This method of determining the contact angles of probe liquids on solid surfaces has proven reliable in confirming surface energy predictions based on the chemical and physical properties of those surfaces tested. Surface free energy calculations for solids were calculated with the van Oss-Chaudhury-Good equation and were likewise consistent with literature values. Contact angles determined for probe liquids were consistent and comparable to literature values. Ten replicates of each surface and treatments were tested independently to determine repeatability of the procedure. Multiple surfaces were analyzed using this method, including N-type silicon wafers, glass microscope slides, 130 thickness gold layers electrosprayed onto both N-type silicon wafers and glass slides, and a carboxyl-terminated self-assembled monolayer (SAM) deposited onto the gold layers. ![]() Once these reference lines were applied, contact angles () of the probe liquids at the three phase boundary were determined using AutoCAD software and geometric principals. ![]() ![]() Using the AutoCAD design window, images of droplets were overlaid with lines and shapes matching all profiles of the images. Digital images (JPG) of 1.01 droplets for a probe liquid triad (ultrapure water, diiodomethane, ethylene glycol) resting on the substrates of interest are produced. ![]() This study reports the development of an economical apparatus and method for measuring contact angles of liquids on solid surfaces using a digital microscope and AutoCAD 2005 drafting software.
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