Dynamic Viscosity, Surface Tension and Wetting Behavior Studies of Paraffin–in–Water Nano–Emulsions
Abstract
This work analyzes the dynamic viscosity, surface tension and wetting behavior of phasechange material nano–emulsions (PCMEs) formulated at dispersed phase concentrations of 2, 4 and10 wt.%. Paraffin–in–water samples were produced using a solvent–assisted route, starting fromRT21HC technical grade paraffin with a nominal melting point at ~293–294 K. In order to evaluate thepossible effect of paraffinic nucleating agents on those three properties, a nano–emulsion with 3.6% ofRT21HC and 0.4% of RT55 (a paraffin wax with melting temperature at ~328 K) was also investigated.Dynamic viscosity strongly rose with increasing dispersed phase concentration, showing a maximumincrease of 151% for the sample containing 10 wt.% of paraffin at 278 K. For that same nano–emulsion,a melting temperature of ~292.4 K and a recrystallization temperature of ~283.7 K (which agree withprevious calorimetric results of that emulsion) were determined from rheological temperature sweeps.Nano–emulsions exhibited surface tensions considerably lower than those of water. Nevertheless,at some concentrations and temperatures, PCME values are slightly higher than surface tensionsobtained for the corresponding water+SDS mixtures used to produce the nano–emulsions. Thismay be attributed to the fact that a portion of the surfactant is taking part of the interface betweendispersed and continuous phase. Finally, although RT21HC–emulsions exhibited contact anglesconsiderably inferior than those of distilled water, PCME sessile droplets did not rapidly spread as ithappened for water+SDS with similar surfactant contents or for bulk–RT21HC.
Origin : Publication funded by an institution
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