Liquid crystal

LIQUID CRYSTALAND IT’S APPLICATION

PRESENTED BY:

ROLL NO. NAME OF STUDENT1413037 KSHITIJ PATIL1413040 VAIBHAV RAO1413052 RINKOO SINGH1413057 TANVI VISHWASRAW1413058 SOURABH WALVEKAR

PRESENTION MADE BY:1413055 SIDDESH VILAS PAWAR

GROUP MEMBERS:

ROLL NO NAME OF STUDENT

1413033 TEJUL PANDIT1413034 SHUBHAM PAREEK1413035 VISHAL

PATANGRAO1413036 RAHUL PATEL

ROLL NO. NAME OF STUDENT1413037 KSHITIJ PATIL1413038 TRISHALA P PAWAR1413039 VIPUL RAJDERKAR1413040 VAIBHAV RAO

ROLL NO. NAME OF STUDENT

1413041 BHUSHAN SABADRA

1413042 MEHUL SANYASHIV

GROUP MEMBERS:ROLL NO: NAME OF STUDENT 1413043 SIDDHESH SAWANT1413044 CHIRAG SHAH1413045 JANAVI SHAH1413046 NIRAV SHAH1413047 KUNJ SHAH1413048 YASH SHAH1413049 MOHAMED SHAYERWALA

ROLL NO: NAME OF STUDENT1413050 RUTVI SHETH1413051 ROHIT SHIVTHARE1413052 RINKOO SINGH1413053 AKASH SUMARIA1413054 MONISH THAKKAR1413055 SIDDESH PAWAR1413056 KRUNAL VANI

1413057

TANVI VISHWASRAW

1413058

SOURABH WALVEKAR

1413059

VAIBHAV YADAV

1413060

CHIRAG THAKKAR

1413061 RAKSHIT RATHOD1413062 SAPNA THAKKAR1413063 MANSI SHAH

DEFINITION

Liquid crystals (LCs) are matter in a state that has properties between those of conventional

liquid and those of solid crystal.

For instance, a liquid crystal may flow like a liquid, but its molecules may be oriented in a

crystal-like way

Also defined on..

There are many different types of liquid-crystal phases, which can be distinguished by their different optical properties (such as birefringence).

LIQUID CRYSTAL..

A state that occurs between a solid & a liquid

Possess properties characteristics of both liquids & crystalline solids

Also possess properties not found in either liquids or solids

May response to external perturbations & some changes colour with temperature

HISTORY• In 1888, Austrian botanical physiologist Friedrich Reinitzer, working at the Karl-Ferdinands-Universitat, examined the physico-chemical properties of various derivatives of cholesterol which now belong to the class of materials known as cholesteric liquid crystals.

• At 145.5 °C (293.9 °F) it melts into a cloudy liquid, and at 178.5 °C (353.3 °F) it melts again and the cloudy liquid becomes clear. The phenomenon is reversible.

HISTORY

Reinitzer had discovered and described three important features of cholesteric liquid crystals

1.THERMOTROPIC PHASE2.LYOTROPIC PHASE

3.METALLOTROPIC PHASE

THEY CAN BE DIVIDED INTO:

Thermotropic liquid crystals are divided as:

(Phase transition depends on temperature)

Nematic

Smectic

Cholesteric/ Chiral

Blue

Discotic

THERMOTROPIC

AS TEMPERATURE INCREASES...

▪ The first liquid crystal phase is the smectic A , where there is layer-like arrangement as well as translational and rotational motion of the molecules.

▪ A further increase in temperature leads to the nematic phase, where the molecules rapidly diffuse out of the initial lattice structure and from the layer-like arrangement as well.

▪ At the highest temperatures, the material becomes an isotropic liquid where the motion of the molecules changes yet again

1: NEMATIC

▪ Simplest form is a nematic liquid crystal

i.e. long-range orientational order but no positional order

▪ The preferred direction is known as director

NEMATIC

• Despite the high degree of orientational order, nematic phase as a whole is in disorder i.e. NO MACROSCOPIC ORDER (orientation within a group is similar but not from one group to another)

• Structure of nematic phase can be altered in a number of ways. E.g. electric or magnetic field or treatment of surfaces of the sample container

• Thus, possible to have microscopic order & macroscopic order

2: SMECTIC PHASES

• The smectic phases, which are found at lower temperatures than the nematic, form well-defined layers that can slide over one another in a manner similar to that of soap.

• The word "smectic" originates from the Latin word "smecticus", meaning cleaning, or having soap like properties.

• The smectics are thus positionally ordered along one direction.

• In the Smectic A phase, the molecules are oriented along the layer normal, while in the Smectic C phase they are tilted away from the layer normal.

SMECTIC PHASES

• SMECTIC phase occurs at temperature below nematic or cholesteric

• Molecules align themselves approx. parallel & tend to arrange in layers

• Not all positional order is destroyed when a crystal melts to form a smectic liquid crystal

• Chiral smectic C liquid crystals are useful in LCDS

3:CHIRAL PHASES

▪ THE CHIRAL NEMATIC PHASE EXHIBITS CHIRALITY (HANDEDNESS). THIS PHASE IS OFTEN CALLED THE CHOLESTERIC PHASE BECAUSE IT WAS FIRST OBSERVED FOR CHOLESTEROL DERIVATIVES

▪ ONLY CHIRAL MOLECULES (I.E., THOSE THAT HAVE NO INTERNAL PLANES OF SYMMETRY) CAN GIVE RISE TO SUCH A PHASE. THIS PHASE EXHIBITS A TWISTING OF THE MOLECULES PERPENDICULAR TO THE DIRECTOR, WITH THE MOLECULAR AXIS PARALLEL TO THE DIRECTOR.

CHIRAL PHASES

- In cholesteric phase, there is orientational order & no positional order, but, director is in helical order.

▪ The structure of cholesteric depends on the pitch, the distance over which the director makes one complete turn– one pitch - several hundred nanometers

▪ Pitch is affected by:-– temperature– pressure– electric & magnetic fields

4:BLUE PHASES

▪ Blue phases are liquid crystal phases that appear in the temperature range between a chiral nematic phase and an isotropic liquid phase.

▪ Blue phases have a regular three-dimensional cubic structure of defects with lattice periods of several hundred nanometers, and thus they exhibit selective Bragg reflections in the wavelength range of visible light corresponding to the cubic lattice.

4:BLUE PHASES• Although blue phases are of interest for fast light modulators or tunable photonic crystals, they exist in a very narrow temperature range, usually less than a few kelvin.

• Recently the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260–326 K) has been demonstrated

• Blue phases stabilized at room temperature allow electro-optical switching with response times of the order of 10−4 s.

liquid crystals are divided as:

2.LYOTROPIC LIQUID CRYSTAL

LYOTROPIC LIQUID CRYSTAL

• A lyotropic liquid crystal consists of two or more components that exhibit liquid-crystalline properties in certain concentration ranges.

• In the lyotropic phases, solvent molecules fill the space around the compounds to provide fluidity to the system.

• In contrast to thermotropic liquid crystals, these lyotropics have another degree of freedom of concentration that enables them to induce a variety of different phases.


• A compound that has two immiscible hydrophilic and hydrophobic parts within the same molecule is called an amphiphilic molecule.

• Many amphiphilic molecules show lyotropic liquid-crystalline phase sequences depending on the volume balances between the hydrophilic part and hydrophobic part.

• These structures are formed through the micro-phase segregation of two incompatible components on a nanometer scale.

• Soap is an everyday example of a lyotropic liquid crystal.


• A liquid crystalline material is called lyotropic if phases having long-ranged orientational order are induced by the addition of a solvent.

• Historically the term was used to describe materials composed of amphiphilic molecules.

• Such molecules comprise a water-loving 'hydrophilic' head-group (which may be ionic or non-ionic) attached to a water-hating 'hydrophobic' group.


• In principle, increasing the amphiphile concentration beyond the point where lamellar phases are formed would lead to the formation of the inverse topology lyotropic phases, namely the inverse cubic phases, the inverse hexagonal phase (HII) and the inverse micellar cubic phase.

• In practice inverse topology phases are more readily formed by amphiphiles that have at least two hyrocarbon chains attached to a headgroup.

• The most abundant phospholipids that are found in cell membranes of mammalian cells are examples of amphiphiles that readily form inverse topology lyotropic phases.

liquid crystals are divided as:

3.METALLOTROPIC LIQUID CRYSTAL

METALLOTROPIC LIQUID CRYSTAL

• Liquid crystal phases can also be based on low-melting inorganic phases like ZnCl2 that have a structure formed of linked tetrahedra and easily form glasses.

• The addition of long chain soap-like molecules leads to a series of new phases that show a variety of liquid crystalline behavior both as a function of the inorganic-organic composition ratio and of temperature. This class of materials has been named metallotropic.

METALLOTROPIC LIQUID CRYSTAL

Liquid crystals consist of anisotropic molecular units, and most are organic molecules.

Materials incorporating metals into anisotropic molecules, described as metallomesogens, have been prepared.

Achieving liquid-crystalline behaviour in inorganic fluids should be possible if the anisotropic structure can be retained or designed into the molten phase.

PROPERTIES OF LIQUID CRYSTAL

▪ Liquid crystal can flow like a liquid, due to loss of positional order

▪ Liquid crystal is optically birefringent, due to its orientation order

▪ Transition from crystalline solids to liquid crystals caused by a change of temperature – gives rise to thermotropic liquid crystals – substances that are most likely to form a liquid crystal phase at a certain temperature are molecules that are elongated & have some degree of rigidity.


▪ Liquid crystal phases are generally cloudy in appearance, which means that they scatter light in much the same way as colloids such as milk.▪ This light scattering is a consequence of fluctuating regions of non-uniformity as small groups of molecules form and disperse.

BIREFRINGENCE


BIREFRINGENCE• The anisotropy of liquid crystals causes them to exhibit birefringence. That is, light that enters

the crystal is broken up into two oppositely-polarized rays that travel at different velocities.

• Observation of a birefringent materal between crossed polarizing filters reveals striking patterns

and color effects.


THERMAL IMAGINGLiquid crystals, like all other kinds of matter, are subject to thermal expansion. expansion.

As the temperature rises, the average spacing between the aligned molecules of a nematic phase increases, thus causing the e-ray to be increasingly retarded with respect to the o-ray.

Inexpensive thermometers can be made by printing a succession of suitably formulated LC mixtures on a paper or plastic strip which is held in contact with the surface whose temperature is to be

TYPICAL CHEMICAL STRUCTURES

▪ cholesterol ester

▪ phenyl benzoates

▪ surfactants such as polyethylene-oxides, alkali soaps, ammonium salts, lecithin

▪ paraffin's

▪ glycolipids

▪ cellulose derivatives

OPTICAL RESPONSE

•Applied voltage changes tilt angle of nematic layers•Tilt Angle changes light transmission

•Abrupt tilt angle change with 270o twist•On/Off response faster•210o used for grayscale

•Nematic exists over larger range than either separate solution does

Temperature Range

ORDER PARAMETERThe description of liquid crystals involves an analysis of order.

A second rank symmetric traceless tensor order parameter is used to describe the orientational order of a nematic liquid crystal, although a scalar order parameter is usually sufficient to describe uniaxial nematic liquid crystals.

TYPICAL CHEMICAL STRUCTURES

▪ cholesterol ester

▪ phenyl benzoates

▪ surfactants such as polyethylene-oxides, alkali soaps, ammonium salts, lecithin

▪ paraffin's

▪ glycolipids

▪ cellulose derivatives

TYPICAL APPLICATIONS...

Many more....

MAKING IT HAPPEN

• LCD displays • dyes (cholesterics) • advanced materials (Kevlar) • membranes • temperature measurement (by changing colors)

• solvents for GC, NMR, reactions, etc.

• Drug delivery

LCD LAYERS...• A liquid-crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals.

• Liquid crystals do not emit light directly.

TWISTED NEMATIC LCD...

A super-twisted nematic display (STN) is a type of monochrome passive-matrix liquid crystal display (LCD).

Application of Liquid Crystal Technology to Telecommunication Devices

A dense wavelength division multiplexed (DWDM) optical network, as with any information network, requires switches to perform routing of the signals. DWDM networks pass several information channels along the same optical waveguide (optical fiber): each channel corresponds to a different wavelength of light with the wavelengths typically separated by less than a nanometer. Consequently DWDM networks require switches that are wavelength selective with very high resolution

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Liquid crystal