Hydrodynamic Effects on Biofilms at the Biointerface Using a Microfluidic Electrochemical Cell: Case Study of Pseudomonas sp.

The anchoring biofilm layer is expected to exhibit a different response to environmental stresses than for portions in the bulk, due to the protection from other strata and the proximity to the attachment surface. The effect of hydrodynamic stress on surface-adhered biofilm layers was tested using a specially designed microfluidic bio flow cell with an embedded three-electrode detection system. In situ electrochemical impedance spectroscopy (EIS) measurements of biocapacitance and bioresistance of Pseudomonas sp. biofilms were conducted during the growth phase and under different shear flow conditions with verification by other surface sensitive techniques. Distinct, but reversible changes to the amount of biofilm and its structure at the attachment surface were observed during the application of elevated shear stress. In contrast, regular microscopy revealed permanent distortion to the biofilm bulk, in the form of streamers and ripples. Following the application of extreme shear stresses, complete removal of significant portions of biofilm outer layers occurred, but this did not change the measured quantity of biofilm at the electrode attachment surface. The structure of the remaining biofilm, however, appeared to be modified and susceptible to further changes following application of shear stress directly to the unprotected biofilm layers at the attachment surface

Kinetics of Multicomponent Polymerization Reaction Studied in a Microfluidic Format

We report a high-throughput study of the kinetics of a multicomponent polymerization reaction in a microfluidic reactor integrated with <i>in situ</i> attenuated total reflection Fourier transform infrared spectroscopy. The technique was used to study the kinetics of an exemplary free-radical polymerization reaction of <i>N</i>-isopropylacrylamide, which was initiated by ammonium persulfate in the presence of the accelerator <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine in water. By monitoring the rate of disappearance of the monomer double bonds, we determined the effects of the concentration of the monomer, initiator, and accelerator on the rate of polymerization and the effect of the pH of the reaction system on the reaction kinetics. This work opens the way for the kinetic studies of complex polymer systems in a microfluidic format

Microfluidic Study of Fast Gas–Liquid Reactions

We present a new concept for studies of the kinetics of fast gas–liquid reactions. The strategy relies on the microfluidic generation of highly monodisperse gas bubbles in the liquid reaction medium and subsequent analysis of time-dependent changes in bubble dimensions. Using reactions of CO₂ with secondary amines as an exemplary system, we demonstrate that the method enables rapid determination of reaction rate constant and conversion, and comparison of various binding agents. The proposed approach addresses two challenges in studies of gas–liquid reactions: a mass-transfer limitation and a poorly defined gas–liquid interface. The proposed strategy offers new possibilities in studies of the fundamental aspects of rapid multiphase reactions, and can be combined with throughput optimization of reaction conditions

Microfluidic Study of Fast Gas–Liquid Reactions

We present a new concept for studies of the kinetics of fast gas–liquid reactions. The strategy relies on the microfluidic generation of highly monodisperse gas bubbles in the liquid reaction medium and subsequent analysis of time-dependent changes in bubble dimensions. Using reactions of CO₂ with secondary amines as an exemplary system, we demonstrate that the method enables rapid determination of reaction rate constant and conversion, and comparison of various binding agents. The proposed approach addresses two challenges in studies of gas–liquid reactions: a mass-transfer limitation and a poorly defined gas–liquid interface. The proposed strategy offers new possibilities in studies of the fundamental aspects of rapid multiphase reactions, and can be combined with throughput optimization of reaction conditions

Microfluidic Studies of CO₂ Sequestration by Frustrated Lewis Pairs

Frustrated Lewis pairs (FLPs) comprising sterically hindered Lewis acids and bases offer the capability to reversibly capture CO₂ under mild reaction conditions. The determination of equilibrium constants and thermodynamic properties of these reactions should enable assessment of the efficiency of a particular FLP system for CO₂ sequestration and provide insights for design of new, efficient formulations of FLP catalysts for CO₂ capture. We have developed a microfluidic approach to studies of FLP–CO₂ reactions, which provides their thermodynamic characterization that is not accessible otherwise. The approach enables the determination of the equilibrium reaction constants at different temperatures, the enthalpy, the entropy, and the Gibbs energy of these reactions, as well as the enhancement factor. The microfluidic methodology has been validated by applying it to the well-characterized reaction of CO₂ with a secondary amine. The microfluidic approach can be applied for fundamental thermodynamic studies of other gas–liquid reactions