Nanostructure of a Photochromic Polymer/Liquid Crystal Hybrid Monolayer on a Water Surface Observed by in Situ X-ray Reflectometry

• Published in: Langmuir Vol. 18; no. 10; pp. 3875 - 3879
• Main Authors: Kago, Keitaro, Seki, Takahiro, Schücke, Randolf R, Mouri, Emiko, Matsuoka, Hideki, Yamaoka, Hitoshi
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.05.2002
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la011384p

The monolayer of a poly(vinyl alcohol) derivative having an azobenzene (Az)-containing side chain (6Az10-PVA) can induce an alignment transition of liquid crystal molecules in the monolayer by the trans−cis conformational change of the azobenzene unit (command effect). As a model system of this dynamic interface, the structural characterization of the mixed monolayer of 6Az10-PVA and a nematic liquid crystal molecule, 4‘-penthyl-4-cyanobiphenyl (5CB), on a water surface was analyzed by in situ X-ray reflectometry. The depth density profile indicated that this hybrid monolayer in the trans-Az state consists of two distinct layers:  a dense lower region and a less dense upper region having the same thickness of ca. 1.5 nm. This suggests that the rod molecules are stretched out in a direction perpendicular to the water surface where 5CB molecules are inserted on the lower side of the Az side chains. Light-induced structural modifications were clearly detected in the hybrid monolayer.