Influence of Shear Flow on the Crystallization of Organic Melt Emulsions – A Rheo‐Nuclear Magnetic Resonance Investigation

There is a need to better understand the influence of shear flow on the crystallization of a molten oil phase in an oil/water emulsion due to its high relevance for industrial processes. The present study focuses on the influence of laminar shear flow on the crystallization kinetics of polydisperse n ‐hexadecane‐in‐water emulsions. The investigation was carried out by rheo‐nuclear magnetic resonance (NMR) spectroscopy in a Taylor‐Couette geometry. An accelerating impact of the shear rate on the overall crystallization kinetics was verified. This effect stems from an increase of the collision frequency of already crystallized droplets with not yet crystallized droplets. Nevertheless, the collision efficiency decreased with higher shear rate

Crystallization Behavior and Nucleation Kinetics of Organic Melt Droplets in a Microfluidic Device

The powerful technique of microfluidics is applied for the first time to investigate the crystallization behavior and nucleation kinetics of monodisperse organic melt droplets in the range of a few nanoliters. Multiple characteristic time scales in the fraction of (un)­crystallized droplets are found. We interpret these findings regarding mechanisms discussed in microfluidics or oil-in-water emulsions and with the help of inverse Laplace transformation. Heterogeneous active centers, for example, various catalytic impurities, cause fast nucleation in multiple droplet populations with different rates. The nucleation of the remaining droplets in the later stage of the experiment is dominated by only one, slower nucleation rate. The related mechanism is most likely surfactant-driven heterogeneous nucleation at the surface or in the droplet volume. Homogeneous nucleation is excluded at this droplet size and the supercooling values examined. Hexadecane (C16) and ethylene glycol distearate (EGDS) are used as exemplary organic melt substances. Our results prove that the application of microfluidics to organic melt droplets enables an optical examination of monodisperse droplets without droplet interactions to study nucleation. This provides new opportunities to investigate fundamental parameters in the field of emulsion crystallization

Author response

Plasma membrane lipid composition must be maintained during growth and under environmental insult. In yeast, signaling mediated by TOR Complex 2 (TORC2)-dependent protein kinase Ypk1 controls lipid abundance and distribution in response to membrane stress. Ypk1, among other actions, alleviates negative regulation of L-serine:palmitoyl-CoA acyltransferase, upregulating production of long-chain base precursors to sphingolipids. To explore other roles for TORC2-Ypk1 signaling in membrane homeostasis, we devised a three-tiered genome-wide screen to identify additional Ypk1 substrates, which pinpointed both catalytic subunits of the ceramide synthase complex. Ypk1-dependent phosphorylation of both proteins increased upon either sphingolipid depletion or heat shock and was important for cell survival. Sphingolipidomics, other biochemical measurements and genetic analysis demonstrated that these modifications of ceramide synthase increased its specific activity and stimulated channeling of long-chain base precursors into sphingolipid end-products. Control at this branch point also prevents accumulation of intermediates that could compromise cell growth by stimulating autophagy. DOI: http://dx.doi.org/10.7554/eLife.03779.00