Thermodynamics of Wettability: A Physical Chemistry Laboratory Experiment

Abstract

In this laboratory experiment, students modify a series of surfaces and explore the effects of varying surface chemistry and texture on wettability by different probe liquids. Students begin by building a simple contact angle goniometer utilizing their mobile phone cameras. Next, they contrast the wettability of planar glass substrates functionalized with alkyl silanes and fluorinated alkyl silanes and calculate surface free energies using Owens/Wendt plots. Subsequently, they synthesize ZnO tetrapods as robust textural elements and spray deposit the tetrapods onto stainless steel meshes to develop hierarchical texturation, which upon subsequent surface functionalization yields superhydrophobic and oleophobic surfaces. The series of experiments allow them to investigate the manner in which textured surfaces deviate from Young's equation and provide a vivid illustration of the thermodynamics of surface wettability. The laboratory exercise further provides a striking visual analogy for illustrating free energy landscapes and serves as a tangible means to demonstrate the role of surface chemistry with regards to the midstream oiltransportation infrastructure.

Demonstrating surface and plasma chemistry with a non-thermal atmospheric plasma

“…Contact angle measurement can be performed using dedicated or self-made goniometer to quickly assess the surface energy of a solid 8,9 . The contact angle of a water drop on a non-polar surface like polyethylene can be lowered significantly by a short treatment with a plasma jet.…”

Optimizing anisotropic transport on bioinspired sawtooth surfaces

“…These phenomena have inspired many materials designed for more efficient surface water transport, for example in coatings that limit biofouling in medical devices. 10 The control of solvent flows [11][12][13][14][15] may allow for easier cleaning and better control of protein adsorption. Butterflies have adapted special structures to take advantage of anisotropic wetting properties.…”

“…Much work has been done to study wettability of various materials, 11,12,14,38,45 however, control of this property has been severely limited in the past. With advances in engineering practices 46 and a focus on surface modification 15 we hope to bring greater control of wetting to industry.…”

Whey Protein Analysis Using the Lowry Assay and 96-Well-Plate Digital Images Acquired Using Smartphones

“…Digital images acquired using electronic devices were also used for pH evaluation, titration, − investigation of friction and wetting, quantifications of abasic sites within DNA nucleotides, measurement of the contact angle, , quantification of surface protein adsorption, measurements of liquid binary diffusivities, measurement of fluorescence quenching, explorations of chemical kinetics, − finding p K a values . and lateral flow assays …”