Thermo-Mechanical Responses of Liquid-Crystal Networks with a Splayed Molecular Organization

• Published in: Advanced functional materials Vol. 15; no. 7; pp. 1155 - 1159
• Main Authors: Mol, G. N., Harris, K. D., Bastiaansen, C. W. M., Broer, D. J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.07.2005; WILEY‐VCH Verlag
• Subjects: Actuators; Liquid crystals; Stimuli-responsive materials; Structure-property relationships
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200400503

Films of liquid‐crystal networks with a splayed molecular alignment over their cross‐section display a well‐controlled deformation as a function of temperature. The deformation can be explained in terms of differences in thermal expansion depending on the average molecular orientation of the mesogenic centers of the monomeric units. The thermal expansion of the anisotropic polymers has been characterized as a function of their molecular structure and the polymerization conditions. As a reference, films with an in‐plane 90° twist have also been studied and compared with the splayed, out‐of‐plane molecular rotation. The twisted films show a complex macroscopic deformation owing to the formation of saddle‐like geometries, whereas the deformation of the splayed structured is smooth and well controlled. The deformation behavior is anticipated to be of relevance for polymer‐based microelectromechanical system (MEMS) technology. Thermal actuators based on thin films of a liquid‐crystal network with a splayed molecular order over their cross‐section (see Figure) show a homogeneous bending deformation (also shown in Figure) upon heating. The origin is a difference in thermal expansion depending on the molecular orientation.