Kinetics of Wetting and Spreading of Droplets over Various Substrates

Abstract

There has been a substantial increase in the number of publications in the field of wetting and spreading since 2010. This increase in the rate of publications can be attributed to the broader application of wetting phenomena in new areas. It is impossible to review such a huge number of publications; that is, some topics in the field of wetting and spreading are selected to be discussed below. These topics are as follows: (i) Contact angle hysteresis on smooth homogeneous solid surfaces via disjoining/conjoining pressure. It is shown that the hysteresis contact angles can be calculated via disjoining/conjoining pressure. The theory indicates that the equilibrium contact angle is closer to a static receding contact angle than to a static advancing contact angle. (ii) The wetting of deformable substrates, which is caused by surface forces action in the vicinity of the apparent three-phase contact line, leading to a deformation on the substrate. (iii) The kinetics of wetting and spreading of non-Newtonian liquid (blood) over porous substrates. We showed that in spite of the enormous complexity of blood, the spreading over porous substrate can be described using a relatively simple model: a power low-shear-thinning non-Newtonian liquid. (iv) The kinetics of spreading of surfactant solutions. In this part, new results related to various surfactant solution mixtures (synergy and crystallization) are discussed, which shows some possible direction for the future revealing of superspreading phenomena. (v) The kinetics of spreading of surfactant solutions over hair. Fundamental problems to be solved are identified.

Investigation of Single and Binary of “Sandwich” Type Convex Liquid Capillary Bridges, Stretched between Two Flat Surfaces (Experimental Approach)

“…The pressure inside any droplet (circular axisymmetric shape) differs from the surrounding vapor/air pressure. We believe that, because of the nature of the CB stretching process, the contact angle of the stretched CB quasi-static method corresponds to the static receding contact angle of a droplet, which is closer to the equilibrium contact angle as stated in [23]. Therefore, in this paper the appropriate qualification for the contact angle is static and receding.…”

“…The solid/liquid contact angle is a characteristics, related directly to wettability and it is important that it is determined correctly. Issues related to its measurement are discussed in [22,23]. As mentioned in [23], the equilibrium static contact angle of capillary shapes, according to the thermodynamics, contradicts the Laplace equation for the convex surfaces.…”

“…Issues related to its measurement are discussed in [22,23]. As mentioned in [23], the equilibrium static contact angle of capillary shapes, according to the thermodynamics, contradicts the Laplace equation for the convex surfaces. The pressure inside any droplet (circular axisymmetric shape) differs from the surrounding vapor/air pressure.…”

Sessile droplets on deformable substrates

“…Under low slope approximation Jacobi equations for the four unknown functions ( ) are generated, where , = 1, 2 for the system of equations (11) and (12) For a simplified disjoining/conjoining pressure isotherm (see Figure 2), Eqs. (15) and (16) become linear differential equations corresponding to all Jacobi's functions. Initial conditions for four Jacobi's functions [16,32]:…”

“…Disjoining/conjoining pressure approach was first introduced by Derjaguin for droplets on solid substrates [12]. More recently it was shown that this approach can also be used for droplets on deformable substrates [11,[13][14][15][16][17]]. 2 of 16 Recently, experimental studies on droplet wetting of deformable substrate have gained a lot of interest primarily due to technological advances in imaging techniques [18][19][20][21][22].…”