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Questions tagged [liquid-crystal]

Liquid crystals (LCs) are matter in a state that has properties between those of conventional liquid and those of solid crystal.

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How to call ellipse packing structures?

My research group and I are trying to figure out what is the correct terminology for two different packing structures of 2D ellipses. The two structures are displayed below as Structure A and ...
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Why my optical limiting behavior is Descending? (on input intensity- output intensitydiagram)

I measure some nonlinear optical materials and I know that output intensity respect to input intensity should be ascending like this diagram. but for me, for one of my materials, this diagram is ...
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What's the difference between Equivalence and Degeneracy?

I'm in a middle of an advanced stat-mech course, and we are now learning about liquid crystals (LC). In the last tutorial, we developed the Landau Free Energy of the LC system near the transition ...
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Non-linear corrections to the Oseen-Frank free energy density

A nematic liquid crystal is essentially a fluid of long, rod-like molecules whose average orientation is dictated by a vector field $\mathbf {\hat {n}} $. The so-called Frank-Oseen (free) energy (...
Daniel Castro's user avatar
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Transition from nematic phase to smectic phase in calamitic liquid crystals

I am a math student and not very good at physics. I am so confused when I read the paper about the mathematical problems in liquid crystals. My question is about the nematic phase and smectic phases. ...
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Persistence length by De Gennes: how to make sense of the definitional equation?

I want to understand how De Gennes comes up with the concept of persistence length in microemulsions, and in particular a convenient equation that relates this persistence length to the thickness of ...
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Why do LCD pixels at the very edges of the screen "disappear" when looking at a shallow angle?

I've noticed something curious about my LCD screens (one of them is a TUF VG32VQ1B and the other an AOC I2269VW, if it makes a difference): If I look at them at a shallow angle, any bright line of ...
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Help to identify physics behind Valve patent on "variable optical correction using spatially varying polarizers"

Apparently, there is a way to vary optical power by employing spatially varying polarizers. The patent is almost unreadable. My understanding is that they propose to stack spatially varying polarizers ...
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Do acoustic waves in liquid crystals have transverse modes?

According to a previous question: Modes of propagation in media acoustic waves in media can be decomposed in two kinds of modes: longitudinal and transverse; solids being the only one where they are ...
Elkin Montoya's user avatar
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Order parameter

Order parameter: Suppose, for simplicity, that the molecules composing a nematic or cholesteric liquid crystal are rigid and rodlike in shape. Then we can introduce a unit vector v") along the ...
Rasha rashed's user avatar
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How does this red liquid crystal display (LCD) work?

This Casio G-3110 has a passive display showing red when two black layers of what appears to be ordinary LCD overlap. How does this work? When tilted as in this photo the black layers do not fully ...
David Jonsson's user avatar
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Deforming a nematic line defect to a uniform configuration

In Nakahara section 4.9, "Defects in nematic liquid crystals", it is discussed that the order parameter for a nematic should be the real projective plane $\mathbb{R}P^2$, which has ...
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Bond Orientational Correlation Function

Firs this question has some similarity with Bond order correlation function and Bond Orientational Correlation Function - how exactly to calculate but its a little bit different , so having those ...
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Thermal hysteresis and its physical significance in lipid membranes?

We usually associate the phenomenon of hysteresis with memory in the system. For example, magnetic hysteresis is the basis of hard disks(if I recall it correctly). There are also electronic circuits(...
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Liquid crystals resource recommendation

I'm going to work with liquid crystals during my summer internship and I am so woefully unprepared. Could you please recommend me some book or some review articles that cover the essential concepts ...
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Bond order correlation function

I am trying to compute the bond order correlation function, $g_6$. It is defined based on the bond order parameter: $$\psi_6(x_i) = \frac{1}{N_i}\sum_{i=1}^{N_i}{\exp(i6\theta_i^j)}$$ where $\theta_i^...
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Are the curvature Frank elastic constants of the liquid crystal the no-zero elements of the 6x6 elastic (stiffness) matrix?

I was reading Landau's book on elasticity theory, and it raised this doubt. Can anyone help me?
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How can I deduce the magnetic susceptibility tensor of a biaxial liquid crystal in its nematic phase?

I know from de Gennes' book [1] that the (magnetic) susceptibility tensor $\chi_{\alpha\beta}$ of an uniaxial liquid crystal in its nematic phase can be written as \begin{align} \chi_{\alpha\beta}&...
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What it means to be that liquid crystals are thermodynamically stable?

When we heat some solids, they don't pass into liquid state directly. Rather they form a mesomorphic phase called liquid crystals.Now when we heat liquid crystal, they are converted into pure liquids. ...
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Defect in liquid crystals

What are +1 and -1 topological defects in liquid crystal ? What are 1/2 and -1/2 topological defects in liquid crystals ? I put a lot of time to search for it but I could not find an easy ...
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Generating X-ray diffraction patterns from atomic coordinates

I have a list of atomic coordinates for a periodic system as a result of a molecular dynamics simulation. I want to use those coordinates and predict what it's 1D diffraction pattern looks like. The ...
Ben Coscia's user avatar
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What is Landau-de Gennes Expansion?

I am an undergraduate student in an introduction to condensed matter physics course and I am struggling to understand the process of Landau expansion of order parameter S as it relates to liquid ...
goat1123's user avatar
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LCD's working principle [closed]

In the image's information it says ''Liquid crystal device windows are in the group of electrically activated smart windows in which normal "off" condition of the glazing is a translucent milky white. ...
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3 answers
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Why we use liquid crystals in LCDs?

Does anyone know why do we use Liquid crystals in LCD's.Why can't we use transistors to switch light on/off instead of using polarizing filters to change pixels light/dark.Is there any specific reason ...
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What is the viscosity difference between a solid and a liquid

The pitch drop experiment, for example, shows bitumen as a liquid, even though it appears to be a solid, and then there is the "glass: solid or liquid" debate. Is there a numerical value in viscosity ...
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Deformation in the nematic phase of a liquid crystal survived in solid state

Does anyone know if I cool a liquid crystal with a deformed nematic phase quickly it will preserve the deformation in the crystal lattice? I didn't never see that in classical books on liquid crystals....
Caetes's user avatar
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Full time derivative of the Frank-Oseen energy. Mathematical problem

I am studying liquid crystal theory with the book Kleman, Lavrentovich, Soft Matter Physics. In the Ericksen-Leslie theory, Frank-Oseen energy density is: $$ f=0.5*(K_1*div^2 (n)+K_2 *(n*curl(n))^2+...
Mikhail Genkin's user avatar
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Why use class multiplication to describe topological entangling and merging?

I'm studying some references about topological defects in ordered media like Soft matter physics: An introduction by Kleman and the Review modern physics paper The topological theory of defects in ...
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1 answer
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Equivalent tensor order parameters of nematic liquid crystals?

I found in the literatures two different definitions of the tensor order parameter of nematic liquid crystals. One is $$ Q_{ij}=\frac{S}{2}(3n_{i}n_{j}-\delta_{ij}), $$ where $S$ is the scalar order ...
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How to calculate excluded volume in Onsager's hard-rod model?

Can somebody please provide a derivation of how to calculate excluded volume of two rods with angle of intersection being $\gamma$. rods are cylinders, capped with semi-spheres. Onsager theory of hard ...
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Is the $2\pi$ disclination topologically stable for a 2d nematic liquid crystal?

For a three dimensional liquid crystal, a $2\pi$ or charge $1$ disclination is topologically unstable. The is generally explained as the disclination can lose its core singularity by "escaping from ...
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Difference between various theories of liquid crystals

Can somebody explain as to what is the difference between various theories of liquid crystals? Maier-Saupe Theory Onsager Theory Landau theory What's the advantages and disadvantages or limitations ...
nitin's user avatar
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Molecular field meaning in Liquid Crystal Theory

Given the Frank-De Gennes free energy $F = \int f(\boldsymbol{p},\nabla\boldsymbol{p}, ...)\ d\boldsymbol{x},$ for liquid crystals (see De Gennes-Prost, p. 107, formula 3.21), the vector $$h_{i}=-\...
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What is the difference between emission wavelength and lasing wavelength?

I'm reading an article on liquid crystal lasers and they're saying periodicity determines lasing wavelength and cavity geometry determines emission wavelength. What is the difference?
user136128's user avatar
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Does the Night Mode of the screen display (LCD) save more energy? [closed]

In some cases, we can enable the Night Mode (reversing the bright and dark color of the display; such as White Text, Black Background) for the screen display. LCD(Liquid-crystal display) seems to be ...
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