Photoregulated binding ability of azoaromatic polymer for surfactant

Abstract

Water‐soluble polymeric azodyes containing an azobenzene moiety in their side chain, p‐phenylazoacrylanilide (PAAn)–acrylamide (AAm) copolymers, were synthesized and the adsorption‐desorption behavior of sodium dodecyl sulfate (SDS) onto these copolymers in water was investigated by means of conductivity measurements, with attention to the hydrophobicity of the copolymer. The conductivity of the PAAn‐AAm copolymer/SDS complex aqueous solution decreased with increasing PAAn composition in the copolymer. This result indicates that the SDS molecules adsorbed onto the copolymer. The adsorption state of SDS molecules on the copolymer was considered to take a micellelike form. When the hydrophobicity of the PAAn‐AAm copolymer was decreased by means of the photoisomerization of an azodye moiety, the conductivity of the PAAn‐AAm copolymer/SDS aqueous solution increased. This phenomenon can be explained as a result of desorption of SDS molecules from the copolymer. When the light source was cut off, the conductivity took on its original value. This indicated that SDS was desorbed by the photochemical trans to cis and adsorbed by cis to trans isomerization of the PAAn moiety.