T H E R M O C H R O M I C . L I Q U I D . C H R Y S T A L S

LCR Hallcrest
1820 Pickwick Lane
Glenview, IL 60026

http://www.davisliquidcrystals.com/
info@hallcrest.com
847.998.8580

Pressure Chemical Co.
3419 Smallman Street
Pittsburgh, PA 15201

http://www.presschem.com/kits.htm
1.800.722.5247


Liquid crystals are chemical compounds and mixtures that exhibit the mechanical properties of liquids and the optical characteristics of solids. Liquid crystals that change color with changes in temperature are known as thermochromic liquid crystals (TLCs). Their scientific name is cholesteric liquid crystals.

The cholesteric (also known as chiral nematic) liquid crystal phase consists of molecules in a helical structure, containing a chiral (non-symmetrical) center, which produces intermolecular forces that favor alignment between molecules at a slight angle to one another.

This leads to the formation of a structure that can be visualized as a stack of very thin 2-D nematic-like layers with the director in each layer twisted with respect to those above and below. The variation of the director axis tends to be periodic in nature. The period of this variation (the distance over which a full rotation of 360° is completed) is known as the pitch, p. The pitch is varying with temperature and it can also be affected by the boundary conditions when the chiral nematic liquid crystal is sandwiched between two substrate planes.

Commonly used in LCD displays (example: alarm clock)

Layer #3 = Twisted nematic liquid crystals.

Feverscan, by LCR Hallcrest

FeverScan products utilize thermo chromic liquid crystal (TLS) technology for the measurement of clinical temperature trends in the healthcare environment. Liquid crystals are chemical compounds and mixtures that exhibit the mechanical properties of liquids and the optical characteristics of solids. FeverScan thermometers are composed of a series of discrete temperature events, each event shows a green color as the indicated temperature is attained.