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Figure 2 shows the FTIR-ATR spectra of the original and the POEGMA-coated TiO 2 nanoparticles. The
characteristic peak at 1726 cm -1 , which corresponds to the carbonyl stretching vibration of the polymer, verifies the presence
of the polymer brushes onto the surface of the particles. Two additional strong peaks are also observed at 2965 cm -1 and
1245 cm -1 attributed to the C-H and the C-O-C stretching vibrations of the polymer, respectively.
Table 1 summarizes the TGA measured weight loss for various polymer coated samples over the 200 to 600 °C
range. A 2 - 21 wt% loss was obtained attributed to the pyrolysis of the polymeric component of the hybrid material. As
seen in Table 1 there is a strong dependence of the polymer content on the solvent medium used for the polymerization. The
higher polymer content was found for reactions carried out in water, while the presence of methanol reduced substantially
the polymerization rate and thus the thickness of the synthesized brushes. Moreover, the polymerization in xylene was more
efficient than that in a methanol/water mixture.
Table 1. Weight loss of the hybrid materials
Sample
Weight loss
TiO 2 - POEGMA (water) 21.4 %
TiO 2 - POEGMA (methanol/water 4/1) 4 %
TiO 2 - PDMAEMA (xylene) 4.8 %
TiO 2 - PDMAEMA (methanol/water 4/1) 2 %
TiO 2 - PMMA (xylene) 6.7 %
ZnO - PDMAEMA (xylene) 8.4 %
ZnO - MMA (xylene) 4 %
The efficiency of the polymer brushes to stabilize the inorganic nanoparticles in various media was investigated by
dispersion stability tests. Figure 3a shows the initial and the hydrophilic polymer - coated TiO 2 nanoparticles in water 12 h
after dispersion. A remarkable improvement in the dispersion stability for the POEGMA and the PDMAEMA modified
nanoparticles is observed suggesting the effectiveness of the polymer coating. Figure 3b shows the original and the
PDMAEMA-modified ZnO nanoparticles. In this case there is a dramatic change in the dispersability of the inorganic
nanoparticles in water which implies the complete modification of the nanoparticle surface properties from hydrophobic to
hydrophilic upon attachment of the hydrophilic polymeric chains.
(a)
(b)
Figure 3. (a) Aqueous dispersions of the initial and the polymer modified TiO 2 nanoparticles, 12 h after dispersion, and
(b) Dispersions of the original and the PDMAEMA coated ZnO nanoparticles in water.
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