Study On Preparation And Wettability Control Of PU/CNF Shape Memory Composite

Wettability is an important property of solid surface.With the development of super-wetting materials,smart wetting materials or surfaces have aroused widespread attention because of intelligent responsiveness and controllability.Shape memory materials?SMP?can perceive external stimuli and respond corresponding morphological changes,showing great advantages in the field of intelligent wettability.However,the researches about shape memory super-wetting smart materials are mainly focused on thermal or optical responsive SMP that have some limitations in applications in no-loss droplet manipulation,biomedicine and so on.Therefore,the study of intelligent control of wettability based on new SMP would be necessary.In this work,we constructed a fast water-responsive shape memory polyurethane-cellulose nanofiber?PU-CNF?composite,and new intelligent responsive super-wetting materials were prepared.Based on the shape memory performance,smart and reversible control of surface microstructures and macro-wettability were studied and the applications of the super-wetting smart materials in the fields of micro-droplet manipulation,micro-reactor were explored.Bacterial cellulose nanofibers?CNF?were prepared by sulfuric acid hydrolysis and then introduced into polyurethane matrix by solvent casting to obtain the fast water responsive shape memory PU-CNF composites.The microstructures of the composites were tested and characterized and the water-responsive shape memory properties were studied.The mechanism of water-responsive shape memory was explored by model fitting combining with the characterizations of mechanical property.In addition,we demonstrated the applications of the composite in the field of smart capture in water.Results show that the CNF rigid percolation network can be formed in polymer matrix and the introduction of CNFs can enhance the water affinity of composited material.The formation and destruction of CNF percolation network can be induced by the absorption and desorption of water molecules,together with the good elastic recovery of polymer matrix PU,endowing the composite fast and efficient water-responsive shape memory property.Based on the water responsive shape memory PU-CNF composite,superhydrophobic shape memory switchable adhesive smart materials?s-PU/PU-CNF?were prepared by the composite of pillared superhydrophobic layer?s-PU?on its surface and the surface adhesion can be controlled smartly.Based on the stretch-recovery shape memory property,the pillar spacing on the micro-structured surface can be controlled reversibly,and the smart,reversible switching of surface adhesive states from superhydrophobic pining state to superhydrophobic sliding state is realized.In addition,inspired by the structure and the switchable adhesion of gecko toe pads,the micro-pillar arrangement of micro-structured s-PU surface?“skin”?from plane state to curve state can be controlled intelligently based on the curving-unfolding shape memory of PU-CNF substrate?“muscle”?.As a result,the surface adhesion can be switched reversibly from superhydrophobic high adhesive state to superhydrophobic low adhesive state.Based on the shape memory smart adhesive property,we have realized the applications of the smart materials in micro-droplets manipulation and micro-reactors.Benefiting from shape memory ability,different strain/curvature and corresponding adhesive states can be memorized and fixed without sustained stimulus or external forces,overcoming the disadvantage that similar materials need continuous external force or stimuli in previous reports.Shape memory superhydrophobic composited film?h-PU/PU-CNF?was obtained based on the shape memory PU-CNF composite and the introduction of micro-nano hierarchical structured microarray layer and the wettability of micro-structured surface was controlled smartly.By controlling surface micro-pillar spacing based on stretch-recovery shape memory of the composite,the surface wettability can be reversibly switched from superhydrophobicity to hydrophobicity.In addition,by controlling surface chemical composition based on O₂ plasma treating-heating treating,the switching between superhydrophobicity and superhydrophilicity can be realized.Futhermore,by combining both of the factors above,reversible switching among multiple different wetting states in hydrophobicity-hydrophilicity and superhydrophilicity-hydrophilicity can be achieved.Therefore,based on water-responsive shape memory composites,the reversible switching of multi-wettability from superhydrophobicity to superhydrophilicity can be realized on the same surface by concerted regulation of surface microstructures and surface chemical composition.