The microencapsulation process is the most versatile, widely applicable, and successful way of stabilizing, packaging, and protecting liquid crystal and leuco dye products.
A microcapsule is a small sphere of material consisting of two phases. The first, the internal phase, is the liquid crystal or leuco dye material within the capsule that is responsible for the thermochromatic properties. The internal phase is surrounded by a water-soluble material, the external phase, which forms a protective wall around it. In the microencapsulation process, the internal and external phases are mixed at high speeds to create an oil in water emulsion of the desired particle size. This is typically between 5 – 50 microns for liquid crystal and 1 – 10 microns for leuco dyes. Process conditions (mixing speed, temperature, and pH) are then precisely controlled to ensure that the external phase surrounds the internal phase. The external phase of the resulting mixture can then be cross-linked to strengthen the microcapsule walls.
Benefits of microencapsulating liquid crystal and leuco dyes:
- The difficult to work with unsealed internal phase is converted into an easier to use water-based form.
- The unsealed internal phase is protected from the environment where degradation can occur.
- Each individual droplet of liquid crystal is totally encased, inhibiting crystallization of the mixture, and preventing extrusion of the oily, unsealed internal phase from coated or printed films.
- Microcapsules of different liquid crystal formulations can be mixed to produce coatings and films with multiple color plays.
Please see the Handbook on Thermochromic Liquid Crystal Technology which is available for download under the resource tab for a comprehensive review of this topic.