Solvent concentration profile

Solvent Concentration Profile of Poly(methyl methacrylate) Dissolving in Methyl Ethyl Ketone... 

A novel approach to determine the solvent concentration profile in a photoresist undergoing dissolution via fluorescence quenching and laser interferometry is introduced. Fluorescence arising from phenanthrene dye labels in a l-/im-thick polymethylmethacrylate)... 

UMMETAL. Solvent Concentration Profile of Poly (methyl methacrylate) 387... 

Figure 7. Fickian Precursor in the MEK Solvent Concentration Profile.

Solvent Concentration Profile ofPoly (methyl methacrylate) 397... 

Another consideration unique to TLC is the variation in solvent concentration in the direction of elution (18). The phase ratio r is simply the weight of solvent per weight of adsorbent measured at various distances from the dip line. The change in r generates the solvent concentration profile. The decrease in phase ratio is an important consideration in subsequent discussions of the fractionation mechanism. 

Another indication that precipitation and not adsorption is operative depends on the observation that samples of the same molecular weight migrate identical distances from the dip line, independent of their starting positions on the TLC plate (15). This of course would not be the case if adsorption governed chromatographic mobility. To explain these phenomena, Inagaki has proposed that the solvent concentration profile results... 

Figure 4. Schematic solvent concentration profiles. Phase ratio, r (weight of solvent per weight of adsorbent) as a function of reduced distance z/z/iwol from the dip line.

A number of experiments are possible which will add final clarification to questions concerning the details of the mechanism. Modem column chromatographic methods can be used to evaluate the role of the adsorbent. In a column, no solvent concentration profile exists, and there are at least two papers which indicate adsorption separations can be successful (22, 23). More extensive work is necessary to characterize the solvent concentration profile to improve the quantitative agreement between bulk precipitation concentrations and in situ precipitations in TLC. 

Fig. 24. Solvent concentration profiles, expressed as the solvent volume fraction, ul, and boundary locations for Case II swelling at several dimensionless times. Theoretical predictions have been adapted from the work of Papanu et al. [57], using the following parameters Lq = 10 cm X = 0.876 K = 9.0x10" cm/(satm) a, = 532 atm V, = 76.5 cm /mol Dq = 10 " cm /s M = 200000 T = 323 K and Pe = 1.0.

To perform simulations with the model, the system methyl ethyl ketone (MEK)/polystyrene was used as a model system. The effect of the polymer molecular weight on the dissolution mechanism vm investigated. Figure 5 shows the solvent concentration profile in the polymer (Mn = 52,000) as a function of normalized position based on the undeformed coordinate system. The center of the slab is at =... 

Numerous drying rate data have been obtained in laboratory drying experiments using thermo-gravimetric analyzers as shown in the previous chapters. However it was difficult to know the actual dr5dng rate or solvent concentration profiles in the pilot or production scale dryer from these experimental results. 

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