Based On The Cassie-Baxter State Anti-liquid Interference And Anti-bacterial Adhesion Wearable Flexible Strain Sensor Research

Wearable flexible strain sensor has gradually put into the field of consumer goods,medical health,industry and military.In the future,it will be more challenging and promising due to its gradually entering into strategic emerging industry,like electronic medicine,artificial intelligence,biochip,health industry and cloudy data,etc.In order to realize the application in many fields,wearable flexible strain sensor not only need to overcome the problem of optimizing itself sensing property,like ultra-sensitivity and high stretch ability,but also need to solve the urgent issue of resistant liquid interference and maintain electronic sensing under complex working environment,such as water,acid,alkali,salt,microbiology,etc,which could interfere flexible strain sensor,making an instability conductivity,further causing electronic sensing instability and service life reduction.For instance,bacteria adhere to the sensor surface,it will cause microbial corrosion and damage the conductive pathway.Water or other molecules will interfere electronic sensing and cause contamination when they are permeating conductive layer.The traditional technology to avoid liquid interference is using polymer to package sensor,but there are some problems such as poor sensor performance and complex packaging process.Therefore,it is of great significance to propose a research strategy replacing encapsulation method to construct a Cassie-Baxter wetting state directly on the surface of wearable flexible electronic strain sensor and reveal its mechanism.In this paper,we put forward an anti-liquid-interfering and bacterially anti-adhesive strategy of wearable flexible strain sensor.Through comprehensive study on the wettability and electronic sensing of MWCNT/G-PDMS wearable strain sensor in Wenzel wetting state,the mechanism of liquid effect on tensile strain sensing was explored.By theoretical analysis,anti-liquid-interfering and bacterially anti-adhesive strategy of F/Ag/MWCNT/G-PDMS wearable flexible strain sensor(FAMG)based on Cassie-Baxter wetting state with ultra-sensitive and high stretchable ability was designed.The sensor was designed with sandwich structure,superelastic PDMS as flexible base,a Layer-By-Layer APTES and MWCNT/G as middle bonding layers,Ag NPs and fluorine-polymer as outer layer.In this paper,the key technology theory of anti-liquid-interference and bacterial anti-adhesion is expounded from the aspects of micro/nano-structure,surface wetting theory and electronic sensing mechanism.The main contents of this paper are as follows:(1)MWCNT/G-PDMS wearable strain sensor in Wenzel wetting state was constructed.Through the analysis of the wettability and adhesion of the water/oil/bacterial droplets on the surface of wearable flexible strain sensor,the influence of the liquid on the sensing performance was explored.Combining with the self-cleaning,hydrophobicity,bacterial anti-adhesion and underwater anti-oil ability of the sensor,a model of anti-liquid-interfering to electronic sensing was put forward.The results show that the conductive layer of MWCNT/G-PDMS wearable flexible strain sensor based on Wenzel wetting state is a micro-structured plane with a thickness of about 5?m,and the surface of strain sensor is prone to adhere water,oil and bacterial droplets. MWCNT/G-PDMS wearable strain sensor could not resist most liquid(green tea,black tea, orange juice,cola,milk,HCl(pH=1),NaOH(pH=10),NaCl(0.4mol/L)and bacteria liquid(10~4CFU/mL)to interfere sensing due to no self-cleaning ability,superhydrophobicity,bacterial anti-adhesion and underwater anti-oil ability.Moreover,due to the interference and infiltration of other impurities,the conductive path changes,resulting in the serious degradation of the sensing performance of MWCNT/G-PDMS wearable strain sensor in Wenzel wetting state.(2)Based on the analysis of the model of liquid interference to electrical performance,an ultra-sensitive and high stretchable wearable flexible strain sensor based on Cassie Baxter state is proposed.Through the analysis of the structure and morphology,the sensor has a micro/nano structured conductive layer with a thickness of 5-10?m,and the conductive materials are evenly distributed and the structure is stable.By analyzing the wettability and adhesion of water/oil/bacterial droplets on the surface of the sensor,the correlation of liquid interference to resistance was explored.The results showed that the sensor has excellent anti-liquid-interference due to its self-cleaning,hydrophobicity,bacterial anti-adhesion and underwater oil-repellency.Because water,oil and bacterial droplets were not easy to adhere to the sensor surface,their electrical properties were not affected by the liquid(green tea,black tea,orange juice,cola,milk and acid solution(pH=1),alkaline solution(pH=10),salt solution(0.4mol/L)and bacterial solution(10~4CFU/mL)),ensuring the stability of its electrical properties.The sensor exhibited a sensitivity of 2059,a stretching range of 0.1-170%,a minimum testing value of0.1%,a response and recovery time of 150ms,and a stable electrical performance after 1000stretching cycles.At the same time,it can accurately and synchronously monitor the whole range of human motion in complex environment.In the simulated artificial rainfall environment,FAMG sensor could accurately monitor and measure the electronic bird regardless of the influence of liquid.It can also ignore the influence of bacterial fluid,and carry out multi-directional and comprehensive monitoring of human movement(pulse,wrist,elbow,knee)in human body testing.This showed that FAMG sensor had good resistance to liquid interference and bacterial adhesion,as well as excellent electrical properties.(3)The mechanism of the anti-liquid-interference to sensing performance was revealed.Through the analysis of the structure morphology and surface wettability of FAMG wearable flexible strain sensor.It was revealed that the multilevel hierarchical surface with Cassie-Baxter wettability state was the key technical theoretical basis of anti-liquid-interference.By studying the wettability of oil and water on the sensor surface,and the adhesion of bacterial droplets,it was revealed that the wetting characteristics of super-hydrophobicity and underwater oleophobicity were the inner mechanism of bacterial anti-adhesion.(4)The sensing mechanism of ultra-sensitive and high stretchable FAMG wearable flexible strain sensor was studied.Based on the analysis of 3D morphology and electrical properties,it was revealed that crack generation effect of MWCNT/G conductive layer and terminal crack extension effect of APTES/MWCNT/G intermediate isolation layer are the mechanism of ultra-sensitivity.Bridging effect of MWCNTs and sliding effect of APTES/MWCNT/G intermediate isolation layer are the main factors of wide extension range.