Abstract
Flow of molecularly ordered fluids, like liquid crystals, is inherently coupled with the average local orientation of the molecules, or the director. The anisotropic coupling—typically absent in isotropic fluids—bestows unique functionalities to the flowing matrix. In this work, we harness this anisotropy to pattern different pathways to tunable fluidic resistance within microfluidic devices. We use a nematic liquid crystalline material flowing in microchannels to demonstrate passive and active modulation of the flow resistance. While appropriate surface anchoring conditions—which imprint distinct fluidic resistances within microchannels under similar hydrodynamic parameters—act as passive cues, an external field, e.g., temperature, is used to actively modulate the flow resistance in the microfluidic device. We apply this simple concept to fabricate basic fluidic circuits, which can be hierarchically extended to create complex resistance networks, without any additional design or morphological patterning of the microchannels.
Highlights
The advent of microfluidics has opened up possibilities to study flows within micron-sized confinements and past minute obstacles
We present a simple concept of tuning fluidic resistance in microfluidic channels by utilizing the anisotropic flow-director coupling inherent in liquid crystalline materials
The work presented here outlines the first steps towards realization of fluidic networks by harnessing anisotropic interactions present in flows of liquid crystalline materials
Summary
The advent of microfluidics has opened up possibilities to study flows within micron-sized confinements and past minute obstacles. The use of complex fluids as the transport medium in microfluidic confinements has provided interesting pathways to create and study novel phenomena, leading to numerous applications. As a consequence of the three viscosity coefficients, and the inherent coupling between the flow and the director fields [9,10], the dynamics of the LC flows are rich in complexity, leading to a variety of interesting phenomena like the generation of a transverse pressure gradient in a Poiseuille flow [11], anomalous colloidal rheology [12], and tunable flow shaping in microfluidic confinements [13]. We present a simple concept of tuning fluidic resistance in microfluidic channels by utilizing the anisotropic flow-director coupling inherent in liquid crystalline materials. The concepts demonstrated here can be applied to fabricate microfluidic networks of higher complexity for guiding and patterning microflows using anisotropic fluids
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