(3af) Bridging Scales: Multicomponent Interactions in Thin Films and Fluid Interfaces

Engineering soft and biological materials with microscopic precision is becoming increasingly reliant on molecular-level information. This poses a challenge for both theorists and experimentalists, who are tasked with resolving widely disparate length scales in order to develop useful predictions of material behavior. My research program aims to bridge these scales by incorporating coarse-grained, molecular details into continuum models of thin films and fluid interfaces while benchmarking against in-house experiments.

The broader aims of my research focus on new avenues in (1) colloidal materials design, (2) synthetic biology, and (3) industrial solution processing. In each aim, the interactions among dissimilar chemical components play an integral role in the microscopic flow physics.

(1) Developing computational tools for predictive self-assembly of colloids at fluid interfaces

Computational advances are sorely needed and will enable economical design of two-dimensional (2D) composites and electronic materials. In these applications, the ability to predict the spatial structure of self-assembled colloidal particles is essential for tuning functional material properties. The underlying physics is rich, involving an interplay among capillarity, electrostatics, and hydrodynamics. My knowledge of these interactions, combined with my training in numerical methods and large-scale computation, uniquely positions me to develop new computational methods to simulate colloidal assembly at interfaces.

(2) Modeling multicomponent biomembranes for “bottom-up” construction of artificial cells

Replicating the complex interactions between various lipids, proteins, fatty acids, and glycerides in cell membranes is one of the grand challenges of synthetic biology. To date, relatively few studies have incorporated molecular specificity and functionality into continuum models of multicomponent vesicles. Such models can answer biologically relevant questions that are beyond the scope of traditional molecular dynamics. To this end, I will leverage my expertise in membrane dynamics and heterogeneous bio-interfaces to understand the role of specific molecular components in membrane remodeling events and cellular transport processes.

(3) Engineering solute-substrate interactions in dynamically evolving thin films

Industrial solution processes (e.g., casting, printing) often involve multicomponent thin films flowing over solid substrates. As research has progressed, it is becomingly increasingly obvious that the detailed interactions between soluble components and the substrate (e.g., due to diffusioosmotic slip or heterogeneous disjoining pressure) have a nontrivial impact on thin-film flows. Understanding these effects will enable better flow control and spark new ideas for manipulating fluids by tuning solute-substrate interactions. Given my background in thin-film modeling and prior collaborations with experimentalists, I am well poised to tackle new problems in multicomponent thin-film flows of practical and fundamental interest.

Research Experience:

I am a trained theoretician with a strong expertise in complex fluids and soft / biological materials. During my PhD at Stanford, I combined boundary element simulations with lubrication theory to discover that vesicle flow in microfluidic channels can be suppressed using non-circular channel cross sections [1-3]. This non-intuitive effect, verified by experiments [3], is caused by a symmetry-breaking flow in vesicle membranes and suggests a working principle for microfluidic cell sorting based on membrane fluidity. In my secondary project, I developed simulations of the time-dependent thin-film flow of silicone oil mixtures evaporating over curved glass [4]. My results revealed the delicate interplay between disjoining pressure, capillary pressure, and Marangoni stresses in stabilizing multicomponent thin films, which is important for coating processes on substrates with topography [4].

In my postdoctoral work at UC Santa Barbara, I broadened my expertise to heterogeneous surfactant monolayers, colloidal interactions at interfaces, and rheometric techniques. Native lung surfactant lines the curved air-water interface of the pulmonary alveoli, enhancing lung compliance and stability. I showed, using continuum theory, that alveolar curvature promotes circular domain morphologies in lung surfactant monolayers, which affects the partitioning of fatty acids, cholesterol, and proteins in the lung [5]. I also studied the effect of interfacial curvature gradients on domain-domain interactions [6], based on prior models for colloids at fluid interfaces. In a separate collaboration, I uncovered the role of surface tension in oscillatory squeeze flow rheometry of low-viscosity fluids (e.g., water) [7], which opens up new possibilities for studying the surface properties of liquids using commercially available measurement tools.

Selected Publications:

[1] J. M. Barakat and E. S. G. Shaqfeh. The steady motion of a closely fitting vesicle in a tube. J. Fluid Mech.835, 721-761. 2018. doi: 10.1017/jfm.2017.743

[2] J. M. Barakat and E. S. G. Shaqfeh. Stokes flow of vesicles in a circular tube. J. Fluid Mech. 851, 606-635. 2018. doi: 10.1017/jfm.2018.533

[3] J. M. Barakat, S. M. Ahmmed, S. A. Vanapalli, and E. S. G. Shaqfeh. Pressure-driven flow of a vesicle through a square microchannel. J. Fluid Mech. 861, 447-483. 2019. doi: 10.1017/jfm.2018.887

[4] M. R. Hakim*, J. M. Barakat*, X. Shi, E. S. G. Shaqfeh, and G. G. Fuller. Evaporation-driven solutocapillary flow of thin liquid films over curved substrates. Phys. Rev. Fluids 4, 034002. 2019. doi: 10.1103/PhysRevFluids.4.034002 (∗ = co-first author)

[5] J. M. Barakat and T. M. Squires. Shape morphology of dipolar domains in planar and spherical monolayers. J. Chem. Phys. 152 (23), 234701. 2020. doi: 10.1063/5.0009667

[6] J. M. Barakat and T. M. Squires. Induced capillary quadrupoles in curvature gradients. in prep.

[7] J. M. Barakat, Z. R. Hinton, N. J. Alvarez, and T. W. Walker. Surface-tension effects in oscillatory squeeze-flow rheometry. in prep.

Teaching Interests:

My aim as an educator is to foster the same level of passion and curiosity that drove me to pursue a career in research and teaching. I served as Teaching Assistant (TA) in three courses, one at Columbia, where I was the first undergraduate TA in the department, and two courses at Stanford. For my graduate TA work, I was recognized as an Outstanding Teaching Assistant by the department. I participated heavily in teaching-based outreach by organizing science workshops for elementary and high school students (Stanford Splash and Bay Area Science Festival). At the college or graduate level, I have particular interest in teaching foundational courses in transport phenomena, thermodynamics, and mathematical methods (both analytical and numerical). I aim to develop my own special topics course in capillarity and interfacial phenomena, where I will teach important topics related to surface tension, membrane biophysics, and nonlinear transport at interfaces. Finally, I am a proponent of diversified teaching tools (e.g., active learning) as well as modernizing chemical engineering curricula through incorporation of computer programming and numerical algorithms into traditional courses.