Restricted Dislocation Motion in Crystals of Colloidal Dimer Particles: Supplementary Materials

The colloidal dimer particles are templated from sacrificial α-Fe2O3 (hematite) core particles prepared via aging of a condensed Fe(OH)3 gel as described in [1]. In a typical synthesis, 50 mL of FeCl3 (2.0 M) is mixed with 45 mL of NaOH (6.0 M) and 5 mL of the shapemodifier, Na2SO4 (0.6 M), before being placed in an oven set at 100°C for 8 days. To make the nonmagnetic particles investigated in this study, a layer of rhodamine isothiocyanate-modified silica is then coated on the αFe2O3 cores using a base catalyzed sol-gel reaction under sonication at 30°C for 4 hours. A reaction mixture comprised of 0.4% hematite powder, 0.25% rhodamine dye solution, 7.1 M deionized water, 0.92 M ammonia, and 17.4 mM tetraorthoethylsilicate added batch-wise to isopropyl alcohol medium produces fluorescent silica shells approximately 65 nm thick. The shells are stabilized with a non-ionic surfactant, polyvinylpyrrolidone (30000 molecular weight), and finally the hematite cores are selectively etched by dissolution in 18% hydrochloric acid solution at room temperature. Before use, the colloidal suspension is titrated to pH 7, washed via repeated centrifugation and decanting, and redispersed in deionized water. This synthesis protocol routinely produces 95% pure dimer particles.