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.
Highlights
The importance of liquid crystals in the field of materials science is enormous, from theoretical and experimental reasons and, from the point of view of applications
The results presented in this manuscript, all for bulk and confined samples, are addressed in two parts, one for each of the studied properties: (1) We start with the calorimetric data, in which we can observe the deep depression in phase transition temperatures and the change in the shape of the heat capacity (Cp) peaks in the confined samples
In order to check the influence of the random confinement on the analysed physical properties of the 4O.8 compound, we have prepared ten different samples: one bulk 4O.8 sample, seven more with different concentrations of γ-alumina nanoparticles
Summary
The importance of liquid crystals in the field of materials science is enormous, from theoretical and experimental reasons and, from the point of view of applications. The fluidity of mesophases like the nematic (N) or smectic A (SmA) phases, among others, makes the molecules of the liquid crystal likely to orient ad lib by the application of small perturbations to the material (in form of electric or magnetic fields, simple chemical surfactants...). The results presented in this manuscript, all for bulk and confined samples, are addressed in two parts, one for each of the studied properties: (1) We start with the calorimetric data, in which we can observe the deep depression in phase transition temperatures and the change in the shape of the heat capacity (Cp) peaks in the confined samples Both effects are higher as the concentration of nanoparticles in the liquid crystal increases. A comparison between dispersions of γ-alumina and Aerosil nanoparticles is performed; (2) The behavior of the static and the complex dielectric permittivities, which allow us to interpret the molecular dynamics, is presented and discussed
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