# Rheo-acoustic gels: Tuning mechanical and flow properties of colloidal gels with ultrasonic vibrations

## TL;DR

This study introduces rheo-acoustic gels, demonstrating how ultrasonic vibrations can dynamically tune the mechanical and flow properties of colloidal gels through controlled softening and fluidization effects.

## Contribution

It presents the first systematic investigation of ultrasonic vibrations on colloidal gels, revealing mechanisms for real-time property tuning and potential for smart material design.

## Key findings

- Ultrasonic vibrations cause significant softening of colloidal gels.
- Vibrations reduce gel yield stress and promote shear-induced fluidization.
- The fluidization process is governed by an effective temperature related to acoustic intensity.

## Abstract

Colloidal gels, where nanoscale particles aggregate into an elastic yet fragile network, are at the heart of materials that combine specific optical, electrical and mechanical properties. Tailoring the viscoelastic features of colloidal gels in real-time thanks to an external stimulus currently appears as a major challenge in the design of "smart" soft materials. Here we introduce "rheo-acoustic" gels, a class of materials that are sensitive to ultrasonic vibrations. By using a combination of rheological and structural characterization, we evidence and quantify a strong softening in three widely different colloidal gels submitted to ultrasonic vibrations (with submicron amplitude and frequency 20-500 kHz). This softening is attributed to micron-sized cracks within the gel network that may or may not fully heal once vibrations are turned off depending on the acoustic intensity. Ultrasonic vibrations are further shown to dramatically decrease the gel yield stress and accelerate shear-induced fluidization. Ultrasound-assisted fluidization dynamics appear to be governed by an effective temperature that depends on the acoustic intensity. Our work opens the way to a full control of elastic and flow properties by ultrasonic vibrations as well as to future theoretical and numerical modeling of such rheo-acoustic gels.