Rheological behavior and structural interpretation of waxy crude oil gels.

A waxy crude oil which gels below a threshold temperature has been investigated under static and dynamic conditions, using a combination of rheological methods, optical microscopy, and DSC. Particular attention is given in this work to the influence of the mechanical history on gel strength and to describing the time-dependent rheological behavior. The gels display a strong dependence of the yield stress and moduli on the shear history, cooling rate, and stress loading rate. Of particular interest is the partial recovery of the gel structure after application of small stress or strain (much smaller than the critical values needed for flow onset) during cooling, which can be used to reduce the ultimate strength of the crude oil gel formed below the pour point. A second focus of this study is to further develop the physical interpretation of the mechanism by which wax crystallization produces gelation. Gelation of the waxy crude oil studied is suggested to be the result of the association between wax crystals, which produces an extended network structure, and it is shown that the system displays features common to attractive colloidal gels, for one of which, fumed silica (Aerosil 200) in paraffin oil, rheological data are reported. The colloidal gel model provides a simple and economical basis for explaining the response of the gelled oil to various mechanical perturbations and constitutes a fruitful basis from which to develop technologies for controlling the gelation phenomenon, as suggested by the rheological results reported.

Study of gelling behavior of poly(vinyl alcohol)-methacrylate for potential utilizations in tissue replacement and drug delivery.

The need of innovative, multifunctional biomaterials for the partial or complete tissue replacement is the driving force for the search of improvements of the performances of the available materials and in the formulation of new ones. Addressing the focus to vitreous substitution, we have explored the possibility of using injectable aqueous solutions of poly(vinyl alcohol), PVA, derivatives able to form hydrogels in the ocular cavity upon UV-vis irradiation with visible light. In particular, we describe the features of hydrogels from methacrylate grafted PVA, PVA-MA, in terms of structural characteristics, degradation processes, release of low- and high- molecular weight molecules, and in vitro gelation kinetics. The mechanical properties, drug delivery tests, and rheology tests suggest that PVA-MA derivatives have the potential to become a useful material for vitreous substitution.