Contact angles experimental details

Before we can discuss the experimental techniques used to measure the surface tension, we need to introduce the so called contact angle 0. When we put a drop of liquid on a solid surface the edge usually forms a defined angle which depends only on the material properties of the liquid and the solid (Fig. 2.8). This is the contact angle. Here we only need to know what it is. In Chapter 8, contact angle phenomena are discussed in more detail. For a wetting surface we have 0 = 0. 

The pore volumes and pore sizes were measured with a Micromeri-tics Model 910 mercury porosimeter by assuming a contact angle of 130 degrees. Oil products were routinely analyzed for hydrogen and nitrogen contents with a Perkin-Elmer Model 240B elemental analyzer. More details on this experimental work have been reported by Crynes (13). 

ADSA-P has been employed in various surface tension and contact angle studies, including static (advancing) contact angles [69.70], dynamic (advancing) contact angles at slow motion of the three-phase contact line [4, 71—74], and contact angle kinetics of surfactant solutions [75]. A schematic of the experimental setup for ADSA-P sessile drops is shown in Fig. 6. More details are available elsewhere [66[. 

This result is general and can be applied to any two fluids, provided the meniscus has a spherical shape. The difficulty in using this technique arises when the contact angle is not known or when the capillary is not a perfect cylinder. This means that the experimental system is usually calibrated using a system of known interfacial tension. Other problems arise when the meniscus is not perfectly spherical. These have been discussed in detail by Adamson [Gl]. 

Interfadal tension between two fluid phases is a definite and accurately measurable property depending on the properties of both phases. Also, the contact angle, depending now on the properties of the three phases, is an accurately measurable property. Experimental approaches are described, e.g., in Refs. 8,60, and 63 and in Ref. 62, where especially detailed discussion of the Wilhehny technique is presented. Theories such as harmonic mean theory, geometric mean theory, and acid base theory (reviewed, e.g., in Refs. 8, 20, and 64) allow calculation of the soHd surface energy (because it is difficult to directly measure) from the contact angle measurements with selected test liquids with known surface tension values. These theories require introduction of polar and dispersive components of the surface free energy. 

A major part of these projects was also dedicated to understanding the bulk and solution structural organization of such polymers and here we would like to refer the reader to appropriate literature [56, 58]. While it was shown that the am-phiphile nature of the terpolymer system, and in particular the phosphorylcholine (PC) groups, played an Important role in the structure organization and molecular mobility of the copolymers, the results displayed in the present discussion focus on how the presence of these PC groups impacted on the surface properties of the copolymer synthesized. With this aim in mind, surface analytical techniques such as XPS and ToF-SIMS were used and complemented with contact angles and biolog leal In-vltro assays to characterize the dynamics of the copolymers surface and as sess the extent of the resistance to the non-specific attachment of cells on samples coated with the PC copolymers (for experimental details, refer to [56,58]). 

It is usually called axisymmetric drop shape analysis.The interfacial tension and contact angles are determined from the shape of the axisymmetric menisci of both sessile and pendant drops. The employed strategy is to fit the shape of an experimental drop to the theoretical drop profile according to the Laplace equation, using surface tension as adjustable parameter. Details of the methodology together with a program to implement it can be found elsewhere. ... 

Even in a complete wetting situation, the macroscopic dynamic contact angle has then a finite value which has been studied in great details both theoretically and experimentally. The properties of the liquid in the vicinity of the contact line are not however well described by macroscopic concepts, it is now well established that an advancing liquid front is preceded by a... 

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