Micellar kinetic resolution

Time resolved SAXS/SANS allow a structural observation of kinetic processes on the nanoscale (1-100 nm) on a time scale ranging from milliseconds to hours. This allows micellar kinetics to be followed in real time, giving direct structural information of the process and its evolution. Synchrotron SAXS can reach smaller time scales and exhibits better resolution compared to neutron-based methods. However, SANS offers the possibility for contrast variation via simple H/D exchange chemistry, which opens up a world of possibilities for the investigation of kinetics in soft matter systems, in particular transport and exchange processes that otherwise would be invisible in scattering experiments. As most of these techniques have become available over recent years with advancements in both instrumentation and sample environments, there is a need for an overview of the development and the possibilities that are now available in the field of soft matter in general and micellar systems in particular. 

Capillary electrophoresis (CE) is an emerging analytical technique for determination of catechins. The majority of CE studies involve the analysis of catechins in tea infusion, extracts as well as supplements. The three variants of CE suitable for the analysis of catechins include capillary zone electrophoresis (CZE), micellar electro-kinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC) with UV detection. In general, the resolution of MEKC was found to be superior to CZE for separation of catechins. MEEKC is a relatively new technique, and the few reports available suggest that it offers a performance similar to MEKC. CE conditions are often quite complex, and many factors, such as buffer composition, pH, presence of surfactants, and column temperature, can all affect the quality of separation and should be optimized individually. On the other hand, CE offers several advantages over HPLC. The short analysis time (<20 minutes), low running costs, and reduced use of solvents make it an attractive alternative for routine analysis of catechins. 

Fig. 18 Velocity profiles as a function of time at 7 = 10 s obtained in a Couette device of gap e using PTV. The spatial resolution is 10p,m. The micellar system is the 6.3% w/v CPCl and NaSal at molar ratio R = [Sal]/[CPCl] = 0.5,in 0.5M H2O NaCl brine at T = 23°C. The kinetics of formation of the banding structure is composed of two main stages, (a) A short-time response where the flow stays homogeneous most of the time with increasing and decreasing local shear rates respectively at the inner and outer walls, (b) Growth of the low shear rate band from the outer wall. Reprinted with permission from Hu et al. [157]...

---