Chiral LCs confined in spheroids exhibit new families of morphologies as a result of geometrical frustration.

Liquid crystalline (LC) oils offer the basis of stimuli-responsive LC-in-water emulsions. Although past studies have explored the properties of single-phase LC emulsions, few studies have focused on complex multicompartment emulsions containing co-existing isotropic and LC domains. In this paper, we report a study of multiphase emulsions using LCs and immiscible perfluoroalkanes dispersed in water or glycerol (the latter continuous phase is used to enable characterization). We found that the nematogen 4′-pentyl-4-biphenylcarbonitrile (5CB) anchors homeotropically (perpendicularly) and weakly at liquid perfluorononane (F9) interfaces, consistent with the smectic layering of 5CB molecules. The proposed role of smectic layering is supported by experiments performed with 4-(trans-4-pentylcyclohexyl)­benzonitrile, a nematogen that possesses a cyclohexyl group that frustrates the smectic packing and leads to tilted orientations at the F9 interface. By employing perfluorocarbon and hydrocarbon surfactants in combination with multiphase 5CB and F9 emulsion droplets dispersed in a continuous water or glycerol phase, we observe a range of emulsion droplet morphologies to form, including core–shell and Janus structures, with internal organizations that reflect an interplay of interfacial (anchoring energies; F9 and glycerol) and elastic energies within the confines of the geometry of the emulsion droplet. By comparing experimental observations to simulations of the LC–perfluorocarbon droplets based on a Landau-de Gennes model of the free energy, we place bounds on the orientation-dependent interfacial energies that underlie the internal ordering of these complex emulsions. Additionally, by forming core–shells emulsion droplets from 5CB (shell) and perfluoroheptane (cores), we demonstrate how a liquid-to-vapor phase transition in the perfluorocarbon core can be used to actuate the droplet and rapidly thin the nematic shell. Overall, the results reported in this paper demonstrate that multiphase LC emulsions formed from mixtures of perfluoroalkanes and LCs provide new opportunities to engineer hierarchical and stimuli-responsive emulsion systems.

absorption spectra due to surface plasmon resonances; [2] and the elastic moduli of polystyrene polymer films decrease substantially below 40 nm. [3] These examples highlight how nanoscopic confinement provides an important route for expanding the palette of materials structures and properties. Of particular relevance to the study reported in this paper, liquid crystals (LCs) are known to be strongly influenced by confinement. [4][5][6] For example, confinement of LCs can lead to changes to topological defects present in a sample, [4] alteration of optical properties [5] and changes to the way in which LCs respond to external fields (e.g., electric fields). [6] The majority of past studies, however, have focused on confinement of LCs on the micrometer-scale with fewer studies exploring the submicrometer-scale. [7][8][9][10][11][12][13][14][15][16][17][18][19] The majority of past studies of LCs in submicrometer-scale confinement have involved the use of droplets of nematic LCs. [9][10][11][14][15][16][17][18][19] These studies have reported internal LC configurations that depend on droplet size and the chemistry of the confining surfaces. Gupta et al. [19] observed that nematic droplets confined within multilayered polyelectrolyte shells of poly(styrene sulfonate) and poly(allylamine hydrochloride) changed from a bipolar configuration to a radial configuration as the diameter decreased from 3 µm to 700 nm. An additional study by Zou et al. [9] found that a confinementinduced bipolar-to-radial configuration transition in nematic droplets occurred when the LC was in contact with an adsorbed layer of poly(styrenesulfonic acid) but not poly(styrenesulfonate sodium), suggesting that the effects of confinement are modulated by surface interactions. In contrast, Peng et al. [18] have reported that nematic nanodroplets confined in SiO 2 capsules assumed a uniform internal alignment as the droplet diameter decreased to 200 nm, with either tangential or homeotropic anchoring on the capsules. In addition to changes in internal structure, phase transitions from isotropic to nematic phases have been reported to occur at temperatures that increase, decrease, or are invariant with nanodroplet size. [15,18] These conflicting observations likely arise from differences in interfacial chemistry and/or LC elastic properties. More broadly, however, they both highlight the opportunity that exists to tune LC properties via nanoconfinement but also pinpoint the need for additional studies of LC nanodroplets, including investigations of the effects of confinement on nanodroplets formed from LCs other than nematics.Limits on the resolution of far-field optical microscopy also make studies of LC droplets on the submicrometer-scale Liquid crystal (LC) emulsions represent a class of confined soft matter that exhibit exotic internal organizations and size-dependent properties, including responses to chemical and physical stimuli. Past studies have explored micrometer-scale LC emulsion droplets but little is known about LC ordering within subm...

Organizing nanoparticles in a controlled way allows us to monitor their optical properties, in particular if it concerns metallic nanoparticles. It is particularly interesting to organize them on top of liquid crystal films to take advantage, in a second step, of the easy actuation of liquid crystals with external parameters like temperature, electric fields, etc…We show that despite their fluidity, nematic and smectic films allow formation of well-ordered hexagonal domains of gold spherical nanoparticles (AuNPs) at their surface but we also show that both nematic films and AuNP domains impact each other. Using Optical Microscopy, Atomic Force Microscopy (AFM), Scanning Electron microscopy (SEM), and Spectrophotometry, we compare nematic, polymer stabilized nematic and smectic films with AuNP domains made of NPs of diameter 6nm. On The liquid crystal films depressions are revealed below the AuNP domains whereas the AuNP domains appear well-organized but with a hexagonal period shortened with respect to AuNP monolayers formed on hard substrates. We interpret these features by the anchoring tilt imposed by the AuNP domains on the molecules. The smectic-A layers characteristic of the nematic surface transform into smectic-C layers which induce formation of depression. The energy penalty associated with the local smectic-A/smectic-C transition induces the shortening of the AuNP domain period in order to decrease the AuNP domain surface. The observed large depth of the polymer stabilized nematic depressions below AuNP domains may be explained either by an increased size of the polymer stabilized smectic layers close to the surface or by an increased number of polymer stabilized smectic liquid crystal smectic layers close to the surface with respect to pure nematic films.