Energy balance in dense microemulsions |
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Authors: | Donatella Senatra C Ziparo Cecilia M C Gambi and L Lanzi |
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Institution: | (1) Department of Physics and CNISM University of Florence, via Sansone 1, 50019 Sesto Fiorentino, Florence, Italy;(2) CRS-Soft Matter (CNR-INFM) Università di Roma ‘La Sapienza’, p.le A. Moro 2, 00185 Roma, Italy;(3) European Laboratory for Non-linear Spectroscopy (LENS), via Carrara 1, 50019 Sesto Fiorentino, Florence, Italy |
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Abstract: | A water-in-oil microemulsion composed of water, AOT and decane with volume fraction φ=0.50 and molar ratio X=40.8 was analysed by DSC. The percolation and the bicontinuous transitions as well as the melting endotherms and the freezing
exotherms were measured. The main attention was focussed on the system energy balance. It was found that, by freezing the
samples after the occurrence of the percolative transition, the total heat released is significantly less than the heat absorbed
in the melting endotherms. A simple geometrical model was used as an analysis tool of the aforementioned energy difference.
Since the system studied exhibits a percolative transition of dynamic type, on approaching the percolation threshold temperature
(T≤T
p) and a static percolation for T≥T
p, the structural change from the connecting water-droplet-cluster to a connecting water channel was schematised in the model
as a change from a sphere-necklace to a water-cylindrical channel of equal volume and equal length. The surface energy associated
with the formation of the two different geometrical surfaces was evaluated and the amount of saved energy compared with the
experimentally measured one. |
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Keywords: | dense microemulsions energy balance percolation and bicontinuous transitions by DSC |
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