Preparation And Performance Research Of Visual Mechanical Sensitive Sensor Based On Polymer Dispersed Cholesteric Liquid Crystal

Visual mechanical sensitive sensor is a kind of sensor which can transform mechanical information into visual monitoring signals.Compared with traditional electronic pressure sensor,its components are simple and it is easier to monitor.At present,visual mechanical sensitive sensors are mostly prepared on the basis of triboluminescent materials and photonic crystal materials.But they can not realize the visual memory of force and the reusability of sensors at the same time.Cholesteric liquid crystal can produce the structural colors with high brightness and high contrast ratio.The polymer dispersed cholesteric liquid crystal(PDCLC)by using the polymer network to anchor the cholesteric liquid crystal has excellent characteristics of bistability and force's,electrical stimulation response,which can develop color under pressure,store the color after removing pressure and eliminate color under electrical stimulation,so it is expected to solve the current problems of visual mechanical sensitive sensors.In this paper,the PDCLC material system was constructed by adjusting and controlling the preparation process and formulation parameters,and the visual mechanical sensitive sensor with visual memory of force and reusability was prepared.Based on the study of the influence of polymer network micro structure on the performance and the force-light responsive mechanism of the sensor,the structure required to be design to prepare visual mechanical sensitive sensor based on high sensitivity,motion tracking and surface texture detection.The specific conclusions are as follows:Firstly,the PDCLC material system was constructed by UV induced phase separation technology,and visual mechanical sensitive sensor were prepared.The internal polymer network structure of the sensor prepared by different processes and formulations was characterized by scanning electron microscopy,then the process and formula parameters were optimized.The results showed that when the exposure time was less than 1 min or the exposure temperature was higher than 40?,the PDCLC system could not be formed in the sensor.When the monomer content was15?35 wt%and functionality was 1.14?1.67,respectively,PDCLC system could form in the sensor.The polymer network became denser and the mesh size of polymer network became smaller with the increase of monomer content or functionality.Based on the sensors formed by PDCLC system,the performance of the sensors with different polymer network micro structure was further characterized.It was found that with the decrease of the mesh size of the polymer network,that is,the increase of polymer network density,the pressure responsive sensitivity and visual contrast ratio decreased,while the driving voltage was increased.Secondly,the deformation under pressure of the sensor was simulated by Abaqus software.Combined with results of the micro area optical responsive test,the relationship among the pressure,deformation and optical response was established,and the force-light responsive mechanism was revealed.The results showed that the pressure visualization response of the sensor was closely related to the lateral deformation of polymer network in PDCLC layer.The cholesteric liquid crystal in the lateral deformation region underwent shear motion under pressure,which changed from the focal conic state to the planar state,and then sensor produced visual response.Under the same pressure,the larger the lateral deformation,the stronger the visual response of the sensor.Finally,in order to enhance the applicative value of the sensor,this paper adjusted the thickness and the elastic modulus of the conductive substrate,optimized the design of the sensor and prepared sensor based on high sensitivity,motion tracking and surface texture detection.It was found that the lower the thickness and elastic modulus of the upper conductive substrate,the higher the sensitivity.If conductive PP film was chosen as the upper conductive substrate,when the thickness was 50?m and the elastic modulus was 425 MPa,the maximum sensitivity of sensor would be 0.015 k Pa^-1.And the lower the thickness and elastic modulus of the upper conductive substrate,the lower the quality of the ball that the sensor can track,the higher the visibility of the trajectory.If conductive PET film was chosen as the upper conductive substrate,when the thickness was 25?m and the elastic modulus was 3205 MPa,the sensor can track the trajectory of a ball with a quality of 0.88 g and the responsive pressure is about 22 k Pa.When the sensor used rigid ITO conductive glass whose thickness was 1.1 mm as the upper conductive substrate,it didn't respond to the pressure applied to the rigid glass from the top,but responded to the pressure applied to the flexible substrate from the bottom,so the surface texture of the object can be detected by the sensor.