Nanoscopic Aggregation in Amphiphilic Random Copolymer Bulk Films Studied with Photochemical Hole Burning

Abstract

Nanoscopic aggregation and highly constrained nanoenvironments within bulk films of amphiphilic random copolymers have been studied for the first time by using photochemical hole burning spectroscopy at low temperatures. Films containing sodium sulfonate (A) and cyclododecyl (CD) or lauryl (LA) groups) with tetraphenylporphine (TPP) dispersed in the copolymers, as well as for TPP covalently bound to the copolymer chains, were prepared. Temperature cycle experiments were carried out for the copolymer films with different ratios of the hydrophilic and hydrophobic groups. Holes burned in the copolymer films with CD and sodium sulfonate groups were thermally more stable than those expected for hypothetical systems where the groups are randomly dispersed with the corresponding ratios. The discrepancy can be attributed to the “pinning down” of TPP in constrained configurations of CD aggregation in the films. On the other hand the increase in hole width in the copolymer films of LA groups with sodium sulfonate was enhanced compared to those expected for hypothetical systems where sodium sulfonate and LA groups are randomly dispersed with the corresponding ratios. The results could be attributed to the aggregation of LA groups, with the preferential inclusion of TPP within it, in the films.