Dispersions absorber dyes

Time resolved hole burning spectra were measured by means of a femtosecond transient absorption spectrometer system. A second harmonics of a mode locked cw Nd + YAG laser (Quantronix, 82MHz) was used for a pumping source. A synchronously pumped rhodamine 6G dye laser with a saturable absorber dye jet (DODCl/DQOCI) and dispersion compensating prisms in the cavity was used. The output of the dye laser (lOOfs fwhm, 600pJ/pulse) was... 

A very effective approach to dispersing water-insoluble absorber dyes is to use the emulsification-dispersion process described above for coupler molecules. NS dispersions of such dyes are straightforward. A limitation that must be considered is whether or not the dye will transform after formation from an amorphous physical state into a crystalline state. Absorption properties often change upon crystallization. 

Comminution techniques also effectively produce solid particle dispersions of absorber dyes. Aqueous... 

Precipitation into submicron-sized particles is another direct approach. Precipitation by pH shifting can be an effective approach for dyes that have weak acid functionality. A number of different families of such dyes have been dispersed by acidification of weakly alkaline dye solutions, in the presence of stabilizers such as surfactants and polymers. Alternatively, solvent shifting has been demonstrated to be an effective method of preparing absorber dye dispersions. Recent work by Brick et al. (14) has shown how such dyes can be very effectively precipitated from a variety of water-miscible organic solvents. Finally, another approach for incorporation of absorber dyes is to precipitate or condense them on the surface of a high-surface-area carrier species, such as colloidal silica. Such preparations can be prepared by pH- and solvent-shifting processes, in the presence of the carrier particles. 

Figure 10.12 The dependence of dye dispersed (absorbance units) on amounts of NaDS bound by 0.1% solutions of HSA and BSA. Arrows indicate the points at which F = CMC for the two proteins. Symbols HSA (O) BSA ( ). (b) The relation of total NaDS concentration (B -h F) of dye dispersed ( ) and of Na bound (B) by 0.1 % HSA. The solid diagonal represents the solubilization by micelles without protein. The broken line shows the free NaDS concentration (F). Symbols (O) dye solubilization ( ) binding. From Steinhardt et al [81] with permission.

Colorant Mixing. A colorant, whether a dye dissolved in a medium or pigment particles dispersed in it, produces color by absorbing and/or scattering part of the transmitted light. If only absorption is present, the Beer-Lambert law appHes ... 

In order to develop the dyes for these fields, characteristics of known dyes have been re-examined, and some anthraquinone dyes have been found usable. One example of use is in thermal-transfer recording where the sublimation properties of disperse dyes are appHed. Anthraquinone compounds have also been found to be usehil dichroic dyes for guest-host Hquid crystal displays when the substituents are properly selected to have high order parameters. These dichroic dyes can be used for polarizer films of LCD systems as well. Anthraquinone derivatives that absorb in the near-infrared region have also been discovered, which may be appHcable in semiconductor laser recording. 

Dyeing Mechanism. Unmodified polyester fibers are very hydrophobic and absorb only minimal amounts of water and are therefore only dyeable with hydrophobic disperse dyes. The mechanism of dyeing is by simple partition, the so-called soHd solution mechanism. The dyeing process can be described by the general scheme... 

Vat dyes are used to colour both components in pale depths on polyester/cellulosic fibre blends [44] but coloration of the polyester component in this case is more closely analogous to disperse dyeing (section 1.6.5). Anthraquinone disperse dyes resemble those vat dyes that are substituted anthraquinone derivatives and in both instances it is exclusively the virtually water-insoluble keto form that is absorbed by the polyester fibre. 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

An aqueous dispersion of a disperse dye contains an equilibrium distribution of solid dye particles of various sizes. Dyeing takes place from a saturated solution, which is maintained in this state by the presence of undissolved particles of dye. As dyeing proceeds, the smallest insoluble particles dissolve at a rate appropriate to maintain this saturated solution. Only the smallest moieties present, single molecules and dimers, are capable of becoming absorbed by cellulose acetate or polyester fibres. A recent study of three representative Cl Disperse dyes, namely the nitrodiphenylamine Yellow 42 (3.49), the monoazo Red 118 (3.50) and the anthraquinone Violet 26 (3.51), demonstrated that aggregation of dye molecules dissolved in aqueous surfactant solutions does not proceed beyond dimerisation. The proportion present as dimers reached a maximum at a surfactant dye molar ratio of 2 5 for all three dyes, implying the formation of mixed dye-surfactant micelles [52]. 

Only a limited range of nitro, azo and anthraquinone disperse dyes exhibit adequate fastness to dry heat, light and weathering for application on polyester automotive fabrics. The structure of Cl Disperse Yellow 86 was modified to incorporate UV absorbers of the benzophenone, benzotriazole or oxalanilide types into the dye molecule. The derived dyes showed better fastness properties than the parent unsubstituted dye. Positioning of the photostabilising moiety within the dye molecule had little influence on the light fastness obtained, however. Built-in benzophenone residues were more effective than the other two types [177]. Nevertheless, several further monoazo and nitrodiphenylamine disperse dye... 

The largest proportion (80%) of FBA systems is based on stilbene (88) which itself absorbs at 324 nm. The parent molecule is usually substituted in the 4-position or disub-stituted in the 4,4 -positions. The introduction of sulfonic acid groups into the stilbene skeleton confers water solubility and hence affinity for hydrophilic fibres such as cotton. Products for use on hydrophobic substrates such as polyester require characteristics similar to those of disperse dyes. 

In contradistinction to the spectra obtained in the mica dispersion, Pseudocyanine, when added to the colloidal silver and silver halide systems of Figures IB and 1C, yielded no H-bands but formed well defined J-bands. The latter also exhibited a weak secondary peak located near the absorption maximum of dissolved, unperturbed dye. Although the position and intensity of the J-band varied with the substrate (4, 17, 38, 61), the differential spectra obtained in these silver systems exhibited marked similarities. An increase in the concentration of the substrate produced in both cases a monotonic change in the absorbance of the M-... 

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