through 20-gauge (nominal inner diameter: 0.6 mm) needles into rotating 40 wt.-% PEI (branched; average molecular weight, M w~2 5 000; water-free; Aldrich) solutions in methanol.The SWNT/PEI composite fibers were characterized by SEM (LEO 1590 VP microscope) and micro-Raman spectroscopy (Jobin± Yvon Horiba high-resolution LabRam micro-Raman spectrometer; helium±neon Spectra Physics laser, model 127, with excitation wavelength, k exc = 632.8 nm; resolution =~1 cm ±1 ). The mechanical properties of these fibers were measured at room temperature with an Instron MicroTester (using a 1 cm gauge length and a constant strain rate of 0.9±1.2 % min
±1. Four-probe electrical conductivities were obtained from resistance values measured using a Keithley 2000 Multimeter and using the fiber-shell area (not including the area corresponding to the void space in the cross section). Thermal analysis was performed using a thermogravimetric analyzer (PerkinElmer Pyris 1 TGA) and a differential scanning calorimeter (PerkinElmer Pyris Diamond DSC). An Axisymmetric Flow-Focusing Microfluidic Device** By Shoji Takeuchi, Piotr Garstecki, Douglas B. Weibel, and George M. Whitesides* This paper describes a microfluidic axisymmetric flowfocusing device (AFFD) fabricated in poly(dimethylsiloxane) (PDMS) that produces polymer-coated droplets with size distributions significantly more narrow than those generated using conventional microencapsulation methods.[1±3] The AFFD confines droplets in the central axis of a microfluidic channel; this confinement protects droplets from shear, or from damage re-COMMUNICATIONS Adv. Mater.