Surface characterization contact angle data

To summarize, while contact angle measurements represent a potentially powerful and practical tool for characterizing the nature and wettability of sohd surfaces, variability leading to errors in interpretation can arise from various sources. That means that proper attention must be focused on experimental conditions, equilibria, sohd and liquid purity, and so on, to ensure the best possible data. Even when all precautions have apparently been taken, interpretation must be done with the above-mentioned caveats in mind. Nevertheless, contact angle data should never be excluded from studies or processes in which wetting and spreading are involved. 

AU theories, in combination with contact angle data and information from liquid interfaces, will be used later in the book (Chapter 6) for estimating the interfacial tensions of solid-interfaces (solid-liquid, soUd-soUd) and for characterizing solid surfaces and thus for understanding important phenomena such as wetting, lubrication and adhesion. Charter 15 offers a more detailed presentation of theories for estimating the interfacial tension as weU as some comparisons between them. 

Characterize the polyethylene (PE) and Teflon (PTFE) surfaces of Example 15.1 using the PSP method and, when needed, the reported (in Example 15.1) contact angle data for water and methylene iodide (MI). 

How can solid surfaces be characterized using contact angle data and a theory for the interfacial tension How many experimental data are needed ... 

In conclusion, it should be noted that the width of the transition region between a thin liquid film and Plateau border is usually very small — below 1 pm. That is why the optical measurements of the meniscus profile give information about the thickness of the Plateau border in the region r > (Figure 5.16). Then, if the data are processed by means of the Laplace equation (Equation 5.101), one determines the contact angle, a, as discussed above. Despite that it is a purely macroscopic quantity, a characterizes the magnitude of the surface forces inside the thin liquid film, as implied by Equation 5.148. This has been pointed out by Derjaguin and Princen and Mason. ... 

A more detailed characterization of the pore-size characteristics of AGM can be obtained with the mercury intrusion technique. This is based on the principle that the external pressure required to force a non-wetting liquid into a pore against the opposing force of surface tension depends on the pore size. The technique is widely employed to characterize porous materials, and provides data on pore diameter, pore-size distribution, and pore volume. Some caution must be apphed in interpreting the results, however, because of the assumptions that are made concerning cylindrical pores, contact angle, and the surface tension of mercury. 

Relatively few data are available for the wetting of low-energy surfaces by liquid metals. Reliable contact angles are available, however, for mercury (y v =485 dynes per cm.) on three different surfaces. When plotted as a function of (y y - y )j their data points suggest that a linear limiting relation also characterizes the wetting properties of this liquid metal. 

Characterization of the membrane surface It should be emphasized that the properties of the membrane surface strongly affect membrane performance. Contact angle is often used as a measure of surface hydrophilicity or hydrophobicity. X-ray photoelectron spectroscopy (XPS) provides the data on atomic compositions at the membrane surface. Recently, attentions have been focused on the nodular structure as well as the roughness at the membrane surface that can be measured by atomic force microscopy (AFM). 

Temperature-dependent spreading experiments were carried out at 6"C, 26 C and 40"C on trimethylsilyl-modified silicon wafers (10 pi surfactant solution drops). Prior to these experiments the wafer pieces were energetically characterized by contact angle measurements versus water, hexadecane, pentadecane and tetradecane (Table 2). The data for the strictly non-polar alkanes (yiv = were used to calculate Ysv (Neumann [12], Eq. 1) and Ysv " (Good [13], Eq. 2). The practical identity between Ysv and indicates that this surface is of a non polar character. 

---