ABSTRACT
Human hair is a biopolymer constituted mainly of keratin intermediate filaments, lipids, pigments and water. Cosmetic treatments usually interact with the hair at the molecular level, inducing changes in its components and modifying the physicochemical and mechanical properties of the fibers. Here, the effect of acid straightening on the morphology and ultrastructure of Caucasian hair was investigated by a group of complementary experimental methods: wide-, small- and ultra-small-angle X-ray scattering; high-resolution 3D X-ray microscopy; quasi-elastic neutron scattering and inelastic neutron scattering; thermogravimetry-mass spectrometry; and differential scanning calorimetry (DSC). X-ray diffraction patterns showed that acid straightening associated with a flat iron (â¼180°C) changed the cortex of the fiber, shown by denaturation of the intermediate filaments (measured by DSC). The increase in the spacing of the lipid layers and the observation of the dehydration behavior of the fiber provided indications that water may be confined between these layers, while neutron spectroscopy showed alterations in the vibration mode of the CH2 groups of the lipids and an increase of the proton (H+) mobility in the hair structure. The latter may be associated with the extremely low pH of the formulation (pH ≃ 1). Additionally, this investigation showed that bleached hair (one-time bleached) is more damaged by the action of acid straightening than virgin hair, which was shown by a threefold increase in the percentage of total porosity of the tresses. The obtained results demonstrate that the investigation approach proposed here can provide very important thermodynamic and structural information on induced changes of hair structure, and certainly can be applied for the evaluation of the action mode and efficiency of cosmetic treatments.
ABSTRACT
We have studied the influence of chelating agents (glycerin and sucrose) on the structural and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles synthesized via co-precipitation method. The Rietveld refinements from X-ray diffraction patterns confirm that all samples are single phase identified in a cubic crystalline system belonging to the space group Fd-3m. Besides, we have verified that the addition of chelating agents produces a decreasing in the particles average size from 14(2) to 5(1) nm. Magnetization measurements as a function of temperature show a decrease in the blocking temperature (T(B)) to sample obtained with addition of sucrose. A superparamagnetic behavior at room temperature was observed by magnetic measurements as function of field in the sample with 0.020 mol/L of sucrose. The results show that character chelating of sucrose reduces the coalescence effect and magnetic interaction in the CoFe2O4 nanoparticles. These results suggest that sucrose could be an alternative to control the structural and magnetic properties of other oxides nanoparticles.
ABSTRACT
Ni(1-x)FexO nanoparticles have been obtained by the co-precipitation chemical route. X-ray diffraction analyses using Rietveld refinement have shown a slight decrease in the microstrain and mean particle size as a function of the Fe content. The zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves show superparamagnetic behavior at high temperatures and a low temperature peak (at T = 11 K), which is enhanced with increasing Fe concentration. Unusual behavior of the coercive field in the low temperature region and an exchange bias behavior were also observed. A decrease in the Fe concentration induces an increase in the exchange bias field. We argue that these behaviors can be linked with the strengthening of surface anisotropy caused by the incorporation of Fe ions.
