Overview

Soil, much like living organisms, has evolved over millions of years, developing distinctive mechanical and transport properties shaped by nature’s design. Its microscopic structure governs critical functions such as soil stability, carbon sequestration, groundwater storage, and nutrient delivery. Soil microstructure and composition follow evolutionary design rules, optimizing porosity and functionality in response to persistent natural forces. By decoding these rules, particularly by understanding the emergence of exotic properties through multiscale interactions among heterogeneous components, we can engineer a new class of adaptive, sustainable matter. The ultimate goal is to create truly circular materials with programmed functionalities, and we are pursuing three complementary directions to achieve this.

How do complex soil systems possess simple structure-property rules?
Soil materials often follow universal structure–property relationships, in spite of their complexities. By deconstructing the multiscale mechanics of natural soils through minimally complex laboratory analogs, we uncover material-control on macroscale mechanics. Viewing challenges in soil mechanics through the lens of soft matter physics has provided new insights into longstanding unsolved questions. For example, we showed that the timescales embedded in the rearrangement dynamics of cohesive and frictional constituents dictate brittle-to-ductile failure transition in soft soil systems (Nat Comms 2024). We validated this framework by applying it to natural flows, demonstrating that the proposed material deformation mechanism can precisely differentiate between sand-rich and clay-rich soil slurry flows, reconciling previous disagreements in the literature (PNAS 2022, Nat Comms 2024). Extending the framework to characterize material haptic properties further reveals how the unique balance of cohesive, frictional, and viscous elements in baseball rubbing mud, a naturally harvested material, produces a soft substance with unusual gripping properties, used in Major League Baseball as a de-glossing material (PNAS 2024).

How does microscopic surface details tune macroscale soft mechanics?
Engineering complex materials with programmable mechanical properties is the central challenge in the field of soft matter mechanics. We addressed this by developing model experimental systems and characterization tools to investigate how colloidal surface anisotropy governs the flow and mechanical properties of dense suspensions. By synthesizing polymer-based colloids with tunable surface roughness and employing a custom-built confocal rheometer, we directly linked microscale structure to macroscopic mechanics. This work produced the first experimental 3D sheared contact networks in dense suspensions, revealing how nearest-neighbor interactions dictate suspension shear thickening (Phy Rev Lett 2021). Furthermore, by connecting the elasticity of dense colloidal suspensions to their thermal structure at jamming, we bridged the mechanics of colloidal systems with those of granular materials (Soft Matter 2020), and provided hydrodynamic origins to engineer elasticity in these suspensions (J Rheo 2022). These findings demonstrated that macroscopic elasticity and shear-thickening properties in dense suspensions emerge from mesoscale contact networks, which can be tuned through the microscopic roughness of colloidal particles.

How do bacterial interactions with soft particles give rise to emergent behavior?
This question lies at the core of transport in soil, microplastic mixing in oceans, fermentation bioreactors, and wastewater treatment processes. Using colloidal poly(styrene) tracers dispersed in E. coli suspensions as model soft-living dynamics systems, we decoupled the effects of bacterial concentration on tracer dispersal (Phy Fluids 2022). We further discovered the emergence of bioconvection as a function of bacterial concentration, which significantly enhances mixing (J Fluid Mech 2024). These findings provide new insights into living matter–mediated transport across both natural and industrial environments.

The ultimate goal is to deepen understanding of soil structure by reimagining it as a complex soft material and translating these insights into precision engineering applications for meta-soil development, geomimetic materials, and earth-inspired processes.