Liquid crystal compositions and devices
AssigneeBecton, Dickinson and Company
InventorJames L. Fergason
Life of this patent
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Abstract
The disclosure is of a method of modifying the hysteretic behavior of liquid crystal compounds. The method is based on the discovery that there is a relationship between the hysteretic phenomena exhibited by liquid crystals and the viscosity of the composition including the liquid crystals. The disclosure is also of manufacturing methods (devices and compositions) which exploit the discovery.
Claims32
A temperature indicating composition, which comprises;
- in homogeneous admixture
- (a) an optically active liquid crystal compound characterized in part by an intrinsic left-handed helical structure;
- and
- (b) a liquid crystal compound selected from those having an intrinsic right-handed helical structure, nematic liquid crystals and mixtures thereof;
- the proportions of (a) and (b) being such as to provide said composition with a cholesteric-to-liquid transition point, a twisting power such that the resulting composition will selectively scatter visible light below said liquid transition point;
- and a liquid viscosity of from about 20 to 6500 poise at the liquid transition point temperature.
A method of increasing the hysteretic recovery time of a liquid crystal compound having a cholesteric-to-liquid transition point and which selectively scatters visible light below said transition point but ceases to scatter visible light above the transition point, which comprises;
- homogenously admixing with said compound a proportion of a liquid crystal having a liquid viscosity of about 25 to 6500 poise, said proportion being sufficient to achieve a liquid viscosity in the admixed composition of about 20 to 6500 poise at the cholesteric-to-liquid transition point of the composition.
A process for inhibiting the growth of domains in the isotropic liquid state of a cholesteric-to-liquid crystal composition, which comprises;
- adjusting the viscosity of said liquid state composition to about 20 to 6500 poise while retaining the twisting power of the cholesteric liquid crystal composition to selectively scatter visible light below the cholesteric-to-liquid transition point.
An improved temperature recording device, which comprises;
- an opaque support member;
- a cholesteric liquid crystal composition disposed on said support member, said composition comprising a mixture of
- (a) an optically active liquid crystal compound characterized in part by an intrinsic left-handed helical structure and a liquid viscosity of between about 25 poise and 6500 poise;
- and
- (b) a liquid crystal compound selected from those having an intrinsic right-handed helical structure, nematic liquid crystals and mixtures thereof;
- the proportions of (a) and (b) being such as to provide said composition with a cholesteric-to-liquid transition point, a twisting power such that the resulting composition will selectively scatter visible light below said liquid transition point, and will cease to scatter visible light above said cholesteric-to-liquid transition point;
- and a liquid viscosity of from about 20 to 6500 poise at the liquid transition point temperature.
A temperature indicating cholesteric liquid crystal composition, which comprises;
- an optionally active liquid crystal composition characterized by an intrinsic helical structure such as to provide a clearing point for the composition within the range of from about 10.degree. to about 70.degree. C. and a twisting power whereby the composition will selectively scatter visible light at a temperature below the clearing point, said composition having a viscosity of from 20 to 6500 poise at the clearing point temperature.
Dependencies are inferred from the claim text.