arXiv subjects

Chenzhuo Li

Publications and source records attributed to Chenzhuo Li.

3 recordsLinked to original sources

arXiv2026

Following the thread: surface and bulk solvent migration in silicone elastomers from local volumetric swelling

Poroelastic materials, consisting of a permeable solid matrix infiltrated with fluid, are ubiquitous in natural and engineering contexts. In poroelastic polymer solids, the elastic matrix swells to equilibrium when immersed in a solvent bath; thus, the network elasticity couples to the solvent transport. Despite the ubiquity and importance of poroelastic theory in describing phenomena as diverse as earthquakes and biological tissues, there is a paucity of experimental data that probe the local network response to controlled stress and solvent boundary conditions. Here, we first probe the baseline diffusion kinetics of a polymeric solvent during free swelling of a polydimethylsiloxane (PDMS) network with well-characterized silicone oils. In situ 3D spatiotemporal measurements identify a flux-limited interfacial boundary condition, contradicting the canonical fully drained assumption. This correction eliminates an order-of-magnitude underestimation of diffusivity in standard bulk analysis. The swelling equilibrium is accurately captured by a Flory-Rehner theory that requires modification to include the effective finite extensibility of the filled network. Solvent migration is then studied using a bending configuration for three material preparations: as-prepared, mobile-phase-free, and fully swollen in silicone oils. The as-prepared and mobile-phase-free beams show no discernible volumetric change or force relaxation, whereas local in situ measurements directly resolve tensile-side dilation and compressive-side contraction, yielding the effective diffusivities in agreement with the force-relaxation data. These measurements rigorously benchmark solvent diffusivity in polymer networks, underscoring the importance of unambiguous interfacial boundary conditions and shedding light on mechanics and engineering across poroelastic polymers and geomaterials.

cond-mat.soft↗

arXiv2024

3D characterization of kinematic fields and poroelastic swelling near the tip of a propagating crack in a hydrogel

In fracture mechanics, polyacrylamide hydrogels have been widely used as a model material for experiments, benefited from its optical transparency, fracture brittleness, and low Rayleigh wave velocity. To describe the brittle fracture in the hydrogels, linear elastic fracture mechanics comes as the first choice. However, in soft materials such as hydrogels, the crack opening can be extremely large, leading to substantial geometric nonlinearity and material nonlinearity at the crack tip. Furthermore, poroelasticity may also modify the local mechanical state within the polymer network. Direct characterization of the kinematic fields and poroelastic effect at the crack tip is lacking. Here, based on a hybrid method of digital image correlation and particle tracking technique, we retrieved high-resolution 3D particle trajectories near the tip of a slowly propagating crack and measured the near-tip 3D kinematic fields, including the displacement fields, rotation fields, stretch fields, strain fields, and swelling fields. Results confirmed the complex multi-axial stretching near the crack tip and the substantial geometric nonlinearity, particularly on the two wakes of the crack where rotation exceeds $30^{\circ}$. Comparison between the measured and predicted displacement and strain fields, derived from linear elastic fracture mechanics, highlights a disagreement in the direct vicinity of the crack tip, particularly for displacement component $u_x$ and through-thickness strain component $\varepsilon_{zz}$. Significant swelling, due to the poroelastic solvent migration, is also observed, with a strong correlation to the local stretch. Our experimental method, without any assumption of the material properties, can be readily extended to study 3D crack tips in a huge varieties of materials, and our results can shed light on the fundamental fracture mechanics.

cond-mat.soft↗

arXiv2023

Crack tip kinematics reveal the cohesive zone structure in brittle hydrogel fracture

When brittle hydrogels fail, several mechanisms conspire to alter the state of stress near the tip of a crack, and it is challenging to identify which mechanism is dominant. In the fracture of brittle solids, a sufficient far-field stress results in the complete loss of structural strength as the material `unzips' at the tip of a crack, where stresses are concentrated. Direct studies of the so-called small-scale yielding zone, where deformation is large, are sparing. Using hydrogels as a model brittle solid, we probe the small-scale yielding region with a combination of microscopy methods that resolve the kinematics of the deformation. A zone over which most of the energy is dissipated through the loss of cohesion is identified in the immediate surroundings of the crack tip. With direct measurements, we determine the scale and structure of this zone, and identify how the specific loss mechanisms in this hydrogel material might generalize for brittle material failure.

cond-mat.mtrl-sci↗