Inherently high tendency of the elementary particles of detonation nanodiamond (EPDND, average diameter 2.6±0.5nm) to aggregate is reinforced by intense surface electrostatic fields, both positive and negative, which cause Coulombic interfacial interactions to form tight and voluminous agglutinates. These unfavorable assets of EPDND have hampered developments of applications of this novel nanoparticles, and more convenient forms of EPDND have been sought for a long time. The best conceivable form of EPDND in its handling for applications would be dry powder agglomerated by only weak interparticle forces but can be readily broken up to achieve monodisperse state. If one can freeze the random orientations of EPDNDs in solution and remove solvent keeping this orientation, we would expect to obtain anhydrous and weakly aggregating powder.
After succeeding in significantly reducing the level of contamination mainly by oxides of Fe and Zr, we began to prepare such a dry powder from aqueous colloidal solution of EPDND by freeze drying and recently obtained practicable products. At the present, ‘fumed diamond powder (FDP)’, as we tentatively name it, looks like hard hydrogel which used to retain about 20% of water and form heavy and dark colored and extensively aggregated powder, but is totally different. FDP is brownish colored, light but fine powder which easily emits almost invisible small particles like smoke (hence ‘fumed’) under small shock like bottling and transfering. It dissolves much more quickly than hard hydrogen in a few solvents including dimethyl sulfoxide (DMS), N-methylpyrrole, PAO 4 and jojoba oil (the last two cases needed to add 5 times weight of LB400 and MO-60 surfactant, respectively, to achieve clear solution). A clear 3% DMSO solution prepared in this way and centrifuged to remove dust gave an intensely black colored but clear solution having particle-size distribution of a single log-normal shaped peak centered at 5.1nm, suggesting the light aggregation spontaneously dissociated down to dimers.
More details on the properties and behaviors of FDP will be given in the presentation. We expect FDP to develop as the most favorable form of nanodiamonds when their applications are explored.
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