RESUMO
During automotive engine operation, water may contaminate engine oil, inhibiting its role in maintaining safe engine operation. In many cases, engine oil must be capable of emulsifying any water contamination to avoid such problems. This study focuses on the impact of small molecule surfactant concentration structure and concentration in emulsions comprised of engine oil, water, and E85 fuel to understand the effects on emulsion stability and formulation optimization. Three small molecule surfacatants were tested; glycerol dioleate (GDO), glyceryl monooleate (GMO), and oleamide (OA). Three characterization methods were used to investigate their effects; the current state of the art, ASTM D7563, microscopy, and diffusing wave spectroscopy (DWS). We found that DWS could yield insights into mechanisms of emulsion stability that are otherwise inaccessible through other experimental techniques. Specifically, utilizing DWS, we are able to extract specific emulsion stability mechanisms associated directly with molecular features for the three surfactants examined.
RESUMO
The direct cross-linking of Au/Ag alloy nanoparticles (NPs) into high surface area, mesoporous Au/Ag aerogels via chemical oxidation of the surface ligands is reported. The precursor alloy NPs with composition-tunable morphologies were produced by galvanic replacement of the preformed Ag hollow NPs. The effect of Au:Ag molar ratio on the NP morphology and surface plasmon resonance has been thoroughly investigated and resulted in smaller Au/Ag alloy NPs (4-8 nm), larger Au/Ag alloy hollow NPs (40-45 nm), and Au/Ag alloy hollow particles decorated with smaller Au NPs (2-5 nm). The oxidative removal of surfactant ligands, followed by supercritical drying, is utilized to construct large (centimeter to millimeter) self-supported Au/Ag alloy aerogels. The resultant assemblies exhibit high surface areas (67-73 m(2)/g), extremely low densities (0.051-0.055 g/cm(3)), and interconnected mesoporous (2-50 nm) networks, making them of great interest for a number of new technologies. The influence of mesoporous gel morphology on surface-enhanced Raman scattering (SERS) has been studied using Rhodamine 101 (Rd 101) as the probe molecule. The alloy aerogels exhibit SERS signal intensities that are 10-42 times higher than those achieved from the precursor Au/Ag alloy NPs. The Au/Ag alloy aerogel III exhibits SERS sensing capability down to 1 nM level. The increased signal intensities attained for alloy aerogels are attributed to highly porous gel morphology and enhanced surface roughness that can potentially generate a large number of plasmonic hot spots, creating efficient SERS substrates for future applications.
