Point Defects, Topological Chirality, and Singularity Theory in Cholesteric Liquid-Crystal Droplets

Pollard, Joseph; Posnjak, Gregor; Čopar, Simon; Muševič, Igor; Alexander, Gareth P.

doi:10.1103/physrevx.9.021004

Cited by 30 publications

(34 citation statements)

References 59 publications

(86 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At much larger length scales (e.g. mm), continuum mechanics calculations yield results which positively correlate with experiments [29][30][31]. The mesoscale region in between remains difficult to explore computationally, although we have recently demonstrated a phenomenological correspondence between coarsegrained simulations and continuum studies which could prove useful to develop accurate multiscale studies for LC droplets [32].…”

Section: Introductionmentioning

confidence: 52%

Liquid crystal droplets under extreme confinement probed by a multiscale simulation approach

2021

View full text Add to dashboard Cite

In this work, we computationally investigate liquid crystal (LC) droplets in the size range 0.03-1 μm, confined within shells of combined anchoring conditions. Two different types of surface were defined to promote homeotropic and planar degenerate anchoring, respectively. We identified the LC behaviour within the nanoscale droplets using a bespoke multiscale simulation approach. To study 30 nm droplets, we used coarse grained simulations within the dissipative particle dynamics formalism; to study 0.1 μm and larger droplets, we used a finite element method based on the Landau-de Gennes theory. Good agreement between the two methods was observed in our prior analysis and was confirmed in the present work. We explicitly study droplets of size 0.1 and 1 μm by using continuum mechanics calculations. Our results for the largest droplet are consistent with those available in the literature, suggesting that the extension to smaller droplets presented here is realistic, and therefore can be helpful for innovations in which device intensification could be achieved using LC nanodroplets.

show abstract

Section: Introductionmentioning

confidence: 52%

Liquid crystal droplets under extreme confinement probed by a multiscale simulation approach

2021

View full text Add to dashboard Cite

show abstract

“…Oblate CLC droplets have an average aspect ratio of l = a / b ≈ 2.5, where a and b are the lengths of the semi‐major and semi‐minor axes, respectively, as measured by the fluorescent confocal microscope images in Figure S2 and Movie S1, Supporting Information. Accompanying the shape deformation, the point defect in the spherical CLC droplet changes to a ring defect in the oblate CLC droplet under the constraint of constant layer spacing, [ 49,50 ] as directly confirmed by the time sequences shown in Figure 2e and Movie S2, Supporting Information. Within the ring defect, that is, the central region of the oblate droplets, the helical axis of CLCs is perpendicular to the horizontal film plane and is suggested by the circular symmetry of the oblate CLC droplets, as shown in Figure S3, Supporting Information.…”

Section: Figurementioning

confidence: 73%

3D‐Printed Biomimetic Systems with Synergetic Color and Shape Responses Based on Oblate Cholesteric Liquid Crystal Droplets

Yang

Ruan

et al. 2021

Advanced Materials

View full text Add to dashboard Cite

Living organisms in nature have amazing control over their color, shape, and morphology in response to environmental stimuli for camouflage, communication, or reproduction. Inspired by the camouflage of the octopus via the elongation or contraction of its pigment cells, oblate cholesteric liquid crystal droplets are dispersed in a polymer matrix, serving as the role of pigment cells and showing structural color due to selective Bragg reflection by their periodic helical structure. The color of 3D‐printed biomimetic systems can be tuned by changing the helical pitch via the chiral dopant concentration or temperature. When the oblate liquid crystal droplets are heated up to isotropic, the opaque and colored biomimetic systems become transparent and colorless. Meanwhile, the isotropic liquid crystal droplets tend to become spherical, causing volume contraction along the film plane and volume dilation in the perpendicular direction. The internal strain combined with the gradient distribution of the oblate isotropic liquid crystal droplets result in corresponding shape transformations. The camouflage of a biomimetic octopus and the blossom of a biomimetic flower, both of which show synergetic color and shape responses, are demonstrated to inspire the design of functional materials and intelligent devices.

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

Point Defects, Topological Chirality, and Singularity Theory in Cholesteric Liquid-Crystal Droplets

Cited by 30 publications

References 59 publications

Liquid crystal droplets under extreme confinement probed by a multiscale simulation approach

Liquid crystal droplets under extreme confinement probed by a multiscale simulation approach

3D‐Printed Biomimetic Systems with Synergetic Color and Shape Responses Based on Oblate Cholesteric Liquid Crystal Droplets

Field generated nematic microflows via backflow mechanism

Contact Info

Product

Resources

About