Relaxation Behavior of Polymer Chains at Solid Interfaces
Keiji TANAKA (Department of Applied Chemistry, Kyushu University)
Polymer composites including inorganic nano-fillers have been widely used in a variety of engineering fields. The performance and functionality of the composites are closely related to the quality of the interface between the polymer and the inorganic material. As the interaction between them is attractive and the interface is well defined, the fillers are dispersed homogeneously and thus the reinforcement is effective. We have studied the local conformation of polystyrene (PS) in a film at the interface with an inorganic solid by sum-frequency generation (SFG) vibrational spectroscopy, and claimed that it is strongly dependent on the method of preparation of the film [1] in addition to the surface energy of the solid substrate [2]. It should be emphasized that the chain orientation at the interface was not well relaxed even at a temperature higher than the bulk glass transition temperature (Tg) unless the thermal annealing was applied for extremely longer than the bulk terminal relaxation time [3]. This finding is in good accordance with the idea of an interfacial dead layer in terms of mobility as well as our parallel claim that the Tg elevates in close proximity to the substrate interface [4]. This information should be of importance in the design of the interface in polymer composites. To improve the interface affinity, reactive compounds such as silane coupling agents and ammonium salts have been applied for the surface treatment of silica fillers and crays, respectively. Introduction of functional groups to polymer chains is also effective. However, it is far from clear for the moment what happens with the polymer structure and the dynamics at the interface after such an interfacial modification. This may be a reason why perfect control of the interfacial interaction between the polymer and the inorganic material has not yet been attained. We also characterize terminally-functionalized PS at an inorganic interface in thin film geometry, where the interfacial information is enhanced thanks to the large ratio of the interfacial area to the total volume [5]. This enables us to visualize polymer behavior at interfaces with inorganic solids and thus develop better strategies for the interfacial design of polymer composites.
References
[1] H. Tsuruta, Y. Fujii, N. Kai, H. Kataoka, T. Ishizone, M. Doi, H. Morita, K. Tanaka. Macromolecules 2012, 45, 4643-4649.
[2] M. Inutsuka, A. Horinouchi, K. Tanaka. ACS Macro Lett. 2015, 4, 1174-1178.
[3] M. Sen, N. Jiang, J. Cheung, M. K. Endoh, T. Koga, D. Kawaguchi, K. Tanaka. ACS Macro Lett. 2016, 5 504-508.
[4] K. Tanaka, Y. Tateishi, Y. Okada, T. Nagamura, M. Doi, H. Morita. J. Phys. Chem. B. 2009, 113, 4571-4577.
[5] S. Shimomura, M. Inutsuka, K. Tajima, M. Nabika, S. Moritomi, H. Matsuno, K. Tanaka. Polymer J. doi:10.1038/pj.2016.58.
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