The impact of external factors on the color of the dye

External factors such as solvent, temperature, concentration of the dye, the dye was added to the electrolyte, so will the light irradiation dye in solution , or in a state change of dyed fabrics, resulting in a color change of the dye.

I. Effect of a solvent medium and

The absorption wavelength of the dye solution with the solvent polarity change in the size change. When the dye is dissolved in a polar solvent , polar solvents with increasing polarity of the dye is increased, thereby to reduce the excitation, absorption wavelength is shifted to a longer wavelength, the dye solution color deepened.

Many dye and solvent may also generate hydrogen and solvates thereof , which will change the color of the dye solution.

Color dyes on the fiber (in addition to optical factors, such as scattering and refraction different fiber) will vary fibers of different polarity. Generally, the fibers exhibit high polarity on the darker, less polar fibers in the lighter. For example, disperse dyes in color yield on cellulose acetate fibers shallower polyamide fibers; cationic dyes in color yield compared with polyester fibers as a pale polyacrylonitrile fibers.

Solutions of different pH values, will change the nature of the dye molecules conjugated system an electron withdrawing group or an electron donating group, the dye color change. For example, Basic Green in the alkaline solution becomes white precipitate from the original green, and then an acid is added back to the original green.

AZO amino or hydroxyl different positions in the dye molecule , the solution when the pH value changes, the color of the dye will be different effects occur. This property can be used as the acid, base indicator. For example, direct dyes Congo red, red when dissolved in water, it becomes blue with acid, when alkali and becomes red.

Second, the impact of the concentration on color

When the dye concentration is small , the dye is present in a monomolecular state in a solution, however, if the dye concentration, the dye molecules condensing dimeric or multimeric integration. Aggregated molecules π electron excitation energy higher than that of single molecules, thus moving the dye absorption spectra to shorter wavelength, lighter color. For example, λmax crystal violet monomolecular state is 583nm, which is a dimer max 540nm. The extent of dye on the fiber aggregate can also affect the color of the fabric, with the insoluble azo dyes and vat dyes dyed fabric is the truth shade change was boiled soap.

Third, the effect of temperature on color

Changes in temperature will affect the aggregation tendencies of the dye , thereby promoting a change in color of the dye. When the temperature increases, the degree of aggregation of the dye decreases, absorption wavelength is shifted to a longer wavelength, having a dark color effect. Part of the organic compound and the dye color is generated with a reversible change in temperature, a phenomenon known as thermal discoloration.

Fourth, the effect of light on color

Part of an azo, thioindigo, cyanine dyes in a stable trans configuration at room temperature general , when exposed to light, the dye will trans - cis structure becomes, after leaving the light source, and return to cis trans structure. Different dye absorption spectra of trans and cis configuration, showing different colors, a phenomenon known as photochromic properties.

It is the photochromic dye in the light irradiation caused by changes in the structure using the dye color change color.

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