Seminar Part 2 - Siddhartha Das - Electroosmotic Transport in Soft Nanochannels Probed Using Atomistic Simulations and Machine Learning

Mechanical Engineering Seminar

Tuesday, April 7, 2026

10:15 a.m., 3540 Engineering Building

Electroosmotic Transport in Soft Nanochannels Probed Using Atomistic Simulations and Machine Learning

Siddhartha Das

Professor

Department of Mechanical Engineering

University of Maryland

Email: sidd@umd.edu; Webpage: www.smiel.umd.edu

Abstract:

Charged nanochannels develop unbalanced charge layers (often known as electric double layers or EDLs) at their surfaces: electroosmosis refers to triggering a fluid motion by making these charges move in the presence of an applied or an induced electric field. In this talk, I shall discuss my group’s work on employing atomistic molecular dynamics (MD) simulations and machine learning (ML) for probing the electroosmotic (EOS) transport in soft nanochannels, or nanochannels grafted with charged polyelectrolyte chains present in the form of brushes. First, we shall discuss the case of the EOS transport in nanochannels grafted with the anionic poly-acrylic acid brushes screened with sodium counterions. MD simulations enable us to identify three remarkable events: (1) overscreening of the PAA brush layer; (2) the presence of an excess of coions outside the brush layer triggering a coion-driven EOS transport; (3) reversal in the direction of the EOS transport by increasing the strength of the electric field. Second, we discuss the same problem, but for the case where the PAA brush layer is screened by different types of monovalent, divalent, and trivalent counterions and show the effect of the counterion nature and valence in dictating the above-discussed phenomena. Third, we study the pressure-driven flow in nanochannels grafted with the PAA brushes: we show that the coion-driven EOS transport (in this case, induced electric field driven EOS transport) triggers the most remarkable electroslippage effect where there is simultaneous electrokinetic energy generation and flow enhancement. Fourth, we study the EOS transport in nanochannels grafted with cationic PMETA [poly(2-(methacryloyloxy)ethyl) trimethylammonium] brushes having tri-methyl ammonium (TMA) functional groups. TMA groups trigger apolar solvation by virtue of which the counterions (chloride ions) are very weakly bound to the brushes. As a result, in the presence of an applied electric field, these ions get driven out of the brush layer, localize at the brush-bulk interface, move very fast in presence of the electric field, and trigger an EOS flow with a non-linearly large flow strength. In addition, the PE brushes themselves demonstrate anti-electrophoretic effect, where the brushes get tilted in a direction towards the voltage of same sign. Finally, we provide a linear discriminant analysis (LDA) based ML approach, that enables a much faster analysis of the problem of the EOS transport in such cationic brush grafted nanochannels.

Bio:

Dr. Siddhartha Das is currently a Professor in the Department of Mechanical Engineering, University of Maryland, College Park. His research focuses on the science and engineering of soft and colloidal materials, small-scale fluid mechanics, and additive manufacturing. He received his B.S. (or B-Tech.) and Ph.D. from the Indian Institute of Technology (IIT) Kharagpur. He completed post-doctoral research at University of Twente and University of Alberta (as Banting Postdoctoral Fellow). He has published 210+ 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), advised/advising more than 35 M.S., Ph.Ds., and postdocs, and received numerous awards and accolades, which include (1) promotion to Associate Professorship with an early tenure, (2) election as Fellows of the American Physical Society (in the Division of polymer Physics), Royal Society of Chemistry, Institute of Physics, and Institution of Engineering and Technology (U.K.), Linnean Society of London, (3) selection as a Mid-Career Achievement Awardee of the AES Electrophoretic Scoiety, (4) selection as emerging investigator by journals such as Physical Chemistry Chemical Physics and Soft Matter, (5) selection as pioneering investigator by the journal Chemical Communications,  (6) IIT Kharagpur Young Alumni Achiever Award, (7) Hind Rattan award (which translates to “Jewel of India” award), (8) Junior Faculty Outstanding Research Award from the School of Engineering, University of Maryland, and (9) Being recognized in the Stanford’s list of top 2% scientists for years 2020-2024.