Thickness Dependence of Surface Chain Conformation in Poly(methyl methacrylate) Films Investigated by Sum Frequency Generation Vibrational Spectroscopy

• Published in: Macromolecules Vol. 57; no. 13; pp. 6190 - 6198
• Main Authors: Xu, Jianquan, Bao, Senyang, Jiang, Zhenwei, Li, Bolin, Han, Xiaofeng, Wang, Xinping
• Format: Journal Article
• Language: English
• Published: American Chemical Society 09-07-2024
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.4c00792

To explore the substrate effect on chain conformation, sum frequency generation vibrational spectroscopy was used to investigate the variation in the surface structure of a supported poly­(methyl methacrylate) film with different thicknesses of the polymer film (h) and adsorbed layer (h ads). The average local chain conformation at the surface was employed as a phenomenological marker and described by a chain arc model. With the decreasing of h, the surface conformation approached from the unperturbed surface conformation to that of adsorbed chains, which indicated the existence of a conformation gradient near the substrate. It was also found that the distance of chain conformation perturbed by the substrate effect was dependent on the formation of an irreversible adsorption layer and increased linearly with h ads. This linear dependence is consistent with the correlation between the propagation distance of the substrate effect on chain mobility and h ads; therefore, the conformation gradient may be the probable origin of the long-range substrate effect.