CdSe nanoparticles dispersed in ferroelectric smectic liquid crystals: Effects upon the smectic order and the smectic-Ato chiral smectic-Cphase transition

Abstract

Spherical CdSe nanoparticles, surface-treated with oleylamine and tri-octylphosphine, dispersed in ferroelectric liquid crystals, can efficiently target disclination lines, substantially altering the macroscopic properties of the host compound. Here we present an ac calorimetry and x-ray diffraction study demonstrating that for a large range of nanoparticle concentrations the smectic-A layer thickness increases monotonically. This provides evidence for enhanced accumulation of nanoparticles at the smectic layers. Our results for the Smectic-A (SmA) to chiral smectic-C (SmC) phase transition of the liquid crystal S-(+)4-(2'-methylbutyl)phenyl-4'-n-octylbiphenyl-4-carboxylate (CE8) reveal that the character of the transition is profoundly changed as a function of the nanoparticle concentration. Large transition temperature shifts are recorded. Moreover, the heat-capacity peaks exhibit a crossover trend to a step-like anomaly. This behavior may be linked to the weakening of the SmA and SmC order parameter coupling responsible for the observed near-tricritical, mean-field character of the transition in bulk CE8. At lower temperatures, the presence of nanoparticles disrupts the phase sequence involving the tilted hexatic phases most likely by obstructing the establishment of long-range bond-orientational order.

Effect of CdSe quantum dots doping on the switching time, localised electric field and dielectric parameters of ferroelectric liquid crystal

“…Compared to the literature, our findings with respect to the unchanged SmA*-SmC* phase transition temperature under heating and cooling for the nondoped and doped FLC mixture are in line with the QD/FLC (FELIX 16/100) nanocolloids presented in [22] while reduction in phase transition under cooling has been reported by the use of FLCs based on single molecules DOBAMBC and CE8, respectively, for CdSe QDs-nanocolloids. [18,21] Substantial reduction of τ with QDs doping could be explained considering the modulation of localised electric field E ! loc asẼ loc 1 E ext þẼ dep þẼ ion (whereẼ ext ,Ẽ dep andẼ ion represent external, depolarised and ionic electric field, respectively).…”

“…[21] It was reported that under cooling, SmA*-SmC* phase transition temperature decreases as more as larger the amount of dispersed CdSe is. SmA* and SmC* phase ranges became narrow in the same sequence.…”

“…[18,21] In our former electrooptical and dielectric experiments on FLC nanocolloids, [22,23] FLC mixtures derived from SmC-phenylpyrimidines and a chiral non-LC terphenyl compound were used, which show, under heating and cooling, only slight shift of 1-2°C in SmC*-SmA* phase transition for the nondoped FLC mixture and for the FLC-nanocolloids. We decided to perform electrooptical and dielectric studies of our FLC-CdSe QDs-nanocolloids.…”

“…We decided to perform electrooptical and dielectric studies of our FLC-CdSe QDs-nanocolloids. Moreover, higher doping concentration was used in DOBAMBC-CdSe QDs (1 wt%) [18] and CdSe QDs/FLC (FELIX 16/ 100) (1 and 2 wt%), [21] and authors also described the possibility of the agglomeration of the dopant which could produce adverse effect on the electrooptical and dielectric properties. Keeping these views in mind, we decided that it is worth to perform a systematic study with very low doping concentration 0.05 wt% to higher concentration 1.0 wt% of CdSe QDs and analyse its effect on phase transition, electrooptical and dielectric parameters of FLC.…”

Formation of periodic domains and change in physical properties of paramagnetic copper doped ZnO nanoparticle dispersed ferroelectric liquid crystal system

“…During the last decade, the incorporation of various NPs in the FLC material, with different concentrations, is a noble approach for altering the properties of pristine FLC. In addition to this, NP driven vertical alignment by polymeric NPs and effect on the smectic ordering and phase transition temperature with the help of CdSe NPs has also been reported for the better understanding of the guest-host interaction in the NP-FLC composites [16][17][18]. Dispersion of NPs in the FLC matrix perturbs the FLC geometry because of the larger size of NPs as compared to FLC molecular dimension.…”