The mobilities of micro- and nano-particles at interfaces of nematic liquid crystals

Abras, Daniel; Pranami, Gaurav; Abbott, Nicholas L.

doi:10.1039/c1sm06794j

Cited by 18 publications

(25 citation statements)

References 59 publications

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“…Nematic LCs possess direction-dependent (Miesowicz) shear viscosities with the direction of lowest viscosity being parallel to the director. 29–31 In common thermotropic liquid crystals, the Miesowicz viscosity corresponding to shear flow with velocity perpendicular to the director is often ~10× larger than the viscosity parallel to the director. 29 Because experimental determination of Miesowicz viscosities of lyotropic LCs is difficult as general and facile methods to manipulate the surface anchoring of lyotropic LC phases do not exist, we estimated the apparent viscosity experienced by the motile P. mirabilis-flhDC in nematic DSCG to be μ~ 0.7 Pa·s by comparing the average velocity in nematic DSCG to previous measurements of P. mirabilis-flhDC motility in solutions of known viscosity.…”

Section: Resultsmentioning

confidence: 99%

Dynamic self-assembly of motile bacteria in liquid crystals

et al. 2014

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This paper reports an investigation of dynamical behaviors of motile rod-shaped bacteria within anisotropic viscoelastic environments defined by lyotropic liquid crystals (LCs). In contrast to passive microparticles (including non-motile bacteria) that associate irreversibly in LCs via elasticity-mediated forces, we report that motile Proteus mirabilis bacteria form dynamic and reversible multi-cellular assemblies when dispersed in a lyotropic LC. By measuring the velocity of the bacteria through the LC (8.8 +/− 0.2 μm/s) and by characterizing the ordering of the LC about the rod-shaped bacteria (tangential anchoring), we conclude that the reversibility of the inter-bacterial interaction emerges from the interplay of forces generated by the flagella of the bacteria and the elasticity of the LC, both of which are comparable in magnitude (tens of pN) for motile Proteus mirabilis cells. We also measured the dissociation process, which occurs in a direction determined by the LC, to bias the size distribution of multi-cellular bacterial complexes in a population of motile Proteus mirabilis relative to a population of non-motile cells. Overall, these observations and others reported in this paper provide insight into the fundamental dynamical behaviors of bacteria in complex anisotropic environments and suggest that motile bacteria in LCs are an exciting model system for exploration of principles for the design of active materials.

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Section: Resultsmentioning

confidence: 99%

Dynamic self-assembly of motile bacteria in liquid crystals

et al. 2014

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Section: Resultsmentioning

confidence: 99%

“…Our experimental results reported above and recent coarse grain modelling [ 25 ] support, however, the proposition that elastic distortions (and defect core energies) are minimized by the partitioning of a colloid to a defect. Accordingly, we estimate the magnitude of the elastic forces driving the colloid to the defect as: [ 34,35 ] = E Ka elastic (1) in which K is the elastic constant of the LC (using the "one constant" approximation), and a is the radius of the PS colloid (0.5 µm). Using a typical value for an elastic constant for a low molecular weight LC, K = 10 −11 N, [ 20,36 ] we calculate E elastic ≈ 5 × 10 −18 J.…”

Section: Resultsmentioning

confidence: 99%

Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles

Wang

Miller

Pablo

et al. 2014

Adv Funct Materials

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The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystalline droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the liquid crystal (LC) droplets and result in heterogeneous populations of patchy microparticles. To address this issue, here we demonstrate that adsorbate-driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface-driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus-like” microparticles. By using magnetic colloids, we illustrate the utility of the approach by synthesizing magnetically-responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.

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“…The dark-field microscopy allows direct real-time visualization of colloidal particles smaller than the diffraction limit [21,[26][27][28]30,32,45] due to the strong scattering of visible light from gold NPs [50] having the appearance of bright spots on a dark, uniform background. The size of these spots does not directly correspond to the actual dimensions of the NPs but represents their scattering cross section that, in addition to the particle size, is determined by diffraction-limited resolution [50].…”

Section: A Diffusion Of Rodlike Convex Pentagonal Nanoprisms Alignedmentioning

confidence: 99%

“…It was found that the diffusivity of gold NPs can be affected by chemical functionalization of their surface [25] and the mobility of gold NPs on the LC-aqueous interface is significantly different relative to microparticles insensitive to the details of the interfacial environment [32].…”

Section: Introductionmentioning

confidence: 99%

Rotational and translational diffusion of anisotropic gold nanoparticles in liquid crystals controlled by varying surface anchoring

2013

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We study translational and rotational diffusion of anisotropic gold nanoparticles (NPs) dispersed in the bulk of a nematic liquid crystal fluid host. Experimental data reveal strong anisotropy of translational diffusion with respect to the uniform far-field director, which is dependent on shape and surface functionalization of colloids as well as on their ground-state alignment. For example, elongated NPs aligned parallel to the far-field director translationally diffuse more rapidly along the director whereas diffusion of NPs oriented normal to the director is faster in the direction perpendicular to it while they are also undergoing elasticity-constrained rotational diffusion. To understand physical origins of these rich diffusion properties of anisotropic nanocolloids in uniaxially anisotropic nematic fluid media, we compare them to diffusion of prolate and oblate ellipsoidal particles in isotropic fluids as well as to diffusion of shape-isotropic particles in nematic fluids. We also show that surface functionalization of NPs with photosensitive azobenzene groups allows for in situ control of their diffusivity through trans-cis isomerization that changes surface anchoring.

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The mobilities of micro- and nano-particles at interfaces of nematic liquid crystals

Cited by 18 publications

References 59 publications

Dynamic self-assembly of motile bacteria in liquid crystals

Dynamic self-assembly of motile bacteria in liquid crystals

Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles

Rotational and translational diffusion of anisotropic gold nanoparticles in liquid crystals controlled by varying surface anchoring

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