Surface flotation of particles on liquids. Principles and applications

Surface flotation was modeled by a spherical particle residing at the liquid/gas interface and forces operating in the system. Basing on this model and known expressions for the forces, different equations were presented, which relate (1) attachment contact angle with particle central angle as a function of particle size and density as well as liquid density and surface tension, (2) detachment contact angle as a function of particle size and density as well as liquid density and surface tension for the case when the particle starts to sink in the liquid, and (3) recalculated rest contact angle for the case when the mass of particle is neglected. The presented formulas can be useful for determination of attachment, detachment, and rest contact angles, and for selection of reference liquids for Washburn-type techniques of contact angle determination as well as for finding the critical surface tension of wetting.

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► Surface flotation was modeled by a spherical particle at the liquid–gas interface.
► We present practical aspects of the derived equations.
► Surface flotation equations and experiments provide useful parameters of the system.