Article pubs.acs.org/Langmuir
Effect of Solvent Polarizability on the Assembly and Ordering of Nanoscale Polyhedral Oligomeric Silsesquioxane Films Guennadi Evmenenko,*,†,‡ Scott L. Cockroft,§ and Pulak Dutta† †
Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3112, United States Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, Illinois 60208-3108, United States § EaStCHEM School of Chemistry, University of Edinburgh, King’s Buildings, West Mains Road, Edinburgh EH9 3JJ, United Kingdom ‡
ABSTRACT: Understanding the factors that affect molecular self-assembly is crucial to building designed nanoscale structures. We have deposited nanoscale films of polyhedral oligomeric silsesquioxane (POSS) onto polished silicon substrates from a range of organic solvents. We studied these films using synchrotron X-ray reflectivity and found that dip-coating from benzene, toluene, or chloroform results in near-substrate ordering only, but when acetone, hexane, or THF is used, self-assembled layers are formed throughout the entire deposited film. We conclude that solvent polarizability is the factor that determines the alignment of the POSS molecules. We have successfully tested this prediction using additional solvents selected on the basis of their calculated polarizabilities.
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moieties and the corresponding groups in the polymer.6 These materials are more sensitive to external stimuli than chemically bonded composites and have considerable promise for tunable biodegradability and biofunctionalizability. Again, recent studies show that the drop in the differential capacitance observed in room-temperature ionic liquids is strongly related to the loss of dispersion interactions in the vicinity of the electrodes.7 These examples illustrate that even at room temperature the most important cohesive mechanism in molecular and soft condensed matter often has a direct quantum origin: this is the dispersion interaction, which is the attractive component of van der Waals forces. Another important aspect of the behavior of ultrathin films (
