Time of half-dyeing

Table 3.13 Times of half-dyeing on viscose [108] and diffusion coefficients in cellophane film [109] for direct dyes at 90 °C...

Cl Direct Structure Diffusion coeff. in cellophane film x 1014 (m2/s) Time of half-dyeing on viscose yarn (min)... 

There is a roughly inverse relationship for a series of structurally related dyes between the time of half-dyeing and the saturation solubility in an appropriate substrate, as illustrated for several 4-alkylamino derivatives of 1-anilinoanthraquinone on cellulose acetate (Table 3.17). It is interesting that methylamino and 2-hydroxyethylamino substituents confer good solubility in this substrate, but ethylamino groups are even less effective than isobutylamino groups in this respect [114]. 

Table 3.17 Times of half-dyeing and solubilities of disperse dyes in cellulose acetate at 85°C [114]...

Table 3.18 Times of half-dyeing of disperse dyes on cellulose acetate at 85 °C [115]...

The thermodynamic considerations deal with the end results of the chemical potential after equilibrium has been established. To the practical dyer it is much more important to have information about the rate at which equilibrium is being established under different conditions. Rate-of-dyeing graphs are prepared by plotting the amount of dye adsorbed on one coordinate, and time on the other. If the observations are carried to complete exhaustion the curve is asymptotic and the end point is approached so gradually that its accurate determination is extremely difficult. For this reason the time of half dyeing (Ij) is used because, at this point, the slope of the curve is comparatively steep and the time can be ascertained with accuracy. 

Although there are exceptions, the times of half-dyeing and levelling at 85°C (185°F) are greater with the less soluble compounds. The effect of a surface-active assistant is to make the water phase more attractive and, therefore, to reduce the percentage exhaustion at equilibrium. 

Table 3.5 Time of half dyeing (f ) and percentage exhaustion at equilibrium %E at Em) of control et al., 1998b)...

Figure 3.7 shows the behavior of the dyebath exhaustion for different types of plasma gases. The resnlts demonstrate that plasma treatment can infinence the dyeing behavior of wool to different extents. Table 3.6 shows the time of half dyeing and final dyebath exhaustion derived from Figure 3.7. 

Table 3.6 Time of half dyeing and final bath exhaustion for chrome...

Sample Time of half dyeing (min) Final bath exhaustion (%)... 

The times of half-reduction of five typical vat dyes are listed in Table 3.3. Most of the commercially important products give values within the range 25-500 seconds. Few dyes are as slow to reduce as Cl Vat Red 1 and even fewer are reduced as quickly as flavanthrone. In fact, when these times were measured the average particle size of the sample of flavanthrone under test was greater than that of the Cl Vat Green 1 sample, which was reduced at least ten times more slowly [26]. 

Table 3.3 Times of half-reduction of typical vat dyes [26]...

Precursor frequency The precursor frequency of cells that have divided in response to a stimulus is the proportion of cells present at the time of the addition of the stimulus that were destined to begin division. It is a measure of the potential of a mixed population of cells for response to any particular activator and can be determined, by flow cytometry, with the use of fluorescent tracking dyes that stain cells with stability but dilute by half each time a cell divides. 

Kinetic studies in sediment/water systems with Direct Red 2, Acid Black 92, Acid Red 4, Acid Red 18, and Direct Yellow 1 lead to linear and biphasic plots of dye loss over time. For all but Direct Yellow I, dye loss was usually preceded by a lag or adaptation phase. Acid Black 92 and Direct Red 2 were transformed completely in less than 24 and 48 hours, respectively, but Acid Yellow 151 and Direct Yellow 1 showed half-lives of greater than 2 years. The rapid initial drop in concentration of all dyes observed, with the exception of Acid Red 18, was presumed to be due to sorption. Tests to determine the effect of pH on... 

The Cibacron LS range of reactive dyes for cotton, sold by Ciba Speciality Chemicals, was developed in record time by a small team practising a new faster-to-market philosophy. In total it took two years to develop and introduce the new products, half the time it normally takes. 

In 2004 another epidemiological study was undertaken of 459 cases of bladder cancer in New Hampshire, U S A, by the Dartmouth Medical School at Lebanon, and they were matched against 665 people who did not have the disease. This study found that men who used hair dye were less likely to suffer bladder cancer, whereas for women there was a slightly higher risk, although in both cases the observations were not statistically significant. Another survey, this time of more than half a million women, and carried out by the American Cancer Society, found no link at all between hair dyes and bladder cancer. 

The purpose of the rotaxane is to protect the squaraine from nucleophilic attack, likely to occur under physiological conditions, and so enhance the lifetime of the probe in vivo. Indeed, the half-life of the probe is 100 times longer than a non-rotaxane analogue that incorporates a commercial sulfonated carbocyanine dye in place of the squaraine moiety. Furthermore the near infrared spectral nature of the dye means that it gives a strong signal even through centimetres of soft tissue. 

Since 1973, the U.S. International Trade Commission has reported the manufacture and sales of dyes by application class only. In 1972, the last year for which statistics are available by chemical class, 3900 metric tons of triarylmethane dyes were manufactured, which represents approximately 4% of total dyestuff production in the United States. At that time, there were 185 triarylmethane dyes Us ted in the Colour Index. From the latter half of the 1970s through the 1980s, annual dye production in the United States, including triarylmethane dyes, changed very litde. In 1981, methyl violet, with an annual production of 725 t, was the only triarylmethane dye for which production statistics were available. Some triarylmethane dyes were imported, eg, malachite green (163 t in 1981), methyl violet (40 t), new fuchsine (30 t), and other dyes totalling less than 15 t. 

You have been asked to measure the volume of a small lake. You dump in 5.0 L of a 2.0 M solution of a dye, which degrades with a half-life of 3.0 days. You wait exactly 1 week for the lake to become well mixed (during this time, assume no water is lost) you then take a 100 mL sample. The dye s concentration in this sample is 2.9 x 10-6 M. What is the lake s volume Remember M is moles per liter. 

Determine the effect of elapsed time on overhead-product concentration. It is reasonable to assume that about 35 to 50 percent of the dye intermediate can be removed efficiently at the initial, relatively low reflux ratio of 5. In this case, assume that 2100 lb of the 5000 lb is thus removed. It is also reasonable to assume that this takes place during half of the 6 h allotted in step 2 for recovering this intermediate. (Note that the shorter the allotted time, the bigger the required column diameter.)... 

As an initial approximation of the ideal solvent strength for HPLC, the results of TLC studies on acetylated cellulosic plates with various methanol-water mixtures and natural dye extractions were graphed (R/ vs. methanol concentration). An acetylated cellulosic TLC system is not directly comparable to a C-18 HPLC system, but TLC results were nonetheless useful as a rough estimate of solvent strength. In practice, approximately two-thirds of the solvent strength required to elute natural dyes with TLC was necessary to achieve a similar separation of major sample components with HPLC. After individual solvent concentrations were determined, samples of known dyes extracted from wool were eluted in each of the three pairs of solvents (the concentration used for each individual solvent-water system was reduced by one-half) and adjustments were made until each sample eluted with a kf value no larger than 10. Retention times and kf values are equivalent expressions of relative retention of a sample on the column if the flow rate is the same for all trials. With a flow rate of 1.4 mL/min, the maximum time... 

The kinetics of the oxidation of iodide by the oxidized state of c -[Ru (dcbpy)2-(NCS)2] sensitizer adsorbed on nanocrystalline Ti02 films was measured by transient laser spectroscopy [92]. Figure 16 shows the transient absorption kinetics recorded in propylene carbonate with various electrolytes added. In all cases, the recovery of the ground-state absorption of the dye, after the fast electron injection into the solid, does not follow a simple kinetic law. In the absence of any electrolyte (trace a), the time needed to reach half of the initial absorbance (/1/2) through back electron transfer is 2 ps. Total recovery of the initial absorption, however, requires several hundreds of microseconds to milliseconds. Traces b, c, and d were recorded after addition of a common concentration of 0.1 m of iodide in the form of tetra-butylammonium (TBA+), Li+, and Mg + salts, respectively. Addition of the electrolyte in all three cases led to a considerable acceleration of the dye regeneration with ti/2 < 200 ns and complete suppression of the slow kinetic tail. 

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