**14. Thermochromic cellulose fiber**

Marcin Rubacha et al. [54] developed a method to get thermochromic pigment added cellulosic fiber called Lyocell. 1–10% chromicolor AQ-INK magenta type 27 pigmentation was used as a thermochromic modifier.

#### **15. Photochromic polymers**

A photo chromic polymer has photo chromic, chromophoric groups inside the polymer backbone chain. The chromophoric group respond to external radiative stimuli during the photo-irradiation of the polymers, there are change in physical chemical and optical properties of polymer in reversible manner. In 1967 Lovrien attempted to produce a polymer chain with photo irradiation sensitive properties by incorporating azo chrysophenine into polymethacrylaic acid. In 1970 Agolini and Gay [55] investigated photo chromic polyamides incorporating azo benzene. The potential application of photo chromic polymers are in photo chromic glasses, UV sensors, halographic recording media, non linear optics and memory devices.

#### **16. Textile printing**

Feczko et al. [56] printed cotton fabric by using photo chromic dyes based on Ethyl cellulose –spirooxazine nano particles with light absorbers. They use microencapsulation technique to incorporate photochromic colorants. Vikova [57] applied photo chromic pigments on different fabrics such as cotton, polyester and poly acrylonitrile by screen printing using pigment printing method.

#### **17. Sol –gel coating methods**

A sol is dispersion of solid particles in liquid where particles are sufficiently small (0.1–1.0 μm). Due to inorganic nature [58] of layers formed by the sol gel process it possess strong wear resistance and very thin nanometric sized layers. The preparatory materials in preparing sols are inorganic metal salts or organometallic compounds. The preparatory materials are submitted to series of hydrolysis and polymerization reactions to produce colloidal suspension or sol, once the polymerization is completed the colloidal form of the sol developed. Cheng et al. [59–61]

prepared silica as a matrix material for fixing the photo chromic dye 5 Chloro 1,3 dihydro-1,3,3 trimethyl spiro on the surface of wool fabric through sol–gel process.
