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 wi th previous work, the grafting ratio of azobenzene on the LPS backbone coul d be controlled more accurately and the low molar mass impurity, which migh t influence the concerted action of the azobenzene units as command moietie s on the surrounding LC molecules, could be readily removed by repeated pre cipitation. The results of our measurements indicate that inserting a flexi ble disiloxane segment into the spacer of the side group can improve the ph oto-driven response. The response steepness of a LC cell is 20 times that o f our previous result. However, the response speed also depends on the spac er 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 %.