Preparation Of Stimulus-responsive Hydrogels And Their Applications In Sensor Devices

Multimodal sensors,which can achieve different sensing functions for different environmental stimuli in the same device,are emerging multifunctional electronic devices with a wide range of applications in wearable devices,human-computer interaction,the Internet of Things and other fields that have attracted attention.Capacitive sensors,for example,often consist of a sensing dielectric layer in various forms and upper and lower electrodes,which sense external stimuli by detecting changes in capacitance.Currently,traditional polymer elastomers such as polydimethylsiloxane(PDMS),polyurethane(PU)and polyacrylate(VHB)are often the first choice for dielectric layers,but due to the low capacitance of polymer elastomer materials,when performing highly sensitive pressure sensing,their sensing signals are inevitably disturbed by the coupling effect of the electric field at the edges,affecting the sensitivity of the device’s pressure sensing.In this experiment we have therefore designed a multimodal capacitive sensor using a temperature-stimulated responsive hydrogel(PC-gel)as a dielectric layer.By modulating the temperature and varying the ion concentration in the hydrogel network,different sensing mechanisms are achieved,enabling the device to switch between pressure sensing and non-contact sensing.In chapter 2,common acrylamide(AAm)was chosen as the monomer and the phase transition material calcium chloride hexahydrate was used as the solvent to prepare temperature-stimulated responsive hydrogels(PC-gel)by a one-pot method.By regulating the temperature,calcium chloride hexahydrate was able to switch between the ionic and ion-free states.We used XRD and SEM to characterize the microstructure and properties of the hydrogels,demonstrating that calcium chloride hexahydrate underwent a phase transition in the hydrogel network.The mechanical and electrical properties of the two states were tested before and after the temperature stimulation of PC-gel,and it was found that the mechanical and electrical properties of the hydrogels in the two states were significantly different.The PC-gel ionic state hydrogel can be used to detect small signals due to its small impedance and modulus.In chapter 3,a multimodal capacitive sensor with a "sandwich" structure is prepared using the PC-gel as the dielectric layer and a flexible conductive film as the upper and lower electrodes.Based on the large differences in the capacitance and impedance values of the PC-gel before and after temperature stimulation,a switch between pressure sensing and non-contact sensing is achieved in the same device based on different sensing principles.As the different sensing methods do not affect each other,the pressure sensing of conventional multimodal sensors is not interfered with by the electric field coupling at the edges and the sensitivity of the pressure sensing is further improved.In addition,in order to widen the range of sensor devices,a sensor array is prepared by arranging and combining single devices for the identification of the spatial position of the pressure and the spatial position of the finger in the vicinity.When the finger passes over the device array,the direction of movement of the finger can be identified according to the change in capacitance,providing a new idea for the development of multimodal sensors.