Thermoresponsive Nanoassemblies: Layer-by-Layer Assembly of Hydrophilic-Hydrophobic Alternating Copolymers

Multilayer films were assembled using the sequential alternate adsorption of a hydrophilichydrophobic copolymer, poly(styrene-alt-maleic acid) (PSMA), and poly(ethylene oxide) (PEO). The film buildup was followed using quartz crystal microgravimetry, and it was demonstrated that the incorporation of 0.2 M sodium chloride into the adsorption solution increased the adsorbed amount by a factor of approximately 2. Ten bilayer films of PSMA/PEO were shown to have a thickness of approximately 200- 500 nm, depending on the specific adsorption conditions used. The surface roughness of the films was examined using scanning force microscopy and shown to be dependent on both the adsorption conditions used and the terminal layer of the assembly. Films prepared at higher ionic strength had a rougher surface, and films terminated with PSMA were rougher than those terminated with PEO. The films were shown to have a strong affinity for Rhodamine B, with the dye concentration in the film exceeding that in the adjacent solution by a factor of approximately 7.3 x 10⁴. The absorbed dye was then released by elevating the temperature of the film, with the release rate dependent on the temperature of the release solution. The inclusion of the hydrophobic domains was shown to have a strong influence on the thermoresponsive behavior of the assemblies.