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Surface Forces and Equilibrium of Liquids on Solid Substrates
Published in Victor M. Starov, Manuel G. Velarde, Wetting and Spreading Dynamics, 2019
Victor M. Starov, Manuel G. Velarde
In the case of oil droplets on the glass surface, when the dispersion component is the only component of the Derjaguin’s pressure acting in thin films, the dispersion interaction is repulsive, that is, the Hamaker constant is positive. Below we mostly consider the case of thin liquid films on solid substrates where the Hamaker constant is positive. Note that in this book the definition of the Hamaker constant is slightly different from Eq. (1.10) () Πm=Ah3,A=−AH6π
Material-related and various dependences of adhesion force on piezo velocity revealed on an AFM at moderate humidity
Published in The Journal of Adhesion, 2023
Tianmao Lai, Siyuan Qiu, Runsheng Wang
where, AH is the Hamaker constant, D0 is the effective distance. The Hamaker constant includes all physic-chemical information of the contacting surfaces. Therefore, various constants should be used for different interfaces. If the silica/silica interface is an example with the mediums of air and water in the contact zone, AH = 6.50 × 10−20 J (air) and 0.77 × 10−20 J (water), respectively.[37] If D0 = 0.165 nm,[36] then FvdW = 79.6 nN (air) and FvdW = 9.4 nN (water) for the silica/silica interface, respectively. With the consideration of surface roughness, the vdW force is rewritten as[38]
Dewetting of thin wetting film supported by different solid substrates: a review
Published in Phase Transitions, 2022
Tirumala Rao Kotni, Jayati Sarkar, Rajesh Khanna
Thin films that vary with density show different dewetting dynamics compared to constant density films. Effective interactions between thin wetting film and solid surface due to density fluctuations create instabilities in thin film that have been studied theoretically [78, 79]. Any local variation in density with film thickness is reported to cause a variation in Hamaker constant as the effective Hamaker constant depends on liquid–liquid and solid–liquid Hamaker constants which in turn are affected by the density. However, greater liquid–liquid Hamaker constant leads to spinodal dewetting, while greater solid–liquid Hamaker constant results in complete wetting. However, the stabilization of the unstable thin films with the variation in density is reported to transform the dewetting into pseudo-dewetting state and the stable film is destabilized. These films also influence length scales and time scales of instabilities. Density variation also causes Marangoni effect due to the creation of surface tension gradient in thin film. Time of rupture increases as the Marangoni in thin film increases and droplet peaks become flattered due to the transportation of the liquid from peaks to troughs [80]. Here surface tension plays a major role in dewetting of thin films.
Flow behavior of magnetic steel powder
Published in Particulate Science and Technology, 2021
The van der Waals force is proportional to the Hamaker constant, H, particle diameter, D and inversely proportional to the separation between particles (Equation 10). The value of the Hamaker constant is affected by the surface condition of the powders, such as the presence of oxides. Literature also presents values of the Hamaker constant for iron particles that cover two orders of magnitude. Deviation from spherical particles will also affect the effective separation of the particles. It is difficult to know any of the parameters accurately. Using estimates of the parameters allow the van der Waals forces to be calculated to an order of magnitude, which is significantly smaller than other cohesive forces. Such a calculation shows that a highly accurate determination of the van der Waals force is not essential to understand the behavior of the power ensemble in the current study.