An optical toolbox for total control of droplet microfluidics

The use of microfluidic drops as microreactors hinges on the active control of certain fundamental operations such as droplet formation, transport, division and fusion. Recent work has demonstrated that local heating from a focused laser can apply a thermocapillary force on a liquid interface sufficient to block the advance of a droplet in a microchannel (C. N. Baroud, J.-P. Delville, F. Gallaire and R. Wunenburger, Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys., 2007, 75(4), 046302). Here, we demonstrate the generality of this optical approach by implementing the operations mentioned above, without the need for any special microfabrication or moving parts. We concentrate on the applications to droplet manipulation by implementing a wide range of building blocks, such as a droplet valve, sorter, fuser, or divider. We also show how the building blocks may be combined by implementing a valve and fuser using a single laser spot. The underlying fundamentals, namely regarding the fluid mechanical, physico-chemical and thermal aspects, will be discussed in future publications.     

On the Road Toward More Efficient Biocompatible Two-Photon Excitable Fluorophores

Red-to-NIR absorption and emission wavelengths are key requirements for intravital bioimaging. One of the way to reach such excitation wavelengths is to use two-photon excitation. Unfortunately, there is still a lack of two-photon excitable fluorophores that are both efficient and biocompatible. Thus, we design a series of biocompatible quadrupolar dyes in order to study their ability to be used for live-cell imaging, and in particular for two-photon microscopy. Hence, we report the synthesis of 5 probes based on different donor cores (phenoxazine, acridane, phenazasiline and phenothiazine) and the study of their linear and non-linear photophysical properties. TD-DFT calculations were performed and were able to highlight the structure-property relationship of this series. All these studies highlight the great potential of three of these biocompatible dyes for two-photon microscopy, as they both exhibit high two-photon cross-sections (up to 3650 GM) and emit orange to red light. This potential was confirmed through live-cell two-photon microscopy experiments, leading to images with very high brightness and contrast.     

Convergence to a propagating front in a degenerate Fisher-KPP equation with advection

We consider a Fisher-KPP equation with density-dependent diffusion and advection, arising from a chemotaxis–growth model. We study its behavior as a small parameter, related to the thickness of a diffuse interface, tends to zero. We analyze, for small times, the emergence of transition layers induced by a balance between reaction and drift effects. Then we investigate the propagation of the layers. Convergence to a free boundary limit problem is proved and a sharp estimate of the thickness of the layers is provided.     

Thermoregulated Microemulsions by Cyclodextrin Sequestration: A New Approach to Efficient Catalyst Recovery

The combination of imidazolium surfactants with α‐cyclodextrins (CDs, in green) was used as a control element in the thermoregulated aqueous olefin hydroformylation. The self‐assembly of the imidazolium surfactants (red) favors the micellization process at high temperatures, whereas at lower temperatures the complexation of the surfactant monomers into the α‐CDs is favored.

     

Linear High Molar Mass Polyglycidol and its Direct α-Azido Functionalization

Summary: Linear polyglycidols with narrow chain dispersity and controlled high molar masses were prepared in a few hours by monomer-activated anionic polymerization of protected monomers, ethoxyethyl glycidyl ether and tert-butyl glycidyl ether, using a system composed of tetraoctylammonium bromide as initiator and triisobutylaluminum, used in 1.5 to 5-fold excess compared to the initiator, as co-initiator and monomer activator. This synthetic approach was shown to give various polyglycidol-based copolyethers in particular with propylene oxide or butene oxide. α-Azido,ω-hydroxy-poly(ethoxyethyl glycidyl ether) and other polyethers were directly prepared when tetrabutylammonium azide was used as initiator. Size exclusion chromatography and matrix-assisted laser desorption/ionization time-of-flight characterizations as well as “click” reactions were used to demonstrate the efficiency of the functionalization.     

Photoinduced magnetism in core/shell Prussian blue analogue heterostructures of K(j)Ni(k)[Cr(CN)6]l·nH2O with Rb(a)Co(b)[Fe(CN)6]c·mH2O

Core/shell and core/shell/shell particles comprised of the Prussian blue analogues K(j)Ni(k)[Cr(CN)(6)](l)·nH(2)O (A) and Rb(a)Co(b)[Fe(CN)(6)](c)·mH(2)O (B) have been prepared for the purpose of studying persistent photoinduced magnetization in the heterostructures. Synthetic procedures have been refined to allow controlled growth of relatively thick (50-100 nm) consecutive layers of the Prussian blue analogues while minimizing the mixing of materials at the interfaces. Through changes in the order in which the two components are added, particles with AB, ABA, BA, and BAB sequences have been prepared. The two Prussian blue analogues were chosen because B is photoswitchable, and A is ferromagnetic with a relatively high magnetic ordering temperature, ~70 K, although it is not known to exhibit photoinduced changes in its magnetic properties. Magnetization measurements on the heterostructured particles performed prior to irradiation show behavior characteristic of the individual components. On the other hand, after irradiation with visible light, the heterostructures undergo persistent photoinduced changes in magnetization associated with both the B and A analogues. The results suggest that structural changes in the photoactive B component distort the normally photoinactive A component, leading to a change in its magnetization.