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Francesca Lionetto, Alfonso Maffezzoli
Rheological characterization of concentrarted nanoclay dispersions in an organic solvent
Appl. Rheol. 19:2 (2009) 23423 (8 pages)
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Nanoclay dispersions in organic solvents are widely used in cosmetics for a variety of gels and creams, whose properties
depend on the powder content and the processing method. The control of the shear applied during processing is therefore
essential for achieving the required properties.This study demonstrates the utility of applying rheological measurements for
characterizing cosmetic products based on nanoclays and relating their viscoelastic properties to end-use performances. In
particular, a rheological characterization of bentonite dispersions in isododecane at different clay content and shear history
is presented. For each inorganic content, both mixed samples and samples subjected to several calendering runs were studied.
The effect of shear and clay content on the viscoelastic properties was investigated by a combination of oscillatory shear
experiments under small-deformation conditions and by X-Ray diffraction. The tested samples showed a gel-like behaviour
with a final structure depending on the applied shear stress. By increasing the inorganic content in the dispersion, a reduction
in the gel stability to a further shear application was observed. Two models, developed for colloidal gels,were used to fit
the rheological results enabling to evaluate the microstructure and the degree of dispersion of the tested samples and to
relate the colloidal structure to the elastic properties.
► Cite this publication as follows:
Lionetto F, Maffezzoli A: Rheological characterization of concentrarted nanoclay dispersions in an organic solvent, Appl. Rheol. 19 (2009) 23423.
Francesca Lionetto, Francesco Montagna, Alfonso Maffezzoli
Ultrasonic Dynamic Mechanical Analysis of Polymers
Appl. Rheol. 15:5 (2005) 326-335
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The propagation of ultrasonic waves in polymers depends on their viscoelastic behaviour and density, resulting
significantly affected by phase transitions occurring with changing temperature and pressure or during chemical
reactions. Therefore, the application of low intensity ultrasound, acting as a high frequency dynamic mechanical
deformation applied to a polymer, can monitor the changes of viscoelastic properties associated with the
glass transition, the crystallization, the physical or chemical gelation, the crosslinking. Thanks to the non-destructive
character (due to the very small deformation amplitude), low intensity ultrasound can be successfully used
for polymer characterization. Moreover, this technique has a big potential as a sensor for on-line and in-situ
monitoring of production processes for polymers or polymer matrix composites. Recently, in the laboratory of
Polymeric Materials of Lecce University a custom made ultrasonic set-up for the characterization of polymeric
material, even at high temperatures, has been developed. The ultrasonic equipment is coupled with a rotational
rheometer. Ultrasonic waves and shear oscillations at low frequency can be applied simultaneously on the
sample, getting information on its viscoelastic behaviour over a wide frequency range. The aim of this paper is
to present the potential and reliability of the ultrasonic equipment for the ultrasonic dynamic mechanical analysis
(UDMA) of both thermosetting and thermoplastic polymers. Three applications of UDMA to different polymeric
systems will be reviewed, concerning the cross-linking of a thermosetting resin, the crystallisation from
melt of a semicrystalline polymer and the water sorption in a dry hydrogel film. From the ultrasonic velocity and
attenuation measurements, the viscoelastic properties of the tested polymers are evaluated in terms of complex
longitudinal modulus and compared with the results of conventional dynamic mechanical analysis, carried
out at low frequency.
► Cite this publication as follows:
Lionetto F, Montagna F, Maffezzoli A: Ultrasonic Dynamic Mechanical Analysis of Polymers, Appl. Rheol. 15 (2005) 326.
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