FEATURES OF PHOTOMECHANICAL RESPONSE IN MONOLAYERS COMPOSED OF A CHARGED AMPHIPHILIC AZOBENZENE POLYMER

Monolayers of photochromic azobenzene (At) containing amphiphilic poly mers based on neutral [poly(vinyl alcohol) (PVA)] and cationic [polyal lylamine (PAA)] materials were spread on a water surface, and mechanic al response induced by photoirradiation was investigated. Observation of photomechanical effects in charged monolayers is reported for the f irst time. In comparison with the behavior of monolayers of the neutra l PVA-based polymer, the monolayer of the cationic PAA derivative was found to show improved photomechanical response in terms of accelerate d response and unchanging expanding ability even at higher surface pre ssures. UV-visible absorption spectroscopic measurements of the monola yers at the air-water interface revealed that the aggregation of the A z side chain of the PAA derivative is more suppressed than the PVA mon olayer possibly due to the lateral charge repulsion. Morphological obs ervation by Brewster angle microscopy indicated that the domain struct ures of the monolayers of PVA- and PAA-based polymers in the trans sta te are completely different. The neutral monolayer gave rigid and cont inuous domains without holes, whereas domains of the cationic monolaye r exhibited highly amorphous characteristics with numbers of featurele ss holes. Such differences in the Az packing state can be correlated w ith variation of the photomechanical response in the two Az monolayers . Addition of a polyanion in the subphase was found to impede substant ially the film expansion of the trans PAA-based monolayer due to the i nterfacial ionic crosslinking.