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Flexible Non-Contact Distance Sensor Based On "rGO/cationic Latex" Electrostatic Self-Assembly

Posted on:2021-08-28Degree:MasterType:Thesis
Country:ChinaCandidate:J X YanFull Text:PDF
GTID:2518306308491534Subject:Textile chemistry and dyeing and finishing works
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The electronic skins(E-skins)are integrated with flexible sensors which can convert various environmental stimuli into electric signals,thus acting as human skins.These functions indicate that the E-skins would have broad applications in certain fields,including wearable health monitoring and robotic skin.Therefore,such devices attract great interests of worldwide scientific researchers.At present,most of the current flexible sensors sense stress,strain,and pressure,by deforming themselves under physical contact.However,after the repeated deformations,the active sensing materials are prone to fatigue,whose internal structure will be changed or damaged.This results in the instable and deteriorated responding performances.Proximity sensor can sense the distance between the sensor and the measured conductor approaching it.The sensing mechanism indicates that the sensing not only avoid biological pollution caused by physical contact,but is free from physically deformed,which would improve the stability and durability of the sensors.Although the non-contact sensor has been studied for several years,most reports are limited at the level of phenomenon description,and there is lacking of systematic and in-depth research on the mechanism of non-contact sensing and the regulation of sensing performances.In this thesis,we used electrostatic self-assembly method to compound positively cross-linked polymethyl methacrylate(PMMA)latex with negatively charged graphene oxide(GO).After the reduction of the compound latex,a stable dispersion of r GO@PMMA composite latex was prepared.Then,during the following procedures,r GO@PMMA latex was mixed with low glass transition temperature(-42?)cationic polybutyl acrylate(PBA)latex,and was dried into a composite latex film:r GO@PMMA/PBA film.The film was a dielectric material,which could be assembled as a non-contact sensor by connecting electrodes.The sensor worked with capacitive principle.Then,both the mechanism and the performance of the sensor were investigated.It was found:1.During the preparation of PMMA latex by emulsion polymerization,semi-continuous polymerization technology was used to graft the cationic monomer methacryloxyethyl trimethyl ammonium chloride(DMC)onto the surface of PMMA particles and to increase the zeta potential of PMMA latex.When the dosage of DMC was increased from 0 to 0.8wt%,the zeta potential of PMMA latex was increased from+35m V to+49m V.The PMMA latex with high zeta potential was used to compound with GO,and a stable and dispersed r GO@PMMA composite latex was obtained after reduction the GO@PMMA with ascorbic acid.A maximum loading of r GO of 6wt%was acquired for PMMA with 86.5 nm in diameter and DMC dosage of 0.8wt%.2.After mixing the r GO@PMMA composite latex with PBA,the latex mixture remained stable.Therefore,the casted composite latex film had a uniform structure in terms of thickness and r GO@PMMA distribution.When the content of r GO@PMMA in the composite film gradually increased from 1%to 20%,the dielectric constant of the film gradually increased accordingly from6.2 C2/(N*M2)*to 13.7 C2/(N*M2).3.Using the composite film as the dielectric material,the assembled sensor has the ability of non-contact sensing,which could respond regularly to the vicinal conductor or dielectric object,and identify the distance between the sensor and the approaching object.The performance of the sensor conforms to the predictions combining the"Microcapacitance model"and"Cauchy model".Furthermore,the predicted optimal content of r GO@PMMA agreed well with the experimental value.By increasing the area and thickness of the r GO@PMMA/PBA composite film assembled in the sensor,the performances of the sensor to long-distance objects and short-distance objects were improved,respectively.4.The non-contact sensor had high flexibility.After 200 cycles of tension test at 100%strain,the response performance of the sensor was nearly unchanged.When the size of the composite film assembled in the device was 2cm*1cm*0.03mm(length*width*thickness),non-contact sensor could respond to the thin aluminum sheets:0.1*0.1mm~2 in area with a distance of 1cm and1.0*1.0mm~2 in area with a distance of 14cm.Non-contact sensors could also be used for object speed and acceleration measurement,determination of electrolyte concentration in solution,and identification of the grounding state of objects.Therefore,non-contact sensor has great application prospects in the fields of remote detection,human-computer interaction and intelligent robots.
Keywords/Search Tags:Capacitive sensing sensor, Electrostatic self-assembly technology, Latex film formation, Graphene, Polymer-based conductive composite, Proximity response
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