Characteristics of Domains Appearing in Nematic Liquid Crystals Below the Threshold Voltage of Chevrons

Nasta, L.; Lupu, A.; Giurgea, M.

doi:10.1080/00268948108072718

Cited by 18 publications

(5 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This would mean that either the primary bifurcation becomes subcritical, which is not expected from theory, or there is a ("hidden") bifurcation leading to an inhomogeneous state already below the dielectric instability. According to some older measurements the possibility of a first transition to a state with "wide domains" (with width ∼ d) appears to exist [25][26][27]18], but this phenomenon has not been cleared up. In any case this cannot be the general explanation.…”

Section: Discussionmentioning

confidence: 99%

Pattern formation from defect chaos — a theory of chevrons

Rossberg

Kramer

1998

Physica D: Nonlinear Phenomena

View full text Add to dashboard Cite

For over 25 years it is known that the roll structure of electroconvection (EC) in the dielectric regime in planarly aligned nematic liquid crystals has, after a transition to defect chaos, the tendency to form chevron structures. We show, with the help of a coarse-grained model, that this effect can generally be expected for systems with spontaneously broken isotropy, that is lifted by a small external perturbation. The linearized model as well as a nonlinear extension are compared to simulations of a system of coupled amplitude equations which generate chevrons out of defect chaos. The mechanism of chevron formation is similar to the development of Turing patterns in reaction diffusion systems.

show abstract

Section: Discussionmentioning

confidence: 99%

Pattern formation from defect chaos — a theory of chevrons

Rossberg

Kramer

1998

Physica D: Nonlinear Phenomena

View full text Add to dashboard Cite

show abstract

“…The calamitic nematics mentioned above occasionally exhibit a third type of morphology at onset: the 'prewavy' pattern (also called wide domains) [11][12][13][14][15][16][17]. It manifests itself in stripes much wider than d (q c < π/d) and with q c n. In contrast to 'conductive' or 'dielectric' NR, however, the 'prewavy' pattern is only visible with crossed polarisers.…”

Section: Introductionmentioning

confidence: 99%

Electroconvection in nematic mixtures of bent-core and calamitic molecules

et al. 2009

View full text Add to dashboard Cite

The onset of electroconvection in binary mixtures of a bent-core and a rodlike nematic has been characterized by measuring the threshold voltage U(c) and the critical wave number of the pattern in a wide range of frequencies f. In the mixtures rich in bent-core molecules, a "conductive-prewavy2-patternless-prewavy1" morphological sequence has been detected with an unusual negative slope of U(c)(f) at high frequencies. This latter scenario seems to be related to the bent-core component, as it disappears with increasing the concentration of rodlike molecules. In addition, one of the parameters most relevant for electroconvection, the electrical conductivity, has also been varied by ionic salt doping. It has been found that the above effect of the banana-shaped molecules on the electroconvection scenarios can be suppressed by the conductivity.

show abstract

“…Focusing on the in-plane (= ĉ) director field, the modulations occur along the direction of prealignment of the in-plane director (from this point of view they give rise to "bend" distortions). In fact, there is a long history of observations of such modulated states under an electric field in highly-doped MBBA [29,30,31,32] and other nematic materials [33,34] at high frequency, often without detectable convection rolls. They come under the name of "wide domains" [29,30,33] or "prechevrons" [31,32].…”

Section: Discussionmentioning

confidence: 99%

“…In fact, there is a long history of observations of such modulated states under an electric field in highly-doped MBBA [29,30,31,32] and other nematic materials [33,34] at high frequency, often without detectable convection rolls. They come under the name of "wide domains" [29,30,33] or "prechevrons" [31,32]. Since such structures cannot be explained purely statically, it seems reasonable to assume that they are secondary structures of the type discussed here.…”

Section: Discussionmentioning

confidence: 99%

Modulated structures in electroconvection in nematic liquid crystals

2003

View full text Add to dashboard Cite

Motivated by experiments in electroconvection in nematic liquid crystals with homeotropic alignment we study the coupled amplitude equations describing the formation of a stationary roll pattern in the presence of a weakly damped mode that breaks isotropy. The equations can be generalized to describe the planarly aligned case if the orienting effect of the boundaries is small, which can be achieved by a destabilizing magnetic field. The slow mode represents the in-plane director at the center of the cell. The simplest uniform states are normal rolls, which may undergo a pitchfork bifurcation to abnormal rolls with a misaligned in-plane director. We present a new class of defect-free solutions with spatial modulations perpendicular to the rolls. In a parameter range where the zigzag instability is not relevant these solutions are stable attractors, as observed in experiments. We also present two-dimensionally modulated states with and without defects which result from the destabilization of the one-dimensionally modulated structures. Finally, for no (or very small) damping, and away from the rotationally symmetric case, we find static chevrons made up of a periodic arrangement of defect chains (or bands of defects) separating homogeneous regions of oblique rolls with very small amplitude. These states may provide a model for a class of poorly understood stationary structures observed in various highly conducting materials ("prechevrons" or "broad domains").

show abstract

Characteristics of Domains Appearing in Nematic Liquid Crystals Below the Threshold Voltage of Chevrons

Cited by 18 publications

References 5 publications

Pattern formation from defect chaos — a theory of chevrons

Pattern formation from defect chaos — a theory of chevrons

Electroconvection in nematic mixtures of bent-core and calamitic molecules

Modulated structures in electroconvection in nematic liquid crystals

Contact Info

Product

Resources

About