Preparation And Photomechanical Actuation Of Carbon Nanotube Elastomer Composites

In the present dissertation, we have summarized the recent research progress about micromechanical actuators based on carbon nanomaterials. Carbon nanotube polymer elastomeric composites with reversible response to near-infrared (NIR) light have been successfully fabricated by the optimal methodologies, and their photomechanical actuation behaviors have been systematically investigated including three Chapters.The hydroxylated multi-walled carbon nanotubes (MWCNTs) were dispersed into a liquid silicone rubber by ultrasonication and mechanical stirring. The resulting stable black suspension was extracted by an injector and then injected to the preheated silicone oil for curing process and hence, obtaining poly(dimethyl)siloxane (PDMS) composite fibers containing uniformly-dispersed MWCNTs. At the start of test the composite fibers have a pre-strain applied to them with different values, and has been allowed to induce the nanotube alignment in the PDMS matrix. It was found that the composite fibers expanded on actuation with NIR (808nm) irradiation at low pre-strain (ε≤10%) while the composite fibers contracted at high pre-strain (10%≤ε≤40%) upon NIR stimulation. After stopping NIR light, the composite fibers recovered to their initial state immediately. Moreover, the actuation stress (output force) triggered by the fibers increases with increasing the applied pre-strain. The actuation stress also increases with increasing the irradiation area and light power. However, pure PDMS fiber has no photomechanical response to NIR light.The as-synthesized liquid-crystal monomer, hydroxylated-MWCNTs, UV initiator and crosslinker were homogeneously mixed by unltrasonication and mechanical stirring. The resultant suspension was cast onto a glass or PTFE substrate and then photopolymerized by UV-light exposure to produce liquid-crystalline elastomer composite films containing well-dispersed MWCNTs. It was found that MWCNTs absorbed and transformed NIR light into thermal energy which was then served as a nano-hearting source and thermal conduction pathway to heat the LCE matrix rapidly. Meanwhile, the absorbed thermal energy triggered a nemacti-isotropic phase transition of LCE, resulting in a fast and reversible response with large shape change of the composite films. The strain rate and deformation appeared to be3.6%s-1and47%at low nanotube loading-levels (～0.3wt%), respectively. Graphene oxide (GO) and reduced graphene oxide (RGO) were applied to fabricate PDMS composites and their photomechanical actuation behaviors were compared with MWCNT/PDMS and MWCNT/LCE composites. It was found that the elastomer composites filled by MWCNTs had faster response rate and larger strain than those filled by the same loading of GO and RGO in the same matrix. However, LCE compsites showed faster response rate and larger strain compared to PDMS compsites due to the intrinsic large doformation caused by phase transition of LCE during heating. Moreover, RGO/PDMS compsites had better photo-actuated properties with respect to GO/PDMS composites because of the improved absorption ability of NIR light after reduction of GO.