Multibubble interactions for acoustic control of soft matter viscoplastic rheology

• Applicant: Professor Dr. Claus-Dieter Ohl
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Fluid Mechanics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 575389690

Gas bubble oscillations in liquids are a cornerstone of fluid dynamics with relevance to acoustics, cavitation, and biomedical applications. While single-bubble dynamics in Newtonian and viscoelastic fluids are well understood, the collective behavior of bubbles in viscoplastic (yield-stress) media remains poorly characterized. Recent studies have shown that bubble oscillations in viscoplastic fluids such as Carbopol gels can trigger localized yielding, exhibit nonlinear hysteresis, and influence the surrounding rheology. However, existing models are limited to isolated bubbles and fail to capture inter-bubble coupling, trapping, or irreversible restructuring. This proposal aims to fill this gap through a combined experimental and theoretical investigation of multibubble dynamics in viscoplastic environments. We hypothesize that ensembles of acoustically excited microbubbles can serve as active rheological agents, inducing controllable microstructural transitions and modulating the mechanical state of the medium. To test this, we will (i) conduct high-speed imaging of bubble ensembles in well-characterized viscoplastic gels, (ii) develop an acoustic rheometry platform to quantify rheological changes under controlled ultrasound, (iii) use AFM (atomic force microscopy) to map residual deformation and stiffness changes post-oscillation, and (iv) build comprehensive predictive models coupling bubble dynamics with nonlinear rheology. Our preliminary work demonstrates both experimental feasibility and reasonable agreement with theoretical predictions. The proposed research will establish the first quantitative framework for bubble-induced rheological control in viscoplastic media and unlock strategies for designing acoustically reconfigurable soft materials.

• DFG Programme: Research Grants
• International Connection: Australia
• Cooperation Partner: Professor Dr. Hongjie An