Template‐Based Fabrication of Nanometer‐Scaled Actuators from Liquid‐Crystalline Elastomers

Abstract

Microelectromechanical systems (MEMS) have recently found strong interest in academia and industry. They result from the integration of mechanical elements, sensors, actuators, and electronics onto a silicon substrate. [ 1 ] The miniaturization of integrated systems offers the advantage of high effi ciency at low fabrication costs and novel functionalities. This emerging technology has led to a strong demand for micro-and nanometerscaled actuators. [ 2 ] Liquid-crystalline elastomers (LCEs) [3][4][5][6] are a class of functional materials that have been used for the fabrication of actuators for many years. Consisting of weakly crosslinked polymer chains that are covalently linked to stiff, shape-anisotropic molecules (mesogens), they combine the ability of self-organization from liquid crystals with the entropy elasticity of elastomers. Depending on the ambient conditions, these mesogens can either be in an unordered state (isotropic phase) or self-organized into ordered liquidcrystalline phases. In the isotropic phase, the polymer chains can adopt the entropically favored random-coil conformation. On the other hand, if the mesogens align into a liquid-crystalline phase, the polymer chains have to respond to the resulting anisotropic environment and adapt an anisotropic conformation. A phase transition between the liquid-crystalline and isotropic phases thus allows switching of the polymer backbone between these two conformations. This conformational change comes along with a macroscopic change of the sample's dimensions, [ 7 ] which enables the utilization of LCEs as materials for actuator applications. [ 6 , 8 , 9 ] Every stimulus that leads to a phase transition in the liquid-crystalline material (heat, UV light, presence of a solvent) can be used to trigger the actuation process. As a result of the reversibility of liquid-crystalline phase transitions, the change in shape is reversible as well. It has to be mentioned that these shape-changing effects can only be

One-piece micropumps from liquid crystalline core-shell particles

“…The LCE shell composed the three-core mesogen shown in Fig. 1b, which has previously been processed in microfluidic and templating devices 17,18,30 , but not for making core-shell particles. Attached to the rigid mesogenic unit are three flexible side chains, one of which comprises a polymerizable acrylate group.…”

“…Crucial to the preparation of LCEs is the uniform orientation of the anisotropic structural units, the so-called mesogens, along a common axis, the director. Commonly done in a two-step crosslinking process accompanied by mechanical stretching of a film 16 , novel approaches such as micro-and nano-templating 17,18 and inkjet printing techniques 19 recently opened up new possibilities to downscale LCE actuators for micro-sized applications. Ohm et al 20,21 designed a microfluidic set-up that allows a continuous production of micrometre-sized LCE fibres and particles by photopolymerization of an LC monomer to obtain LCEs with customizable actuator geometry and control over the orientation of the director.…”

Reversible and Rapid Laser Actuation of Liquid Crystalline Elastomer Micropillars with Inclusion of Gold Nanoparticles

“…As such, one can overcome the diffi culties of direct heating scheme used in previous work for actuating micropillars, [ 11,13,39 ] which are energy ineffi cient and highly undesirable in operating microactuator devices. Considering the great interest in the development of LCE based micro and nanoactuators, [39][40][41][42][43][44] we expect the new approach presented in this work can be a viable avenue to enable high-performance LCE-based micro and nanoactuating technologies.…”

A new era for liquid crystal research: Applications of liquid crystals in soft matter nano-, bio- and microtechnology

“…starting with a non-polymerized system of reactive mesogens that can be aligned using conventional liquid crystal alignment layers prior to cross-linking, or applying a two-stage cross-linking process with a moment of uniaxial stretching in between. Recently a few interesting alternative approaches were added to the toolbox for making liquid crystal elastomer actuators, including micro-or nanotemplating [291,292] and inkjet printing [293]. Another highly original recent addition, allowing the production of quite peculiar liquid crystal elastomer objects, was introduced by the Zentel group.…”