Submersed micropatterned structures control active nematic flow, topology, and concentration
Kristian Thijssen*, Dimitrius A. Khaladj*, S. Ali Aghvami, Mohamed Amine Gharbi, Seth Fraden, Julia M. Yeomans, Linda S. Hirst, and Tyler N. Shendruk
PNAS September 21, 2021 118 (38) e2106038118; https://doi.org/10.1073/pnas.2106038118
Coupling between flows and material properties imbues rheological matter with its wide-ranging applicability, hence the excitement for harnessing the rheology of active fluids for which internal structure and continuous energy injection lead to spontaneous flows and complex, out-of-equilibrium dynamics. We propose and demonstrate a convenient, highly tunable method for controlling flow, topology, and composition within active films. Our approach establishes rheological coupling via the indirect presence of fully submersed micropatterned structures within a thin, underlying oil layer. Simulations reveal that micropatterned structures produce effective virtual boundaries within the superjacent active nematic film due to differences in viscous dissipation as a function of depth. This accessible method of applying position-dependent, effective dissipation to the active films presents a nonintrusive pathway for engineering active microfluidic systems.
This revised edition continues to provide the most approachable introduction to the structure, characteristics, and everyday applications of soft matter. It begins with a substantially revised overview of the underlying physics and chemistry common to soft materials. Subsequent chapters comprehensively address the different classes of soft materials, from liquid crystals to surfactants, polymers, colloids, and biomaterials, with vivid, full-color illustrations throughout. There are new worked examples throughout, new problems, some deeper mathematical treatment, and new sections on key topics such as diffusion, active matter, liquid crystal defects, surfactant phases and more.
• Introduces the science of soft materials, experimental methods used in their study, and wide-ranging applications in everyday life.
• Provides brand new worked examples throughout, in addition to expanded chapter problem sets and an updated glossary.
• Includes expanded mathematical content and substantially revised introductory chapters.
This book will provide a comprehensive introductory resource to both undergraduate and graduate students discovering soft materials for the first time and is aimed at students with an introductory college background in physics, chemistry or materials science.
Nanoparticle-based hollow microstructures formed by two-stage nematic nucleation and phase separation
Sheida T. Riahinasab, Amir Keshavarz, Charles N. Melton, Ahmed Elbaradei, Gabrielle I. Warren, Robin L. B. Selinger, Benjamin J. Stokes & Linda S. Hirst
Nature Communications volume 10, Article number: 894 (2019)
read the paper here
Rapid bulk assembly of nanoparticles into microstructures is
challenging, but highly desirable for applications in controlled
release, catalysis, and sensing. We report a method to form hollow
microstructures via a two-stage nematic nucleation process, generating
size-tunable closed-cell foams, spherical shells, and tubular networks
composed of closely packed nanoparticles. Mesogen-modified nanoparticles
are dispersed in liquid crystal above the nematic-isotropic transition
temperature (TNI). On cooling through TNI,
nanoparticles first segregate into shrinking isotropic domains where
they locally depress the transition temperature. On further cooling,
nematic domains nucleate inside the nanoparticle-rich isotropic domains,
driving formation of hollow nanoparticle assemblies. Structural
differentiation is controlled by nanoparticle density and cooling rate.
Cahn-Hilliard simulations of phase separation in liquid crystal
demonstrate qualitatively that partitioning of nanoparticles into
isolated domains is strongly affected by cooling rate, supporting
experimental observations that cooling rate controls aggregate size.
Microscopy suggests the number and size of internal voids is controlled
by second-stage nucleation.