Abstract
In this study, a new type of temperature sensor device was developed. The circular electrode of the thermally sensitive sensor was modified with tetramethyltin (TMT) and O2 plasma to form a thin SnOxCy conductive layer on the electrode surface. The nano-Au particles (AuNPs) were subjected to O2 plasma pretreatment to form peroxide groups on the surface. The thermally sensitive sensor made by mixing the treated AuNPs with N-isopropylacrylamide (NIPAAm) solution and then applying UV-induced grafting polymerization of the NIPAAm-containing solution onto the electrode substrate. The composite hydrogels on the electrode introduce thermo-sensitive polymeric surface films for temperature sensing. Using the ambient environment resistance test to measure the resistance, the lower critical solution temperature (LCST) of AuNPs mixed with NIPAAm hydrogel was found to be 32 °C. In common metallic materials, the resistance increased during environmental temperature enhancement. In this study, at ambient temperatures higher than the LCST, the electrode resistance decreases linearly due to the shrinkage structure with AuNPs contacting the circuit electrode.
Highlights
There are many types of commercially available temperature sensor elements such as thermistors, resistance-type temperature sensors, thermal couples and temperature sensing, etc
P(NIPAAm)-based hydrogels absorb water and exist in swollen states below the lower critical solution temperature (LCST). They undergo an abrupt and drastic shrinkage in volume as the medium temperature is raised above the LCST
A new type temperature sensor was successfully produced by UV-induced grafting polymerization of NIPAAm monomer onto AuNPs and immobilization of grafted AuNPs onto the electrode substrate. It combines the advantages of electrical conductivity of AuNPs with temperature sensibility of NIPAAm hydrogel
Summary
There are many types of commercially available temperature sensor elements such as thermistors, resistance-type temperature sensors, thermal couples and temperature sensing, etc. The advantages of resistance-type temperature sensors are high linearity, wide linear range, and a high output signal level and accuracy, but the disadvantage is the necessity to have three or four wired circuits, bulky components, and slow conduction and response. Polymerized-N-isopropylacrylamide (P(NIPAAm)) is a well-known thermo-responsive polymer and exhibits a lower critical solution temperature (LCST) of about 32 ◦ C in an aqueous medium. P(NIPAAm)-based hydrogels absorb water and exist in swollen states below the LCST They undergo an abrupt and drastic shrinkage in volume as the medium temperature is raised above the LCST. We provide a simple and novel sensing mechanism on the circuit electrode to exhibit the sensor’s application value to humans
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