ИСТИНА

An important aspect related to the applications of nanodiamonds is the formation of their stable aqueous suspensions, i.e., disaggregation of particles the sizes of which may be hundreds or even thousands nanometers. There are diverse methods of disaggregation, some of which (bead-assisted sonication or laser heating) just destroy non-diamond interlayers and covering shells and, in this way, initiate the reorganization of fresh surfaces rich in unsaturated carbon atoms that have lost their close neighbors. Since the process usually takes place in water, the solvent molecules should inevitably be involved in the surface reconstruction. To clarify the situation, nonempirical calculations of Cn(H2O)m systems (n = 20–110 and m=4–35) were carried out. Two possible variants of the water involvement in the structure relaxation process were considered. One variant implies that water molecules can directly participate in the process at the stage of the primary formation of carbon particle surfaces. Another variant is the interaction of fully relaxed carbon subsystem, the surface of which is rich in diverse unsaturated or variously coordinated carbon atoms, with water molecules, whose initial arrangement is arbitrary, which means that it is not necessarily H-bonded water clusters, but rather independent water molecules. It was found that chemical interaction between active surface sites of carbon particles and water molecules becomes possible only when a certain threshold amount of molecules is present close to the surface and covers a surface part that involves at least two active sites. The probability of the dissociation of a water molecule that leads to the formation of either neighboring or non-neighboring C–OH and C–H surface groups depends on the type of surface sites and their arrangement. The discovered general convexo-concave character of the water hydration shells over surface segments of carbon nanoparticles is found to be determined by the hydrophobic-hydrophilic balance of the surface sites and related to the properties of hydrogen-bonded water molecules, particularly the strength of hydrogen bonds between them.