Surface tension various liquids

The physical properties associated with the parachor, vi2., the liquid surface tension and the density at various temperatures, for benzofuroxan and 5-methylbenzofuroxan are given by Hammick et al. The parachor values were reevaluated by Boyer et al ... 

Roy et al. (R3) define the critical solids holdup as the maximum quantity of solids that can be held in suspension in an agitated liquid. They present measurements of this factor for various values of gas velocity, gas distribution, solid-particle size, liquid surface tension, liquid viscosity, and a solid-liquid wettability parameter, and they propose the following two correlations in terms of dimensionless groups containing these parameters ... 

Stress depressions (Ao) of hard elastic polypropylene, hard elastic high impact polystyrene, and Gore-Tex , a nonelastic, porous. Teflon material were measured when these polymers, under load, were subjected to changes in their environment from air to various nonswelling liquids. The stress depressions were studied as a function of liquid surface tension and viscosity and the strain imposed on the materials. 

The measured normalized wetting rates for various test liquids (for cellulose fibers Fig. 23) ean be transformed into the cosine of the contact angle (cos0) and plotted as a function of the liquid surface tension (Fig. 24). The resulting linear relationship cos 0=1 b(yi — yc) was established empirically by Zisman and Fox [120] and found to hold for solid with low surface tensions. The eritical surface tension yc corresponds to the surface tension of the liquid that will just spread over/wet eompletely the soUd. The constant C reflects the eapillary geometry of the porous solid and may change in a non-predictable manner during the penetration proeess of different test liquids. It was concluded from the experiments performed [112] that there is no need to determine the constant C in order to obtain solid-surface tensions, because the position of the maximum in the C yiv cos 6 vs. yiv plot, which is expected to... 

Thus, the solid surface tension can be determined from experimental contact angles and liquid surface tensions when is known. The latter was determined experimentally for a given set of yiv and 6 data measured on one and the same type of solid surface by a least-squares analysis technique. A weighted mean was calculated as 0.000 1247 (m /mJ) (6). It was found that calculations of y y values with slightly different values have very little effect on the outcome (25). However, it is still an open question as to whether or not p in equation (7.27) is a universal constant, i.e. independent of the solid surface. Such a question can be addressed only after an even larger body of accurate contact angle data on various solids has been generated. 

Tavana and Neumann (2007) illustrated problems of the Fowkes equation even for the non-polar Teflon AF 1600 surface with various liquids and they state that the geometric mean rule tends to be too large when the difference between the solid and liquid surface tension increases, even for rather non-polar systems. Differences in ionization potentials and size of molecules, e.g. fluorocarbons and hydrocarbons, have also been discussed by Fowkes (1964) as one partial explanation of the failure of the theory for specific systems/interfaces. 

It may be seen firom the preceding sections that a variety of methods are available to obtain both liquid surface tensions and static contact angles. Some are cheap, or easily constructed, others less so. They all have their various merits, depending on the (geometric) presentation of the solid to be characterized. They also have their respective disadvantages, e.g., the sessile drop... 

Adsorption may occur from the vapor phase rather than from the solution phase. Thus Fig. Ill-16 shows the surface tension lowering when water was exposed for various hydrocarbon vapors is the saturation pressure, that is, the vapor pressure of the pure liquid hydrocarbon. The activity of the hydrocarbon is given by its vapor pressure, and the Gibbs equation takes the form... 

The uncertainties in choice of potential function and in how to approximate the surface distortion contribution combine to make the calculated surface energies of ionic crystals rather uncertain. Some results are given in Table VII-2, but comparison between the various references cited will yield major discrepancies. Experimental verification is difficult (see Section VII-5). Qualitatively, one expects the surface energy of a solid to be distinctly higher than the surface tension of the liquid and, for example, the value of 212 ergs/cm for (100)... 

Figure X-9 shows plots of cos 6 versus 7l for various series of liquids on Teflon (polytetrafluoroethylene) [78]. Each line extrapolates to zero at a certain 7l value, which Zisman has called the critical surface tension 7 since various series extrapolated to about the same value, he proposed that 7 was a quantity characteristic of a given solid. For Teflon, the representative 7 was taken to be about 18 and was regarded as characteristic of a surface consisting of —CF2 — groups.

The surface of PTFE articles is sHppery and smooth. Liquids with surface tensions below 18 mN/m(=dyn/cm) are spread completely on the PTFE surface hence, solutions of various perfluorocarbon acids in water wet the polymer (78). Treatment with alkafl metals promotes the adhesion between PTFE and other substances (79) but increases the coefficient of friction (80). 

Dynamic similarity occurs in two geometrically similar units of different sizes if all corresponding forces at counterpart locations have a constant ratio. It is necessary here lo distinguish between the various types of force inertial, gravitational, viscous, surface tension and other forms, such as normal stresses in the case of viscoelastic non-Newtonian liquids. Some or all of these forms may be significant in a mixing vessel. Considering... 

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