Mechanically Compliant and Optically Tunable Metal Oxide‐PDMS Nanocomposite Thin Films as a Platform for Flexible Photonic Integration

Abstract The development of flexible optical waveguides for biophotonics requires materials that combine mechanical compliance, optical transparency, and tunable refractive index (RI). This study reports the fabrication of polydimethylsiloxane (PDMS)‐based nanocomposite thin films (NCTFs) incorporating 1 wt% ZnO and TiO ₂ nanoparticles(NPs). NP dispersions are optimized using response surface methodology with a Box–Behnken Design, enabling reproducible control of sonication parameters. This optimization produces sub‐70 nm particle sizes, minimizing Rayleigh scattering at 635 ± 5 nm and directly linking dispersion quality to optical performance. The NCTFs exhibit RI enhancements (1.4149 ± 0.0006 for ZnO and 1.4146 ± 0.0005 for TiO ₂ ), high transparency (>96% for 2 µm films; 97.6% and 82.0% for 60 µm ZnO and TiO ₂ films, respectively), and guided‐mode optical losses of 0.86 and 2.55 dB cm ⁻¹ . Mechanical characterization confirms Young's moduli below 0.53 MPa and surface roughness below 7.02 nm, while FTIR analysis verifies the chemical integrity of the PDMS network. Comparative evaluation reveals composition‐dependent trade‐offs: ZnO composites offer a balanced profile of transparency and compliance, whereas TiO ₂ composites provide stronger RI modulation but higher optical loss. This integrated materials–processing–performance framework establishes a reproducible route toward multilayer waveguides and soft photonic systems for wearable and implantable biomedical devices.