Our hypothesis that longer-chained perfluoroalkyl acids (PFAAs) outcompete shorter-chained PFAAs during adsorption was tested in this study, wherein the adsorption interactions of six frequently detected PFAAs with kaolinite clay were modeled and examined experimentally using various suspension compositions. Competitive adsorption of PFAAs on the kaolinite surface was observed for the first time, and longer-chained PFAAs outcompeted those with a shorter chain. The electrostatic repulsion between adsorbed PFAA molecules is a primary inhibitory factor in PFAA adsorption. An increase in aqueous sodium or hydrogen ion concentration weakened electrostatic repulsions and changed the adsorption free energy. Therefore, the adsorption of a shorter-chained PFAA with weaker hydrophobicity could occur at high sodium or hydrogen ion concentrations. The experimental and modeling data suggest that the adsorption of shorter-chained PFAAs (≤4 perfluorinated carbons) in freshwater with a typical ionic strength of 10(-2.5) is not thermodynamically favorable. Furthermore, by measuring the electrokinetic potential of kaolinite suspension in the presence of PFAAs, we found that the kaolinite surface became more negatively charged because of the adsorption of PFAAs. This observation indicates that the adsorbed PFAA molecules were within the electrical double layer of the kaolinite surface and that they contributed to the potential at the slipping plane. The possible alignments of adsorbed PFAA molecules on the kaolinite surface were then proposed.

With recent advances in the achievable resolution of electron microscopes, a direct method for demonstrating the atomic structure of solid crystals is available. Microscopy Camp was designed to introduce and reinforce current, scientifically acceptable concepts of the atomic structure of solid crystals. Ten middle school students attended Microscopy Camp for two days in August of 2005 at the University of Minnesota. The campers synthesized magnetite (Fe3O4) nanoparticles, characterized the particles by visual inspection and light microscopy, and participated in the characterization of their particles using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). A pre-camp and post-camp assessment was made to gain insight into students’ developing concepts regarding the atomic structure of solid crystals; qualitative results indicate improved post-camp understanding. The second goal of the program was to provide an invaluable experience to middle and high school science student teachers, who were integral to the design and implementation of this program. Finally, the success of Microscopy Camp 2005 critically depended upon the combined expertise of the chemist and science educator, and insights regarding establishing such a partnership and the design of the program are discussed.