Contact angles surfaces

To inspect for contaminants, a water break test is frequently employed. Water, being a polar molecule, will wet a high-energy surface (contact angle near 180 ), such as a clean metal oxide, but will bead-up on a low-energy surface characteristic of most organic materials. If the water flows uniformly over the entire surface, the surface can be assumed to clean, but if it beads-up or does not wet an area, that area probably has an organic contaminant that will require the part be re-processed. 

Being sensitive to the chemical composition of the outermost layers of the surface, contact angle measurement is widely used for characterizing polymer surfaces. Surface characterization for polymers using contact angle measurement and XPS will now be described in detail, as these are the most widely used methods. 

Hybrid organosilicon-organophosphazene polymers have also been synthesized (15-18) (structure ) (the organosilicon groups were introduced via the chemistry shown in Scheme 11). These are elastomers with surface contact angles in the region of 106°. Although no biocompatibility tests have been conducted on these polymers, the molecular structure and material properties would be expected to be similar to or an improvement over those of polysiloxane (silicone) polymers. 

The low temperature ene reactions of 4-substituted-l,2,4-triazoline-3,5-diones (RTD) were used to modify polydiene surfaces. Hydrophilic surfaces (contact angles with water of 30-50°) were obtained on polybutadiene, poly-isoprene and styrene-butadiene copolymers by first treating the polymer at room temperature with RTD (R=Ph,... 

The use of lightly crosslinked polymers did result in hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although qualitatively they appeared to remain hydrophilic, reliable contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene triblock copolymer thermoplastic elastomer did not show improved permanence of the hydrophilicity over other polydienes treated with PhTD. The block copolymer film was cast from toluene, and transmission electron microscopy showed that the continuous phase was the polybutadiene portion of the copolymer. Both polystyrene and polybutadiene domains are present at the surface. This would probably limit the maximum hydrophilicity obtainable since the RTD reagents are not expected to modify the polystyrene domains. 

Table 1. Air/water/surface contact angles measured using the Wilhelmy plate method on surfaces incubated with deionised water for 10 minutes.

The relationship between the cosine of the drop /surface contact angle and the three surface tensions is given by Young s equation, as follows ... 

A number of studies have examined fibril formation in the presence of different solid nonbiological surfaces, as summarized in Table 1. While many of these studies have focused on the formation of fibrils, the wettability and RMS of some surfaces have been characterized. Typical surface contact angles are also presented in Table 1 to aid comparison between these surface-based experiments. 

The problem here consists in listing the material parameters because, in activated sludge, they fluctuate strongly (much in contrast to ore flotation). Surely, the degree of hydrophobicity (wettability) of the particle surface (contact angle, ) will be of importance. Furthermore, the pH value, the concentration of the flocculant (poly-electrolyte), cF, the portion of solids, [Pg.30]

Amphiphilic copolymers have been prepared that have reduced surface contact angles and are effective as emulsifying agents or absorbents. These materials were prepared by reacting poly[styrene-b-poly(ethylene-butylene)-g-succinic anhydride-b-polysty-rene)] [Kraton G 1901 ] with methoxypolyethylene glycols having M s between 2000 and 8000 daltons. 

Plasma treatment penetrates through a porous structure, i.e., it is not limited to the exposed surface. Contact angle cannot be measured because a water droplet penetrates quickly into the fabric. Contact angle can be measured but a water droplet penetrates slowly into the fabric. 

Figure 18.5 Surface contact angle changes of PTFE with exposure time in an argon RF plasma 2 seem argon, lOOmtorr, and 7W RF.

Figure 18.9 Surface contact angle changes of LTCAT Ar treated PTFE with varying (a) argon flow rate at 6.0 A arc current and (b) arc current at 1500 seem argon for 10 s exposure to a low-temperature cascade arc torch.

Figure 18.10 Surface contact angle changes of PTFE with exposure time in a low-temperature cascade arc torch at sample positions of 9 in. (in glow) and 14 in. (out of glow) from the torch inlet 1500 seem argon, 6.0 A arc current.

Figure 18.11 Surface contact angle changes of LTCAT treated PTFE film with aging time 1500 seem argon, 6.0 A arc current.

Figure 18.12 Surface contact angle changes of LTCAT treated PTFE (a) dependence on hydrogen feed rate at 6.0 A arc current, 1500 seem argon flow rate, and 1.0 min treatment, and (b) dependence on exposure time at 6.0 A arc current, 1500 seem argon flow rate, 20 seem hydrogen, 1.0 min treatment.

Samples on silica surface Contact angle (degrees)... 

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