Coassembly of Poly(N-isopropylacrylamide) with Dodecyl and Carboxyl Terminal Groups with Cationic Surfactant: Critical Comparison of Experimental and Simulation Data
Abstract
Comicellization of poly(N-isopropylacrylamide) with dodecyl and carboxyl terminal groups (mPNIPAm) with cationic surfactant N-dodecylpyridinium chloride was studied by scattering techniques (light scattering, SAXS), isothermal titration calorimetry, fluorescence spectroscopy, and coarse-grained simulations using dissipative particle dynamics (DPD) as a function of charge ratio of N-dodecylpyridinium (DP+) ions to mPNIPAm terminal carboxylate groups, Z = [DP+]/[COO-]. While both experimental results and DPD data indicate that up to Z = 2 tails of the surfactant enter and swell the dodecyl core of mPNIPAm micelles, the further increase in the size of the core for Z > 2 caused by the dehydration and collapse of inner parts of PNIPAm chains observed by SAXS is not reproduced by DPD simulations.
Nevertheless, the study demonstrates that the simplified coarse-grained model can account for hydrogen bonding and elucidate the mechanism of comicellization. The study shows that the electrostatic interactions modify appreciably the behavior of mPNIPAm, but the assembly with cationic surfactant is governed by hydrophobic interactions.