Contact angle hematite

FIG. 20-37 The variation of adsorption density, oil-droplet contact angle, and oil-extraction recovery of hematite as a function of pH. To convert gram-moles per square centimeter to pound-moles per square foot, multiply by 2.048. [From Raghavan and Fuerstenau, Am. Inst. Ghem. Eng. Symp. Sen, 71(150), 59 (1975).]... 

The presence of pre-adsorbed polyacrylic acid significantly reduces the adsorption of sodium dodecylsulfonate on hematite from dilute acidic solutions. Nonionic polyacrylamide was found to have a much lesser effect on the adsorption of sulfonate. The isotherm for sulfonate adsorption in absence of polymer on positively charged hematite exhibits the typical three regions characteristic of physical adsorption in aqueous surfactant systems. Adsorption behavior of the sulfonate and polymer is related to electrokinetic potentials in this system. Contact angle measurements on a hematite disk in sulfonate solutions revealed that pre-adsorption of polymer resulted in reduced surface hydrophobicity. 

Additional contact angles were measured at 0.001 M SDS concentration. The hematite disk was conditioned in the SDS solution before adding polymer to the solution. The contact angle was measured after adding sufficient quantities of polymer for concentrations of 1, 3, and 5 ppm. For both PAA and PAM, the contact angle remained constant and identical to the value obtained in the absence of polymer. No polymer was able to adsorb on the surfactant-coated disk. It can be concluded that whichever species, surfactant or polymer, adsorbed first was not... 

Figure 9. Contact angles on a hematite disk at 0.001 M SDS, pH 4.1, and 0.001 M NaCl as a function of the polyacrylic acid concentration in which the hematite disk had been preconditioned.

Costanzo, P. M., Wu, W., Giese, R. F., and van Oss, C. J. (1995) Comparison between direct contact angle measurements and thin layer wicking on synthetic monosized cuboid hematite particles Langmuir, 11, 1827-1830. 

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