Flow induced deformation of defects around nanoparticles and nanodroplets suspended in liquid crystals

Gettelfinger, Brian T.; Moreno-Razo, J. A.; Koenig, Gary M.; Hernández-Ortíz, Juan P.; Abbott, Nicholas L.; Pablo, Juan J. de

doi:10.1039/b912551e

Cited by 35 publications

(41 citation statements)

References 31 publications

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“…From the Fresnel integrals [25] we have (11) where a is the tension to the bending ratio: γ 0,1/2 /k c . The boundary conditions written in terms of y and x are as follows:…”

Section: Disclination Space Loopmentioning

confidence: 99%

“…Nematic liquid crystals (NLCs) are anisotropic viscoelastic materials that exhibit the anisotropy of crystals and the fluidity of viscous liquids; their macroscopic orientation is characterized by the unit director vector n. Phase transitions, external electromagnetic fields, shear flows, and confinement usually generate singular and nonsingular orientational defects [1][2][3][4][5][6][7][8][9][10][11][12][13]. Disclination formation in nematic liquid crystals under confinement is the subject of continuing interest since frustration emanating from fixed orientation at curved bounding surfaces is common in applications [13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

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Theoretical predictions of disclination loop growth for nematic liquid crystals under capillary confinement

et al. 2014

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The combination of low elasticity modulus, anisotropy, and responsiveness to external fields drives the rich variety of experimentally observed pattern formation in nematic liquid crystals under capillary confinement. External fields of interest in technology and fundamental physics are flow fields, electromagnetic fields, and surface fields due to confinement. In this paper we present theoretical and simulation studies of the pattern formation of nematic liquid crystal disclination loops under capillary confinement including branching processes from a m=+1 disclination line to two m=+1/2 disclination curves that describe the postnucleation and growth regime of the textural transformation from radial to planar polar textures. The early postnucleation and growth of emerging disclination loops in cylindrical capillaries are characterized using analytical and computational methods based on the nematic elastica that takes into account line tension and line bending stiffness. Using subdiffusive growth and constant loop anisotropy, we found that the solution to the nematic elastica is a cusped elliptical geometry characterized by exponential curvature variations. The scaling laws that govern the loop growth reflect the tension to bending elasticity balance and reveal that the loop dilation rate depends on the curvature and normal velocity of the disclination. The line energy growth is accommodated by the decrease in branch-point curvature. These findings contribute to the evolving understanding of textural transformations in nematic liquid crystals under confinement using the nematic elastic methodology.

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“…From the Fresnel integrals [25] we have (11) where a is the tension to the bending ratio: γ 0,1/2 /k c . The boundary conditions written in terms of y and x are as follows:…”

Section: Disclination Space Loopmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Theoretical predictions of disclination loop growth for nematic liquid crystals under capillary confinement

et al. 2014

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“…48,66,67 Here, the effects of fluid flow are neglected; they are not expected to influence the equilibrium configurations. The Ginzburg-Landau relaxation is carried out numerically using a semi-implicit Euler scheme for the time derivative, whereas for the spatial derivatives, a finite difference approach is employed.…”

Section: Appendix C: Ginzburg-landau Relaxationmentioning

confidence: 99%

Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

Armas-Pérez

Londoño-Hurtado

Guzmán

et al. 2015

The Journal of Chemical Physics

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A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

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“…Microfluidics have lately been used to explore the production and the properties of monodispersed NLC droplets (Hamlington et al 2007;Fernandez-Nieves et al 2007a) and to generate NLC shells (Fernandez-Nieves et al 2007b;Lopez-Leon and Fernandez-Nieves 2009). The flow of an anisotropic fluid around colloidal particles in micro and nano confinements (Stark and Ventzki 2001;Hung et al 2007;Gettelfinger et al 2010) and hydrodynamics of topological defects (Denniston et al 2000;Denniston et al 2001;Toth et al 2002) in pure NLCs have been studied theoretically. Flow-driven director reorientations and effects of surface pretilt in pure NLCs have recently been studied by Sambles and coworkers (Holmes et al 2009(Holmes et al , 2010Jewell et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Functionalization of microfluidic devices for investigation of liquid crystal flows

Sengupta

Schulz

Ouskova

et al. 2012

Microfluid Nanofluid

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Systematic studies of thermotropic liquid crystals in confinement, such as liquid crystals in microfluidic channels, require control of the anchoring conditions on the surfaces. Especially for the case of uniform planar anchoring, the standard method involves a mechanical treatment (rubbing) of the surface that is not applicable to microfluidic devices. In the present study, we report methods for the achievement of well-defined anchoring conditions for liquid crystals in microfluidic channels consisting of polydimethylsiloxane and glass. Various physico-chemical techniques enable to establish homeotropic, degenerate planar, uniform planar, and hybrid anchoring conditions on the surface of the channel walls. We characterize the treated surfaces in terms of wettability and liquid crystal anchoring and determine the director field in the microchannels for the different anchoring configurations using polarizing optical microscopy and fluorescence confocal polarization microscopy. The relevance of the surface anchoring for the flow behavior of the liquid crystal in the microchannel is demonstrated by studying the onset of defect-mediated chaoticlike flow at high Ericksen numbers for the different anchoring cases.

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Flow induced deformation of defects around nanoparticles and nanodroplets suspended in liquid crystals

Cited by 35 publications

References 31 publications

Theoretical predictions of disclination loop growth for nematic liquid crystals under capillary confinement

Theoretical predictions of disclination loop growth for nematic liquid crystals under capillary confinement

Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

Functionalization of microfluidic devices for investigation of liquid crystal flows

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