Experiment 2.2 Contact angle measurements

The value of the equilibrium contact angle (9) at the three-phase line (TPL) produced by a liquid droplet placed on a flat, solid substrate is determined by the balance of interfacial energies at each surface. Thomas Young derived an equation describing this situation in 1804  

Contact angle measurements are of fundamental importance in a range of industrial and everyday processes such as flotation, painting (i.e. the paint must wet the substrate) and weather-proofing. In the flotation process a solid block of the powdered mineral to be floated is often studied using a wide range of collector (i.e. surfactant) solutions to determine optimum flotation conditions. 

In this experiment Yc will be determined for methylated (hydrophobic) soda glass. Both advancing (0a) and receding (0r) angles will be measured in order to estimate the degree of hysteresis in each case. Use the values of both 0a and 0r, as well as the average, to produce several Zisman plots. 

Follow a similar procedure to measure the receding angle (0r) but slowly withdraw liquid into the syringe and measure the minimum angle just before the TPL moves. 

The hydrochloric acid vapour evolved is toxic and all reactions should be carried out in a fume cupboard. 

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We thank John Frackoviak, Avi Kornblit, Nick Ciampa and Hans Stocker for fabrication of the topographic substrates and for performing some of the reactive-ion etching experiments. We also thank Molly Heilman for doing chromatographic analysis of some of the resins, and Ken Takahashi, Frank Ventrice and Reddy Raju for contact angle measurements, assistance with Tg measurements and helpful discussions. 

The adsorption of alkyl and aryl isocyanides on Au film [26, 32, 33], powder [36, 37] and nanoparticles [39, 41, 42] has been studied using several different techniques IR methods (RAIR, ATR-IR, DRIFT), Raman methods (SERS), X-ray methods (NEXAFS), ellipsometry (OE, SWE) and contact angle measurements (ACA). The gold surface is not oxidized under normal conditions consequently, the experiments were performed in air at room temperature. The gold film was obtained by physical vapor deposition of 100-200 nm of gold on different substrates glass [28, 33], mica [33], silicon [25, 27, 31, 32], ZnSe crystal [26]. A... 

Acknowledgement The authors wish to acknowledge Deutsche Forschungsgemeinschaft (DFG) and European Graduate College (EGS 720) Advanced Polymer Materials for the financial support. The authors are also thankful to A. Rudolph for XPS measurements, M. Dziewiencki for contact angle measurements and K. Kretschmer for help with SPR experiments. 

Procedure. With the exception of poly (ethylene terephthalate), 20/ films of each polymer were prepared by the evaporation or approximately 4% solutions in quartz or glass dishes of 50 cm.2 area for extraction experiments. For contact angle measurements, films were evaporated on acid-cleaned microscope slides by a dipping technique. Tetrahydrofuran was used with poly (vinyl chloride), methylene chloride with the other polymers. 

In all the experiments, oscillations of the triple line around the final position (corresponding to 0F = 40-45° and RF s 3-3.5 mm) are observed. Curves in Figure 2.3 show that the first contact angle, measured after about 1 ms, is close to the final value 0F, but at this moment the drop is clearly non-spherical (Figure 2.4). Thereafter, oscillations around RF and 0F are observed which decay in about 102 ms. At this time, the droplet becomes a nearly spherical cap (Figure 2.4). Because external forces act at the moment of impact of the drop on the solid, it is... 

The second set of experiments was performed to investigate the effect of equivalence ratio. An addition of N2O totaling 4% of the total oxidizing-species reactant flow was selected. Contact angle measurements showed that (a) the wettability of the polymer surface improved, relative to treatment with methane/air flames, and... 

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