PAA solutions

Therefore, addition of a polybase in a PAA solution results in decrease of free COOH concentration and consequently increase of pH. 

Figure 11 Power characteristics of a Rushton turbine stirrer under given geometric conditions, measured in two differently scaled vessels (scale 1 2) and fitting the flow behavior of the viscoelastic fluid [polyacrylamide (PAA) solution] by changing its viscosity. Source From Ref 13.

Figure 11 depicts the power characteristics of a Rushton turbine stirrer in geometrically similar cylindrical vessels (///D = l D/J=2) without baffles. To keep the Hedstrom number constant at different scales, viscosity of the PAA solutions had to be fitted as discussed above. 

Typical potentiometrie titration data for the latices and also for the PAA solutions are shown in Figure 3 in the form of a plot of effective pK (15) against degree of ionisation (a1). 

Ford und Ulbrecht [41] performed homogenization measurements with aqueous CMC and PAA solutions in a vessel with a screw stirrer arranged in a central draught tube. The pumping direction of the screw could be changed as well. Initially, the liquid with a lower viscosity rested in a layer on top of the more viscous one (volume ratio cp = 1). The data measured were first represented in the space n0, Reefr, Fig. 22, whereby peff was taken from the flow curve of the homogenized mixture at the shear rate of y 5 s-1, which was effective in the draught tube. 

The power characteristic for viscoelastic fluids (Reher, 1969 Schiimmer, 1970) can also be described accurately by a relationship of the type Ne (Re ). Additional parameters to account for viscoelastic properties are needed only when the ratio of tangential to normal stresses is less than two (Reher, 1969). Power characteristics for the turbine stirrer in aerated non-Newtonian fluids (carboxymethylcellulose [CMC] and polyacrylamide [PAA] solutions) have been presented by Hocker and Langer (1962). 

In its final state, this polyimide cannot be processed thus processing occurs before the imidization step. PAA solutions may be spin-coated onto the appropriate substrates and then thermally treated. This sequence establishes the molecular order in the material (lj 2) and in-plane orientation (3). Further development of residual stresses is also associated with this coating process. 

Linear Mass Experiments. Using long strips of natural rubber (60 cm X 2 mm X 0.5 mm) coated with a 15% PAA solution in NMP, the mass per unit length of the sample was obtained as a function of temperature. The technique involves measuring the tension on the sample and the time of flight of a traveling wave on the sample (M. Chipalkatti,... 

Results of force-temperature experiments for a PAA solution on rubber are shown in Figure 2. For the first cycle, the initial load is that of the rubber since the coating is still in the liquid state and cannot support a load. At this load the rubber is just below its thermoelastic inversion point and its contribution to the force change is negligible. 

Polyamic acid (PAA) solutions are deposited by either spinning or spraying. They are cured by heating at a controlled rate from 50 C to 350-420 C to evaporate solvents and reaction products (primarily H2O) and convert the PAA to PI. Multiple coats are deposited to achieve the thick (20-40 pm) planarized dielectric layers required for high Impedance TFML interconnects. Figure 3 shows a cross-section of 5 pm thick conductor lines planarized with 25 pm (three coatings) of spray-coated PI. 

In a number of polymer solutions (e.g. aqueous polyacrylamide (PAA) solutions [195]) a Newtonian flow behavior is observed at very low and extremely high shear rates y. The constant viscosity at very low y is known as the zero-shear viscosity /tg. 

Fig. 2.9 Dependences of Ne upon Co / = Re/Fr for different values of Q for a turbine stirrer with d/D — 0.3 in aqueous glycerine and CMC solutions. The middle and bottom graphs apply for aqueous PAA solution and prove the considerable influence of the stirrer type upon gas cushion formation in a viscoelastic liquid from [216).

The experimental data with turbine stirrers in viscoelastic aqueous PAA solutions (see central graph of Fig. 2.9) showed a very much pronounced decrease in Ne numbers than with the Newtonian or pseudoplastic fluids. This already started in the turbulent range at Re = 5 x 10 and was also caused by trailing vortices behind the stirrer paddles. Viscoelastic liquids exhibited normal stress, which damped the turbulence and even promoted the development of gas cushions at comparatively high Re numbers [192]. 

The relationship, which is valid for turbine stirrers with d/D < 0.45, Newtonian liquids in the range of Re = 10 to 10 and Fr > 0.6 Ne x/(Q, Re = according to expression (2.25), is shown in Fig. 2.11 as a dashed curve. The plotted experimental data were those from Hocker and Langer [216, 217], obtained with water, glycerine, CMC solutions and PAA solutions as converted by Henzler [192] and were well represented by equation (2.25) in a relatively narrow range of A, otherwise they were by 15% higher. 

The adjustment factor C could be seen as a weighting factor, which took the relative contributions of viscous and elastic behavior into consideration. With the help of the term (1 -h CWi) , Ford and Ulbrecht [129] succeeded in correlating the mixing times in CMC and PAA solutions with different concentrations in the laminar flow range. 

In the gassing of viscoelastic fluids (e.g. PAA-solutions) the sorption characteristics for D/d > 2.5 (e.g. turbine stirrer) are also dependent upon the stirrer speed, since then the effect of the stirrer is ever more strongly limited by its immediate surroundings, and this even more so the more intensively the liquid is sheared. For D/d < 1.67 (e.g. MIG stirrer), on the other hand, the same results are obtained as in pseudoplastic liquids, see equation (4.41). 

Pyrene excimer fluorescence was used as a sensitive proximity probe in the intermolecular complex system. Upon addition of PAA solution, the intramolecular mobility of the PEG chain was suppressed resulting in decreased intramolecular excimer formation. Simultaneously, the local concentration of PEG is increased in the vicinity of PAA. The excimer formation seems to result from the arrangement of pyrene groups which is already pre-formed in the ground state. The effect of complexation is observed to be more pronounced in the PEG-PAA with a higher molecular weight of PAA. A more complete account of this work will appear elsewhere. (16,17)... 

A procedure similar to that which we have already reported was employed [9,10]. This involves the preparation of a pre-polymer poly(amic acid) (PAA) solution in DMAc, followed by imidization in suspension in paraffin oil. A typical procedure for the preparation of linear functionalized spherical polyimide particulates was as follows. A round-bottomed 3-necked flask was flushed with N2 and charged with a diamine in DMAc. The diamine was completely dissolved in DMAc. While solution was mechanically stirred, finely ground pyromellitic dianhydride (PMDA) was added to the mixture on an ice bath in small portions, and then stirring continued overnight at room temperature. Paraffin oil with poly(maleic anhydride-co-octadec-l-ene)(l l) (O.Swt% in oil) as a suspension stabilizer was added to the flask. The PAA solution was suspended for 2hr at 60T) at the speed of 400rpm. After that, imidization was initiated by dropwise addition of a mixture of acetic anhydride (4.0 molar excess of PMDA used) and pyridine (3.5 molar excess of PMDA used). After 24hr, the polyimide particulates were filtered, washed with dichloromethane and then dried at 80 °C in a vacuum oven. 

To obtain crosslinked polyimide particulates tris(2-aminoethyl)amine as a crosslinking agent was added to the PAA solution suspended in paraffin oil. After 24hr, a mixture of acetic anhydride and pyridine was added to give crosslinked polyimide. 

Figure 25. Steady shear viscosity variation with shear rate for 15% styrene-methyl acrylate copolymer suspension in a 2 wt% PAA solution (171).

Epoxidation of unsaturated compounds is usually carried out in the industry by means of anhydrous solutions of peracetic acid (PAA) in ethyl acetate. The PAA solutions are manufactured by the oxidation of acetaldehyde with ozonized oxygen. 

The composition of the distillate depends mainly on the concentration of the introduced aqueous H2O2. The product contains 35-55% PAA, 1-3% H2O2,8-20% CH3COOH and 34-45% H2O. The advantage of the PAA solution lies in the relatively low concentration of acetic acid and in the absence of strong mineral acids [12]. 

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