Direct observation of photoisomerization of a polymer monolayer on a watersurface by x-ray reflectometry

X-ray reflectivity (XR) measurements were carried out for monolayers of pol y(vinyl alcohol) containing a photochromic azobenzene side chain (6Az10-PVA ) on a water surface. Kiessig fringes were observed for specular measuremen t for 6Az10-PVA monolayers on a water surface. By the irradiation of visibl e and ultraviolet light, azobenzene shows a photoisomeric conformational ch ange between trans and cis forms, respectively. The structural change of a 6Az10-PVA monolayer on a water surface was detected by in-situ XR measureme nt. By analyzing the XR data, it was indicated that the thickness of the mo nolayer became thicker for the trans form than for the cis form. This refle cts that the side chain should stretch to the direction perpendicular to th e water surface with the conformational change from cis to trans form, in a ddition to the longer chain length for the trans form.