PIV measurements of flow within plugs in a microchannel

The use of two-phase flow in lab-on-chip devices, where chemical and biological reagents are enclosed within plugs separated from each other by an immiscible fluid, offers significant advantages for the development of devices with high throughput of individual heterogeneous samples. Lab-on-chip devices designed to perform the polymerase chain reaction (PCR) are a prime example of such developments. The internal circulation within the plugs used to transport the reagents affects the efficiency of the chemical reaction within the plug, due to the degree of mixing induced on the reagents by the flow regime. It has been hypothesised in the literature that all plug flows produce internal circulation. This work demonstrates experimentally that this is false. The particle image velocimetry (PIV) technique offers a powerful non-intrusive tool to study such flow fields. This paper presents micro-PIV experiments carried out to study the internal circulation of aqueous plugs in two phase flow within 762 μm internal diameter FEP Teflon tubing with FC-40 as the segmenting fluid. Experiments have been performed and the results are presented for plugs ranging in length from 1 to 13 mm with a bulk mean flow velocity ranging from 0.3 to 50 mm/s. The results demonstrate for the first time that circulation within the plugs is not always present and requires fluidic design considerations to ensure their generation. © Springer-Verlag 2006

Inclusion complexes of rosmarinic acid and cyclodextrins: stoichiometry, association constants, and antioxidant potential

The interaction between beta-cyclodextrin (beta-CD) and the polyphenol rosmarinic acid (RA) is here reported by H-1 NMR titration experiments. The formation of an aqueous soluble inclusion complex is confirmed and valuable information regarding mode of penetration of guest into beta-CD, stoichiometry, and stability of the complex is obtained. The analysis by the continuous variation method shows the undoubted formation of 1:1 beta-CD/RA complex. Additionally, the estimated apparent association constants reveal the importance of the asymmetry of the RA in the complexation; the incorporation of the catechol moiety closer to the carboxylic group is more favorable (K = 2,028 M-1) than from the other end of the RA molecule (K = 1,184 M-1). Finally, we have also investigated the antioxidant activity and storage stability of the beta-CD/RA complexed system; the presence of beta-CD was found to produce a remarkable enhancement on the antioxidant activity