While contact angle (CA) goniometry involving placing a drop of liquid on a surface and measuring the resulting angle has been around for many years, we have only recently developed a system to account for the underlying surface’s micro-scale roughness.
Many surface modification and coating technologies that are used for optimizing wetting and adhesion properties influence both surface chemistry and roughness. Understanding the mechanisms that impact wetting by separating these two factors can be a useful tool in product development processes and in quality control. Roughness correction of contact angles also enables the calculation of fundamental surface free energy on rough surfaces.
We have applied a method using the structured lighting technique called fringe projection phase-shifting (FPPS) to measure the underlying surface roughness parameters, including the area factor and then use this measured roughness to correct contact angles. Several different types of surfaces have been tested including papers and boards, ceramic tiles, wood polymer composites and titanium metals commonly used in implants. Our measurements show that this methodology is applicable to all industries where there is a need for better understanding of the wettability of the surface itself or of the properties of the different coatings or surface treatments. Basically, allowing the separation of the surface texture’s contribution to wetting from that of the surface chemistry itself. As this method is based on optical characterization, diffusive reflective sample surface is demanded for roughness characterization.
The phase-shifted fringe illumination patterns are sequentially projected onto the studied surface. A digital camera captures the fringe patterns from which the 3D shape of the object is reconstructed by phase-shift coding. The 2D and 3D roughness parameters are calculated from the 3D shape of the object.
Both surface chemical and topographical properties are important for applications and processes where wetting and adhesion behavior needs to be optimized. This method measures surface wettability via contact angle and measures the underlying surface roughness by using FPPS. For surfaces that exhibit both surface texture and surfaces chemistry this allows for separating the contributions from each component. It is then possible to separately change either the texture or chemistry to probe the effect of the modification.
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