1007319-13-2Relevant academic research and scientific papers
Kinetico-mechanistic study of the thermal cis-to-Trans isomerization of 4,4a?2-dialkoxyazoderivatives in nematic liquid crystals
Garcia-Amoroì?s, Jaume,Martiì?nez, Manuel,Finkelmann, Heino,Velasco, Dolores
, p. 1287 - 1293 (2010)
4,4a?2-Dialkoxy-substituted azobenzenes are usually required for technical applications. Here, we study the mechanism through which the azo-dye thermally isomerizes from the unstable cis isomer to the more stable trans isomer when it is incorporated in the nematic liquid-crystalline state. We have determined the kinetic and thermal activation parameters for this process in different nematic environments. Their comparison with those values obtained in isotropic media demonstrates that the mechanism through which the thermal cisto-trans isomerization takes place is the inversion pathway in all the physical states studied. The nematic order increases the rate of the thermal cis-to-trans isomerization process. This fact is related to a cooperative interaction established between the mesogen molecules and the azo-dye. This effect is not present in the isotropic state. ? 2010 American Chemical Society.
Influence of the photo-active azo cross-linker spacer on the opto-mechanics of polysiloxane elastomer actuators
Garcia-Amoros, Jaume,Finkelmann, Heino,Velasco, Dolores
scheme or table, p. 1094 - 1101 (2011/09/14)
Nematic liquid single crystal elastomers (LSCEs) that contain azobenzenes as cross-linkers have a clear application in the field of light-controlled actuators. They are able to modify their macroscopic dimensions upon irradiation with UV light and furthermore relax back thermally or by irradiation with visible light. Many efforts have been put forward to improve the photo-mechanical effect. However, there are no previous studies about the role of the length of the photo-active cross-linker spacer on the opto-mechanics of light-controlled actuators. In this way, we have prepared several photo-active side-chain nematic polysiloxane LSCEs that contain 4,4′- dialkoxyazobenzenes as cross-linkers, which bear spacers of different lengths. The opto-mechanical behaviour of the different LSCEs prepared has been analyzed. The use of photo-active cross-linkers with long spacers yields actuators with higher mechanical responses under irradiation with UV light. Neither the irradiation nor the thermal relaxation time of the actuator depends on the spacer length.
