Research
RESEARCH VISION
NMML is an experimental mechanics research laboratory to study the response of materials at various length and time scales. The goal is to understand the complex interactions of multiple physical phenomena, especially the electro-thermo-mechanical behavior of materials and their systems. At small length scales (especially at the micro/nanometer), a world of enigmas remains veiled, awaiting elucidation. We aim to unravel these mysteries and use the knowledge gained to drive innovation. By understanding the intricate interactions, we hope to uncover new opportunities for transformative advances. NMML envisions materials as blank canvases on which intricate designs can be created. This vision goes beyond the limitations of traditional macroscopic materials. Taking inspiration from nature, our ultimate goal is to engineer novel macroscale materials with a hierarchical architecture, which are carefully assembled from micro and submicrometer building blocks.
Recent Research Highlights
Durable and impact-resistant thermoset polymers for the extreme environment of low Earth orbit
K.M. Chang, D. Das, L. Salvati III., L.M. Dean, R. Keshari, M. Garg, D.D. Dlott, I. Chasiotis, N.R. Sottos, Extreme Mechanics Letters, 64, 102089, (2023). doi: 10.1016/j.eml.2023.102089
This study explores the degradation of polymers in low-Earth orbit (LEO), taking into account factors like extreme thermal cycling, solar radiation, micrometeoroid impacts, orbital debris, and the erosive effects of atomic oxygen (AO) combined with UV radiation. The investigation focuses on polydicyclopentadiene (pDCPD), a robust thermoset, subjected to (AO+UV)-induced erosion and high-velocity impact. Incorporating silica nanoparticles into pDCPD markedly reduces the AO-erosion rate, bringing it closer to the performance exhibited by fluoropolymers. The resistance of pDCPD to AO-erosion correlates with crosslink density. Hypervelocity impact tests demonstrate that pDCPD surpasses epoxies in impact resistance, with minimal change observed following surface AO-erosion in LEO. The addition of nanoparticles does not visibly affect high-velocity impact resistance. Overall, these findings propose that pDCPD/SiO2 nanocomposites could function as high-performance structural materials with superior impact and erosion resistance compared to epoxy-based materials for space applications.
Measuring Local Electrical Conductivity of Elastomeric Nanocomposites Subjected to Large Deformations
Moronkeji, O. E., Das, D., Lee, S., Chang, K. M., & Chasiotis, I., Journal of Composite Materials, 57(4), 507-519, (2023). doi: 10.1177/00219983231156253
The study reveals exciting findings on the behavior of 12 wt.% and 20 wt.% carbon black (CB)-PDMS nanocomposites under strain. By using Conductive Atomic Force Microscopy, we found that 25 x 25 μm2 area serves adequately as a representative surface element for both macro and local behavior. Poisson's effect increased the through-thickness conductivity with strain. Below the electrical percolation threshold (12% CB), electric current density increased significantly beyond 23% strain while local sites transitioned to Ohmic conductance from dominant tunneling conductance in the undeformed state. Above the percolation threshold (20% CB), specimens showed a linear increase in microscale electric current density with strain and Ohmic conductance prevailed at large strains. PDMS/CB nanocomposites with their unique electrical and mechanical properties, hold potential for a wide range of applications in the field of flexible electronics.
Probing Time-Dependent Deformation Behavior of Collagen Fibrils
Yang, F., Das, D., Karunakaran, K., Genin, G. M., Thomopoulos, S., & Chasiotis, I., Acta Biomaterialia, 163, 63-77, (2023). doi: 10.1016/j.actbio.2022.03.005
Yang, F., Das, D., & Chasiotis, I., Optics and lasers in engineering, 150, 106869, (2022). doi: 10.1016/j.optlaseng.2021.106869
In this study, we delved into the intricate mechanical dynamics of nanoscale biological structures. A breakthrough methodology (employing advanced optical microscopy and closed-loop proportional-integral-derivative (PID) control) was devised to investigate individual mammalian collagen fibrils, uncovering their non-linear viscoelastic characteristics under a hydrated environment. These findings not only emphasize the pivotal role of collagen fibrils as foundational components of connective tissues but also open new avenues for comprehending their behavior.
Moreover, a comprehensive exploration was conducted through stress relaxation and creep tests on individual collagen fibrils. The results unveiled strain-dependent stress relaxation and stress-dependent creep phenomena, elegantly captured by the adaptive quasi-linear viscoelastic (QLV) model. This study seamlessly bridges the understanding between collagen fibrils and larger-scale collagenous tissues, offering a coherent insight into their shared time-dependent attributes.
This work significantly advances our grasp of collagen fibril mechanics, potentially paving the way for impactful applications in regenerative medicine and the realm of biomaterials research.