Two papers from the UC Santa Barbara Mechanical Engineering Department have been selected by the Soft Matter Editorial Board as part of their 2022 Highlights Collection.  According to the journal: this online collection of twenty papers “features some of the most exciting articles published in Soft Matter during 2022.”  Al Crosby (Editor in Chief) reflects: “2022 was an exciting year for Soft Matter! So many great papers advancing the field and demonstrating its extensive, positive impact. To try to capture this exciting year in Soft Matter, the Editorial Board has selected these Soft Matter papers as a highlight collection”. 

The first paper, “High-throughput microscopy to determine morphology, microrheology, and phase boundaries applied to phase separating coacervates” was published by the Valentine Lab in April 2022.  This collaborative work was led by Professor Megan Valentine, Professor Matthew Helgeson (UCSB Chemical Engineering) and Assistant Professor Mengyang Gu (UCSB Probability and Applied Statistics) with support from the National Science Foundation (NSF) BioPACIFIC Materials Innovation Platform and UCSB Materials Research Laboratory (MRL), an NSF MRSEC. 

The paper describes the development of new high-throughput approaches to studying the evolution of composition, rheology, and morphology during phase separation in multiphase complex fluids called coacervates.  The experimental study led by Yimin Luo, former Valentine Lab postdoc who is now an Assistant Professor of Mechanical Engineering and Materials Science at Yale University, and graduate student Chelsea Edwards, established the use of high throughput microscopy and microrheology for coacervate screening and characterization.

“I was thrilled to learn that our Soft Matter paper had been selected as a 2022 Editorial Board Highlight,” said Valentine. “In addition to providing key scientific insight into the structures, mechanics, and phase behavior of complex fluids, this work developed an important platform for rapid screening and provides critical links between formulation and rheology for multi-phase material discovery.”

Caption: Microrheology encodes dynamics of ongoing phase separation.  Scale bar 100 mm.

The second paper, “Transition to the viscoelastic regime in the thinning of polymer solutions” was led by Associate Professor Alban Sauret. The study, which was supported by the National Science Foundation, investigated the capillary flow dynamics leading to the viscoelastic regime during the breakup of a drop polymer solution and was led by Sreeram Rajesh, a graduate student in the department, and Virgile Thiévenaz, a former postdoc in the Sauret Lab. Understanding the formation of droplets of complex fluids is important in manufacturing processes. The thinning and breakup of a polymer solution drop, a non-Newtonian fluid, is characterized by multiple regimes, such as an initial Newtonian fluid-like thinning, followed by a non-Newtonian viscoelastic regime, where a cylindrical ligament-type structure appears. The entire process happens within a few tens of milliseconds. The study provided a framework to describe the transition between the different regimes. “It is exciting to see our results selected by the Editorial Board of Soft Matter,” said Sauret, “but it also illustrates the great quality of the works performed by our students in the department.”

Caption: formation and break-up of a droplet of polymer solution