Soft and Active Interfaces: Enhanced Liquid Flows in Polymer-Functionalized Nanochannels, Self-Assembly via Active Drops, and Reduced Conductivity of Printed Nanoparticle Traces

Soft matter systems have sparkled great excitement owing to their extensive applications in a vast number of disciplines ranging from energy and biomedical engineering to drug discovery and additive manufacturing. In this talk, I shall discuss my group’s research findings on three distinct soft material systems. The first system that will be discussed is the soft nanofluidic system, represented as nanochannels grafted with charged polyelectrolyte (PE) brushes. This system is probed using all-atom molecular dynamics (MD) simulations, revealing highly interesting water and ion properties around the PE brush systems, including overscreening (OS) of PE brush charges. Subsequently, liquid transport in such PE-brush-grafted nanochannels is probed, unraveling OS-induced (1) coion-driven electroosmotic (EOS) transport, (2) a reversal in the direction of the EOS transport with an increase in the electric field strength, and (3) simultaneous energy generation and flow enhancement in pressure-driven transport. The second system that will be discussed is active drops: the evaporation of such drops is investigated using semi-analytical approaches. The combination of additional activity-induced stress and the mass loss (due to evaporation) leads to the formation of punctured drops and the generation of ring-galaxy-like particle deposition patterns. Finally, the behavior of printed and sintered metal-nanoparticle ink traces, with the nanoparticles consisting of a layer of polymeric stabilizers (ligands), will be discussed. It will be shown that contrary to the existing belief, even after sintering, these polymeric layers are not completely removed hindering a direct metal-metal contact, eventually reducing the conductivity of these traces.

Dr. Siddhartha Das is currently an Associate Professor in the Department of Mechanical Engineering, University of Maryland, College Park. His research focuses on the science and engineering of soft materials, small-scale fluid mechanics, and additive manufacturing. He received his BS (or B-Tech) and PhD from the Indian Institute of Technology Kharagpur. He completed post-doctoral research at University of Twente and University of Alberta (as Banting Postdoctoral Fellow). He has published 180+ journal papers in world-renowned journals (such as Nature Materials, PNAS, PRL, JACS, APL, Matter, Nucleic Acid Research, Nature Communications, Advanced Materials, and ACS Nano), graduated more than 20 MS, PhDs, and postdocs, and received numerous awards and accolades, which include (1) promotion to Associate Professorship with an early tenure, (2) election as Fellows of Royal Society of Chemistry, Institute of Physics, and Institution of Engineering and Technology (U.K.), (3) selection as emerging investigator by journals such as Physical Chemistry Chemical Physics and Soft Matter, (4) IIT Kharagpur Young Alumni Achiever Award, (5) Hind Rattan award, (6) Junior Faculty Outstanding Research Award of the School of Engineering, University of Maryland, and (7) Being included in the Stanford’s list of top 2% scientists for years 2020, 2021, and 2022.