Dynamics of swelling and drying in gels

Polymeric hydrogels swell by absorbing a remarkable amount of water. These materials are widely used in a variety of engineering applications, and predicting the rates of swelling and drying is a key aspect of designing for these applications, but these processes are complex and highly nonlinear. Using a mathematical model and a series of experiments, we showed here that swelling and drying are inherently transient and strikingly different. These results pave the way for more sophisticated prediction and control of swelling and drying.

Read the paper: Bertrand et al., PRApplied 2016

Wettability control on multiphase flow in porous media

The simultaneous flow of multiple fluid phases through a porous solid occurs in many natural and industrial processes—for example, rainwater infiltrates into soil by displacing air, and carbon dioxide is stored in deep saline aquifers by displacing brine. It has been known for decades that wetting—the affinity of the solid to one of the fluids—can have a strong impact on the flow, but the microscale physics and macroscopic consequences remain poorly understood. Here, we study this in detail for the first time by systematically varying the wetting properties of a microfluidic porous medium. Our high-resolution images reveal the fundamental control of wetting on multiphase flow, elucidate the inherently 3D pore-scale mechanisms, and help explain the striking macroscopic displacement patterns that emerge.

Read the paper and watch some videos: Zhao et al., PNAS 2016

Talk at the Isaac Newton Institute

Watch Chris talk about large-deformation poroelasticity and swelling at a workshop on "Melt in the Mantle" at the Isaac Newton Institute in Cambridge, UK. It was a fascinating and interdisciplinary event focused on the physics of flow, transport, and deformation in the multiphase systems. Don't miss the other talks:

  • Workshop 1 - From Foundations to State-of-the-Art in Magma/Mantle Dynamics
  • Workshop 2 - From the Grain to the Continuum: Two Phase Dynamics of a Partially Molten, Polycrystalline Aggregate
  • Workshop 3 - From the Continuum to the Tectonic: the Magma/Mantle Dynamics of Planet Earth

Large deformations of a soft porous material

In porous materials, deformation of the solid skeleton is mechanically coupled to flow of the interstitial fluid. Soft porous materials such as soils, gels, and biological tissues often experience very large deformations. Here, we provide an overview of the physics of poromechanical coupling and the mathematical theory of large-deformation poroelasticity, and then study the importance of large deformations in the context of two uniaxial model problems.

Read the paper and download the associated MATLAB code: MacMinn et al., PRApplied 2016.

Fluid-driven deformation of porous materials

Fluid flow can deform a porous material if the pressure is large enough, or if the material is soft enough. These poromechanical deformations occur across biophysics and geophysics, from the mechanics of human tissues to the recovery of oil and gas, but they are notoriously difficul to study in a laboratory setting. Here, we achieved this by injecting fluid into a packing of soft particles.

Left: Injection of fluid (arrows) into a packing of soft particles deforms the packing, opening a cavity around the injection port. Bands of shear failure (red patches) lead to wedge-like displacement patterns reminiscent of flower petals (white to blue).

Read the paper and watch some videos: MacMinn et al., PRX 2015.