Roughness and contact angle

In the context of the structural perturbations at fluid-solid interfaces, it is interesting to investigate the viscosity of thin liquid films. Eaily work on thin-film viscosity by Deijaguin and co-workers used a blow off technique to cause a liquid film to thin. This work showed elevated viscosities for some materials [98] and thin film viscosities lower than the bulk for others [99, 100]. Some controversial issues were raised particularly regarding surface roughness and contact angles in the experiments [101-103]. Entirely different types of data on clays caused Low [104] to conclude that the viscosity of interlayer water in clays is greater than that of bulk water. 

Table 3. Surface Roughness and Contact Angle Hysteresis Plates...

R.N. Wenzel, Surface roughness and contact angle, /. Phys. Colloid Chem., 53, 1466-1467(1949). 

Table 5.7 Roughness and contact angle of PIMs and the hydrophobic property of ionic liquid plasticizers...

The effect of surface roughness on contact angle was modeled by several authors about 50 years ago (42, 45, 63, 64]. The basic idea was to account for roughness through r, the ratio of the actual to projected area. Thus = rA. lj apparent and similarly for such that the Young equation (Eq.-X-18) becomes... 

As can be seen in Table 6.5, ONB in APG solution of concentration C = 100 ppm took place at significantly higher surface temperatures. It should be noted that the ONB in surfactant solutions may not be solely associated with static surface tension Sher and Hetsroni (2002). Other parameters such as heat flux, mass flux, kind of surfactant, surface materials, surface treatments, surface roughness, dynamic surface tension and contact angle need to be considered as well. 

Test methods used to determine the uniformity of substrates are numerous and vary with the type of material. They are generally the same tests used to characterize the material or to determine its fundamental physical properties. Tests that are commonly employed are hardness, tensile strength, modulus, and surface characteristics such as roughness or contact angle with a standard liquid. Often a test similar to the nonvolatile test mentioned above is used to determine if there are any compounds in the substrate that are capable of out-gassing on exposure to elevated temperatures. Moisture content of certain hydroscopic polymers, such as nylon and polycarbonate, is also known to affect adhesion. 

The real surfaces are characterized by a certain extent of roughness. It is assumed that film thickness cannot be lower than the wall roughness value. When film thickness achieves this value, the film ruptured may occur depending on rivulet width, which corresponds to film flow rate at that time. With this statement the system of equations proves to contain the relationship describing the flow rate in a rivulet in the dependence on its length and contact angle. This correlation was obtained by the same way as that for the meniscus flow rate. 

As the untreated surface and the weakly ablated one possess the same surface roughness parameter, contact angles may be compared. Hence for all the test hquids used, the contact angles are by 10-20° lower on the slightly ablated samples than on the untreated surfaces. 

Fig. 6. Effect of roughness on contact angle A, maximum and minimum angle B, Wenzel equation (lower) and Cassie and Baxter equation (upper) 6, and 6 possible receding and advancing angles (Ref. )...

FIGURE 10.15 Comparison between Ising model and CNT results for AGi,eterogeneous / AGhomogeneous as a function of roughness coefficient (contact angle of 90°). (Adapted with permission from Curcio et al., J. Phys. Chem. B, 114,13650-13655. Copyright 2010 American Chemical Society.)... 

For surface roughness evaluation, contact angle of water was measured on a surface coated with a water-repellent agent Heptadecafluorodecyltrimethoxysi-lane, which is a fluoroalkyltrimethoxysilane (FAS), was used as the water-repellent agent the partially hydrolyzed FAS was coated on the flowerlike AI2O3 thin films and dried at 60°C for 20 h. 

Cell proliferation 3 days after the seeding is comparable with tissue PS. For both cell adhesion and proliferation maximum positive effect is seen on the samples carbon coated from the distance 4 cm. In this case the carbon layer is about 32 nm thick and it exhibits the higher roughness, good electrical conductivity and contact angle of about 80°. Low surface roughness and wettability seem to have negative effect on the cell adhesion and proliferation [41]. 

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