Liquid Crystal

LIQUID CRYSTAL

Solid Liquid crystal “fourth state of matter”

Liquid Gas

Images: MacDonald, R. “Liquid Crystals Fascinating State of Matter or "Soft is beautiful". Accessed 7-2006

What is a Liquid Crystal? Liquid Crystal – a stable phase of matter characterized by anisotropic properties without the existence of a 3-dimensional crystal lattice – generally lying between the solid and

INTRODUCTION • Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal.

• liquid crystal (LC) may flow like a liquid, but have the molecules in the liquid arranged and/or oriented in a crystal-like

INTRODUCTION • Liquid crystals can be considered to be crystals which have lost some or all of their positional order, while maintaining full orientational order. • Liquid crystals retain many of the optical qualities -- such as the ability to bend light and change its color

Unique Properties of Liquid Crystals The orientation of Liquid Crystals can be affected by… • Pressure • Temperature • Electrical Field

S. Palmer, LCTec Displays, Inc. 2005

• A liquid crystal (LC) is thermotropic if the order of its components is determined or changed by temperature. • If temperature is too high, the rise in energy and therefore in motion of the components will induce a phase change: the LC will become an isotropic liquid. • on the contrary, temperature is too low to support a thermotropic phase, the LC will become a crystal.

Liquid Crystal Phases There are 2 basic phases

Nematic

&

Smectic

Anisotrpic substances may go through one or several Images from Sheffield Hallum University, United

Liquid crystal phases

When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have a distinct texture The various LC phases (called mesophases) can be characterized by the type of ordering that is present

Nematic Liquid Crystals One of the most common LC phases is the nematic, where the molecules have no positional order, but they do have long-range orientational order. Nematics are polarizable rod-like organic molecules on the order of 20 Angstroms in length.

Smectic Liquid Crystals • Smectic Liquid crystals are different from nematics in that they have one more degree of orientational order than do the nematics. • Smectics generally form layers within which there is a loss of positional order, while orientational order is still preserved.

Smectic Liquid Crystals • There are several different categories to describe smectics. • Smectic A, in which the molecules align perpendicular to the layer planes. • Smectic C, where the alignment of the molecules is at some arbitrary angle to the normal.

Historical overview • Liquid crystal materials were first discovered in 1888 by an Austrian botanist, F. Renitzer. • The first room-temperature nematic liquid crystal was observed in the late 1960s. Unfortunately this crystal had quite a short temperature range as it was affected by impurities. • The major breakthrough came when

Historical overview • The ferroelectric chital smecic (FLC) phase was discovered in 1975 and proved to have a unique form of ferroelectricity. • During the 1970s and 1980s several liquid crystal compounds and phases were discovered, primarily by the industry, but also in several research programs on liquid crystal materials in colleges and universities around the world.

Applications of liquid crystals • Liquid crystals find wide use in liquid crystal displays, which rely on the optical properties of certain liquid crystalline molecules in the presence or absence of an electric field. • A liquid crystal display is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector.

Liquid Crystal Display • Liquid crystal sandwiched between two transparent layers form images.

Polarizer Color filter Color filter glass

Liquid Crystal

Glass polarizer

Backlight © 2007 Prentice-Hall, Inc.

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APPLICATION OF LIQUID • LCDs are found in wrist-watches, calculators, portable computes and various other devices where a low-power display is needed.

Liquid Crystal Display

Applications of liquid crystals • Liquid crystal in fluid form is used to detect electrically generated hot spots for failure analysis in the semiconductor industry. • Liquid crystal memory units with extensive capacity were used in Space Shuttle navigation equipment.

APPLICATION OF LIQUID CRYSTAL • Thermotropic chiral LCs whose pitch varies strongly with temperature can be used as crude thermometers. • liquid crystal displays with wider viewing angles, and displays that can remain in use for years without the need of power.

Suppliers and Markets • Most of this research is situated in Japan due to strong manufacturing capability and high research funds. The most frequently used liquid crystalline phase used today in display devices is the nematic phase. • About 50 % of all nematic materials supplied by Merck-Japan, which is the biggest producer of such materials, goes to these applications.

Suppliers and Markets • The Merck group, which consists of E. Merck Darmstadt, Merck-Japan, Ltd., and Merck Ltd., Poole, holds early patents and is a major supplier (50% worldwide) of nematic liquid crystal materials.

• Their sales breakdown is as follows: 70% to Japan, 25-30% to Southeast Asia, and 12% each to Europe and the United States.

Suppliers and Markets • The joint venture RODIC claims 30% of the liquid crystal material market in Japan. Hoffman-LaRoche in Basel, Switzerland, supplies Southeast Asia, the United States, and Europe

"When it's on, it has focusing power and can be used like reading glasses, and when it's off, it's just like clear glass."

• Because lenses made with nematic liquid crystals can easily change their focusing power, optics researchers have eagerly eyed them as potential replacements for multifocal lenses. But these efforts have been hamstrung by slow response times associated with the relatively thick layers of liquid crystal required. • The lens design features a liquid-crystal layer sandwiched between two thin sheets of glass. Tiny electrodes photolithographically patterned onto the

• You probably use items containing an LCD (liquid crystal display) every day. - They are all around us -- in laptop computers, digital clocks and watches, microwave ovens, CD players and many other electronic devices. - LCDs are common because they offer some real advantages over other display technologies. They are thinner and lighter and draw much less power.

"When it's on, it has focusing power and can be used like reading glasses, and when it's off, it's just like clear glass."

Isotropic Liquids and gases (uniform properties in all directions).

vs.

Anisotropic Liquid Crystals have orientational order

LCD Alignment Natural state

Sharp Technologies,

When coming into contact with a finely grooved surface (alignment layer), LC molecules line up parallel along groove due to their rod-like shape. Coating ITO glass with a layer of PVA and rubbing repeatedly creates these grooves.

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recent applications involve switchable windows that can be changed from clear and opaque with the flip of a switch, liquid crystal displays with wider viewing angles, and displays that can remain in use for years without the need of power.

DEFINITION Normally, we consider matter to have three distinct states: solid, liquid, and gas. However, there are states of matter which do not meet the necessary requirements of any of these three categories. For example, a substances such as mayonnaise is somewhere between a liquid and a solid.

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Liquid crystals are also not quite liquid and not quite solid. Physically, they are observed to flow like liquids, but they have some properties of crystalline solids. Liquid crystals can be considered to be crystals which have lost some or all of their positional order, while maintaining full orientational order. For example, imagine a large number of toothpicks put into a rectangular box and shaken. When you open the box, the toothpicks will be facing in about the same direction, but will have no definite spatial organization. They are free to move, but like to line up in about the same direction. This is a primitive model for nematic liquid crystals. Nematic Liquid Crystals

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Nematics are polarizable rod-like organic molecules on the order of 20 Angstroms in length. Because of their tendency to organize themselves in a parallel fashion, they demonstrate interesting and useful optical properties; the digital watch you used to wear back in the 80's functioned using nematic liquid crystals. Today, many more useful and interesting properties of nematics are known and exploited. Smectic Liquid Crystals

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Smectic Liquid crystals are different from nematics in that they have one more degree of orientational order than do the nematics. Smectics generally form layers within which there is a loss of positional order, while orientational order is still preserved. There are several different categories to describe smectics. The two best known of these are Smectic A, in

• ANALOGY f molecules can be compared to soldiers, then the solid state would be the soldiers standing at attention (facing the same direction and frozen in position), the liquid crystal state would be the soldiers marching in formation (all in the same direction, but free to move), and the liquid state would be the soldiers wandering around at a carnival (free to move around at

New type of thermometer r made which change clr by A liquid crystal (LC) is thermotropic if the order of its components is determined or changed by temperature. If temperature is too high, the rise in energy and therefore in motion of the components will induce a phase change: the LC will become an isotropic liquid. If, on the contrary, temperature is too low to support a thermotropic phase, the LC will become a crystal. There is therefore a range of temperatures at which we observe thermotropic LCs; and most of these have several "subphases" (nematic,

• Liquid crystals retain many of the optical qualities -such as the ability to bend light and change its color -as their more stationary solid crystal counterparts, but they also have the added advantage of a liquid's mobility, so they are easily moved around in an electric field. The combination of these qualities can make liquid crystals change colors when heated, important for such devices as thermometers, or can allow light through the liquid crystal when electricity is applied, creating things like liquid crystal displays, or LCDs. In a standard application, such as a computer screen, the surface is coated with a long-chain molecule, and then rubbed with cloth so that the crystals will face a preferred direction. Rubbing introduces all kinds of imperfections, such as scratches, dust, and static, but it has been very successful at allowing alignment of liquid crystals over

• envisions someday having a blood test based on liquid crystals: for example, a glass plate coated with antibodies to viral proteins. A blood sample could be spread on it, then a layer of liquid crystals; if the blood had proteins in it, it would transmit light differently than if there were not proteins, and this could be immediately apparent to the naked eye.

liquid crystals is in electrooptic devices. These are • Many liquid crystals are simple polymeric organic compounds. We tend to think of polymers as flexible (polythenes etc.) so for liquid crystals the polymers have to incorporate a rigid section, either in the long polymer section (main chain liquid crystals) or attached to the polymer as a 'side chain'. But the basic elements involved are simply C, H, N, O (for example) - so that's what they're made of!

liquid crystals is in electro-optic devices. These are electrically controlled devices that modulate light in a desired way

• In a solid the dipoles are too tightly bound to be easily reoriented by an electric field. In a normal liquid the thermal motion of the molecules normally overcomes the tendency for the dipoles to orient. In a polar liquid crystal, on the other hand, we find just the right combination of order and flexibility to make the dipoles follow the sign of the field. Because the dipoles have a fixed sterical relation to the director, the field will turn the optic axis. This can be used to control the way the optic axis points, or to unwind the helical structure of a chiral tilted smectic phase. Polar liquid