AGGREGATION OF N-ALKANES IN ORGANIC-SOLVENTS

Normal alkanes are abundant in crude oils and diesel fuels. We have mo delled diesel fuels by dissolving a realistic mixture of n-alkanes in toluene or nitrobenzene. The microstructures of those solutions have b een comprehensively studied using the abosolutely calibrated SANS, SAX S and the dynamic light scattering techniques. The data have been coll ected for various paraffin concentrations in the temperature range -20 degrees C to 70 degrees C, covering the region above and below the cr ystallisation temperature of the solutions. Our results indicate that for the paraffin concentration above 10 wt%, hat aggregates of several like paraffin molecules form spontaneously. These aggregates exist in the liquid phase both above and below the paraffin crystallisation te mperature T-c. Remarkably, they coexist with the paraffin crystals at low temperatures. Their concentration decreases with increased tempera ture and they fully dissolve at about T-c + 40 degrees C. From the num erical fits to our SAXS and SANS data we determine the size distributi on and volume fraction of the aggregates. Similar size aggregates are observed using dynamic light scattering and STM. This aggregation proc ess is unexpected and has not been previously reported.