Film Trapping Technique:  Precise Method for Three-Phase Contact Angle Determination of Solid and Fluid Particles of Micrometer Size

Abstract

A novel method for determination of the three-phase contact angle at the surface of a micrometer-sized particle (latex sphere, oil droplet, or biological cell) is described. The particle is entrapped within a liquid film of equilibrium thickness smaller than the particle diameter. Thus a liquid meniscus (a layer of uneven thickness) is formed around the particle. When observed in reflected monochromatic light, this meniscus appears as an interference pattern of concentric bright and dark fringes. From the radii of the interference fringes, one can restore the meniscus shape by using the solution of the Laplace equation of capillarity. In this way the three-phase contact angle of the particle and the capillary pressure can be determined. We demonstrate the applicability of our method to latex spheres from several batch samples (between 1 and 7 µm in diameter) and to oil droplets, stabilized by adsorbed protein layer. The numerical procedures used for contact angle determination are described, and illustrative results are presented and discussed.

Colloid Monolayers as Versatile Lithographic Masks

“…In a first approximation, we assume that, as soon as water penetrates the gap between the hydrophilic glass surface and the mainly hydrophobic 24,25 latex spheres, it forms relatively large contact angles 26 with the spheres. In this way, the particles are strongly attached to the water-air interface.…”

Comparison of different methods to measure contact angles of soil colloids

“…For porous materials, the wicking or capillary rise method is often used [1]. For spherical particles, methods have been developed to determine contact angles based on force measurements [2,3], confocal microscopy [4], and film trapping [5]. The contact angle of colloidal particles, however, is difficult to measure because the small particle size (<2 μm in diameter) poses considerable challenges with existing contact angle measurement methods.…”

Monitoring Entering and Spreading of Emulsion Droplets at an Expanding Air/Water Interface: A Novel Technique

“…In these studies the entry barrier is investigated for static systems in the presence of adsorbed surfactants. Hadjiiski et al (23) and Dickinson et al (24) report on the oil droplet entry barrier for systems containing adsorbed proteins at the air/water and oil/water interfaces, respectively. Bergeron et al (22) described a disjoining pressure cell in which the pressure required to rupture a thin water film sandwiched between bulk air and oil phases can be measured.…”

“…Bergeron et al (22) described a disjoining pressure cell in which the pressure required to rupture a thin water film sandwiched between bulk air and oil phases can be measured. The film trapping technique (16,23) enables similar pressure measurements with the added advantage that oil droplets can be used instead of a bulk oil phase. Using the film trapping technique, protein stabilized-emulsion droplets (diameter 1-3 µm) have been studied (23).…”

“…The film trapping technique (16,23) enables similar pressure measurements with the added advantage that oil droplets can be used instead of a bulk oil phase. Using the film trapping technique, protein stabilized-emulsion droplets (diameter 1-3 µm) have been studied (23). Lobo and Wasan (20) described the use of reflective light microscopy to observe the entering of oil droplets (diameter 300-800 µm) at the air/water interface.…”