Biomedical Engineering Reference
In-Depth Information
samples G-1 and K-2 (see Figs. 6.3 and 6.4), whose IR spectra are
practically identical.
No distinct correlation was found between sedimentation
stability of UDD aqueous suspensions (Table 6.2) and the total
amount of surface functional groups measured by total gas evolution
under pyrolysis of UDD up to 1100°C. It is established, however, that
the stability of UDD suspension is higher for the samples with greater
total amount of CO and CO
desorbed in the temperature range of
400-600°C, as a result of the decomposition of acid anhydride
and lactone groups. The sedimentation stability of a solution of
nanodiamond can be controlled by concentration of acid anhydride
and lactone groups that impart acid properties to diamond
nanoparticles and negatively charge the particle in aqueous solutions
preventing their aggregation [70, 71]. An exception is represented
by the sample CH-7, with low level of surface oxidation and high
stability of aqueous solution. This sample however is characterized
by a high degree of the surface contamination by the hydrocarbon
species [62], which can act as surface-active species causing high
sedimentation stability for this type of UDD.
Thus, the UDDs of different types, synthesized by explosion
technology in different conditions and purified using different
chemical procedures, are different from each other mainly in terms
of concentration and structure of the surface oxygen-containing and
other functional groups. These groups are decomposed by vacuum
pyrolysis giving rise to the formation of volatile gas component.
The temperature profiles of different gases, as shown in Fig. 6.3
can be considered as “fingerprints” of the technology of synthesis
and purification of UDD and can be used for the certification of
ultradispersed nanodiamonds of different types.
2
6.3.5
Influence of Additional Acid Treatment on the
Surface Chemistry of Nanodiamonds of
Different Types
The profound effect of the synthesis technology of UDD on their
surface chemistry is the cause of the different behavior of UDD in
many practical applications. One faces, therefore, the problem of
how to unify the surface properties of UDD of different types for the
purpose of obtaining “standard” products independently of their
origin. One of the possible ways of solving this problem consists
