Date of Thesis
Honors Thesis (Bucknell Access Only)
Bachelor of Science
Molly M. McGuire
Clay minerals with the ability to swell in aqueous environments, or smectites, are a prevalent component of drilling mud, nuclear waste containment materials, and landfill barriers and are thus relevant to many environmental and industrial fields. Smectites are 2:1 phyllosilicates that allow water molecules to incorporate into the quasi-crystal structure, changing the spacing between the many layers of a single particle. Atomic force microscopy (AFM) has been used as an effective technique to study the spacing between smectite layers due to swelling by imaging the topography of individual particles in situ throughout the swelling process. AFM images, or topographic maps of the sample surface, from varying times during swelling can be compared to provide information about layer-to-layer swelling behavior. A novel image analysis method is presented that involves setting a Zmin, or height threshold, to each AFM image, effectively isolating an individual layer in the particle at the Zmin plane. Differences in area at the Zmin plane from image to image are interpreted as evidence of swelling or compression. Through image analysis, both compression and swelling have been observed at different individual layers of the same smectite particle. The results prove the presented method is able to produce information about layer-to-layer swelling that is impossible to determine using previous techniques, such as X-Ray Diffraction (XRD). The heterogeneity in layer-to-layer swelling is likely a result of variable charge density created by isomorphic substitution within the quasi-crystal structure.
Arndt, Diana Strano, "Atomic Force Microscopy Studies of Layer Heterogeneity in Swelling of Nontronites" (2016). Honors Theses. 363.