Environmental Recovery by Magnetic Nanocomposites Based on Castor Oil - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 240

Figure 4. (a) Maghemite nanoparticles in the presence and (b) absence of the magnetic field.
The influence of temperature, stirring speed and time of reaction on the magnetic
force and size of particles was evaluated using a three factor experimental design at
two levels plus a central point (2 3 + 0). The lowest levels used for the stirring speed,
the time of reaction and the annealing temperature were equal to 1,000 rpm, 15 min,
and 150°C, respectively. The highest levels used for the previously mentioned factors
were equal to 3,000 rpm, 45 min, and 250ºC, respectively. The central point experi-
ments were performed in triplicate, adjusting the factors at 2,000 rpm, 30 min, and
200ºC, respectively.
The AFM was used for determination of the characteristic diameter of the pro-
duced maghemite particles. The AFM was performed in a DI Nanoscope IIIa mi-
croscope (LNLS, Brazil--AFM#8421/08 and AFM#9637/10), at non-contact mode,
NSC-10-50, 20N.m -1 and 260 kHz.
The WAXS/SAXS measurements were performed using the beam line of the
Brazilian Synchrotron Light Laboratory (LNLS, Brazil D11A-SAXS1-8507). This
beam line is equipped with an asymmetrically cut and bent silicon (111) monochroma-
tor (λ = 1.743Å), which yields a horizontally focused X-ray beam. A linear position-
sensitive X-ray detector (PSD) and a multichannel analyzer were used to determine
the SAXS intensity I(q) as function of the modulus of the scattering vector q = (4π/λ)
sin θ, 2θ being the scattering angle. All SAXS scattering patterns were corrected for
the parasitic scattering intensity produced by the collimating slits, for the non-constant
sensitivity of the PSD, for the time varying intensity of the direct synchrotron beam
and for differences in sample thickness. Thus, the SAXS intensity was determined
for all samples in the same arbitrary units, so that they can be directly compared to
each other. Since the incident beam cross-section at the detection plane is small, no
mathematical deconvolution of the experimental SAXS function was needed (Souza Jr.
et al., 2009b, 2007).
The SAXS results, shown in Figure 5, indicate that all different maghemites, ob-
tained of each experiment of experimental design, present similar dimensions around
(31.3 ± 0.7) nm. It shows that size of nanoparticles do not depend on these parameters.
This result is according to AFM results, shown in Figure 6. The probability density