Research On Methods And Mechanisms To Improve Piezoresistive Pressure Sensor Performance With Polypyrrole And Composites For Smart Wearables

Smart wearable piezoresistive pressure sensors for body movement detection at ultra-low to medium pressure levels are highly demanding devices that find application in many fields such as healthcare,rehabilitation,sports,etc.These pressure sensors are cost-effective,environmentally friendly,highly sensitive,reliable,and simple to fabricate.However,many researchers are finding it rather challenging to make the best use of these sensors as they focus to do more research.The conductive polymer,polypyrrole（PPy）shows promising abilities to engage with non-toxic,environmentally friendly piezoresistive pressure sensor fabrications.The drawbacks of the PPy such as less solubility,low mechanical properties,and low conductivity able to improve through modifying the process of Py in situ polymerization.Py in situ polymerization is a simple and scalable process,however,the techniques to improve the sensitivity and stability of conductive signals of PPy coated sensors are still not understood fully.The structural properties of the PPy coated substrate play a key role to grab conductive fillers through the process and ensuring reliability for sensor performance.Among the different flexible substrates,macro-porous sponge（MS）,and aerogel（AG）manifest favorable properties that make them suitable for this application and have shown promising performance in making wearable and flexible pressure sensor fabrication.The polydopamine（PDA）coating shows an ability to modify the surface of the substrate by actively adhere the conductive fillers to it.Multi-walled carbon nano tubers（MWNTs）possess the ideal properties to improve the performance of the PPy coating to create highly sensitive sensor fabrication.This research focuses on studying and investigating the PPy based piezoresistive pressure sensor fabrication of high sensitivity and stability of conductive signals with PDA and MWNTs coating modifications on MS and AG substrates.The PPy based sensors with good conductive properties are made through the process of in situ polymerization.The molecular interactions between PDA and PPy show strong physical bonding than that between molecules of PDA.Hence,PPy and PDA when deposited together with a thinner coating of PDA that performs better than a thick coating of PDA and PPy.The thin PDA layer was newly developed by modifying the PDA coating（m-PDA）,by changing the pH level of the PDA solution with para toluene sulfonic acid（p-TSA）.The p-TSA works as a dopant with PPy.The pressure sensor,PDA（0.05 Mp-TSA）/PPy coating deposited on MS shows high performance over 1000 pressure cycles in the 0.95 kPa to 9.5 kPa active in low pressure range.Sensor parameters related to the sensitivity,hysteresis,nonlinearity,repeatability error up and down were recorded as10.69 kPa^-1,13.51%,3.30%,2.70%,and 2.25%respectively.Piezoresistive pressure sensor fabrication with MWNTs/PPy composite was shown to yield an even,thick,and strong coating with high molecular interactions.The MWNTs/PPy coating with AG shows promising performance for pressure sensor development with a high sensitivity of 34.64 kPa^-1in the 0.45 kPa to 4.0 kPa active pressure range.The sensor parameters related to hysteresis,nonlinearity,repeatability error up and down were recorded as 4.08%,12.9%,4.5%,and 9.3%,respectively.The PDA surface modification was not compatible with the process of MWNTs coating.When sodium dodecylbenzene sulfonate（SDBS）was used as the surfactant with MWNTs,it coursed the removal of the PDA coating from the MWNTs/PPy composite.The research findings were proved that the positive approaches adopted to improve sensitivity and stability of conductive signals with PPy based sensors made it possible for them to detect human body movements in the subtle and low-pressure ranges.The piezoresistive pressure sensors with MWNTs/PPy on AG showed higher sensitivity,but lower stability of conductive signals than the pressure sensor with m-PDA/PPy on MS.AG was lighter in weight,able to grab more conductive fillers during the applied process and was more compatible for wearable sensor development for subtle and low-pressure range than MS.Both approaches show profitable outcomes for piezoresistive presser sensor fabrication designed to work at different active pressure ranges.PPy coating with PDA,MWNTs,and AG show positive features that make them suitable for highly sensitive and reliable pressure sensor developments for future prospects.