Surface Structure Relaxation of Poly(methyl methacrylate)

Abstract

Surface structure relaxations caused by temperature changes at the free surface of poly(methyl methacrylate) were studied using IR-visible sum-frequency generation (SFG). A polarization-rotating technique was introduced to enhance the sensitivity of SFG for monitoring the surface structure relaxations during a cooling process. A new surface structure relaxation was observed at 67 degrees C. This temperature does not match any known structure relaxation temperatures for the bulk and is 40 degrees C below the bulk glass transition temperature. As expected for a free-surface phenomenon, the surface relaxation temperature was found to be independent of film thickness in the range of 0.1-0.5 microm.

Understanding molecular structures of silanes at buried polymer interfaces using sum frequency generation vibrational spectroscopy and relating interfacial structures to polymer adhesion

“…SFG allows one to detect the presence, coverage, chemical environment, orientation and orientational ordering of surface or interfacial species, making it an ideal method to study the molecular-level mechanisms that contribute to adhesive bonding. SFG has been extensively used to characterize polymer surfaces and interfaces such as polymer surface structures in air, polymer surface restructuring in water, surface structures of polymer blends and copolymers, solid-polymer interfaces, and polymerbiomolecule interfaces [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. More specifically, it has been used to study polymer-silane interactions including the elucidation of conformations of silanes at polymer interfaces [25,26], the detection of hydrogen bonding between polymer surface groups and silanes [27], and the monitoring of interfacial diffusion of silane molecules into polymer films [28,29].…”

Probing polymer surfaces and interfaces using sum frequency generation vibrational spectroscopy - a powerful nonlinear optical technique

“…Chou and his colleagues studied the surface structure relaxation of PMMA [80]. Two surface transition temperatures were observed at 107°C and 67°C respectively.…”

“…They believed the first transition (107°C) was the bulk-induced structure relaxation since it agreed well with the bulk T g of PMMA. They proposed that the second transition (67°C) might come from either the surface T g (α-relaxation) or β-relaxation since the detected signal comes from the side chain ester methyl groups [80].…”

Gradiently varied chain packing/orientation states of polymer thin films revealed by polarization-dependent infrared absorption

“…It is thus of great importance to investigate the chain packing/orientation state and the related dynamic behavior for a polymer thin film. Different techniques have been applied to study this issue in the past, such as fluorescence microscopy [9][10][11][12], ellipsometry [13][14][15][16], Brillouin light scattering [16][17][18], X-ray reflectivity [3,19,20] and sum frequency generation vibrational spectroscopy [21][22][23][24][25]. It has generally been recognized that a polymer thin film is a metastable material [4] which has distinct physicochemical properties from those of the bulk polymer.…”