| abstract |
A device composed of (1) a color changing indicator, (2) an optional polymeric binder, preferably having gel forming capability, and (3) an activator solvent system which induces a color change in the indicator when device is frozen, in the region of about 0 to −30° C. An example of the device is an indicator of a fine dispersion of partially polymerized diacetylene of the formula: R—C≡C—C≡C—R, where R is a substituent group, e.g., 4BCMU where R═—(CH 2 )OCONHCH 2 COO(CH 2 ) 4 H, dispersed in a mixture of solvents, e.g., 96:4 water:ED (ethylene glycol diacetate), with or without a polymeric binder. When the temperature of the device is lowered to the freezing point of water, the activator solvent phase separates out of the mixture and induces a color change in the indicator. The device can undergo an irreversible color change, e.g., from blue to red, when the activator mixture is frozen in the region of about 0 to −30° C. The device made from the above system can be used as a freeze indicator for monitoring the undesirable freezing of materials, such as emulsions, latex paints, produce foods, flowers, sea foods, and vaccines which require freeze monitoring. |