Formation of Arrayed Droplets by Soft Lithography and Two-Phase Fluid Flow, and Application in Protein Crystallization

This paper presents an overview of our recent work on the use of soft lithography and two-phase fluid flow to form arrays of droplets. The crucial issues in the formation of stable arrays of droplets and alternating droplets of two sets of aqueous solutions include the geometry of the microchannels, the capillary number, and the water fraction of the system. Glass capillaries could be coupled to the PDMS microchannels and droplets could be transferred into glass capillaries for long-term storage. The arrays of droplets have been applied to screen the conditions for protein crystallization with microbatch and vapor diffusion techniques.     

Selectivity in Methanol Oxidation as Studied on Model Systems Involving Vanadium Oxides

Oxidation catalysts are modeled by oxide single crystals, thin oxide films, as well as supported oxide nanoparticles. We characterize the surface of those materials using a variety of surface sensitive techniques including scanning tunneling microscopy and spectroscopy, photoelectron spectroscopy, infrared spectroscopy, and thermal desorption spectroscopy. We find temperature dependent structural transformations from V₂O₅(001) to V₂O₃(0001) via V₆O₁₃(001). V₂O₃(0001) is found to be vanadyl terminated in an oxygen ambient and it loses the vanadyl termination after electron bombardment. It is shown that the concentration of vanadyl groups controls the selectivity of the methanol oxy-dehydrogenation towards formaldehyde. A proposal for the mechanism is made. The results on single crystalline thin films are compared with similar measurements on deposited vanadia nanoparticles. The experimental results are correlated with theoretical calculations and models.     

Andreev reflections in a Bi<Subscript>1.8</Subscript>Pb<Subscript>0.3</Subscript>Sr<Subscript>1.9</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>x</Subscript> break junction

The current-voltage characteristic (CVC) of a break junction made from polycrystalline Bi_1.8Pb_0.3Sr_1.9Ca₂Cu₃O_x is investigated. The experimental CVC has a hysteretic feature that reflects part of the curve with a negative differential resistance. The CVC is discussed within the framework of the Kümmel-Gunsenheimer-Nicolsky theory that takes into account multiple Andreev reflections in superconductor/normalmetal/superconductor junctions.     

Effect of copper on the properties of Pr-Dy-Fe-Co-B sintered magnets

The effect of copper on the properties of magnets (Pr_0.52Dy_0.48)₁₃(Fe₆₅Co_0.35)_{80.3 ? x} Cu _x B_6.7 (x = 0–10) has been studied. Alloying with copper is shown to decrease the sintering temperature and to increase the content of the principal (Pr,Dy)₂(Fe,Co)₁₄B magnetic phase. For compositions with x = 1.3–3.3, copper is found to affect the value and sign of the temperature induction coefficient (TIC). It is shown that the effect of copper on the TIC is determined by the substitution of copper ions for iron ions in lattice sites, which are coupled via an antiferromagnetic exchange interaction.     

Formation of droplets of alternating composition in microfluidic channels and applications to indexing of concentrations in droplet-based assays

For screening the conditions for a reaction by using droplets (or plugs) as microreactors, the composition of the droplets must be indexed. Indexing here refers to measuring the concentration of a solute by addition of a marker, either internal or external. Indexing may be performed by forming droplet pairs, where in each pair the first droplet is used to conduct the reaction, and the second droplet is used to index the composition of the first droplet. This paper characterizes a method for creating droplet pairs by generating alternating droplets, of two sets of aqueous solutions in a flow of immiscible carrier fluid within PDMS and glass microfluidic channels. The paper also demonstrates that the technique can be used to index the composition of the droplets, and this application is illustrated by screening conditions of protein crystallization. The fluid properties required to form the steady flow of the alternating droplets in a microchannel were characterized as a function of the capillary number Ca and water fraction. Four regimes were observed. At the lowest values of Ca, the droplets of the two streams coalesced; at intermediate values of Ca the alternating droplets formed reliably. At even higher values of Ca, shear forces dominated and caused formation of droplets that were smaller than the cross-sectional dimension of the channel; at the highest values of Ca, coflowing laminar streams of the two immiscible fluids formed. In addition to screening of protein crystallization conditions, understanding of the fluid flow in this system may extend this indexing approach to other chemical and biological assays performed on a microfluidic chip.     

Author Index

Authors Index

Author Index     

Molar enthalpy of vaporization of ethanol-gasoline mixtures and their colloid state

Vapour pressure measurements are used to evaluate the enthalpy of vaporization of ethanol-gasoline mixtures. Partial molar values are also derived. The dispersed structure of ethanol-gasoline fuel is studied for the first time using the method of correlation spectroscopy of scattered light. A large range of dispersed particle sizes in different alcohol-gasoline systems is found. The dependence of the mean radius of drops on ethanol content is determined. It is found that coalescence phenomenon occurs in the systems when extra ethanol is added.