Clay minerals ? silicate minerals with sheet-like structures - are major components of soils and sediments. One of the unique properties of these minerals is their ability to swell by incorporating varying amounts of water and exchangeable cations between the layers. The swelling of clay minerals plays a major role in the transport of nutrients and pollutants in the environment, waste containment technologies, and borehole stability. To date, commonly used techniques for studying swelling in the laboratory have only been able to measure the average change in layer separation of many clay layers and consequently are limited in the information they can provide. The study proposed here will use atomic force microscopy (AFM) to investigate clay swelling in situ in an aqueous environment. AFM is used to produce three dimensional images of the surface of a material, and unlike a conventional optical microscope, it can ?see? features up to a million times smaller than the width of a human hair. Changes in swelling within individual isolated stacks of clay layers (quasi-crystals) that accompany modifications to the chemical composition of the surrounding solution can be monitored as they occur. Because the interlayer spacing both between different quasi-crystals and within a given quasi-crystal can be precisely measured with AFM, the inherent heterogeneities of natural minerals can be investigated. Additionally, the acquisition of a series of AFM images over a period of time will provide a detailed picture of the dynamic processes involved in the exchange of cations within the interlayer region and a method to directly measure the rates of swelling change. These studies will offer new insight into the chemical and physical properties that control swelling and the parameters that affect the interactions of various chemical species with clay minerals.
The work proposed here will be conducted solely in collaboration with undergraduate and M.S. student researchers of the Chemistry Department at Bucknell University. These students will be co-authors on the resulting publications and will be intimately involved in all stages of manuscript preparation and presentation of results at national conferences. Gaining hands-on experience with AFM will be a significant educational opportunity for the students on the project. As nanotechnology and nanoscience become increasingly central to chemical research, it is critical that students are exposed to these subjects. AFM, with its abilities to image and manipulate matter at dimensions approaching the atomic scale, is at the core of this revolution.
