The Electrochemistry of Viologens with Various Alkyl Substituents and The Dimerization of Their 1e- Reduced Species in the Absence and Presence of Various Cyclodextrins

We present EQCM study for the electrochemical behavior of various 1-methyl-1'-alkylvilogen (C₁C_nV:n=1, 7-10, 12, 14,16, 18). In some viologens, we discussed the mechanism of CD-induced comproportionation reaction as well as electrodeposition pathway based on the EQCM and the spectroelectrochemical experimental results.     

Water sorption and activation energy in polyimide thin films

The water sorption behavior and the activation energy were investigated for various chemical structure polyimide thin films; BPDA‐PDA, BPDA‐ODA, PMDA‐ODA, and 6FDA‐ODA. The activation energy for the water diffusion varied in the range of 5.53 to 9.27kcal/mol, and was in the increasing order: BPDA‐PDA < BPDA‐ODA < PMDA‐ODA < 6FDA‐ODA. BPDA‐PDA and BPDA‐ODA polyimide films showed relatively well‐ordered morphological structure, which results in relatively low diffusion coefficient and high activation energy. It was found that the diffusion coefficient and the activation energy are significantly related to the in‐plane orientation, crystallinity, and packing order in the polyimide thin films. The morphological structure was predominant factors for the water diffusion coefficient and activation energy in the polyimide thin films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2714–2720, 2000     

Complexes of polyelectrolyte hydrogels with organic dyes: Effect of charge density on the complex stability and intragel dye aggregation

The swelling behavior of polyelectrolyte gels based on poly(diallyldimethylammonium chloride) (copolymers of diallyldimethylammonium chloride and acrylamide with the variable composition) and poly(methacrylic acid, sodium salt) in the presence of organic water soluble dyes (alizarin, naphthol blue black, rhodamine) was studied. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depend on the charges of the polymer network and the dye, and also on the dye concentration. Stability of the gel–dye complexes in a salt solution of NaCl and Al₂(SO₄)₃ was studied. It was shown that the complex stability in the salt solution depends on the charge density of the polymer chains forming the gel. The increase of charge density of polymer generally leads to the enhancement of the complex stability. For the systems with the fraction of charged poly(diallyldimethylammonium chloride) monomer units above 0.5 the release of alizarin to the external solution of Al₂(SO₄)₃ reservoir is practically completely suppressed. The obtained results show that oppositely charged dyes are generally from stable complexes with polyelectrolyte gels. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1209–1217, 1999     

Electric Field‐Aided Formation Combined with a Nanoimprinting Technique for Replicating a Plant Leaf

The surface of the taro plant leaf was replicated using a nanoimprinting technique (NIT) supplemented with an electric field. This field‐aided nanoimprinting method (FA‐NIT) consists of two steps: applying an electric field to a liquid polymer under the plant leaves and the curing process of the polymer with the applied electric field. An appropriate electric field was needed to induce the electrokinetic phenomena of a liquid polymer to obtain a good replicated surface. The roughness fabricated by the FA‐NIT was about 45% higher than the one prepared by NIT. The FA‐NIT method is a good supplementary technique to improve the quality of NIT.

     

Discriminating Among Co‐monomer Sequence Distributions in Random Copolymers Using Interaction Chromatography

Interaction chromatography has been employed to validate that adsorption of poly[styrene‐co‐(4‐bromostyrene)] (PBr_xS) random copolymers, where x denotes the mole fraction of 4‐bromostyrene (4–BrS) in PBr_xS in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co‐monomer sequence distribution in PBr_xS.

     

Nanoscale laser processing and diagnostics

The article summarizes research activities of the Laser Thermal Laboratory on pulsed nanosecond and femtosecond laser-based processing of materials and diagnostics at the nanoscale using optical-near-field processing. Both apertureless and apertured near-field probes can deliver highly confined irradiation at sufficiently high intensities to impart morphological and structural changes in materials at the nanometric level. Processing examples include nanoscale selective subtractive (ablation), additive (chemical vapor deposition), crystallization, and electric, magnetic activation. In the context of nanoscale diagnostics, optical-near-field-ablation-induced plasma emission was utilized for chemical species analysis by laser-induced breakdown spectroscopy. Furthermore, optical-near-field irradiation greatly improved sensitivity and reliability of electrical conductance atomic force microscopy enabling characterization of electron tunneling through the oxide shell on silicon nanowires. Efficient in-situ monitoring greatly benefits optical-near-field processing. Due to close proximity of the probe tip with respect to the sample under processing, frequent degradation of the probe end occurs leading to unstable processing conditions. Optical-fiber-based probes have been coupled to a dual-beam (scanning electron microscopy and focused ion beam) system in order to achieve in-situ monitoring and probe repair.     

Three-dimensional opto-fluidic devices fabricated by ultrashort laser pulses for high throughput single cell detection and processing

Three-dimensional flow-through microchannels were fabricated inside bulk fused silica glass via ultrashort pulsed laser direct writing. The device fabrication sequence takes advantage of the nonlinear volumetric absorption in glass and the subsequent preferential chemical etching process. Optical waveguides were also written into the glass specimen and integrated with the fluidic conduits. Flow tests using both fluorescent particles and red blood cells (RBCs) were conducted on various three-dimensional channel configurations. Experiments showed the possibility for laser-induced cell processing inside the microchannels. To evaluate cytometer functionality, RBCs were detected inside the manufactured microchannel via both transmission and fluorescence probing.     

Wide range parametric study for the pool boiling of nano-fluids with a circular plate heater

The characteristics of boiling and critical heat flux (CHF) behavior of nano-fluids with alumina and silver nano-particles suspended in de-ionized water (pure water) were studied with circular plate heaters in the present study. Enhancements of CHF in nano-fluids in the wide range of particle sizes and concentrations were compared with those in pure water. Also, the effects of the particle deposition on CHF enhancement were investigated. All experiments were performed at the atmospheric pressure condition. The results show that the measured boiling curves in nano-fluids were shifted to the right and CHF were significantly enhanced for different nano-particle sizes and concentrations. The CHF of nano-fluids was increased as the size of the nano-particles decreased. On the other hand, nano-particle concentration value showing the maximum CHF had a critical value. In each pool boiling experiment of nano-fluids, nano-particles were deposited on the heater surface. Assuming that this phenomenon caused the CHF enhancement, pool boiling experiments of pure water were carried out with these nano-particle deposited heaters. The results of these tests were similar to those of the test of the nano-fluids for the CHF enhancement. The main cause of CHF enhancement was found to be the change of the heater surface structure. In order to analyze boiling phenomena of pure water and Al₂O₃ nano-fluids, boiling process was visualized by using a high speed camera.