KEY Ultrathin polymer films are becoming more interesting from technological application and scientific standpoints. Also, polymeric surface functions as biomaterials, adhesives, lubricants, and others, are closely related to the surface aggregation structure of polymeric solids. 1 • 2 Therefore, studies on surface aggregation structure for polymeric thin films are important for practical applications as well as their scientific interest. Surface aggregation structure of polymer thin films has been investigated, both experimentally and theoretically. 3 -6 The stability of aggregation structure for the ultrathin films on solid substrate is of great importance in many industrial applications, and its controlling parameter might be wettability against substrate.7.8 However, it is often experienced that the polymer ultrathin films dewet the substrate upon heating above its glass transition temperature, Tg. 9 • 10 The dewetting of aggregation structure of end-functionalized polymer ultrathin film has been reported.U -13 To achieve long-term stabilization of surface aggregation structure for the ultrathin films, one may use polymers which can be anchored by one end group or two end groups to the substrate via strong chemical interaction. Klein et al. 14 · 15 have showed that the thin films of an oligostyrene liquid, which are forced on a nonwetted Si-wafer surface, rupture within a few minutes. These films may be stabilized and rupture-inhibited for many months by the presence of a polymer brush on the Si-wafer surface, together with some free polymer. The presence of both the brush and a sufficient amount of the free long-chain polymer are necessary for the prevention of rupture. Then the stability of aggregation structure of the end-functionalized polymer ultrathin film must be studied from the viewpoint of the film thickness and the degree of interaction between end group and substrate.In this study, a promising technical approach to avoid the dewetting of aggregation structure for polymer ultrathin films have been proposed via specific interaction between carboxylated polystyrene and aminosilanet To whom correspondence should be addressed.treated Si-wafer. Also, the effects of polymer film thickness on the stability of aggregation structure of the ultrathin polymer films have been studied by using the monocarboxyl-and dicarbo...

Surface molecular motions of monodisperse proton-terminated polystyrene (PS-H), monocarboxyl-terminated PS (PSCOOH) and dicarboxyl-terminated PS (a,w-PS(COOHh) ultrathin films were investigated on the basis of lateral force microscopic (LFM) measurement at 293 K, as a function of number-average molecular weight, M •. and chain end functionality. In the case of the PS-H thin films with M. = 19.7k and 40.4k spin-coated onto Si-wafer, the surface molecular motion was activated in a glass-rubber transition state at 293 K due to the excess free volume induced by a surface localization of chain end groups. Also, in the cases of the PSCOOH (M.=9.7k, 45.9k) and the a,w-PS(COOHh (M.= 12.0k, 51.7k) ultrathin films spin-coated onto Si-wafer and their annealed ones at 393 K for 8 h, the surface molecular motion was also enhanced even at room temperature due to a weak ionic interaction between Si-OH of substrate and-COOH end group. On the other hand, the PSCOOH (M.=9.7k, 45.9k), and the a,w-PS(COOH)2 (M.= 12.0k, 51.7k) spin-coated ultrathin films onto aminosilane-treated Si-wafer did not show any distinct activation of surface mobility owing to a specific interaction between NH 2-group of aminosilane-treated Si-wafer and-COOH end group of PS, being independent of annealing temperature, M. and functionality. KEY WORDS Proton-Terminated Polystyrene I Monocarboxyl-Terminated Polystyrene I Dicarboxyl-Terminated Polystyrene I Lateral Force Microscopy I Surface Molecular Motion I Aminosilane-Treated Si-Wafer I