Using the Meniscus in a Capillary for Small Volume Contact Angle Measurement in Biochemical Applications

Abstract

The contact angle is a sensitive parameter often used to define wettability. With the increasing movement toward smaller liquid volumes in many biochemical applications, a key challenge lies in how to perform measurements in the retainer holding the reagent for rapid evaluation and limited material loss. Here, we report a simple and robust method to determine the contact angle of small volumes using the microscopic imaging of a capillary meniscus that requires only the radius and meniscus height information. An error analysis of the measurement finds the method to be highly accurate. We also uncovered that illumination delivered from the liquid end of the capillary lights up the interface, thereby facilitating the measurement.

Effect of chemical structure of organics on pore wetting

“…Since the quality of meniscus image of the small volume of liquid in a capillary highly depends on the light source and measurement method, a LED light source located under the glass capillary was used for the microscopic imaging to improve the quality of image. The LED light travels from the liquid end up to the meniscus in a dark background to overcome the degree of image distortion problem when a cylindrical capillary is used and therefore facilitate the measurements (Cheong et al, 2011). The outermost boundary of liquid-gas interface was well lit and focused to produce the clear two-phase interface.…”

“…In order to obtain the contact angle of liquid in a capillary, we analyzed the microscopic images by using the method recently proposed by Cheong et al (2011). The contact angle of liquid in a capillary was calculated by only using the capillary radius (r) and meniscus height (h) (Figure 2) of the capillary meniscus as shown in (Eq.2).…”

“…The contact angle of liquid in a capillary was calculated by only using the capillary radius (r) and meniscus height (h) (Figure 2) of the capillary meniscus as shown in (Eq.2). This equation is valid based on the assumptions of small liquid volume applied and neglected gravity effect (Cheong et al, 2011;Zheng et al, 2005). Since the effect of image distortion on meniscus height (h) is not significant, the effect of image distortion on contact angle estimation of liquid in a small pore can be minimized (Cheong et al, 2011).…”

Pore Wetting and Its Effect on Breakthrough Pressure in Water-Wet and Oil-Wet Pores

“…Due to the fact that the quality of meniscus image of a small volume of liquid in a capillary highly depends on the measurement method and light source, a LED light source was placed under the glass capillary. The light travels from the liquid end up to the meniscus in a dark background to overcome the degree of image distortion when a cylindrical capillary is used and therefore facilitate the measurements [25]. The outermost boundary of liquid-gas interface was well lighted and focused to produce the clear two-phase interfacial line [26], [27].…”

“…When the spontaneous dynamic imbibition was completely stopped and the equilibrium status was reached in the capillary, the equilibrium/static contact angle was achieved. To obtain the contact angle of liquid in a pore, we analyzed the microscopic images by using the method recently proposed by Cheong et al [25]. Cheong et al developed a method of measuring the contact angle of small volumes, by only using the capillary radius (r) and meniscus height (h) (see Fig.…”