Moving Fluids with Electric Fields: Sandip Ghosal’s New Book Explores Fluid Control at the Micro and Nanoscale

Microfluidic technology enables precise manipulation of minute fluid samples across a wide spectrum of applications, including medical diagnostics, biological sensing, chemical analysis, and chip cooling. Driving fluid through such tiny channels requires specialized mechanisms, with electric fields providing a powerful alternative to mechanical pumps. 

But moving fluids through spaces that small is not easy. The pumps used in everyday systems become less efficient as the channels shrink. A different method, known as electroosmotic flow, uses electric fields instead of pressure to move fluids.

The fundamental physics and application of this method are detailed in a new book by Northwestern Engineering’s Sandip Ghosal. Electroosmotic Flow and Transport (World Scientific, 2026), bridges fundamental transport theory with practical device design and microfluidic applications.

Ghosal brings more than two decades of research in theoretical fluid mechanics to the text. In 2006, he developed Micro- and Nano-Scale Fluid Dynamics (MECH_ENG 420), a core graduate course at McCormick that has informed both his research program and the textbook's pedagogical structure.

An associate professor of mechanical engineering, Ghosal has published extensively on fluid mechanics and theoretical electrokinetics, authoring dozens of peer-reviewed articles and book chapters on the physics of micro- and nanoscale transport.

Existing literature frequently treats electroosmotic flow as a minor subsection of broader electrokinetic or microfluidic surveys. According to Ghosal, the lack of a dedicated text meant that researchers had to piece together foundational theory and advanced topics from disparate scientific papers.

“Discussions of these advanced topics were scattered across decades of journal literature,” Ghosal said. “This monograph brings those fundamental physical principles together into a unified, accessible framework for graduate students and industry researchers.”

At its simplest, electroosmotic flow is a way to move water through a very narrow channel by applying a voltage rather a pressure differential.

When a fluid contacts a solid surface like glass, chemical reactions leave the surface charged, attracting oppositely charged ions in the liquid to form a microscopic double layer—the Debye layer. An applied electric field acts directly on these mobile ions, which drag the bulk fluid along through viscous forces to generate electroosmotic flow.

“We now have a different way of making water flow in a tube than the usual one, which is to apply pressure,” Ghosal said.

Electroosmotic flow is not especially useful for moving water through household pipes, air-conditioning systems, or other large spaces. It becomes valuable when working with channels of diameter in the range of microns or thinner than a human hair. On that scale, electric fields can move water more efficiently than pressure.

Beyond its role in regulating minute fluid samples in lab-on-a-chip devices, the method provides an effective means of driving flow through complex porous structures.

Powering modern AI models requires extreme compute density, making real-time heat removal a critical hurdle for high-performance processors.

“One way of meeting this challenge is embedding micro-nano fluidic cooling systems within the chip architecture,” Ghosal said.

Idealized models of flow through parallel slits or cylindrical capillaries are essential for answering foundational physical questions, such as identifying when electroosmotic transport outperforms pressure-driven flow. However, practical engineering quickly reveals their limitations. Real microfluidic chips—frequently fabricated by bonding different materials like glass and polymers together—possess inherently non-uniform surface charges. Additionally, as a sample is injected into a channel, partial wall adsorption dynamically alters local charges and flow profiles, creating unwanted band dispersion.

Ghosal’s work addresses these real-world complexities directly, offering streamlined mathematical models that account for irregular channel geometries, surface non-uniformities, and wall adsorption without requiring computationally heavy simulations.

Electroosmotic Flow and Transport is primarily intended for graduate students in engineering, physics, chemistry, materials science, and related fields. Research engineers in industry may also find the book useful for improving computational approaches to fluid flow and transport at extremely small scales.

“After mastering the material, students would be better equipped to tackle any research or design problem on micro- and nanoscales that involves electrokinetic effects, transport, and dispersion,” Ghosal said.