Abstract
Crosslinked liquid crystalline polymers (CLCPs) containing azobenzene (AZO-CLCPs) are a type of promising material due to their significance in the design of light-driven smart actuators. Developing AZO-CLCP composites by incorporating AZO-CLCPs with other materials is an effective way of enhancing their practicability. Herein, we report an AZO-CLCP/CNT nanocomposite prepared by the in situ polymerization of diacrylates containing azobenzene chromophores on carbon nanotube (CNT) sheets. The liquid crystal phase structure of CLCP matrix was evidenced by the two-dimensional X-ray scattering. The prepared pure AZO-CLCP films and AZO-CLCP/CNT nanocomposite films demonstrated strong reversible photo-triggered deformation under the irradiation of UV light at 366 nm of wavelength, as a result of photo-induced isomerization of azobenzene moieties in the polymer network. But compared to pure AZO-CLCP films, the AZO-CLCP/CNT nanocomposite films could much more rapidly return to their initial shapes after the UV light irradiation was removed due to the elasticity effect of CNT sheets. The deformation behavior of AZO-CLCP/CNT nanocomposite films under the light irradiation was also different from that of the pure AZO-CLCP films due to the interfacial interaction between a polymer network and CNT sheet. Furthermore, incorporation of a CNT sheet remarkably increased the mechanical strength and robustness of the material. We also used this AZO-CLCP/CNT nanocomposite as a microvalve membrane actuator, which can be controlled by light, for a conceptual device of a microfluidic system. The results showed that this AZO-CLCP/CNT nanocomposite may have great potential in smart actuator applications for biological engineering, medical treatment, environment detection and microelectromechanical systems (MEMS), etc.
Highlights
Experiment indicated that the switching of the microvalve could be precisely controlled by light. These results showed that this AZO-Crosslinked liquid crystalline polymers (CLCPs)/carbon nanotube (CNT) nanocomposite may have great potential in smart actuator applications for biological engineering, medical treatment, environment detection and microelectromechanical systems (MEMS), etc
We report an effective approach to fabricate photo-actuated AZO-CLCP/CNT nanocomposite films by incorporating CNT sheets into AZO-CLCP matrices through a facile melting process and in situ photo polymerization
The AZO-CLCP/CNT nanocomposite films could deform with similar rapid speeds as the pure AZO-CLCP films could under the irradiation of UV light, and could much more rapidly return to their initial shapes after the UV light was removed
Summary
Photo-actuated actuators are attractive to researchers since they offer an effective means to couple photonic energy into the actuator structures, and bring advantages of simplified systems with wireless functionality, remote control, green energy, and high-level integration [1,2]. Furthermore, the use of polymer materials to fabricate actuators is beneficial due to their high mechanical flexibility, low weight, excellent corrosion resistance, low-noise operation and easy fabrication features [3]. Therefore, photoactive deformable polymer materials would be especially promising for the development of photo-actuated actuators. Among them, crosslinked liquid crystalline polymers (CLCPs) containing photochromic moieties, such as azobenzene, may represent one of the most studied systems [4,5,6,7,8]. As a crosslinking of liquid crystalline (LC) polymer chains makes a strong correlation between LC mesogens and polymers, while CLCPs combine the characteristics of anisotropic aspect of LC and rubber elasticity of polymer networks. The self-organization function of LC systems and the flexibility stemming from the polymer networks allow for large and reversible anisotropic deformation in response to the applied stimuli [9,10]. CLCPs containing azobenzene (AZO-CLCPs) demonstrate a reversible photo-triggered deformation that is typically induced by isomerization of azobenzene between trans and cis, this photo-induced isomerization of azobenzene moieties can disrupt or reversely arrange the molecular ordering, and these molecular scale transitions result in remarkable macroscopic deformation [11,12].
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