Viscosity, activated

The viscosity activation energy is often evaluated to determine the temperature dependence for these viscosity functions. Viscosities at two temperatures are provided in Table 3.7. 

The energy barriers associated with the tautomerism have been determined from quantum yields and luminescence lifetime measurements <84JST(l 14)329). Table 25 lists the activation energies and solvent viscosity activation energies associated with the tautomer in a variety of alcoholic solvents. The data suggest a correlation between the energy barrier associated with proton transfer and the viscosity of the solvent. 

VISCOSITY ACTIVATION ENERGY OF THE N-HEPTANOL-CARBON TETRACHLORIDE SYSTEM. 

A polymer solution (n of 0.5 K at 90 F of 51 Ibm fT viscosity activation energy of 14,900 Btu/lb mole) is fed into a 1-in. i.d. stainless steel tube (10 ft long) at a mass flow rate of 750 Ibm/h and a temperature of 90 F. The velocity profile is fully developed before the solution enters the heated tube. Heat is supplied by steam condensing at 20 psia. 

PVDF Shear rate Apparent viscosity activation energy 132... 

Process NMR is used for chemicals (free/bound moisture, viscosity, activity, loading efficiency in powders, catalysts, liquids, detergents, pigments) and polymers (density, crystallinity, rubber and copolymer content, dispersion of fillers, melt properties, finish content, extent of cure and cross-linking, content of solubles, plasticisers, moisture, etc.). Process NMR is fully operational in the polymer industry, both as on-line units [202] which provide virtually continuous process feedback control as well as off-line and laboratory units for checks of the various processes [198]. The use of NMR for advanced process control has reduced the need for frequent wet tests, has reduced off-spec materials and has improved product transition times. 

Figure 2.5 Comparison of fragility index m values obtained using the calorimetric activation energy Eh and the viscosity activation energy E,. The data are compared with that of Musgraves et al. [61] also obtained from viscosity.

Second derivative of the viscosity activation energy with resnect to temnerature... 

Rates appear to be inversely proportional to viscosity. Activation energies are close to one barrier height, after an allowance is made for the temperature dependence of viscosity. ... 

There is one important caveat to consider before one starts to interpret activation volumes in temis of changes of structure and solvation during the reaction the pressure dependence of the rate coefficient may also be caused by transport or dynamic effects, as solvent viscosity, diffiision coefficients and relaxation times may also change with pressure [2]. Examples will be given in subsequent sections. 

Measuring tire pressure dependence of k at different temperatures shows that the apparent activation energy at constant viscosity decreases with increasing viscosity [46, ( figure A3,6,8). From a detailed analysis one... 

From stochastic molecnlar dynamics calcnlations on the same system, in the viscosity regime covered by the experiment, it appears that intra- and intennolecnlar energy flow occur on comparable time scales, which leads to the conclnsion that cyclohexane isomerization in liquid CS2 is an activated process [99]. Classical molecnlar dynamics calcnlations [104] also reprodnce the observed non-monotonic viscosity dependence of ic. Furthennore, they also yield a solvent contribntion to the free energy of activation for tlie isomerization reaction which in liquid CS, increases by abont 0.4 kJ moC when the solvent density is increased from 1.3 to 1.5 g cm T Tims the molecnlar dynamics calcnlations support the conclnsion that the high-pressure limit of this unimolecular reaction is not attained in liquid solntion at ambient pressure. It has to be remembered, though, that the analysis of the measnred isomerization rates depends critically on the estimated valne of... 

The first term, the apparent activation energy of the encounter reaction, was evaluated from the temperature coefficient of the viscosity of sulphuric acid. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Product Concentrate. An aerosol s product concentrate contains the active ingredient and any solvent or filler necessary. Various propellent and valve systems, which must consider the solvency and viscosity of the concentrate—propellent blend, may be used to deUver the product from the aerosol container. Systems can be formulated as solutions, emulsions, dispersions, or pastes. 

Resin Viscosity. The flow properties of uncured compounded plastics is affected by the particle loading, shape, and degree of dispersion. Flow decreases with increased sphericity and degree of dispersion, but increases with increased loading. Fillers with active surfaces can provide thixotropy to filled materials by forming internal network stmctures which hold the polymers at low stress. 

Antlblaze 19. Antiblaze 19 (Mobil), a flame retardant for polyester fibers (134), is a nontoxic mixture of cycHc phosphonate esters. Antiblaze 19 is 100% active, whereas Antiblaze 19T is a 93% active, low viscosity formulation for textile use. Both are miscible with water and are compatible with wetting agents, thickeners, buffers, and most disperse dye formulations. Antiblaze 19 or 19T can be diffused into 100% polyester fabrics by the Thermosol process for disperse dyeing and printing. This requires heating at 170—220°C for 30—60 s. 

Sodium lauryl sulfate is available in solution, paste, and soHd forms. As a solution its activity ranges between 28—30%, and as a paste it is 55% active. With this detergent in a shampoo, inorganic salts can affect viscosity. In addition, the limited solubiHty of sodium lauryl sulfate requires its judicious use in low cloud point clear shampoo systems. 

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