Mechanoresponsive Performance Optimisation of Natural Rubber-Based Hydrogel for Responsive Human-Computer Interaction

Abstract

Human-computer interaction (HCI) are evolving to increase interactivity and sensitivity to improve the user experience. In this study, an ultra-stretchable and conductive polymer composite hydrogel made of liquid epoxidised natural rubber (LENR), PEDOT:PSS and copper(II) sulphate (CuSO4) is presented, which shows significant potential for HCIs. Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance spectroscopy (NMR) analyses confirm the structural integrity of the composite hydrogels and show a 25% increase in hydroxyl groups and enhanced π-π-π interactions at optimal PEDOT:PSS concentrations. Differential scanning calorimetry (DSC) shows improved thermal stability at increased PEDOT:PSS concentration, especially in the LENR/p(AAM-Co-AA)/20%PEDOT:PSS 1b hydrogel. Its mechanoresponsive properties lead to a 40% change in electrical conductivity upon mechanical stimulation, which is essential for interactive devices. The LENR/p(AAM-Co-AA)/CuSO4/20%PEDOT:PSS 2b hydrogel exhibits improved conductivity, tensile strength, elasticity and stretchability and achieves an LED intensity of (22.9 ± 0.2) × 103 a.u.mm and a low resistivity of 0.0103 Ω.cm after CuSO4 treatment, enabling efficient data transmission. With a capacitance of over 37 ± 4 mF and a toughness of (2.2 ± 0.1) × 109 joules/m3, it significantly improves touch and gesture response times. The touchpad model using the LENR composite hydrogel, along with carbonised Kapton electrodes and PET substrates, adapts to user behaviours for personalised responsiveness and enhanced touch sensitivity. These results provide a robust formulation for LENR/p(AAM-Co-AA)/CuSO4/20%PEDOT:PSS 2b hydrogels that offer sustainable, flexible and responsive solutions for future HCI technologies.

Keywords: hybrid hydrogel, triboelectric nanogenerators, touch panel, Wearable sensor