Controllable Kinematics Of Intelligent Soft Actuators Built Up Layer-by-layer Assembly

Stimuli–responsive intelligent polymer film refers to a type of polymer film that can undergo shape change or motions under external stimuli,which can be used as devices such as sensors,soft robotics,and energy harvest conversion receivers/energy generators in such as biomedical,and mechanical engineering fields.Herein,controllable kinetimatics of polymer films has been a research highlight in the subject of intelligent polymers.In order to prepare flexible polymer actuators that are responsive to external stimuli and show controllable motions,special structural designs are usually required.In this paper,two design methods are reported for the preparation of polymer films with special structures,and the films can generate controllable motions in acetone vapor or humidity conditions.The details are briefly described as follows.?1?A bilayer film actuator that was made of tough stretchable polyvinylidene fluoride?PVDF?layer and brittle hard polystyrene?PS?layer.The PS component increases the flexural modulus of the PVDF layer,with the titanium dioxide?TiO₂?pattern modification between the PVDF and PS interface instead of the traditional surface patterns,so that the composite thin film soft actuator has more stable and controllable motion performance.And the TiO₂ patterns used for interfacial modification will not be destroyed during fast,reciprocating and reversible controllable motion.When the bilayer film actuator is exposed to acetone vapor,the PVDF/TiO₂/PS actuator will generate controllable motion,including counterclockwise/clockwise oscillation rotation,wiggling,wriggling and directional creep crawling,which vary in accordance with the arrangements of the patterns.A series of soft actuators with different angles between the TiO₂ pattern and the long side of the experimental test strips of the bilayer films were designed and prepared,and the kinematic mechanism was demonstrated by the flexible actuator.The soft actuator expands and bends upward by adsorbing acetone vapor on the PVDF side film;then,the local shrinkage caused by the spacial asymmetric absorption and release of acetone causes the film far from the acetone vapor crowns to bend downward?incline to the filter paper soaked with acetone solution?,and the synergistic reaction give rise to the complex,controlled kinematics.A series of software robots have been created to verify the universality of this kinematic mechanism.PVDF/TiO₂/PS soft robots with different geometries can still strictly follow this controllable kinematics law.However,if there is no interface TiO₂ patterning modification between PS layer and PVDF layer,the motion is irregular.This kind of PVDF/TiO₂/PS composite films with controllable kinematics has the potential to prepare acetone vapor responsive sensor devices.In this paper,an application demo of a cargo transport device is prepared by using PVDF/TiO₂/PS composite films.?2?The multilayer polymer film actuator that can control the external stimulus by controlling the gradient characteristics in the thickness direction.However,due to the lack of strong interface interactions,maintaining structural integrity during shape changes remains a challenge.Therefore,in this paper,we propose an improvement method that not only endow the polymer film actuator with a gradient characteristic in the thickness direction,but also provides its ability to maintain structural integrity.The preparation processes are as follows:several composite solutions of sodium alginate?SA?and polyvinyl alcohol?PVA?are arranged at different weight ratios,and the solution is added dropwise layer by layer on the surface of the substrate of the glass sheet.Film with gradient moisture response characteristics in the thickness direction.The multilayer composite film prepared by this design method has heterogeneous moisture sensitivity and moisture absorption properties in the thickness direction,and has strong interfacial interaction between the film layers to ensure that the film actuators have a coordinated directional motion performance.Similar to the bending motion of the stem of Selaginella lepidophylla,which can presenting a specific response under different humidity.A universal comprehensive mathematic model reveals that the directional bending motion is driven by the variation of chemical potential of humidity The energy conversion efficiency from humidity to mechanical motion reaches 81.2%at 25?.By coating with CoCl₂ solution on the surface of the film,the SA@PVA/CoCl₂ composite film can be served as a warning board.When the warning sign which is made of the SA@PVA/CoCl₂ composite film is put in high humidity surrounding environment,the color of it will change from the original Blue to striking,conspicuous Red,which can remind pedestrians to prevent from slipping or falling.According to the responsive characteristics of the composite film during different ambient humidity,When the film is involved in a bidirectional switch,it is capable of turning on/off light emitting diodes according to the ambient humidity,which switch on/off means provides moisture to the environment or not,showing a promising potential in control over humidity–dependent devices.