Electroconvection in nematic liquid crystals via nanoparticle doping

Abstract

It is known that a small fraction of nanoparticles dispersed in a liquid crystal can alter the electrooptic response, completely. The present study on gold nanoparticles dispersed in 5-n-heptyl-2-(4-n-octyloxy-phenyl)-pyrimidine shows that the contrast inversion observed earlier is initiated by a change from parallel to homeotropic anchoring, thereby causing an instability, which in turn leads to the appearance of convection rolls. After rapid cooling from the isotropic phase, the nanoparticle dispersion shows a regular field-induced Fréedericksz transition, like the pure liquid crystal. The electrohydrodynamic instability is presumably an example for the behavior of (+, -) systems that was predicted by de Gennes, and only recently observed experimentally for the first time.

Nanocomposites of a nematic liquid crystal doped with magic-sized CdSe quantum dots

“…Future work will now address the role of electroconvection (or perhaps surface polarization effects 39 ) as described in previous work from our groups using Au NPs in the same N-LC host. 29,37 Finally, images obtained from FCPM studies (x-y scans) confirm the director field in the birefringent stripes, 36 prove homeotropic alignment in the surrounding domains, show that these magic-sized QDs are reasonably well dispersed in the nematic host, and finally that some domains show more significant QD aggregation than others.…”

“…convection rolls or Kapustin-Williams domains), 26,28,29 we here present new, detailed data from optical (textures and defects), electro-optic as well as alignment studies using magic-sized QDs with very low polydispersity index as dopants in the N-LC host LC1 (frequently used in earlier studies). To demonstrate effects of small changes in QD surface disorder or the QD surface composition on the optical, electro-optic and alignment properties of LC1, we selected three CdSe QDs with QD1 30 and QD2…”

Fast algorithms for liquid crystal modelling

“…Here we find that the homogenized equations include the additional effect of the inclusions into the drift along the invariant manifold. By substituting the expanded fields (25) into the governing equations (23) and (24) and solving at each order in η h we obtain the following results. The homogenized equations are…”

“…22 In these cases the liquid crystal alignment is dominated by elastic and electrostatic forces with the dopants acting to alter rather than dominate the properties of the liquid crystal. Their effect, however, can be significant [23][24][25] and may lead to applications related to plasmon tuning in self-assembled structures 26,27 or tunable metamaterials. 28 The existence of an invariant manifold for the Q-tensor equations in the absence of defects can also be used to model in a computationally efficient way nematic liquid crystals doped with nanoparticles.…”

Hydrophobic gold nanoparticles via silane conjugation: chemically and thermally robust nanoparticles as dopants for nematic liquid crystals

“…Based on protocols for investigating NP-doped nematic LCs established in our laboratory [38], we tested seven different concentrations of the silanized Au NPs in Felix-2900-03 (LC1) from 0.25 to 7.5 wt% covering an extended range from low to high NP loadings. Our group has used the same nematic LC for several studies in the past [38,[56][57][58], which will allow us to compare current with prior test results later. Following the sample preparation protocol outlined in §4 provided the first visual clues that these silanized NPs are able to form stable suspensions in nematic solvents such as LC1.…”