Thermochromic temperature sensor

A temperature sensor, comprising:

• a reversible thermochromic color-changing system comprising:
• a dye;
• a developer;
• and
• a solvent;
• wherein upon exposure to a preselected temperature threshold, association or disassociation of said dye and said developer results in a visible color change;
• wherein said color-changing system comprises a color-memory property which facilitates retention of said color change to record said exposure to said temperature threshold;
• and
• wherein said solvent comprises a mixture of (i) one ester having Formula I and a first R group and another said ester having Formula I and a second R group which is different from said first R group, (ii) one said ester having Formula III and another said ester having Formula IV, or (iii) one said ester having Formula VII and another said ester having Formula VIII:
• wherein R in Formula I can be (i) a straight-chain or branched alkyl group, (ii) a straight-chain or branched alkenyl group, or (iii) a straight-chain or branched alkynyl group, wherein any of said groups can be unsubstituted or substituted;
• and
• wherein R in Formula I can have 5, 7, 9, 11, 13, or 19 carbon atoms;
• wherein m and n in Formula VII can each be an integer between 1 and 15;
• and
• wherein m and n in Formula VIII can each be an integer between 2 and 15.