Figure 3: Mechanism of colloidal stability determination.

Si NC concentration as a function of molecular length, n, for n-alkanones (a) and n-alkanenitriles (b) as determined by ultraviolet-visible absorption. The right axis is the average inter-NC separation distance. If electrostatics are the dominant mechanism of colloidal stability, then shorter molecules should achieve higher concentrations. If steric effects were dominant, longer molecules are expected to provide more highly concentrated Si NC solutions. Photographs of the solutions are included at the top of the graph. Error bars reflect uncertainty in mass measurements. (c) The carbonyl region of the ¹³C NMR spectra of Si NCs stabilized in 2-butanone at concentration of 0, 1, 3.5 and 7 mg ml⁻¹. The spectra are normalized and vertically offset for clarity. The downfield shift of the carbonyl peak is due to Si NC surface interactions and resulting interactions in the solvent shells surrounding the NC. Aliphatic carbon peaks (1–3) do not shift relative to neat 2-butanone with increasing Si NC concentration (inset). Error bars correspond to the digital resolution of the spectrometer.