Jaejun Lee
Advisor: Prof. Vladimir V. Tsukruk

will propose a doctoral thesis entitled,

Spatial Gradient Architectures in Soft Elastomeric Materials with Expanded Functionality

On

Tuesday, November 17 at 1:00 p.m.
Molecular Science and Engineering Building (MoSE) Room 3201A

and

Virtually via Zoom

Abstract

Soft elastomeric materials, from elastomeric nanocomposites to soft bioelectronic devices, are conventionally designed with a uniform composition and geometry. This homogeneity imposes similar properties across the materials, limiting their ability to accommodate spatially varying material properties and functional demands and creating abrupt property mismatches at interfaces. Spatial gradient architectures, in which composition or geometry varies gradually and deliberately across a material, offer a strategy to distribute local properties according to these demands without introducing additional material components.

This work investigates spatial gradients in composition and geometry as independent design variables through two systems. In a six-layer laminated cellulose nanocrystal (CNC)/waterborne polyurethane (WPU) elastomer, the MXene content increases from 0 to 2 wt% at a fixed CNC/WPU ratio. At the same average loading as a uniform film, the compositional gradient film shows approximately 50% higher tensile strength while maintaining a comparable strain at break, along with a further 15% reduction in heat capacity change in the soft-segment region and a higher storage modulus, consistent with spatially heterogeneous polymer confinement induced by the compositional gradient. In a liquid metal (LM)/styrene-ethylene-butylene-styrene (SEBS) connector for ultrathin skin electrodes, the thickness increases from 0.5 to 10 μm over 5 cm. The connector follows skin topography, remains conductive to approximately 1100% strain and through 5,000 bending cycles, and gives an electrocardiography (ECG) signal-to-noise ratio of 20.1 dB during bending, compared with 13.7 dB for the corresponding commercial tape-based connector system. The thickness gradient is designed to combine the conformability of the thin region with the mechanical robustness of the thick region, providing a gradual transition that reduces mechanical mismatch across the device interface. 

This work will provide a fundamental understanding of how spatial gradients in composition and geometry govern local material response and overall performance in soft elastomeric materials through studies of gradient architecture, local property distribution, and interfacial mechanics. The proposed research will further extend spatial gradient design to multifunctional material systems by integrating with different types of fillers and enantiomeric polymers to tailor mechanical, thermal, optical, and electrical responses.

Committee Members

Prof. Vladimir Tsukruk (Advisor), MSE

Prof. Meisha Shofner, MSE

Prof. Seung Soon Jang, MSE

Prof. Jerry Qi, ME

Prof. Todd Sulchek, ME