Colloidal Solution of 3 nm Bucky Diamond: Primary Particles of Detonation Nanodiamond

Abstract

The nanodiamond (ND) hydrosol with positively charged $2.7 \pm 0.3$ nm primary particle s behaves as a hydrophobic colloidal dispersion . The coagulation by inorganic electrolyte s with anion charges of −1, −2, −3, and −4 occurs in line with the Schulze–Hardy rule for “positive” sols. The single-charged anions are arranged according to their coagulating ability in the lyotropic series. The sole exception is the hydrophilic HO⁻ ion, which displays much stronger coagulation impact than those of Cl⁻ and BF₄ ⁻ ions. This particularizes the acidic nature of the positive charge of the colloidal species . The last-named readily adsorb anionic dyes, which results in batochromic shifts of their absorption band s. Application of an acid-base indicator bromocresol green allowed estimating the value of the interfacial electrical potential of the nanodiamond particles $\Psi = + 8 9\;{\text{to}}\;\, + 1 2 3\;{\text{mV}},$ depending on the concentration of the hydrosol. These values are higher as compared with those of the zeta-potential , $\varsigma = + 4 3\,\;{\text{to}}\;\, + 6 2\;{\text{mV}}.$ The size distribution of the dispersed system is strongly concentration-dependent. The dilution of the initial 5.0 wt/vol% ND hydrosol by water results in gradual increase in the average particle size, up to ca. 30 nm in 0.01 % colloidal solution . These results of dynamic light scattering were confirmed by transmission electron microscopy . Accordingly, the viscosity of the hydrosol decreases along with dilution. This phenomenon was explained in terms of the periodic colloidal structure s, or colloidal crystal s, formed in concentrated solutions.