Cross linked PDMS optical waveguide with spiropyran for pressure sensing and local threshold visualization

Research background and material design: Flexible optical waveguides have potential applications in pressure/strain sensing for soft robots and personalized medicine. Polydimethylsiloxane (PDMS) provides a robust platform, but how to simultaneously improve sensitivity and integrate visual indicators of local pressure thresholds remains an active research direction. This study prepared spiropyran (SP) crosslinked PDMS optical waveguides with the aim of achieving low-pressure quantitative sensing and producing reversible colorimetric response at local stress/strain thresholds.

Experimental Design and Key Performance

The study used a three factor Box Behnken design to systematically map the interactions between SP concentration, PDMS mixing ratio, and curing conditions with four key performance parameters: transverse compression sensitivity (up to 100 kPa), secant modulus, refractive index (RI), and propagation loss.

. The response surface methodology indicates that the mixing ratio mainly drives the optomechanical response, while the SP concentration significantly affects the refractive index and propagation loss. Under high lateral compression (0.9-2.4 MPa), the activation of force induced color change (SP isomerization towards the anthocyanin) is directly related to the macroscopic strain hardening zone, providing a pressure threshold comparable to human tissue bruising. Although there is no single formula that can simultaneously maximize low pressure sensitivity and photochromic performance while minimizing light attenuation, research has identified outstanding combinations for specific application scenarios. These results establish a robust framework based on polymer science for the rational design of multifunctional, mechanochemical active optical pressure sensors.

Significance for the Polymer Additive Industry

This study introduces spiropyran as a functional crosslinking component into PDMS networks, demonstrating the potential of additive based design in electronic and electrical materials.

. For engineering plastics and flame retardant systems, similar functional approaches can inspire the integration of responsive components in flexible sensing substrates; The design logic of weather stability and antioxidant system is also consistent with the method of regulating the long-term performance of materials through formulation variables in research. In the fields of cables and wires, packaging and potting materials, this synergistic optimization of compression sensitivity, modulus, and optical loss provides a reference formula design path for the development of electronic and electrical materials that combine sensing and indication functions. The study emphasizes the dominant role of mixing ratio and curing conditions in the optomechanical properties, and also suggests the need for precise control of crosslinking and curing processes in engineering plastic processing to balance mechanical and functional properties.

Information source:Spiropyran‐Crosslinked PDMS Optical Waveguides for Pressure Sensing and Visual Cue of Localized Pressure Threshold， Organized by Herun Chemical.