Effects of polymer addition on the rheology of o/w microemulsions |
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Authors: | Romano Lapasin Mario Grassi Nicoletta Coceani |
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Institution: | (1) Department of Chemical Environmental and Raw Materials Engineering University of Trieste piazzale Europa 1, 34127 Trieste, Italy e-mail: romanol@dicamp.univ.trieste.it, IT;(2) Vectorpharma International S.p.A. Via Follatoio 12 34148 Trieste, Italy, IT |
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Abstract: | Microemulsions are profitably employed in the pharmaceutical field to prepare drug delivery systems release for guest drugs
sparingly soluble in water. In particular, they can be used for topical and transdermal administration in place of ointments
or creams, on condition that their rheological properties are properly modulated. The present work concerns the analysis of
the rheological effects produced by the addition of different amounts of Carbopol 940, a polymer widely used for topical applications,
to an O/W microemulsion containing a lipophilic phase (Labrafac Hydro, 21 wt%) and stabilized by the surfactant (Cremophor
RH40)/co-surfactant (Transcutol) couple. The contribution of the disperse phase is evaluated by comparing the linear and nonlinear
properties of the Carbopol/microemulsion system (CM) with those of the corresponding aqueous Carbopol systems with co-surfactant
(CWT) and without co-surfactant (CW). Four polymer concentrations (0.25%, 0.5%, 1%, and 2%) are taken into consideration.
The linear viscoelastic properties of the microemulsions essentially mirror those of the corresponding aqueous Carbopol systems
when the polymer concentration is sufficiently high (1–2%). In these conditions the oil phase is reasonably hosted within
the meshes of the three-dimensional polymeric gel network and gives only a slight contribution to the connectivity of the
whole system. Similar considerations can be drawn from the flow behavior of the systems examined in the low shear region.
Received: 6 February 2000 Accepted: 13 November 2000 |
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Keywords: | Microemulsions Gelling agent Viscoelasticity Flow properties Carbopol |
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