Water, contact angle rearrangement

When the membrane is placed in liquid water, rearrangement and a phase-transition occur. This could be due to surface rearrangements wherein the fluorocarbon-rich skin of the membrane is repelled from the interface between the water and membrane. What this means is that in order to minimize the energy of the system the side chains and backbone of the polymer reorient so that the chains are now arranged at the membrane/ water interface. This hypothesis agrees with the data that show that the water contact angle on the membrane surface becomes more hydrophilic after the membrane is placed in liquid water [32]. The presence of liquid water also results in the removal of a vapor-liquid meniscus, which could also aid in the above rearrangements [28]. 

It is by rearranging this equation and assuming 9 to be zero that we obtain Eq. (4). For practical purposes, plates that are about 2 cm wide satisfy the theoretical requirement of infinite width. For such a plate (assumed to have a uniform surface), the line of contact is straight in the central part of the plate for all liquids of moderate surface tension, including water. If we assume g. A(0, and )/ V to be known, the task of determining a contact angle is reduced to the measurement of a length (the capillary rise h), which can be determined optically, e g., with a cathetometer. 

A useful example is graphite. The contact angle of water on graphite was found to be 85.7° and was 19 dynes per cm. [8,13]. Kwe assume that graphite and water interact entirely by dispersion forces, we can use Equation 4, rearranged as... 

Replicas of these slides were prepared immediately after the contact angle measurements were completed. Saturated monolayers were expected to be stable, but rearrangement in incomplete monolayers, or in monolayers incorporating appreciable amounts of solvent, was considered a definite possibility [2]. Just before the specimen was placed in the evaporator, a water suspension of polystyrene latex spheres of about 0.09-micron diameter was sprayed onto the monolayered surface with a nebulizer. The presence of a sphere in the micrograph allows quick differentiation between holes in a nearly complete film and islands of acid molecules rising above the substrate surface. The spheres... 

When layers of certain block copolymers of ethylene oxide and butylene oxide are contacted with water, there is an initial period when the position of the interface is proportional to tm, where m < 0.5 [32]. That is, initial swelling is not controlled by diffusion but instead by hydration and rearrangement of the long molecules to form the various phases. In the case of (EO)i6(BO)22 small-angle X-ray scattering did detect evidence of both reverse hexagonal and lamellar phases during this initial period, but it was not clear whether all the swollen block copolymer layer consisted of these phases or how the... 

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