Spontaneous Size Selection in Cholesteric and Nematic Emulsions

Tixier, Thomas; Heppenstall-Butler, Mary; Terentjev, Eugene M.

doi:10.1021/la0531953

Cited by 43 publications

(51 citation statements)

References 18 publications

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“…NTA has previously been accurately used to size various nanomaterials including polymeric and metal nanoparticles, micelles, emulsions, viruses, and other colloids. 22−26 NTA is a more accurate sizing technique than DLS when polydisperse samples are used because the motion of individual particles is tracked. Although DLS does not track individual particles, it does evaluate light scattering from particles in a sample simultaneously.…”

Section: Resultsmentioning

confidence: 99%

On the Role of Specific Interactions in the Diffusion of Nanoparticles in Aqueous Polymer Solutions

Mun

Hannell²,

Rogers

et al. 2013

Langmuir

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Understanding nanoparticle diffusion within non-Newtonian biological and synthetic fluids is essential in designing novel formulations (e.g., nanomedicines for drug delivery, shampoos, lotions, coatings, paints, etc.), but is presently poorly defined. This study reports the diffusion of thiolated and PEGylated silica nanoparticles, characterized by small-angle neutron scattering, in solutions of various water-soluble polymers such as poly(acrylic acid) (PAA), poly(N-vinylpyrrolidone) (PVP), poly(ethylene oxide) (PEO), and hydroxyethylcellulose (HEC) probed using NanoSight nanoparticle tracking analysis. Results show that the diffusivity of nanoparticles is affected by their dimensions, medium viscosity, and, in particular, the specific interactions between nanoparticles and the macromolecules in solution; strong attractive interactions such as hydrogen bonding hamper diffusion. The water-soluble polymers retarded the diffusion of thiolated particles in the order PEO > PVP > PAA > HEC whereas for PEGylated silica particles retardation followed the order PAA > PVP = HEC > PEO. In the absence of specific interactions with the medium, PEGylated nanoparticles exhibit enhanced mobility compared to their thiolated counterparts despite some increase in their dimensions.

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Section: Resultsmentioning

confidence: 99%

On the Role of Specific Interactions in the Diffusion of Nanoparticles in Aqueous Polymer Solutions

Mun

Hannell²,

Rogers

et al. 2013

Langmuir

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“…Emulsion droplets can be prepared by various techniques, such as photopolymerization [91], ultrasonication [92], shearing of droplets and subsequent crystallization fractionation [93, 94], droplet break-off in a co-flowing stream (microfluidics) [95], and dispersion polymerization [91, 96, 97]. However, the majority of these methods do not permit control over LC droplet size in the range that is optimal for LC sensing (1-10 μm, see below).…”

Section: Lc-in-water Emulsions As Sensorsmentioning

confidence: 99%

“…First, by using the above-described polymer templating method to fabricate water-dispersed PEM-coated 5CB droplets of a controlled size, Gupta et al [80] demonstrated that decreasing the size of the LC droplets led to spontaneous bipolar-to-radial ordering transitions below a critical droplet diameter of approximately 800 nm (R ≈ 400 nm) (Figure 17C-M). Although many theoretical scaling arguments predicted the size-dependent stability of director configurations within LC droplets [92, 100, 101], these arguments generally predict a spontaneous transition to a uniform director configuration within sub-micrometer sized LC droplets (Figure 17A and B) rather than a transition to the radial configuration. Gupta et al [80] also showed that the sensitivity of LC droplets which undergo a bipolar-to-radial ordering transition in the presence of interfacial adsorbates can be adjusted by controlling the size of the droplets (Figure 17N).…”

Section: Lc-in-water Emulsions As Sensorsmentioning

confidence: 99%

Chemical and biological sensing using liquid crystals

Carlton

Hunter

Miller

et al. 2013

Liquid Crystals Reviews

332

236

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The liquid crystalline state of matter arises from orientation-dependent, non-covalent interaction between molecules within condensed phases. Because the balance of intermolecular forces that underlies formation of liquid crystals is delicate, this state of matter can, in general, be easily perturbed by external stimuli (such as an electric field in a display). In this review, we present an overview of recent efforts that have focused on exploiting the responsiveness of liquid crystals as the basis of chemical and biological sensors. In this application of liquid crystals, the challenge is to design liquid crystalline systems that undergo changes in organization when perturbed by targeted chemical and biological species of interest. The approaches described below revolve around the design of interfaces that selectively bind targeted species, thus leading to surface-driven changes in the organization of the liquid crystals. Because liquid crystals possess anisotropic optical and dielectric properties, a range of different methods can be used to read out the changes in organization of liquid crystals that are caused by targeted chemical and biological species. This review focuses on principles for liquid crystal-based sensors that provide an optical output.

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“…22 In the experiment, 1 the abundance of surfactants may have reduced below W. For lyotropic nematics made of self-assembled molecular aggregates similar to worm-like micelles, W / Ͼ 1 has been observed for domains in a biphasic system. 20,23 The mechanism revealed by the heart-shaped bubble has potential applications in other complex fluids that feature nematic-isotropic interfaces, such as nematic emulsions 24 and polymer-dispersed liquid crystals ͑PDLC͒. 25 In selfassembly of colloids for making photonic crystals, 26 a nematic matrix will afford better control of the spatial periodicity as well as the possibility of nonspherical voids with better performance and tunability.…”

Section: Phys Fluids 19 041703 ͑2007͒mentioning

confidence: 99%

Heart-shaped bubbles rising in anisotropic liquids

et al. 2007

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This Letter reports on numerical simulations motivated by experimental observations of an unusual inverted-heart shape for bubbles rising in an anisotropic micellar solution. We explain the bubble shape by assuming that the micelles are aligned into a nematic phase, whose anchoring energy on the bubble competes with the interfacial tension and the bulk elasticity of the nematic to modify the interfacial curvature. Numerical results show that bubbles with sufficiently strong planar anchoring rising in a vertically aligned nematic indeed assume the observed shape. The parameter values required are compared with the experimental materials and conditions. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2722421͔To investigate the impact of solids on viscoelastic liquids, Akers and Belmonte 1 dropped spheres of diameter d ϳ 1 cm into an aqueous solution of the worm-like micellar system cetylpyridinium chloride ͑CPCl͒/sodium salicylate ͑NaSal͒. Occasionally air bubbles were entrained into the fluid, and would rise in the wake of the ball ͑Fig. 1͒. Such a bubble assumes a peculiar shape while in the near wake, resembling an inverted heart or a spade ͑a͒. The upper surface has sloped shoulders that join in a point. The bottom is relatively flat with a small conical protrusion in the middle. As it rises, both points on top and bottom quickly retract and the bubble appears roughly spherical ͑b͒. Further up, the bubble assumes the familiar shape with a round top and a long pointed tail at the bottom ͑c͒. The last image resembles that seen of bubbles in viscoelastic polymer solutions, 2,3 the tail being produced by the tensile stress in the wake of the bubble. The inverted-heart shape in the first image, on the other hand, has never been reported before. A possible explanation is that the micellar solution has been temporarily transformed into an anisotropic nematic liquid in the near wake of the falling ball. The ordered micelles have a preferred orientation, known as the "easy direction," 4 with respect to the bubble surface, deviation from which is penalized by an anchoring energy. 5,6 Such surface anchoring may compete with the interfacial tension and the bulk molecular order and force the bubble into the peculiar shape. Farther away from the ball, the micelles relax and lose the nematic order, and the bubble shape reverts to that commonly seen in viscoelastic liquids.Although Akers and Belmonte did not present direct evidence for the orientational order in the near wake, a flowinduced nematic state can be inferred from two facts. First, a falling ball produces strong elongation in its wake that tends to modify the microstructural conformation of the fluid. Both flexible polymers and worm-like micelles have been observed to align into "birefringent strands" in the near wake. 7,8 Second, semidilute and concentrated micellar solutions are known to undergo an isotropic-to-nematic transition under shear, for surfactant concentrations down to 1.09 wt. %. 9-11 At higher concentrations, micelles commonly exhibit a nematic...

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Spontaneous Size Selection in Cholesteric and Nematic Emulsions

Cited by 43 publications

References 18 publications

On the Role of Specific Interactions in the Diffusion of Nanoparticles in Aqueous Polymer Solutions

On the Role of Specific Interactions in the Diffusion of Nanoparticles in Aqueous Polymer Solutions

Chemical and biological sensing using liquid crystals

Heart-shaped bubbles rising in anisotropic liquids

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