Surface properties tension measurements

Less detailed approaches to the calculation of surface properties from measures of polarity have also been made. The interaction parameter, ( >, can be calculated with some accuracy from independently measured values of the dipole moment, molecular polarizability and ionization energy (Good, ). Wu (23) has separated polar and dispersive components of interfacial and surface tensions and has demonstrated that adhesion depends on a matching of the polarities of the adherent materials. 

A solid, by definition, is a portion of matter that is rigid and resists stress. Although the surface of a solid must, in principle, be characterized by surface free energy, it is evident that the usual methods of capillarity are not very useful since they depend on measurements of equilibrium surface properties given by Laplace s equation (Eq. II-7). Since a solid deforms in an elastic manner, its shape will be determined more by its past history than by surface tension forces. 

Both tear resistance and hysteresis increase on incorporation of silica, but the effect is less pronounced as compared to the stress-strain properties. Tension set of the ZnO-neutralized m-EPDM system is low (around 20%) and incorporation of filler causes only a marginal increase in set due to chain slippage over the filler surface, as previously discussed. Measurement of physical properties reveal that there occurs an interaction between the filler surface and the polymer. Results of dynamic mechanical studies, subsequently discussed, support the conclusions derived from other physical properties. 

The surface properties are of particular interest for composites and coatings. The n = 6 monomer will wet Teflon, and PTFE filled composites can be prepared. The critical surface tension of wetting for the fluoromethylene cyanate ester resin series has been determined from contact-angle measurements on cured resin surfaces. As indicated in Table 2.2, it parallels the fluorine composition and begins to approach the PTFE value of 18 dyn/cm. 

Some of the compounds described in this chapter were studied for specific physical properties. Surface tension measurements with solutions of 9-16 in 0.01 M hydrochloric acid demonstrated that these zwitterionic X5Si-silicates are highly efficient surfactants.21 These compounds contain a polar (zwitterionic) hydrophilic moiety and a long lipophilic z-alkyl group. Increase of the n-alkyl chain length (9-15) was found to result in an increase of surface activity. The equilibrium surface tension vs concentration isotherms for 9 and 16 were analyzed quantitatively and the surface thermodynamics of these surfactants interpreted on the molecular level. Furthermore, preliminary studies demonstrated that aqueous solutions of 9-16 lead to a hydrophobizing of glass surfaces.21... 

Surface tension measurements. Solutions of the betaines were prepared with quartz-condensed, distilled water, specific conductance, 1.1 X 10" mho cm" at 25°C. All surface tension measurements were made by Wilhelmy vertical plate technique. Solutions to be tested were immersed in a constant-temperature bath at the desired temperature 0.02°C and aged for at least 0.5 h before measurements were made. The pH of all solutions was > 5.0 (usually, in the range 5.5-5.9), where surface properties show no change with pH. 

The aggregation behavior of C21-DA salt in dilute electrolyte medium appears to resemble that of certain polyhydroxy bile salts (25,16). That C21-DA, with a structure quite different from bile acids, should possess solution properties similar to, e.g., cholic acid is not entirely surprising in light of recent conductivity and surface tension measurements on purified (i.e., essentially monocarboxylate free) disodium salt aqueous solutions, and of film balance studies on acidic substrates (IX) The data in Figure 3 suggest that C21-DA salt micelles Incorporate detergents - up to an approximate weight fraction of 0.5 -much like cholate Incorporates lecithin or soluble... 

Unfortunately, little direct information is available on the physicochemical properties of the interface, since real interfacial properties (dielectric constant, viscosity, density, charge distribution) are difficult to measure, and the interpretation of the limited results so far available on systems relevant to solvent extraction are open to discussion. Interfacial tension measurements are, in this respect, an exception and can be easily performed by several standard physicochemical techniques. Specialized treatises on surface chemistry provide an exhaustive description of the interfacial phenomena [10,11]. The interfacial tension, y, is defined as that force per unit length that is required to increase the contact surface of two immiscible liquids by 1 cm. Its units, in the CGS system, are dyne per centimeter (dyne cm" ). Adsorption of extractant molecules at the interface lowers the interfacial tension and makes it easier to disperse one phase into the other. 

Fig. 10 relates the composite extraction index (see above) obtained in the low-shear aqueous test system for these Tween surfactants, and adhesion tensions measured against various solids. Adhesion tensions against platinum and bitumen saturated pyrophyllite are irregularly related to tar sand extraction, while the adhesion tension against a fresh pyrophyllite surface is linearly (inversely) related to tar sand extraction. This is the first linear correlation between a measurable property of a surfactant solution and tar sand extraction which we have been able to obtain, and there appears to be no such finding in the literature. Fig. 11 gives the relations between extraction of bitumen with the paddle mill, solvent-aqueous-surfactant extraction and adhesion tensions measured against platinum, bitumen saturated pyrophyllite and hydrated (48 hours in water) pyrophyllite. 

In fact, one finds from surface tension measurements that some proteins are considerably more hydrophobic (such as hemoglobin) than others (such as bovine serum albumin, ovalbumin). These properties of proteins have been extensively investigated. 

Mixed surfactant systems are of importance from a fundamental and practical point of view. Therefore, many recent papers have reported on the micellar properties of mixed surfactant solutions. For example, Tokiwa et al. have measured the NMF spectra W Ingram has measured surface tension ( 5). Previously, we have reported the solution properties of anionic-nonlonlc surfactant mixed systems from the point of view of electrical (., 7) and surface tension measurements (8-10), and investigated the mixed micelle formation. 

One of the most important things to bear in mind in studying van der Waals forces is that this topic has ramifications that extend far beyond our discussion here. Van der Waals interactions, for example, contribute to the nonideality of gases and, closer to home, gas adsorption. We also see how these forces are related to surface tension, thereby connecting this material with the contents of Chapter 6 (see Vignette X below). These connections also imply that certain macroscopic properties and measurements can be used to determine the strength of van der Waals forces between macroscopic objects. We elaborate on these ideas through illustrative examples in this chapter. 

The changes in surface properties were analysed both by contact angles and gas permeabilities measurements. The contact angles values for a family of typical liquids are reported on Table 1. The resulting surface tensions, ys, for PE, EVOH and EVO-NO (34,... 

The choice between the static methods (Wilhelmy plate method and the du Noiiy ring method) should primarily be based on the properties of the system being studied, in particular, the surfactant. As mentioned in UNITD3.5, the transport of surfactant molecules from the bulk to the surface requires a finite amount of time. Since static interfacial tension measurements do not yield information about the true age of the interface, it is conceivable that the measured interfacial tension values may not correspond to equilibrium interfacial tension values (i.e., the exchange of molecules between the bulk and the interface has not yet reached full equilibrium and the interfacial tension values are therefore not static). If the surfactant used in the experiment adsorbs within a few seconds, which is the case for small-molecule surfactants, then both the Wilhelmy plate method and the du Noiiy ring method are adequate. If the adsorption of a surfactant requires more time to reach full equilibrium, then the measurement should not be conducted until the interfacial tension values have stabilized. Since interfacial tension values are continuously displayed with... 

The time required to conduct an interfacial tension experiment depends largely on the properties of the surfactants and less on the chosen measurement method. A notable exception is the drop volume technique, which, due to the measurement principle, requires substantial ly more time than the drop shape analysis method. Regardless of the method used, 1 day or more may be required to accurately determine, e.g., the adsorption isotherm (unit D3.s) of a protein. This is because, at low protein concentrations, it can take several hours to reach full equilibrium between proteins in the bulk phase and those at the surface due to structural rearrangement processes. This is especially important for static interfacial tension measurements (see Basic Protocol 1 and Alternate Protocols 1 and 2). If the interfacial tension is measured before the exchange of molecules... 

D. Q. M. Craig, El. S. R. Lievens, K. G. Pitt, and D. E. Storey, An investigation into the physico-chemical properties of self-emulsifying systems using low frequency dielectric spectroscopy, surface tension measurements and particle size analysis, Int. J. Pharmaceut. 96 147-155 (1993). 

One of the greatest difficulties in making surface tension measurements is ensuring the purity of the substance studied. Minute amounts of impurity, by concentrating at the surface, can make an appreciable difference in measured surface properties. Small amounts of reactive or condensable impurities in the gas phase can also greatly influence measured surface tensions. 

Films of the complexes are stable in water at a pH of 7 while they dissolve at pH 5. This can be explained by the pKa value of retinoic acid, which is, for example, 6.05 in 150 mM NaCl and 6.49 in 5 mM NaCl [163]. Therefore, the anionic retinoic moieties within the complexes will be protonated at pH values lower than the pKa which lead to the cleavage of the ionic bonds in the complexes. The first experiments to evaluate the release properties of retinoic acid from thin films of the complexes were performed by using FTIR and surface tension measurements. Films were immersed in solutions of 0.15 m sodium chloride at pH 5 for both methods. The increase of the absorbance at 1255 cm-1 (C-0 stretch vibration) [186] in the FTIR spectra was used as a qualitative measure for the release of retinoic acid from the PEI-retinoate complexes. For comparison, the spectra of the complex and of the non-com-plexed retinoic acid are shown at wave numbers around 1255 cm 1 (Fig. 26, insert curves a and b). The time-dependency of the absorbance, which is a relative measure of the amount of released retinoic acid, is shown in Fig. 26. It can be seen that the increase of the absorbance, and therefore the release... 

Table 3.3 provides surface tensions yLV for common adhesive liquids and critical surface tension yc for various solids. A brief discussion of how these properties are measured follows. 

Physical properties of the three test fuels are presented in Table I. Except for the surface tension of No. 6 fuel oil, which was a typical value, all properties were measured for the specific samples tested. The primary differences between the SRC-II middle distillate and the No. 2 fuel were the higher specific gravity, surface tension, and viscosity of the SRC-II. The No. 6 grade fuel, a residual fuel oil, had a much higher viscosity than either of the distillate fuels. Both the SRC-II and No. 2 fuel oil were sprayed at a nominal temperature of 80°F to simulate usage in a non-preheat combustion system. The No. 6 fuel oil was sprayed at temperatures ranging from 150° to 240°F in order to assess spray formation processes and spray quality over a broad range of viscosities. 

Compatibility of polymers implies a semi-quantitative measure can be used to predict whether two or more polymers are compatible. The use of one of the semi-quantitative approaches, solubility parameter, was demonstrated by Hughes and Britt (22). It was concluded (8) that one parameter was insufficient to predict the compatibility. In this paper, we now introduce critical surface tension which is determined from the surface properties of a polymer. Though both of these parameters have been related by Gardon (15), we are inclined to use the latter because we can further describe the wettability between two polymers. For instance, by the use of yc, we can predict equally well that compatibility between polystyrene and polybutadiene can be improved if butadiene is... 

The interface between plastic and wood fibres strongly influences the mechanical properties of a plastic/wood fibre composite. A means for evaluating the effectiveness of surface treatment on the wood fibres in the PVC/wood fibre composites is presented that investigated the adhesion between PVC and laminated wood veneers. Wood veneers were first treated with gamma-aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated PP for surface modification. The chemical modification made on the wood surfaces was then characterised by different complementary surface analytical techniques X-ray photoelectron spectroscopy and surface tension measurements. 63 refs. 

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