Design of Functional Materials Based on Liquid Crystalline Droplets

Miller, Daniel S.; Wang, Xiaoguang; Abbott, Nicholas L.

doi:10.1021/cm4025028

Cited by 137 publications

(187 citation statements)

References 100 publications

(357 reference statements)

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“…[10] When nematic LCs are confined to water-dispersed microdroplets, the interfacial interactions of the LC set the orientation of the LCs at the droplet surface (i.e., surface anchoring). [11, 12-14] To accommodate the surface anchoring conditions, the LC within the interior of the droplet assumes a variety of configurations that involve elastic strain of the LC (e.g., splay, bend, etc.) [14-18] and topological defects (localized regions where the LC effectively melts).…”

Section: Introductionmentioning

confidence: 99%

“…[11, 12-14] To accommodate the surface anchoring conditions, the LC within the interior of the droplet assumes a variety of configurations that involve elastic strain of the LC (e.g., splay, bend, etc.) [14-18] and topological defects (localized regions where the LC effectively melts). [15, 16, 19, 20, 21] At equilibrium, the ordering of the LC within the microdroplets reflects minimization of the combined contributions of surface anchoring, bulk elastic deformations and topological defects to the free energy.…”

Section: Introductionmentioning

confidence: 99%

“…[15, 16, 19, 20, 21] At equilibrium, the ordering of the LC within the microdroplets reflects minimization of the combined contributions of surface anchoring, bulk elastic deformations and topological defects to the free energy. [14-18] In the study reported in this paper, we demonstrate that reversible manipulation of the surface anchoring of LC droplets decorated with colloids can be used to switch the configurations of LC droplets so as to sweep the colloids into unique locations on the droplet surface for the synthesis of homogeneous populations of patchy microparticles. [12, 14, 22, 23] …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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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“…Experiments and simulations have also shown that the defects that arise in LC droplets can be used to localize individual nanoparticles or pairs of nanoparticles with considerable precision (16, 17). More generally, droplets offer an effective, yet simple means for confining LCs, thereby controlling the balance of interfacial and elastic contributions to the free energy and the response of LCs to external cues (18,19). Depending on surface anchoring, LC droplets can exhibit two primary morphologies (20).…”

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confidence: 99%

Nanoparticle self-assembly at the interface of liquid crystal droplets

Rahimi

Roberts

Armas-Pérez

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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102

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Nanoparticles adsorbed at the interface of nematic liquid crystals are known to form ordered structures whose morphology depends on the orientation of the underlying nematic field. The origin of such structures is believed to result from an interplay between the liquid crystal orientation at the particles' surface, the orientation at the liquid crystal's air interface, and the bulk elasticity of the underlying liquid crystal. In this work, we consider nanoparticle assembly at the interface of nematic droplets. We present a systematic study of the free energy of nanoparticleladen droplets in terms of experiments and a Landau-de Gennes formalism. The results of that study indicate that, even for conditions under which particles interact only weakly at flat interfaces, particles aggregate at the poles of bipolar droplets and assemble into robust, quantized arrangements that can be mapped onto hexagonal lattices. The contributions of elasticity and interfacial energy corresponding to different arrangements are used to explain the resulting morphologies, and the predictions of the model are shown to be consistent with experimental observations. The findings presented here suggest that particle-laden liquid crystal droplets could provide a unique and versatile route toward building blocks for hierarchical materials assembly.growing body of theoretical and experimental work has sought to direct the assembly of molecules and nanoparticles at interfaces by exploiting the elastic forces that arise in liquid crystals (LCs) (1-5). Nematic LCs possess orientational order along a unit vector, the so-called nematic director. They also exhibit defects-regions of low order whose morphology and position depends on a delicate balance between elastic, enthalpic, and interfacial contributions to the free energy. The orientation of nematic LCs and any corresponding defects can be perturbed by introducing particles. The symmetry and structure of the director field around a particle also depends on the interaction between the LC and the particle, often referred to as anchoring. Particles with perpendicular (homeotropic) anchoring induce either dipolar or quadrupolar symmetry in the LC, leading to formation of point defects or Saturn-ring defects, respectively (6). Particles with planar anchoring induce quadrupolar symmetry, which is accompanied by two surface defects, generally referred to as boojums (6). Distortions of the nematic field cost elastic energy and therefore give rise to anisotropic, long-range interactions between particles. Indeed, particles in nematic LCs aggregate and "bind," thereby minimizing the volume of defects and the large free energy that is associated with their elastic strain. Equilibrium particle arrangements in nematic LCs depend strongly on the topology of the underlying defects. Homeotropic particles with point, dipolar defects form chains along the nematic director, whereas quadrupolar, Saturn-ring defects form kinked chains that are perpendicular to the nematic director (7). Particles with planar anchor...

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“…Liquid crystalline droplets of polymeric mesogens dispersed in continuous polymer phases have been investigated previously, but recently these droplets have demonstrated remarkable orientational sensitivity to interfacial interactions. 31 Our spherical nematic droplets have a radial structure (Figure 3) where the director field � is orthogonal to the droplet surface, or in other words, the GO basal plane is tangential to the surface (Figure 3d top) -the easy direction of orientation imposed by surface tension forces. Figure 3b shows the orientation of the slow axis measured with the birefringence mode and Figure 3c the orientation of high transmittance direction measured using the diattenuation mode.…”

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confidence: 99%

pH dependent isotropic to nematic phase transitions in graphene oxide dispersions reveal droplet liquid crystalline phases

et al. 2014

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a Size fractionation, amplified by the surface charge density of graphene oxide (GO) sheets, broadens the pH dependent isotropic (I) to nematic (N) phase transition in aqueous dispersions of graphene oxide (GO). In this biphasic region, a highly organized droplet nematic phase of uniform size (20 ± 2.8 μm diameter) with an isotropic interior is observed.Suspensions of 2D sheet-like materials exhibit transition from a disordered isotropic (I) phase to ordered nematic (N) phase. As noted by Onsager, 1 despite their loss of orientational entropy, the N phase, is stabilized by a gain in excluded volume (or configurational) entropy. Graphene -a single atom thick layer of carbon atoms is receiving immense attention owing to the combination of properties such as large intrinsic mobility of electrons, massive surface area, immense mechanical strength and large thermal conductivity. Although significant progress has been made in the solid-state synthesis of graphene, liquid-phase graphene possess opportunities for large-scale synthesis and novel mesophases that may lead to ordered macroscopic structures such as thin films and fibers with enhanced electrical, mechanical and optical properties.2, 3 Graphene solvated in chlorosulfonic acid 2 and stabilized by surfactant 4 exhibit liquid crystalline behavior, as well as their composites with discotic molecules.5 Chemically oxidized graphene sheets or graphene-oxide (GO) suspensions in water, the most accessible precursor to graphene-based materials, not surprisingly demonstrate I-N phase transitions, too.6-10 These studies have shown that the nematic phases of graphene exhibit 'brush-like' texture in massively organized continuous domains that may reach length-scales of millimeters. These length-scales are relevant to achieving macroscopcially ordered materials and fluid-phase alignment. However, graphene sheets are flexible and although this flexibility is likely to yield isolated droplet liquid crystalline phases, yet such confined phases have not been reported so far. The ability to form highly ordered N phases from GO arises because GO can be stabilized in aqueous solvent by electrostatic repulsive forces between the particles as demonstrated by large (-20 to -40 mV) zeta potential measurements.11-13 The charged functional groups are primarily carboxylic groups on the edges and hydroxyls on the basal planes, which can be protonated/deprotonated by change in pH, thus surface charging of these particles depend on the pH. pKa of GO is ~ 4 for the carboxylic groups and ~9 for the phenolic groups, 14 however GO suspensions can be stable at lower pH through hydrogen bonding between the oxidized groups and water molecules. 15 In addition, the basal plane contains hydrophobic domains that make GO sheets amphiphilic, and the ionisable groups render this amphiphilicity a dependence on pH and size of the GO sheets with smaller GO sheets being more hydrophilic than larger GO sheets. 13,[16][17][18] It can thus be expected that the I-N phase transitions are dependent upon factors suc...

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Design of Functional Materials Based on Liquid Crystalline Droplets

Cited by 137 publications

References 100 publications

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

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

Nanoparticle self-assembly at the interface of liquid crystal droplets

pH dependent isotropic to nematic phase transitions in graphene oxide dispersions reveal droplet liquid crystalline phases

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