Institute of Physics
National Academy of Sciences, Kyiv, Ukraine
Long-range forces between ultra-fine particles imbedded in liquid crystal (LC) matrices result in intriguing colloids. Embedded inorganic particles in LC contribute to the properties of the LC matrix. For example, doping of a LC with ferromagnetic particles resulted in a strong enhancement of magnetic properties of the LC . Large (>>µm) colloidal particles form defects in LC matrices due to strong director deformations and ensembles of these particles and defects can form complex structures. Small (<<µm) particles at its high concentration (> 2-3% by weight) create almost a rigid LC suspension. Recently we showed that at low concentrations LC nanocolloids appear similar to a pure LC with no readily apparent evidence of dissolved particles, but possess unique properties. The diluted suspensions are stable, because the small concentration of nanoparticles does not significantly perturb the director field in the LC, and interaction between the particles is weak. At the same time, the nanoparticles share their intrinsic properties with the LC matrix due to the anchoring with the LC. In particular, doping a nematic LC matrix with ferroelectric nanoparticles results in a suspension, which possesses reveals ferroelectric properties inherent to the nanoparticles. Here we report a number of unique properties of ferroelectric liquid crystal suspensions. They show sufficient extension of the nematic temperature range, strong increase of dielectric anisotropy, εa, and birefringence, na, that is a result of significant increase of the order parameter, S, in compare with pure liquid crystal. A physical origin of peculations of ferroelectric suspensions is due to a strong electric field from the particles that effect the orientation ordering of LC molecules.
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Acknowledgments : The results were obtained in frame of mutual collaboration between scientists from Kent State University (USA ; West, Lee), Hoseo University (Korea ; Cheon), Kyiv Shevchenko University (Ukraine ; Reshetnyak), Institute of Physics Ukrainian Academy of Sciences (Ukraine ; Buchnev, Tereshchenko, Reznikov), Southampton University (UK ; Dyadyusha, Kaszmarek, Sluckin), Columbia University (USA, O’Brien, Huang)