Single-Material Solvent Actuator From Poly(inoic Liquid) Janus Inverse Opals Based On Directional Wetting

Solvent actuator has attracted wide research attention owing to it can produce great mechanical energy based on tiny humidity change or solvent vapor change,and being applied in smart muscles,robotic and etc.Generally solvent actuator is produced from the two-layer structure,which easily suffer from declamination of the two layers owing to stress restriction and poor interlayer adhesion during frequent bending process.In this paper,we put forward a novel single-materials hydrophilic/hydrophobic Janus solvent actuator of poly(ionic liquid-co-methyl methacrylate)poy(IL-co-MMA),by combining the well-ordered periodic structure of photonic crystals with the excellent solvent response property of PIL.The main content is as following:1.Fabrication of hydrophilic/hydrophobic Janus Poly(IL-co-MMA)actuator.The Janus poly(IL-co-MMA)inverse opal was fabricated by infiltrating the mixing solution of ionic liquid monomer,methyl methacrylate and photoinitiator into the interstice of photonic crystal template,subseqent photopolymerization and the removal of PC template.The geography Janus property of the sample was characterized by SEM,AFM,having one large-pore structure on the top surface,and one small-pore structure on the bottom surface.The chemical Janus properyt of the sample was characterized by XPS,EDX,having a more hydrophilic PIL on the top surface,and a more hudyrophobic PMMA at the bottom surface.2.Formation mechanism of the Janus property of Poly(IL-co-MMA)actuator.Geography Janus property of the sample is aroused from the gradient light intensity along the thickness direction during photo-polymerization process.The strong light would result in more polymerization and infiltration of monomer/polymer at the top surface,forming large-pore structure;the weak light results in less polymerization and infiltration of monomer/polymer at the bottom surface,forming small-pore sturcture.The chemistry Janus property is aroused from that IL showed extremely high polymerizability in the methanol system compared to MMA.The formed upward methanol(low boiling point)evaporation flux resulted in a gradient distribution of the methanol along the thickness during the photopolymerization process,which may have induced the polymerization gradient of MMA.This gradient would be favorable for the polymerization of MMA at the bottom,with less methanol,but unfavorable for the MMA polymerization at the top,with much methanol.3.Actuation behavior and applications of Janus of Poly(IL-co-MMA)actuator.The actuation behavior(such as bending angle,curvature,and the actuating rate)of sample was investigated by changing the solvent type,the content of the ionic liquid,and the pore size.The recylability of the actuator has also been investigate.In additional,the actuator was extended for some applications,such as stucture color/spectra monitoring actuating porcess,lifting a carge,or driving an engine.