Self-assembly of surfactant vesicles that transform into viscoelastic wormlike micelles upon heating

Unilamellar vesicles are observed to form in aqueous solutions of the cationic surfactant, cetyl trimethylammonium bromide (CTAB), when 5-methyl salicylic acid (5mS) is added at slightly larger than equimolar concentrations. When these vesicles are heated above a critical temperature, they transform into long, flexible wormlike micelles. In this process, the solutions switch from low-viscosity, Newtonian fluids to viscoelastic, shear-thinning fluids having much larger zero-shear viscosities (e.g., 1000-fold higher). The onset temperature for this transition increases with the concentration of 5mS at a fixed CTAB content. Small-angle neutron scattering (SANS) measurements show that the phase transition from vesicles to micelles is a continuous one, with the vesicles and micelles coexisting over a narrow range of temperatures. The tunable vesicle-to-micelle transition and the concomitant viscosity increase upon heating may have utility in a range of areas, including microfluidics, controlled release, and tertiary oil recovery.     

A queuing approach for inventory planning with batch ordering in multi-echelon supply chains

This paper presents stylized models for conducting performance analysis of the manufacturing supply chain network (SCN) in a stochastic setting for batch ordering. We use queueing models to capture the behavior of SCN. The analysis is clubbed with an inventory optimization model, which can be used for designing inventory policies . In the first case, we model one manufacturer with one warehouse, which supplies to various retailers. We determine the optimal inventory level at the warehouse that minimizes total expected cost of carrying inventory, back order cost associated with serving orders in the backlog queue, and ordering cost. In the second model we impose service level constraint in terms of fill rate (probability an order is filled from stock at warehouse), assuming that customers do not balk from the system. We present several numerical examples to illustrate the model and to illustrate its various features. In the third case, we extend the model to a three-echelon inventory model which explicitly considers the logistics process.     

On the Relative Preference of Enamine/Iminium Pathways in an Organocatalytic Michael Addition Reaction

The right path : The mechanism of organocatalyzed Michael addition between propanal and methyl vinyl ketone is investigated using the density functional and ab intio methods. The kinetic preference for the formation of key intermediates is established in an effort to identify the competing pathways associated with the reaction. The effect of co‐catalyst/protic solvent on the energetics of the reaction is also studied