Work

Stressing and probing with light: A thermo-optical investigation of soft solids

Year: 2026

Type: article

Abstract: Internal stresses in arrested soft solids can be generated not only by mechanical loading but also by spatially nonuniform temperature fields, which impose incompatible thermal strains and activate coupled thermoelastic and poroelastic responses. Here, we introduce an all-optical stress-and-probe protocol that combines localized near-infrared photothermal forcing with space-resolved dynamic light scattering. The setup provides (1) thermal-lensing readout of the evolving refractive-index field and (2) photon-correlation imaging of local dynamics, complemented by speckle-based velocimetry to reconstruct displacement and velocity fields. We apply the method to two contrasting soft solids. In a thermoresponsive physical gel, continuous irradiation produces a slowly strengthening lensing signal that persists after the pump is switched off; refractive-index reconstruction indicates contributions beyond purely thermo-optic effects, consistent with irreversible microstructural reorganization. Concomitantly, correlation functions reveal a long-lived modification of the relaxation dynamics, supporting a scenario where constrained thermoelastic stresses imprint residual strain and drive postexcitation stress relaxation. In an ultraweak polystyrene colloidal gel with nearly temperature-independent constitutive properties, the sample deformation is driven by a buoyancy-driven convection, whose magnitude scales with the thermal expansivity of water and increases with pump power, crossing from largely elastic recovery to partial irreversibility. Overall, this optical platform enables controlled access to ultralow, spatially distributed thermal stresses and offers a route to study stress transmission, plasticity, and cyclic photothermal fatigue in soft solids.

Source: Physical Review Research

DOI: 10.1103/5m7y-k8kc

Authors: Rafael Gervasone, Arianna Erba, Roberto Piazza, Stefano Buzzaccaro

Institution: Politecnico di Milano

Language: English

Topic: Material Dynamics and Properties

Subfield: Materials Chemistry

Field: Materials Science

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,625

Funder: Agenzia Spaziale Italiana