Improvement of LPS-based command surfaces: Effect of inserting a flexible disiloxane segment into the azo side chain on photo-driven response

A new synthetic route for azo grafted ladder-like polysilsesquioxanes (LPS) used for fabricating command surfaces has been developed. In comparison with previous work, the grafting ratio of azobenzene on the LPS backbone could be controlled more accurately and the low molar mass impurity, which might influence the concerted action of the azobenzene units as command moieties on the surrounding LC molecules, could be readily removed by repeated precipitation. The results of our measurements indicate that inserting a flexible disiloxane segment into the spacer of the side group can improve the photo-driven response. The response steepness of a LC cell is 20 times that of our previous result. However, the response speed also depends on the spacer length and the content of azo side groups. Using azo grafted LPS with a shorter spacer as the material for the command surface, the response speed is faster than with a longer spacer. Optimum response can be achieved at an azo content of 10 mol %.