A comparative study of nematic liquid crystals doped with harvested and non-harvested ferroelectric nanoparticles: phase transitions and dielectric properties

Abstract

International audienceno abstrac

Ferroelectric Nanoparticles in Liquid Crystals: Recent Progress and Current Challenges

“…The effects of ferroelectric nanoparticles on the properties of a single component liquid crystal such as 5CB still remain among major research interest [ 72 , 107 , 108 ]. Electro-optics (including the Freedericksz transitions in nematic and smectic-A liquid crystals) [ 98 , 119 ]; dielectric [ 85 , 102 , 105 , 118 , 123 ], electrical [ 85 , 86 , 92 , 93 , 100 , 102 , 103 , 107 , 116 , 121 , 122 ], and viscoelastic [ 90 , 96 , 122 ] properties; phase transitions and pre-transitional effects [ 80 , 94 , 95 , 96 , 107 , 112 , 113 , 118 , 122 , 123 ] in liquid crystals doped with ferroelectric nanoparticles are also receiving due attention during this time period. Another new direction gaining interest of the scientific community includes studies of hybrid liquid crystal-ferroelectric nanoparticles composite materials in the terahertz and microwave regions [ 91 , 120 ].…”

“…A very important aspect of current research is an increasing use of the harvested nanoparticles in experimental studies with the goal to distinguish between direct effects of the nanoparticle’s ferroelectricity on the properties of liquid crystals and concurrent effects such as the dilution effect, screening effect, etc. [ 77 , 85 , 94 , 105 , 112 , 118 , 123 ].…”

“…During the harvesting procedure, the harvested nanoparticles with permanent dipoles are accumulated on the inner wire electrode whereas non-ferroelectric nanoparticles remain in the fluid harvesting medium. Recent experiments with harvested ferroelectric nanoparticles provide new insights into the effects of their intrinsic ferroelectricity on the properties of liquid crystals [ 77 , 85 , 96 , 101 , 123 ]. It should be noted that ideal harvesting assumes non-charged ferroelectric nanoparticles.…”

“…Pure dilution effect ( ) can cause the reduction of the clearing temperature and the order parameter [ 126 ]. In the case of ferroelectric nanoparticles both competing effects (the effect of the nanoparticle’s polarization (Equations (3)–(5)) and the dilution/anchoring effects (Equation (6)) should be considered [ 112 , 118 , 123 ].…”

“…The applied electric field aligns dipoles of nanoparticles causing the amplification of the nanoparticle polarization. This amplification can affect the order parameter, phase transition temperatures, and the measured dielectric permittivity of the samples [ 112 , 118 , 123 ]. At the same time, techniques not utilizing electric field can yield different results for the same measured physical quantities.…”