1 research outputs found
Simultaneous Phase Transfer and Surface Modification of TiO<sub>2</sub> Nanoparticles Using Alkylphosphonic Acids: Optimization and Structure of the Organosols
An
original protocol of simultaneous surface modification and transfer
from aqueous to organic phases of anatase TiO<sub>2</sub> nanoparticles
(NPs) using alkylphosphonic acids (PAs) is studied. The influence
of the solvent, the nature and concentration of the PA, and the size,
concentration, and aggregation state of the TiO<sub>2</sub> NPs was
investigated. Complete transfer was observed for linear alkyl chains
(5, 8, 12, and 18 C atoms), even at very high sol concentrations.
After transfer, the grafted NPs were characterized by <sup>31</sup>P solid-state MAS NMR. The dispersion state of NPs before and after
phase transfer was monitored by dynamic light scattering (DLS). Small-angle
neutron scattering (SANS) was used to characterize the structure of
PA-grafted NPs in the organic solvent. Using a quantitative coreāshell
model cross-checked under different contrast conditions, it is found
that the primary particles making up the NPs are homogeneously grafted
with a solvated PA-layer. The nanometric thickness of the latter is
shown to increase with the length of the linear carbon chain of the
PA, independent of the size of the primary TiO<sub>2</sub> NP. Interestingly,
a reversible temperature-dependent aggregation was evidenced visually
for C<sub>18</sub>PA, and confirmed by DLS and SANS: heating the sample
induces the breakup of aggregates, which reassemble upon cooling.
Finally, in the case of NPs agglomerated by playing with the pH or
the salt concentration of the sols, the phase transfer with PA is
capable of redispersing the agglomerates. This new and highly versatile
method of NP surface modification with PAs and simultaneous transfer
is thus well suited for obtaining well-dispersed grafted NPs