Critical surface tension determination

Talde 2. The "Miscellaneous Liquids for Critical Surface Tension Determinations... 

Take the data from Fig. X-12 on the propyl monolayers and make a Zisman plot to determine the critical surface tension for the surface. 

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. 

Despite the conflicting evidence, Heyes and Trahar (1984) believe there is sufficient evidence to confirm the presence of sulphur on mineral surface. They leached the surface of floated pyrrhotite from a typical test with cyclohexane and have examined the leach solution in a UV spectrophotometer. They found that sulphur could be extracted from the surface of pyrrhotite, which had been floated in the absence of collector. As can be seen from Fig. 2.26, the spectrum from the leached pyrrhotite was compared with the spectrum of sulphur dissolved in cyclohexane indicating that sulphur was present at the siuface. Kelebek and Smith (1989) used UV spectrophotometer to determine sulphur in the ethanol extract from the surface of floated galena and chalcopyrite showing that the amount of sulphur on the minerals can be correlated with their flotation rate which was found to be first order within the critical surface tension range. 

Critical surface tension (Yc) of the oiled CDC Ni-plated sheets apparently is determined by the polar group concentration of oil and metallic elements (Cr and Ni). Yc increases with increasing the polar group concentration of oil and, therefore, the improvement of adhesion due to the higher polarity of oil was also supported by thermodynamical aspect (wettability). 

The ability of a liquid to "wet" the membrane material is an indication of that liquids ability to establish and maintain such an interfacial layer. Liquids of surface tension values less than the critical surface tension iy ) of the membrane material are capable of completely "wetting" the polymer. It may be possible therefore, to select membrane materials capable of accomplishing specific separations by their ability to be wet by one solution component but not by the other. For this reason Yc membrane materials is important. By employing the standard techniques of Zisman (43), the critical surface tension for PSF and CA were determined to be 43.0 and 36.5 dynes/cm, respectively. This data indicates that PSF is more readily wet by a larger number of liquids than is CA. Similar measurements for the various sulfonated polysulfones are underway. 

Liquids used to determine the critical surface tension of methylated glass... 

The word "aspects is intentionally used in the title of this book because of the broadness it allows in the subject matter. It allows a discussion of principles such as in Chapter 20. Here the principles have been established, and reference has been made to their possible utilization in determining the critical surface tension of an insect. Perhaps this paper will stimulate workers to do obvious research which could yield data explaining the specificity in control of various insects. The word aspects also allows a discussion of the direct use of these physicochemical principles to solve formulation problems such as the paper by Freed and Witt on the translocation of herbicides in plants. Thirdly, this symposium contains papers dealing with phenomena that clearly are physical and colloidal but which have not as yet been the subject of rigorous physical chemical studies. For example, in Lyon s paper the effect of varying crystal size is shown to be very important in controlling... 

Determination of Critical Surface Tension. The method for the determination of contact angles was described in previous papers (37, 38). For this study, we used only one goniometer manufactured by Rame-Hart, Inc. The temperature was controlled at 20 °C. with an environmental chamber. The precision was 2° for the contact angle measurement. The liquids used were alcohols, Polyglycols P-1200, 15-200, and E-200, ethylene glycol, formamide, glycerol, and water. 

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... 

Critical surface tensions (yc) of a series of functional polymers were determined. These results are compared with those calculated on the basis of solubility parameter (8) according to the following equation ... 

There are some uncontrollable factors affecting the determination of critical surface tension—e.g., the type of liquids used, the type of interaction between a liquid and a solid, the homogeneity of surface, etc. An ideal correlation should be made from the direct surface tension, if available, of a polymer melt. 

Critical surface tensions of functional polymers were experimentally determined. This set of data and the data on elastomers obtained previously were used to elucidate the proposed solubility parameter-surface tension relationship and the proposed parachor-surface tension relationship. The results show that the former has a higher correlation coefficient than the latter. The correlation coefficients, including three highly hydrogen-bonded polymers, are 0.731 for the former and 0.299 for the latter. Otherwise, they are 0.762 for the former and 0.178 for the latter. For the size of samples examined, we can conclude that the proposed solubility parameter-relationship is more effective than the proposed parachor-relationship in calculating critical surface tension of a polymer. 

Laboratory in carrying out the analysis of variance. The author appreciates the help of Ryong-Joon Roe of E. I. duPont de Nemours and Co. for sending his manuscript prior to publication and E. G. Shafrin of the Naval Research Laboratory for discussing experimental techniques in the determination of critical surface tension. The author is indebted to both referees for many valuable comments. 

Wettability. A description of the contact angle goniometer and the scheme used in determining the critical surface tension of wetting (yc) are described elsewhere (15, 18). 

Surface tension studies of the most common fluorosilicone, poly(3,3,3-trifluoropropylmethylsiloxane) (PTFPMS), give unexpected results. Compared with (PDMS), PTFPMS has a higher liquid surface tension, a similar critical surface tension of wetting, and a considerably lower solid surface tension, as determined by water and methylene iodide contact angles and the method of Owens and Wendt (67). These results are summarized in Table X (7, 67, 72-74, 76, 77), in which PTFPMS is compared with two other fluorocarbon polymers, poly(tetrafluoroethylene) (PTFE) and poly(chlorotrifluoroethylene) (PCTFE). PTFE behaves like PTFPMS, whereas PCTFE behaves like PDMS. 

Mohandas and co-workers (18), confirming previous findings of Weiss and Blumenson (19), have also shown that cells in an environment free of adsorbable proteins (which rapidly modify the surface properties of polymeric or inorganic substrates) will exhibit a similar direct relationship between their adhesion and the critical surface tension of the surface they contacted. DiflFerential adhesion of red blood cells was measured by determining the fraction of cells retained on a surface after the application of well-calibrated shear stresses (IS). In protein-free experiments, the red cells (themselves dominated in adhesive interactions by their protein membranes) had greatest adhesion to glass, intermediate adhesion to polyethylene and siliconized glass, and least adhesion to Teflon. 

---