We report on the development of a dilute suspension of ferroelectric particles in a nematic liquid-crystal (LC) host. We found that the submicron particles do not disturb the LC alignment and the suspension macroscopically appears similar to a pure LC with no readily apparent evidence of dissolved particles. The suspension possesses enhanced dielectric anisotropy, and is sensitive to the sign of an applied electric field.

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We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy and capacitance studies. The resulting colloids normally remain homogeneous, but the nematic orientational coupling is significantly amplified. In particular cases, the nematic orientation coupling increases by 10% for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases up to 40 Celsius degrees compared to the pure LC host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square of the orientational order parameter.PACS numbers: 64.70. Md, 82.70.Dd, Colloids in which the solute is liquid crystalline (LC) are known to possess an extremely rich set of behaviors [1,2,3,4,5]. The anchoring between the LC and microcolloidal particles ( 1µm) can produce long-range orientational distortions around the particles. This results in strong inter-particle interactions -sometimes repulsive and sometimes attractive -in the mesophase. The interactions can give rise to well-ordered structures of particles in the liquid crystal matrix (both lattices and chains) [2,3]. However, in most cases a prerequisite for interesting LC colloidal behavior has been a high concentration dispersion, typically with particle volume fraction c part 30%. In such systems aggregated particles produce director distortions extending over macroscopic scales. These suspensions scatter light strongly, and possess unique structural, mechanical, electro-and magneto-optical properties [5,6].Recently, we have shown that even at low concentrations (c part 1%), LC colloids differ strongly from the pure host material [7,8,9,10]. These colloids consist of submicron ferroelectric particles suspended in the LC host. In these systems, unlike in classic LC colloids, the suspensionmatrix interaction is insufficient to disturb the LC orientation. This small concentration dramatically increases the dielectric anisotropy, significantly decreases the Freedericksz transition voltage, and significantly accelerates electric field-induced director reorientation.In this letter, we report results which show that these phenomena are general properties of liquid crystal suspensions containing ferroelectric colloidal nanoparticles. The addition of impurities normally decreases the nematic clearing temperature T N I [11]. However, our measurements show massive increases in T N I , of the order of 40 • C, for mass impurity concentrations of the order of 0.2%. These results imply an increase in the effective nematic interaction parameter. Measurements of the birefringence, dielectric anisotropy and order parameter in the suspension are consistent with this picture.We have also constructed a theoretical model. The ferroelectric particles in the suspension produce large electric fields in their neighborhood. These electric fields produce induce...

We report the first clear demonstration of drag on colloidal particles by a moving nematic-isotropic interface. The balance of forces explains our observation of periodic, strip-like structures that are produced by the movement of these particles.PACS numbers: 61.30.Jf, 64.70.Md, Colloidal dispersions of small particles in nematic liquid crystals are a novel, interesting type of soft matter. The difference from ordinary colloids arises from the orientational ordering of the liquid crystal molecules and the resulting structure in the colloid. Topological defects [1,2,3,4] and additional long-range forces between the colloidal particles [5] are immediate consequences of this ordering. The nematic-induced interparticle interaction brings a new range of effects to the system: supermolecular structures [6,7,8,9], cellular structures [10,11], and even a soft solid [12] can be observed. Colloidal dispersions in liquid crystals also have a wide variety of potential applications [13].A range of problems similar to those of polymer dispersed liquid crystals also arise in nematic colloidal dispersions. The nematic ordering makes it difficult to suspend small particles in a liquid crystal host. Particles often segregate into agglomerates distributed nonuniformly in the cell. The resulting spatial distribution of the particles is difficult to control. Our research explores the factors that affect the spatial distribution of these particles and indicates ways to control the complex morphology of these systems.In this paper we report the first demonstration of drag on colloidal particles by a moving nematic-isotropic (NI) interface. We calculate a critical radius above which the particles cannot be captured by the moving interface. We predict that this critical radius is sensitive to the viscous properties of the host liquid crystal, the value of the anchoring coefficient of the liquid crystal on the particle surface, and the velocity of the moving interface. Most important, we can move particles of specified radius and can control the spatial distribution of these particles in the cell.In order to understand how the particles are moved by the nematic-isotropic transition front we used particles of different size as well as particles made of different materials. In the first part of our experiments we used nearly monodisperse spheres of silica (R = 0.005, 0.5, and 1µm). To prove our predictions based on initial experimental observations and to demonstrate the controllability of the spatial distribution of particles in anisitropic colloidal suspensions, we used large polymer particles, R = 8µm [17]. In all cases particles were dispersed at concentrations of φ = 1 − 5wt %, in the liquid crystal 5CB at room temperature (25 0 C) (the isotropic-nematic transition temperature of pure 5CB is T NI ≈ 35 0 C). The sample was subjected to ultrasound in order to uniformly disperse the particles in 5CB. Some of the preparations were made at higher temperatures, in the nematic or isotropic state of the liquid crystal.The homogeneous mixtur...

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We describe techniques to selectively harvest single ferroelectric domain nanoparticles of BaTiO3 as small as 9 nm from a plethora of nanoparticles produced by mechanical grinding. High resolution transmission electron microscopy imaging shows the unidomain atomic structure of the nanoparticles and reveals compressive and tensile surface strains which are attributed to the preservation of ferroelectric behavior in these particles. We demonstrate the positive benefits of using harvested nanoparticles in disparate liquid crystal systems.

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