Sculpting stable structures in pure liquids

Emeršič, Tadej; Zhang, Rui; Kos, Žiga; Čopar, Simon; Osterman, Natan; Pablo, Juan; Tkalec, Uroš

doi:10.1126/sciadv.aav4283

Cited by 28 publications

(63 citation statements)

References 44 publications

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“…In particular, we consider the disclination at the boundary between the dowser and bowser states in a narrow cell, and show that this disclination moves to minimize an effective potential. For this problem, our results are consistent with the theory of Emeršič et al [10]; we show that their effective potential fits into the general framework presented here.…”

Section: Introductionsupporting

confidence: 92%

“…In this section, we consider the motion of a disclination between the dowser and bowser states in a narrow liquidcrystal cell. This problem has already been studied using an effective potential concept by Emeršič et al [10]. We show that their effective potential concept is consistent with the general approach presented in this article.…”

Section: Dowser and Bowser States Under Poiseuille Flowsupporting

confidence: 87%

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Minimization principle for shear alignment of liquid crystals

Tang

Selinger

2020

Phys. Rev. E

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If a static perturbation is applied to a liquid crystal, the director configuration changes to minimize the free energy. If a shear flow is applied to a liquid crystal, one might ask: Does the director configuration change to minimize any effective potential? To address that question, we derive the Leslie-Ericksen equations for dissipative dynamics, and determine whether they can be expressed as relaxation toward a minimum. The answer may be yes or no, depending on the number of degrees of freedom. Using theory and simulations, we consider two specific examples, reverse tilt domains under simple shear flow and dowser configurations under plane Poiseuille flow, and demonstrate that each example shows relaxation toward the minimum of an effective potential. arXiv:1912.11902v1 [cond-mat.soft]

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Section: Introductionsupporting

confidence: 92%

Section: Dowser and Bowser States Under Poiseuille Flowsupporting

confidence: 87%

Minimization principle for shear alignment of liquid crystals

Tang

Selinger

2020

Phys. Rev. E

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“…This work is motivated by recent reports on the unique thermofluidic properties of 5CB in its native form [25][26][27][28] and our own findings related to the macroscopic phase behaviour of 5CB and MeOH. 30 When studied in the bulk, this mixture exhibits an UCST of 24.4°C, a temperature range that can conveniently be accessed.…”

Section: Resultsmentioning

confidence: 99%

“…In recent years, 4-cyano-4′-pentylbiphenyl (5CB) in its native form has attracted significant interest in liquid crystal microfluidics due to unique thermofluidic properties, including a temperature-tunable flow profile and fluidic resistance, as well as temperature-induced molecular reorientation and controlled nucleation and growth of stable reconfigurable domains. [25][26][27][28] Herein, we investigate the fluidic behaviour in a 50/50 v/v blend of 5CB with methanol (MeOH), in particular the influence of temperature. We carefully mix and phase separate the liquid blend and relate the observed flow patterns to the role of temperature-modulated interfacial tension and viscosity.…”

Section: Introductionmentioning

confidence: 99%

Microfluidics of binary liquid mixtures with temperature-dependent miscibility

Fornerod

Amstad

Guldin

2020

Mol. Syst. Des. Eng.

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Liquid-liquid microfluidic systems rely on the intricate control over the fluid properties of either miscible or immiscible mixtures. Herein, we report on the use of partially miscible binary liquid mixtures that lend their microfluidic properties from a highly temperature-sensitive mixing and phase separation behaviour. For a blend composed of the thermotropic liquid crystal 4-cyano-4′-pentylbiphenyl (5CB) and methanol, mixing at temperatures above the upper critical solution temperature (UCST; 24.4°C) leads to a uniform single phase while partial mixing can be achieved at temperatures below the UCST. Thermally-driven phase separation inside the microfluidic channels results in the spontaneous formation of very regular phase arrangements, namely in droplets, plug, slug and annular flow. We map different flow regimes and relate findings to the role of interfacial tension and viscosity and their temperature dependence. Importantly, different flow regimes can be achieved at constant channel architecture and flow rate by varying the temperature of the blend. A consistent behaviour is observed for a binary liquid mixture with lower critical solution temperature, namely 2,6-lutidine and water. This temperature-responsive approach to microfluidics is an interesting candidate for multi-stage processes, selective extraction and sensing applications.358 | Mol. Syst. Des. Eng., 2020, 5, 358-365 This journal isMicrofluidic processes generally rely on the handling of either miscible or immiscible liquid mixtures. In this work, we introduce a novel temperaturebased microfluidic concept that is driven by and engineered through the underlying molecular characteristics rather than active or passive components on the microchannel architecture. We demonstrate how the temperature-dependent properties of regular solutions, namely miscibility, interfacial tension and viscosity, enable the detailed control over mixing and the formation of highly regular flow patterns. Such systems allow seamless switching between mixed and phase separated states in distinct flow regimes, thus offering novel routes for complex multi-stage processes, selective extraction and sensing applications.

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“…Microfluidic functionality can be further expanded by using fluids with internal structure, such as for example nematic liquid crystals, where transport of colloidal cargo 20 , electric field switching of channel resistivity 21 , fabrication of microresonators 22 , manipulation of colloidal particles by groovy interfaces 23,24 , and generation of intertwined field structures 25 have been demonstrated utilizing nematic orientational order and high responsiveness to external fields. Liquid crystals can form complex orientational structures 26 , which are then strongly coupled to the material flow 27 and can lead to flow-induced structural transitions 28 and also activity-driven microfluidics 29 . In a nematic microchannel, the effective fluid resistance is dependent on the orientation profile (director field) of the nematic molecules.…”

Section: Field Generated Nematic Microflows Via Backflow Mechanismmentioning

confidence: 99%

Field generated nematic microflows via backflow mechanism

Kos

Ravnik

2020

Sci Rep

Self Cite

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Generation of flow is an important aspect in microfluidic applications and generally relies on external pumps or embedded moving mechanical parts which pose distinct limitations and protocols on the use of microfluidic systems. A possible approach to avoid moving mechanical parts is to generate flow by changing some selected property or structure of the fluid. In fluids with internal orientational order such as nematic liquid crystals, this process of flow generation is known as the backflow effect. In this article, we demonstrate the contact-free generation of microfluidic material flows in nematic fluids -including directed contact-free pumping- by external electric and optical fields based on the dynamic backflow coupling between nematic order and material flow. Using numerical modelling, we design efficient shaping and driving of the backflow-generated material flow using spatial profiles and time modulations of electric fields with oscillating amplitude, rotating electric fields and optical fields. Particularly, we demonstrate how such periodic external fields generate efficient net average nematic flows through a microfluidic channel, that avoid usual invariance under time-reversal limitations. We show that a laser beam with rotating linear polarization can create a vortex-like flow structure and can act as a local flow pump without moving mechanical parts. The work could be used for advanced microfluidic applications, possibly by creating custom microfluidic pathways without predefined channels based on the adaptivity of an optical set-up, with a far reaching unconventional idea to realize channel-less microfluidics.

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Sculpting stable structures in pure liquids

Cited by 28 publications

References 44 publications

Minimization principle for shear alignment of liquid crystals

Minimization principle for shear alignment of liquid crystals

Microfluidics of binary liquid mixtures with temperature-dependent miscibility

Field generated nematic microflows via backflow mechanism

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