Aminimides. XI. Modified polystyrenes containing pendent aminimide or isocyanate residues

The hydrochloride salt of 1,1-dimethyl-1-(2-hydroxypropyl)amine methacrylimide (DHA) was synthesized and shown to readily homo- and copolymerize with styrene to produce soluble polymers containing pendent quaternary ammonium groups. These polymers may be treated with base to provide modified polystyrenes containing pendent aminimide residues. The latter polymers may be thermolyzed in solution or in the solid phase to produce modified polystyrenes containing pendent isocyanate groups. If the thermolysis is carried out in the presence of “isocyanate reactive” moieties, high molecular weight, crosslinked polymers may be synthesized. The reactivity ratios of DHA · HCl with styrene were determined: r₁ = 0.33 and r₂ = 0.35. The Alfrey-Price Q and e values were also calculated: Q = 0.88 and e = 0.67.     

The role of interfacial segregation and microstructure in interdiffusion between aluminum and silicon

In this investigation, we studied the interdiffusion behavior between polycrystalline silicon (poly-Si) and aluminum where the poly-Si was doped with antimony via ion implantation. Post sintering sample microstructure was determined by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and optical microscopy, and composition was determined by Rutherford Backscattering Spectrometry (RBS) and Scanning Auger Microscopy. As-implanted samples showed interdiffusion during sintering (465° C, dry N₂) independent of Sb concentrations up to 1.1 × 10²¹ cm⁻³ near the Al/Si interface. In samples where the implantation damage was annealed out prior to sintering, interdiffusion is inhibited when the Sb concentration at the interface was above a threshold concentration of 7.3 × 10¹⁹ cm⁻³. This threshold concentration is lower if the segregation of Sb is preserved prior to metallization. We propose that interdiffusion is inhibited by dopant (Sb) passivation of interfacial Si defects, the sites where interdiffusion is believed to initiate. MIT work supported by NSF contract 84-18718-DMR.     

High-efficiency, two-dimensional separations of protein digests on microfluidic devices

High-efficiency, two-dimensional separations of tryptic digests were achieved using glass microfluidic devices. Following micellar electrokinetic chromatography (MEKC) separations in a 19.6-cm-long serpentine channel, the peptides were rapidly sampled into a 1.3-cm-long second-dimension channel, where they were separated by capillary electrophoresis (CE). The turns in the serpentine channel were asymmetrically tapered to minimize geometrical contributions to band broadening and to provide ample channel length for high-efficiency chromatographic separations. Analysis of rhodamine B injections routinely produced plate numbers of 230000 and 40000 in the first (MEKC) and second (CE) dimensions, respectively, corresponding to plate heights of 0.9 and 0.3 microm. The electric field strengths were 200 V/cm for MEKC and 2400 V/cm for CE. In analysis times less than 15 min, two-dimensional separation of bovine serum albumin tryptic digest produced a peak capacity of 4200 (110 in the first dimension and 38 in the second dimension). The system was used to identify a peptide from a tryptic digest of ovalbumin using standard addition and to distinguish between tryptic digests of human and bovine hemoglobin.     

Development of textured antimony sulphoiodide

Processing and characterization techniques which were used to obtain a dense well aligned antimony sulphoiodide ceramic body are described. A technique in which an a.c. field is used to electrically align SbSI crystals for subsequent orthogonal hot pressing is described. Characterization of the microstructure, the mechanical and the electrical properties disclosed that a reasonably strong (∼ 20MPa) piezoelectrically active (d ₃₃=∼ 500 pC N⁻¹) body could be produced. These properties are then compared to those obtained on bodies prepared by other techniques and to those of single-crystal “boules” of SbSI.     

Microchip separations in reduced-gravity and hypergravity environments

Microfabricated fluidics technology, e.g., lab-on-a-chip devices, offers many attractive features for performing chemistry and biochemistry on space-based platforms. We have constructed a portable, battery-operated microfluidic platform that was tested under reduced gravity and hypergravity conditions that would be experienced in space flight and launch. This device consisted of a microchip, microchip holder, two 0-8-kV high-voltage power supplies, a high-voltage switch, a solid-state diode-pumped green laser, an optical train, a channel photomultiplier, and an inertial mass measurement unit all under the control of a laptop computer and powered by 10 D-cell alkaline batteries. The unit was tested on NASA's reduced gravity research aircraft at gravity levels that are relevant to NASA's intended use of bioreporter-based microchips for environmental monitoring of space and planetary environments on manned and unmanned spacecraft. Over the course of two flights, 834 fast electrophoretic separations of four amino acids were performed under a variety of gravitational environments including zero-g, Martian-g, lunar-g, and approximately 1.8-g. All separations were performed in less than 12 s and automatically analyzed. After correction with an internal migration standard, the migration time reproducibilities were all <1% relative standard deviation.     

Two-dimensional electrochromatography/capillary electrophoresis on a microchip

A two-dimensional separation system on a microfabricated device was demonstrated using open-channel electrochromatography as the first dimension and capillary electrophoresis as the second dimension. The first dimension was operated under isocratic conditions, and the effluent from the first dimension was repetitively injected into the second dimension every few seconds. A 25-cm separation channel with spiral geometry for open-channel electrochromatography was chemically modified with octadecylsilane and coupled to a 1.2-cm straight separation channel for capillary electrophoresis. Fluorescently labeled products from tryptic digests of beta-casein were analyzed in 13 min with this system.     

Elemental mapping with elastically scattered electrons

We describe a technique for efficient, quantitative, standardless elemental mapping using a high-angle annular detector in a scanning transmission electron microscope (STEM) to collect elastically scattered electrons. With a single crystal specimen, contrast due to thickness variations, diffraction, and channelling effects can be avoided, so that the resulting image contrast quantitatively reflects variations in impurity concentration. We compare a number of simple analytical approximations to the elastic scattering cross sections and show that a standardless analysis is possible over a wide range of atomic number and inner detector angle to an absolute accuracy of better than 20%.     

Electroosmotically induced hydraulic pumping on microchips: differential ion transport

The theory behind and operation of an electroosmotically induced hydraulic pump for microfluidic devices is reported. This microchip functional element consists of a tee intersection with one inlet channel and two outlet channels. The inlet channel is maintained at high voltage while one outlet channel is kept at ground and the other channel has no electric potential applied. A pressure-induced flow of buffer is created in both outlet channels of the tee by reducing electroosmosis in the ground channel relative to that of the inlet channel. Spatially selective reduction of electroosmosis is accomplished by coating the walls of the ground channel with a viscous polymer. The pump is shown to differentially transport ions down the two outlet channels. This ion discrimination ability of the pump is examined as a function of an analyte's electrophoretic velocity. In addition, we demonstrate that an anion can be rejected from the ground channel and made to flow only into the field-free channel if the electrophoretic velocity of the anion is greater than the pressure-generated flow in the ground channel. The velocity threshold at which anion rejection occurs can be selectively tuned by changing the flow resistance in the field-free channel relative to the ground channel.