Data interpretation contact angle

Any effort, such as that of Good and Girifalco [38], to interpret contact angle data in terms of the relevant solid-fluid interfacial tensions, is also faced with a similar problem with respect to assigning... 

Interaction Parameters. A valuable approach to the problem of interpreting contact angle data has been initiated by Good and Girifalco [38]. As noted above, this approach is based on an expression relating the interfacial tension for two immiscible phases to the surface tensions of the individual phases [36,37]. If one of the phases is a solid, this expression is... 

Bearing these arguments in mind it is not surprising that values of 0O for most systems (see Table I) correlate poorly with data reported in Table II. Until more meangingful surface physicochemical data are available the interpretation, or application of contact angle measurements to develop sorptive models for paper, remains highly questionable. 

The modified Cassie-Baxter equation was successfully used to interpret some of the contact angle data reported for heterogeneous surfaces. 

A more detailed characterization of the pore-size characteristics of AGM can be obtained with the mercury intrusion technique. This is based on the principle that the external pressure required to force a non-wetting liquid into a pore against the opposing force of surface tension depends on the pore size. The technique is widely employed to characterize porous materials, and provides data on pore diameter, pore-size distribution, and pore volume. Some caution must be apphed in interpreting the results, however, because of the assumptions that are made concerning cylindrical pores, contact angle, and the surface tension of mercury. 

A review that puts contact angle measurement techniques in a contemporary context has been published by Good (18). With respect to biomaterials studies, the following limitations of contact angle measurements should be kept in mind during data analysis and interpretation ... 

Relevant to the arguments put forward is the relationship introduced by Girifalco and Good [36,39]. Their expression relates the interfacial tension for two immiscible liquid phases to the surface tensions of the individual liquids. The application of this approach to the interpretation of contact angle data was suggested in a later paper by these authors [38]. Our approach, however, is developed under somewhat different basic assumptions and with rather different results. 

Any discussion leading to the interpretation of contact angle measurements, such as that presented below, presupposes the existence of a body of reliable experimental data. Such data are now available, due to the efforts of Zisman and his collaborators at the Naval Research Laboratory. This situation is the result of solving a number of problems connected with the preparation of suitable solid surfaces. These problems had presented major difficulties in the field of contact angle studies ever since its inception and hence had prevented any substantial progress. 

As already mentioned, the interpretation of data on static contact angles must be done with the understanding that the system in question has been sufficiently weU controlled so that the angle measured is the true angle and not a reflection of some contaminant on the sohd surface or in the hquid phase of interest. Contact angles, for example, can be extremely useful as a... 

To summarize, while contact angle measurements represent a potentially powerful and practical tool for characterizing the nature and wettability of sohd surfaces, variability leading to errors in interpretation can arise from various sources. That means that proper attention must be focused on experimental conditions, equilibria, sohd and liquid purity, and so on, to ensure the best possible data. Even when all precautions have apparently been taken, interpretation must be done with the above-mentioned caveats in mind. Nevertheless, contact angle data should never be excluded from studies or processes in which wetting and spreading are involved. 

Mechanistic interpretations The results of the dynamic and equilibrium displacement experiments are used to evaluate and further define mechanisms by which alkaline floods increase the displacement and recovery of acidic oil in secondary mode and the tertiary mode floods. The data sets used in the mechanistic interpretations of alkaline floods are (a) overall and incremental recovery efficiencies from dynamic and equilibrium displacement experiments, (b) production and effluent concentration profiles from dynamic displacement experiments, (c) capillary pressure as a function of saturation curves and conditions of wettability from equilibrium displacement experiments, (d) interfacial tension reduction and contact angle alteration after contact of aqueous alkali with acidic oil and, (e) emulsion type, stability, size and mode of formation. These data sets are used to interpret the results of the partially scaled dynamic experiments in terms of two-stage phase alteration mechanisms of emulsification followed by entrapment, entrainment, degrees and states of wettability alteration or coalescence. 

Schultz et al. [175] used fl(yP) " as a comparison scale. The parameter a is the area of the adsorbed probe molecule [176]. It is obtained from IGC measurements on neutral reference solids such as polyethylene or PTFE. Some examples are n-hexane, 51.5A ether, 47A chloroform, 44A and acetone, 42.5A. In standard fashion, yP is determined from contact angle measurements on reference solids [176]. Once again, some probes fall under the reference line of the n-alkanes, and the data are difficult to interpret. This constitutes a limiting factor of this method. 

---