Sensitivity of hypersaline Arabian Gulf to seawater desalination plants

Due to the hot, arid nature of its bordering lands, seawater in the Arabian Gulf can have significant evaporation rates leading to hypersaline conditions. If additional desalination plants were to operate along its coast, then the extraction of desalinated water and returned brine waste stream into the Gulf would increase the salinity. This paper uses a tidally and cross-sectionally averaged mathematical model that reveals multiplicative dependence of the salinity on factors associated with river flow, evaporation rates and each of the desalination plants. Present-day desalinated water production rates are in the linear regime, but hypersalinity has exponential sensitivity to the position and volumetric rate of desalinated water extraction.     

Synergism of cellulosic nanowhiskers and graft structure in stereocomplex-based materials: formation in solution and a stereocomplex memory study

Stereocomplexation is one of the approaches to improve polylactide's properties. Along with improving its properties, it also limits stereocomplex formation through solution and stereocomplex memory. The graft structure and presence of nanoparticles have a synergetic effect, improving the stereocomplex formation and its memory. The bio-stereocomplex-nanocomposite materials are generated by stereocomplexation of polylactide-graft-acetylated cellulosic nanowhiskers in the solution. The graft structure containing well-distributed acetylated cellulose nanowhiskers results in unusual stereocomplexation in the solution and influences the stereocomplex memory of the bio-stereocomplex-nanocomposite materials. Perfect stereocomplexes are easily obtained in a relatively short mixing time (5 min) from various solution concentrations up to 20 % (w/v). The bio-stereocomplex-nanocomposites have excellent stereocomplex memory to re-form the stereocomplex after melting, which is the main limitation of stereocomplex materials in industrial processes. This fully bio-based material is a potential ecofriendly candidate for the future.     

Effect of phase change on the rheology and stability of paraffin wax-in-water Pickering emulsions

“Pickering” emulsions are widely found in nature and industry including food, pharmaceuticals, and oil industries. Often, Pickering emulsion studied have a Newtonian dispersed phase. However, the dispersed phase can be non-Newtonian such as one that can be subjected to a phase change under certain experimental conditions. This work examines how changing the physical state of dispersed phase alters the shear stability and bulk viscoelasticity of o/w emulsions. Model silica-stabilized, paraffin wax-in-water emulsions are synthesized. The wax, with a melting temperature of about 55 ^°C is subjected to a phase change by changing the temperature between 15 and 80 ^°C. At lower temperatures (< 55 ^°C), the droplet deformability and particle mobility at the interface are significantly restricted while at higher temperatures (> 55 ^°C), the wax melts and expands, making the emulsion droplets deformable and the particles more relaxed. These directly affect bulk emulsion rheology. Flow curves and oscillatory shear experiments indicate that emulsion droplets are flocculated and the emulsions behave as elastic solids. These properties are directly influenced by temperature, which alters the state of aggregation and network-structure of the emulsion droplets. The effect of emulsion concentration is also analyzed. Three different concentrations are tried—15, 30, and 45 vol% (as measured at 25 ^°C when the wax is solid). At a given temperature, the rheological properties seem to scale with concentration. Further, we show that the emulsions are sensitive to destabilization (gelation) under flow with the sensitivity directly varying with temperature and magnitude of shear fields (steady shear) applied.     

Cross-metathesis of 1,3-dienes with electron-deficient olefins

Cross-metathesis reactions between 1,3-dienes and electron-deficient olefins have been investigated. Terminal monosubstituted 1,3-dienes afforded low yields of the desired CM products due to competing cleavage of the internal double bond. This undesired cleavage is successfully suppressed in the case of 1,3-dienes containing a sterically more congested internal double bond. Methyl vinyl ketone as the coupling partner was shown to provide the best yields.