Optothermally driven colloidal transport in a confined nematic liquid crystal

Škarabot, Miha; Osterman, Natan; Muševič, Igor

doi:10.1039/c7sm00136c

Cited by 6 publications

(5 citation statements)

References 25 publications

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“…Increased temperature would decrease the nematic degree of order (or even melt the nematic to an isotropic phase) and magnitude of the generated flow. Alternatively, colloidal object can be moved also by strong laser beams that locally melt the nematic 51 . Using laser beams to drive nematic flows is a step towards channel free and moving parts free microfluidics, where continuous deformation of fluid's internal structure acts as a local generator of flow.…”

Section: Discussionmentioning

confidence: 99%

Field generated nematic microflows via backflow mechanism

Kos

Ravnik

2020

Sci Rep

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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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Section: Discussionmentioning

confidence: 99%

Field generated nematic microflows via backflow mechanism

Kos

Ravnik

2020

Sci Rep

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“…In turn, thermogravitational convection is difficult to implement on these length scales, because it requires very high temperatures up to ∝100∘C to reach practically suitable fluid velocities ∝μm s−1 [13,14]. Hence, non-gravitational strategies to produce microconvective motion more efficiently using gravity-independent phenomena [3,13,15–17] are actively sought.…”

Section: Introductionmentioning

confidence: 99%

Optothermal grid activation of microflow with magnetic nanoparticle thermophoresis for microfluidics

Zablotsky

Mezulis

Blums

et al. 2022

Phil. Trans. R. Soc. A.

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We report focused light-induced activation of intense magnetic microconvection mediated by suspended magnetic nanoparticles in microscale two-dimensional optothermal grids. Fully anisotropic control of microflow and mass transport fluxes is achieved by engaging the magnetic field along one or the other preferred directions. The effect is based on the recently described thermal diffusion–magnetomechanical coupling in synthetic magnetic nanofluids. We expect that the new phenomenon can be applied as an efficient all-optical mixing strategy in integrated microfluidic devices. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

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“…Another interesting technique lies in designing a self-propelled microparticle by light-induced isomerization of photoresponsive dendrimer molecules adsorbed at the cargo surface [14]. The use of laser traps inducing an optothermal effect is also effective for colloid manipulation [15]; however, this approach requires precise positioning of the laser beam with respect to the microparticle position or even its well-defined movement [16,17]. In chiral nematic LCs, light-induced topological solitons can involve nearby micro-objects in motion [18] and are themselves involved in motion by them [19].…”

mentioning

confidence: 99%

Light-Induced Structures and Microparticle Transportation in a Free-Surface Frustrated Chiral Nematic Film

2022

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Local illumination with a light beam leads to thermo-orientational processes in a frustrated chiral nematic film with a free surface. Light-induced hydrodynamic flow and orientational structure create an adaptive platform for the collection, translation and rotation of suspended spherical microparticles. The demonstrated approach has potential applications in soft robotics, micro-object delivery systems, and other micro- and nanotechnologies.

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Optothermally driven colloidal transport in a confined nematic liquid crystal

Cited by 6 publications

References 25 publications

Field generated nematic microflows via backflow mechanism

Field generated nematic microflows via backflow mechanism

Optothermal grid activation of microflow with magnetic nanoparticle thermophoresis for microfluidics

Light-Induced Structures and Microparticle Transportation in a Free-Surface Frustrated Chiral Nematic Film

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