Improved dispersion tolerance of a Mach-Zehnder modulator by optimizing the modulator voltage and time delay

We present a method for improving the dispersion tolerance of a dual-arm Mach-Zehnder modulator by independently optimizing the applied voltage on each arm and the time delay between them. We found a significant improvement in the dispersion tolerance. Using the negative chirp effect and the time delay, it was possible to extend the transmission distance of 10 Gbit/s optical nonreturn-to-zero signals without any additional electrical or optical components.     

Electrostatic stabilization of colloids in carbon dioxide: electrophoresis and dielectrophoresis

Over the past decade, steric stabilization has been achieved for a variety of inorganic and organic colloids in supercritical fluid carbon dioxide (scCO2). Herein we demonstrate that colloids may also be stabilized in CO2 by electrostatic forces, despite the ultralow dielectric constant of 1.5. Zeta potentials of micrometer-sized water droplets, measured in a microelectrophoresis cell, reached -70 mV corresponding to a few elementary charges per square micrometer of droplet surface. This degree of charge was sufficient to stabilize water/CO2 emulsions for an hour, even with water volume fractions of 5%. Hydrogen ions partition preferentially, relative to bicarbonate ions, from the emulsion droplets to the cores of surfactant micelles in the diffuse double layer surrounding the droplets. The micelles, formed with a low molecular weight branched hydrocarbon surfactant, prevent ion pairing of the hydrogen counterions to the negatively charged emulsion droplets. Dielectrophoresis of the water droplets at a frequency of 60 Hz leads to chains containing a dozen droplets with lengths of 50 mum. The ability to form electrostatically stabilized colloids in carbon dioxide is particularly useful in practical applications, because steric stabilization in CO2 is often limited by the poor solvation of the stabilizers.     

Interfacial Studies of the Formation of Microemulsions of Water in Carbon Dioxide with Fluorinated Surfactants

Measurements of the interfacial tension, γ, for water-CO₂-perfiuoropoly ether (PFPE) ionic surfactant systems are utilized to understand the surfactant affinity for the various phases and adsorption at the interface. A marked decrease in γ with salinity is observed as salt screens electrostatic repulsion and induces microemulsion formation, as confirmed with dynamic light scattering. In several cases, the interfacial tension goes through an unusual maximum with salinity, which is explained in terms of competition between surfactant affinity for the various phases and microemulsion formation. Fundamental studies of interfacial properties provide important insight for designing surfactants and experimental conditions to achieve the desired properties of water/CO² microemulsions and emulsions.     

Surface grafting of glycidyl methacrylate on silica gel and polyethylene beads

Surface grafting of glycidyl methacrylate (GMA) on silica gel and a polyethylene bead was performed by radical polymerization and radiation-induced polymerization, respectively, in order to improve softness. Subsequently, diethylene triamine (DETA), triethylene tetraamine (TETA), and iminodiacetic acid (IDA) were introduced to the grafted GMA for use as affinity columns. The efficiency of the affinity column was investigated by use of bovine serum albumin (BSA) and hemoglobin (Hb) as model proteins. The affinity degree of BSA was higher than Hb for the DETA and TETA column, whereas the affinity degree of Hb was higher than BSA for the IDA column supported by silica gel. The affinity degree of BSA was higher than Hb for the DETA and TTA column supported by polyethylene (PE) beads.     

Direct Fabrication of Free‐Standing MOF Superstructures with Desired Shapes by Micro‐Confined Interfacial Synthesis

Recently, metal–organic frameworks (MOFs) with multifunctional pore chemistry have been intensively investigated for positioning the desired morphology at specific locations onto substrates for manufacturing devices. Herein, we develop a micro‐confined interfacial synthesis (MIS) approach for fabrication of a variety of free‐standing MOF superstructures with desired shapes. This approach for engineering MOFs provides three key features: 1) in situ synthesis of various free‐standing MOF superstructures with controlled compositions, shape, and thickness using a mold membrane; 2) adding magnetic functionality into MOF superstructures by loading with Fe₃O₄ nanoparticles; 3) transferring the synthesized MOF superstructural array on to flat or curved surface of various substrates. The MIS route with versatile potential opens the door for a number of new perspectives in various applications.