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<p>This study explores the interplay between the glass transition temperature (T<sub>g</sub>) and nonlinear optical properties of a novel Polyurethane–Azobenzene–Carbon black (PAC) composite through Spatial Self-Phase Modulation (SSPM). By examining the temperature-dependent formation of SSPM diffraction rings, a strong correlation is established between the material’s thermo-mechanical transition and its optical nonlinearity. Below T<sub>g</sub>, the composite exhibits suppressed SSPM activity due to restricted polymer chain mobility in the glassy state. Above T<sub>g</sub>, enhanced segmental motion enables local refractive index modulation, leading to pronounced SSPM patterns. This transition is confirmed through both visual ring analysis and piecewise linear modeling, enabling accurate estimation of T<sub>g</sub>. Complementary structural and optical characterizations, including XRD, Raman, and UV-Vis absorption spectroscopy, support the amorphous matrix and photoresponsive behavior of the PAC film. Notably, increased UV absorption at 20&#xa0;°C indicates potential pre-transition softening, contributing to nonlinear effects even below bulk T<sub>g</sub>. These results present SSPM as a powerful, non-contact optical tool for probing thermo-mechanical transitions in functional polymer composites and suggest the utility of PAC-based films in optically active sensor platforms.</p>

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Real time detection of glass transition in shape memory polymer composites using spatial self-phase modulation

  • 期刊论文

  • 发表日期：

    2025年12月12日

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  • Jayachandra Bingi,
  • Rupkatha Sutter,
  • C. Parthiban,
  • Reddy G. Ramachandra,
  • Sai Pavan Prashanth Sadhu,
  • Anudeep Vayyeti

摘要

This study explores the interplay between the glass transition temperature (Tg) and nonlinear optical properties of a novel Polyurethane–Azobenzene–Carbon black (PAC) composite through Spatial Self-Phase Modulation (SSPM). By examining the temperature-dependent formation of SSPM diffraction rings, a strong correlation is established between the material’s thermo-mechanical transition and its optical nonlinearity. Below Tg, the composite exhibits suppressed SSPM activity due to restricted polymer chain mobility in the glassy state. Above Tg, enhanced segmental motion enables local refractive index modulation, leading to pronounced SSPM patterns. This transition is confirmed through both visual ring analysis and piecewise linear modeling, enabling accurate estimation of Tg. Complementary structural and optical characterizations, including XRD, Raman, and UV-Vis absorption spectroscopy, support the amorphous matrix and photoresponsive behavior of the PAC film. Notably, increased UV absorption at 20 °C indicates potential pre-transition softening, contributing to nonlinear effects even below bulk Tg. These results present SSPM as a powerful, non-contact optical tool for probing thermo-mechanical transitions in functional polymer composites and suggest the utility of PAC-based films in optically active sensor platforms.