Tag: dyes

A colloidal solution can be purified by the following methods - Dialysis, Electro-dialysis and Ultrafiltration.

The dye is known as a coloured substance which has a great affinity towards the substrate on which it is applied. The basic difference in between dye and pigment is that dye is diffused into the interior of a given fabric from its water solution whereas pigment does not.

Vat dyes can applied directly on fibre and are generally insoluble in water. These can be used only on cotton but can not be used on silk and wool. In this case  dying is a continuous process and is carried out in a large vessel called vat. For this reason these dyes are Known as vat dyes, indigo is an example of vat dyes 

Direct Dye is a class of dyestuff's that are applied directly to the substrate in a neutral or alkaline bath. They produce full shades on cotton and linen without mordant and can also be applied to rayon, silk, and wool. Direct dyes give bright shades but exhibit poor wash fastness. Various after treatments are used to improve the wash fastness of direct dyes, and such dyes are referred to as 'after treated direct colors". Direct dyes are molecules that adhere to the fabric molecules without help from other chemicals.

 Indigo dye is an example of Vat dye, These dyes can be used only on cotton it is a long continuous process which is carried out in a large vessel known as Vat. These dyes are applied directly on the fibre and are generally insoluble in water.

Azo dyes are organic compounds, which contain the coloring azo function (N=M-). The azo function is often bound to an aromatic ring, and the dye can then be broken down to an aromatic amine, arylamine. This can take place either chemically, through reductive cleavage, or through the body's own enzyme system. Some azo dyes can also be broken down to arylamines during storage due to light and high temperature. Some arylamines have been judged to be carcinogenic.

When soap or detergent is added to water, this results in the formation of oil in water type emulsion.
The polar water-soluble ( hydrophilic) head is on the surface of the micelle whereas non-polar oil soluble (hydrophobic) tail is in the centre of the micelle. In the centre of the micelle, small oil droplets are present in which hydrophobic part of micelle dissolves.

The development step uses reducing chemicals, and the exposed silver-halide grains develop to pure silver. The oxidized developer is produced in this reaction, and the oxidized developer reacts with chemicals called couplers in each of the image-forming layers. This reaction causes the coupler to form a color, and this color varies depending on how the silver-halide grains were spectrally sensitized. A different color-forming coupler is used in the red, green, and blue sensitive layers. The latent image in the different layers forms a different colored dye when the film is developed.