Aggregate Structure in Concentrated Liquid Dispersions of Ultrananocrystalline Diamond by Small-Angle Neutron Scattering

Abstract

Aggregates of nanodiamond particles dispersed in polar liquids (H 2 O and DMSO) upon undergoing a special milling procedure are studied by small-angle neutron scattering at a scale of 1-100 nm. The size and fractal character of the aggregates as well as the structural features of nanodiamond particles (size, surface) are compared for both solutions. The structural difference between liquid dispersions and initial nanodiamond powder is analyzed. The concentration effect is followed within an interval of 0.2-10 wt % to conclude about the interaction of the aggregates. It is shown that the developed structure of the aggregates allows their interpenetration in concentrated solutions. The contrast variation procedure using mixtures of nondeuterated and deuterated solvents is performed to judge the homogeneity of the aggregates and to find out their mean scattering length density. The existence of a nondiamond component in the particles is discussed on the basis of the scattering data.

Small-angle scattering from polydisperse particles with a diffusive surface

“…This means that at small β-values the effect of (r) on the moments n R is similar to that in the case of homogeneous particles and explains the fact that the unified exponential/power-law approach can be well applied in the treatment of the experimental SANS data from non-homogeneous DND particles (Avdeev et al, 2009). …”

“…The same deviations were revealed for SANS from ethanol solutions of hydrolyzed TEOS (Avdeev et al, 2004). A recent example of such nonPorod asymptotic behavior of the scattering is related to the detonation nanodiamond (DND) both in powder state (Avdeev et al, 2007b) and in liquid dispersions (Avdeev et al, 2009). It should be noted that there are other types of surface diffusivity corresponding to fractal surfaces with the Porod exponent between 3 and 4 (e.g.…”

“…In SANS experiments with the contrast variation on liquid DND dispersions (Avdeev et al, 2009) the diamond-graphite spatial transition in DND was considered in terms of the "core-shell" approximation, which explained the experimentally detected shift in the mean scattering length density (SLD) of DND as compared to the diamond density and gave about 0.5 nm thickness for the graphite shell in the particles with the total size of about 7 nm. It is, however, clear that the "core-shell" representation cannot explain the above-mentioned deviation from the Porod law, and a "broader" interface is to be introduced for this purpose.…”

“…It is important that the scattering curves from DND are rather smeared because of the particle polydispersity, so the exponential/power-law approach can be formally applied in their treatment (Avdeev et al, 2007b;Avdeev et al, 2009). At the same time, according to profile (1), the DND particles are non-homogeneous, which can have additional effects on the scattering especially in the contrast variation experiments.…”

“…However, in the case of small β (which takes place in practice) a number of simplifying factors can be indicated, thus making it possible to deduce relatively simple expressions for the scattering invariants, which take both the particle heterogeneity and polydispersity into account. The possibilities of the proposed approach are then discussed basing on the model scattering curves and experimental SANS curves obtained previously for the liquid DND dispersions (Avdeev et al, 2009). …”