Dispersion of γ-Alumina Nano-Sized Spherical Particles in a Calamitic Liquid Crystal. Study and Optimization of the Confinement Effects

Abstract

We report an experimental study on confined systems formed by butyloxybenzylidene octylaniline liquid crystal (4O.8) + γ-alumina nanoparticles. The effects of the confinement in the thermal and dielectric properties of the liquid crystal under different densities of nanoparticles is analyzed by means of high resolution Modulated Differential Scanning Calorimetry (MDSC) and broadband dielectric spectroscopy. First, a drastic depression of the N-I and SmA-N transition temperatures is observed with confinement, the more concentration of nanoparticles the deeper this depression is, driving the nematic range closer to the room temperature. An interesting experimental law is found for both transition temperatures. Second, the change in shape of the heat capacity peaks is quantified by means of the full width half maximum (FWHM). Third, the confinement does not noticeably affect the molecular dynamics. Finally, the combination of nanoparticles and the external applied electric field tends to favor the alignment of the molecules in metallic cells. All these results indicate that the confinement of liquid crystals by means of γ-alumina nanoparticles could be optimum for liquid crystal-based electrooptic devices.

Two Glass Transitions Associated to Different Dynamic Disorders in the Nematic Glassy State of a Non-Symmetric Liquid Crystal Dimer Dopped with g-Alumina Nanoparticles

“…Figure 2 shows the specific heat vs. temperature around the N-I phase transition for bulk CBO11O.Py and some of the confined samples. As expected, the dispersion of nanoparticles induces a downward shift in the N-I phase transition temperature together with a suppressed and rounded specific heat peak similar to what is found for other liquid crystals under confinement [ 26 , 28 , 29 , 30 , 31 ]. This effect can be translated to the other phase transitions (N g -N spc , Cr-N and Cr-I), but the depression in temperature is lesser.…”

“…Such a linear dependence is fitted to the relationship $1-\frac{T_{{\text{ρ}}_s}}{T_{\text{bulk}}}=A{\text{ρ}}_{\text{s}}$ where A = 0.078 cm 3 ·g −1 . This behavior differs substantially from that of the 4O.8 monomer confined via the dispersion of the same γ-alumina nanoparticles [26], in which the dependence was not linear. Such a difference could be explained by arguing that, since the CBO11O.Py molecule is larger and more flexible than the 4O.8 one, more dispersive material is needed to induce similar changes in the transition temperatures in the former with respect to the latter.…”

“…However, the arrangement of the molecules in cells undergoes some modifications when an electric field is applied. In addition, as recently published for a LC monomer confined via the dispersion of the same type of γ-alumina nanoparticles, undesired effects due to ionic charges in the cells are diminished for the confined systems with respect to the bulk compound [ 26 , 27 ].…”

“…To overcome such a difficulty, the LC dimer is confined by means of the dispersion of γ-alumina nanoparticles in different concentrations. The effect of such nanoparticles in calamitic LC monomers has been recently studied by some of the authors of this paper [ 26 ]. In the confined system, CBO11O.Py + γ-alumina, crystallization is partially suppressed: the N glassy state is accessible at slower cooling rates and it remains as such when heating up to temperatures above the one where crystallization takes place in bulk CBO11O.Py.…”

Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators

“…These inorganic materials can tolerate high temperatures and provide high reliability. Doping different types of nanoparticles (NPs), such as polyhedral oligomeric silsesquioxane (POSS) [ 19 , 20 ], alumina NPs [ 21 ], metallic NPs [ 22 , 23 , 24 ], and ionic surfactant [ 25 ] into an LC film can induce the microscopic alignment of LC molecules. Achieving LC alignment by dispersing NPs into LCs is an easier method than using conventional polymer layers.…”