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Systems and Methods for Measuring Surface Contact Angles

IP.com Disclosure Number: IPCOM000239761D
Publication Date: 2014-Dec-01
Document File: 7 page(s) / 316K

Publishing Venue

The IP.com Prior Art Database

Abstract

Systems and methods may be implemented in portable instruments for measuring both advancing and receding contact angles on samples of material that can be positioned in a sample holder of a hand-held or bench-top instrument. The hardware and setup are simple, inexpensive, and robust, and the method is applicable to a broad range of surfaces and liquids for measuring contact angles. The methods described differ slightly in how they induce droplet motion, but in both cases, a holographic measurement is used to obtain information about the projected area of the drop on the surface, as well as surface curvature at the edge(s) of the drop(s). Another advantage is that this approach allows multiple drops to be measured at the same time, which improves measurement repeatability and reduces the likelihood of obtaining data from non-representative regions.

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Systems and Methods for Measuring Surface Contact Angles

Abstract

Systems and methods may be implemented in portable instruments for measuring both advancing and receding contact angles on samples of material that can be positioned in a sample holder of a hand-held or bench-top instrument. The hardware and setup are simple, inexpensive, and robust, and the method is applicable to a broad range of surfaces and liquids for measuring contact angles. The methods described differ slightly in how they induce droplet motion, but in both cases, a holographic measurement is used to obtain information about the projected area of the drop on the surface, as well as surface curvature at the edge(s) of the drop(s). Another advantage is that this approach allows multiple drops to be measured at the same time, which improves measurement repeatability and reduces the likelihood of obtaining data from non-representative regions.

Introduction

Contact angle measurements between a drop of liquid and a nominally planar surface are a sensitive measure of the surface energies of the interfaces. Contact angle data is therefore a useful indicator of "wettability," contamination or cleanliness, and adhesion, which are important properties for coating processes and adhesive applications. A holographic sensing approach described herein makes the entire system compact, inexpensive, robust, and accurate.

Contact angle measurements are commonly used as a means to characterize the wetting (ability of the liquid to maintain contact with a solid) or adhesion properties of a surface.
Fundamentally, there is a force balance that exists at the interfaces as shown in Equation 1 and represented in Figure 1 (first described by Thomas Young in 1805).

ܨ௅௏ cos ߠ ൌ ܨௌ௏ െ ܨௌ௅ (1)

Where FLV is the force balance between the liquid and vapor, FSV is the force balance between the solid and vapor, and FSL is the force balance between the solid and liquid.

Vapor

FLV

Liquid

FSV

FSL

Solid

Figure 1: Force Balance at a Solid-Liquid- Vapor Interface Defines Contact Angle

Since the field has been of interest for so long, multiple means of measuring contact angles have been described in the literature; the basic physics and several methods are described in cited academic references: Gao [1], Good [2]. One of the more common methods is a goniometric approach that views the contact angle from the side (as shown in Figure 1) and either automatically fits or prompts the user to define the contact angle, θ. The issue is that the contact angle is essentially part of a metastable system; the only highly repeatable values of the contact angle for a given solid-liquid-vapor system are the limits of the contact angle when the liquid is either advancing over previously un- wetted surface or receding from previously

 



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wetted surface. These are known as the advancing, ߠ, and receding, ߠ, contact angles, respectively, and generally ߠ൒ ߠ. H...