Contact angle measurements liquid films

The critical surface tension has been evaluated by means of advancing contact angle measurements for water, various hydrocarbon liquids and for plasma polymerized fluorocarbon films " " . The most comprehensive, however, is that of Yasuda... 

As we see in Chapter 6, surface tension and contact angle measurements provide information on liquid-liquid and solid-liquid adhesion energies (Fig. 1.26c). Contact angles measured under different atmospheric environments or as a function of time provide valuable insights into the states of surfaces and adsorbed films and of molecular reorientation times at interfaces. 

Gas permeabilities for 02, N2 and CO2 were realised with Lyssy GPM 20 apparatus. Surface tensions of modified and unmodified polymers films were derived from contact angle measurements which were evaluated with six liquids (H20, HCONH2, Hg, CH2I2, tricresyl-phosphate and 1 -bromonaphtalene). 

The wettability of a polymer film normally is determined by static contact angle measurements. The surface free energy (SE) of a polymer can be determined by wettability measurements with two different liquids. The dispersion force and polar contributions to SE, 7 d and 7 p respectively, are also calculated normally by using the Owens and Wendt, and Kaelble methods [146,147], The measurements of contact angles (CA) on a given solid surface is one of the most practical ways to obtain surface free energies. 

Contact angles for a variety of liquids on pure amorphous polymer surfaces have been reported by Zisman and co-workers (12, 13). They have also shown (8) that the diffusion of low-molecular weight compounds from within a solid polymer film to its surface results in adsorption and a subsequent change in the wettability of that surface by specific liquids. In a few instances (9, 10), contact angle measurements have been used to show that surface changes in polymers are induced by ionizing radiation. 

All films prepared for contact angle studies were cast from an excess of dry polymer swollen and fluidized by a small quantity of added liquid (usually triple-distilled water, the last two distillations being in an allquartz apparatus). The pH of these weak gels at the initiation of film formation was always 5. All our surface films were gel-dried rather than sol-dried. Although swelling may not have reached equilibrium prior to film drying, the films were only about 1 mm thick and their surface properties, as determined by contact angle measurements, were always reproducible within 5°. 

Prins and Clint et al. developed a method of contact angle measurement for macroscopic flat foam films formed in a glass frame in contact with a bulk liquid. They measured the jump in the force exerted on the film at the moment when the contact angle is formed. A similar experimental setup was used by Yamanaka for measurement of the velocity of motion of the three-phase contact line. 

The concept for the rupture of a free liquid film or a thin liquid film on a solid substrate is used in some applications, for example in the flotation process. Scheludko et al. (1968) have published first contact angle measurements for liquid films. 

Surface free energies of hydroxylapatite and fluorapatite were determined by Busscher et al. (1987) from contact angle measurements. They found that in vacuum y ranges between 72 and 95 mJ/m. In the presence of a saturated vapor, y was found to be between 28 and 48 mJ/m. The difference in y obtained by the two methods was explained as resulting from the presence of an adsorbed film originating from the liquid droplets employed in the measuring procedure. Face-specific measurements revealed for the 001 crystal face y = 28 3 mJ/m, and y = 48 7 mJ/m on 100 for fluorapatite, and for hydroxylapatite the 001 crystal face y = 39 11 mJ/m, and y = 30 3 mJ/m on... 

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