Morphological transitions in liquid crystal nanodroplets

Tomar, Vikas; Hernández, S. I.; Abbott, Nicholas L.; Hernández-Ortíz, Juan P.; Pablo, Juan

doi:10.1039/c2sm25383f

Cited by 71 publications

(73 citation statements)

References 126 publications

(194 reference statements)

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“…Studies on model water-in-oil nanoemulsions may also provide important evidence for and tests of theories to describe colloidal interactions in non-polar media, a longstanding challenge in colloid science. [149] More broadly, studies have recently demonstrated the formation of nanoemulsions from more complex liquids including liquid crystals, [150,151] ionic liquids [11] and liquid metals. [12] These fluids all possess a number of unique and exotic properties compared to more traditional molecular solvents, and may reveal fascinating colloidal behavior based on the modification of these properties under nanoscopic confinement.…”

Section: Summary Challenges and Opportunitiesmentioning

confidence: 99%

Colloidal behavior of nanoemulsions: Interactions, structure, and rheology

Helgeson

2016

Current Opinion in Colloid & Interface Science

117

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Nanoemulsions exhibit unique behavior due to their nanoscopic dimensions, including remarkable droplet stability, interactions and rheology. These properties are significantly enhanced by nanoscopic droplet size, as well as selection of surfactant and other molecular species in solution. Electrostatic and polymer-induced interdroplet interactions are particularly powerful tools for fine-tuning the interdroplet interactions, and have led to stimuli-responsive nanoemulsion systems that provide deep insight into their unique properties. As such, nanoemulsions have emerged as powerful model systems for studying a number of colloidal phenomena including suspension rheology, repulsive and attractive colloidal glasses, aggregation processes, colloidal gelation and phase instability, and associative network formation in polymer-colloid mixtures. This review summarizes recent advances in understanding the colloidal behavior of nanoemulsions, and provides a unifying framework for understanding the various complex states that emerge, as well as perspective on emerging challenges and opportunities that will advance the use of nanoemulsions in both fundamental colloid science and technological applications. Highlights We review efforts to understand & control colloidal behavior of nanoemulsions.  Electrostatic and polymer-induced interdroplet interactions are discussed.  Repulsive interactions lead to jammed and compressed states at low volume fraction.  Attractive interactions lead to clustering, gelation and colloidal phase separation.  Nanoemulsions are model fluids to study arrested states in colloidal dispersions.

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Section: Summary Challenges and Opportunitiesmentioning

confidence: 99%

Colloidal behavior of nanoemulsions: Interactions, structure, and rheology

Helgeson

2016

Current Opinion in Colloid & Interface Science

117

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“…A lattice array with mesh size of ξ N = ffiffiffiffiffiffiffiffi ffi L=A p nm was used to perform the simulations (approximately four million lattice sites were used to simulate a droplet). The minimization of the free energy was achieved by means of the Euler-Lagrange equation with appropriate boundary conditions [additional details are provided in the Supporting Information and in the literature (47,48)]. Cross-polarizer images were obtained trough the Jones 2 × 2 formalism, which enables simulation of the changes in polarization and phase shift when the light passes through a polarizer, the droplet, and the analyzer.…”

Section: Methodsmentioning

confidence: 99%

Blue-phase liquid crystal droplets

Martínez‐González

Zhou

Rahimi

et al. 2015

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

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Blue phases of liquid crystals represent unique ordered states of matter in which arrays of defects are organized into striking patterns. Most studies of blue phases to date have focused on bulk properties. In this work, we present a systematic study of blue phases confined into spherical droplets. It is found that, in addition to the so-called blue phases I and II, several new morphologies arise under confinement, with a complexity that increases with the chirality of the medium and with a nature that can be altered by surface anchoring. Through a combination of simulations and experiments, it is also found that one can control the wavelength at which blue-phase droplets absorb light by manipulating either their size or the strength of the anchoring, thereby providing a liquid-state analog of nanoparticles, where dimensions are used to control absorbance or emission. The results presented in this work also suggest that there are conditions where confinement increases the range of stability of blue phases, thereby providing intriguing prospects for applications.blue phases | chiral liquid crystals | droplets | confinement B lue phases of liquid crystals (LCs) are characterized by a local director field that forms double-twisted cylinders, arranged into defect regions that are periodically repeated in space (1, 2). The symmetry properties of blue phases (BPs) have attracted considerable attention, as have their potential applications in a wide range of technologies (3-7). Theoretical and computational studies of the bulk structure and dynamics of BPs have helped elucidate their nature (1, 8, 9-15) in considerable detail. In the bulk, however, BPs are only found in a narrow range of temperature, between the cholesteric and the isotropic phases (1-6, 10-18), thereby placing limits on their practical utility. Recent efforts have therefore focused on increasing their stability over wider ranges of temperature and chirality, for example through addition of nanoparticles (19, 20, 21-23), polymers (24-26), or by manipulating their flexoelectricity (14).Confined chiral liquid crystals are of interest for applications in optical devices (27)(28)(29)(30)(31). Simulations of chiral LCs in channels have shown that their defect structure can be manipulated through confinement, thereby raising intriguing prospects for technology (32)(33)(34)(35). Chiral LC droplets have also been studied both numerically (36-38) and experimentally (39,40). More recent, intriguing simulations of planar chiral droplets with strong anchoring by Seč et al. (41) have examined their phase behavior as a function of chirality. In particular, it was reported that the twist bipolar structure (BS) is stable in the low chirality regime, whereas the radial spherical structure (RSS) is preferred at high chirality. The BS state has a cylindrical symmetry, where the director field is uniform along the symmetry axis of the droplet and rotates in the perpendicular direction forming bent cholesteric layers. In the RSS state, the director field also forms curved ...

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“…The interfacial properties of the liquid crystals are essential for the development of display technologies [1,3]. On the other hand, the nematic anchoring in the nematic-vapour interface, together with the elastic properties of the liquid crystal, are determinant to understand the conformation of nematic droplets [4][5][6], which have applications in molecular sensing [7][8][9][10] or electro-optic devices such as privacy windows [11][12][13][14][15][16]. From a microscopic point of view, the interfacial anchoring is well known to be determined by the intermolecular potential details.…”

Section: Introductionmentioning

confidence: 99%

Computer simulation study of the nematic–vapour interface in the Gay–Berne model

Rull

Romero-Enrique

2017

Molecular Physics

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We present computer simulations of the vapour-nematic interface of the GayBerne model. We considered situations which correspond to either prolate or oblate molecules. We determine the anchoring of the nematic phase and correlate it with the intermolecular potential parameters. On the other hand, we evaluate the surface tension associated to this interface. We find a corresponding states law for the surface tension dependence on the temperature, valid for both prolate and oblate molecules.

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Morphological transitions in liquid crystal nanodroplets

Cited by 71 publications

References 126 publications

Colloidal behavior of nanoemulsions: Interactions, structure, and rheology

Colloidal behavior of nanoemulsions: Interactions, structure, and rheology

Blue-phase liquid crystal droplets

Computer simulation study of the nematic–vapour interface in the Gay–Berne model

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