Dispensing picoliter droplets on substrates using dielectrophoresis

Liquid dielectrophoresis is exploited to initiate rapid, transient flow of aqueous liquids along co-planar electrodes patterned on insulating substrates. The flow induced by the non-uniform electric field leads to a new electrostatic equilibrium. A reduced-order model predicts the transient motion of the rivulet. When the field is removed, capillary instability breaks up the rivulet into regularly spaced droplets. Periodic circular bumps patterned on the structure, when spaced according to the most unstable wavelength based on Rayleigh's inviscid theory for the cylindrical liquid jet, lead to uniformly spaced and sized droplets. A correction factor, based on the dimensionless Ohnesorge number, accounts successfully for the effect of viscosity.     

Microscopic Theory of Blue Phases Ⅰ and Ⅱ of Liquid Crystal

The microscopic theory of the blue phases of chiral liquid crystal is proposed. Beginning with the potential between two molecules, by using the cell model of liquid, applying statistical physical method, the distribution function and the free energy of the system are obtained. By using variational approach and zero-order approximation, the differential equation that the order parameter tensor of the blue phase can satisfy is obtained. Then we change the differential equation to the eigenequation problem in quantum mechanics. Considering the symmetry of the blue phases,the order parameter tensors of blue phases Ⅰ and Ⅱ can be made up of the eigenvectors. Our results are the same as the results of Ginzberg-Landau‘s phenomenological theory. The parameters in the order parameter tensors that we calculate in the located system are close to the predecessors‘ results.     

Synthesis of optically active poly(N‐propargylsulfamides) with helical conformation

A novel chiral N‐propargylsulfamide monomer ( 1a ) and its enantiomer ( 1b ) were synthesized and polymerized with (nbd)Rh⁺B^?(C₆H₅)₄ as a catalyst providing poly(1) (poly( 1a ) and poly( 1b )) in high yields (≥99%). Poly(1) could take stable helices in less polar solvents (chloroform and THF), demonstrated by strong circular dichroism signals and UV–vis absorption peaks at about 415 nm and the large specific rotations; but in more polar solvents including DMF and DMSO, poly(1) failed to form helix. Quantitative evaluation with anisotropy factor showed that the helical screw sense had a relatively high thermal stability. These results together with the IR spectra measured in solvents showed that hydrogen bonding between the neighboring sulfamide groups is one of the main driving forces for poly(1) to adopt stable helices. In addition, copolymerization of monomer 1a and monomer 2 was conducted, the solubility of poly(1) was improved drastically. However, the copolymerization had adverse effects on the formation of stable helices in the copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 500–508, 2007     

Pd (II)‐catalyzed vinyl addition polymerization of novel functionalized norbornene bearing dimethyl carboxylate groups

Three novel functionalized polynorbornenes (PNB) with pendant dimethyl carboxylate group (carboxylates—acetate, propionate, and butyrate) are synthesized as a vinyl‐type with a palladium (II) catalyst in high yield. The effects of size of substitutents, molar ratio of monomer to catalyst, solvent polarity, reaction time, and temperature on the polymerization of exo‐norbornene dimethyl propionate were systematically investigated. The low molar ratio and temperature, as well as high polarity of solvent, and long reaction time, are favorable for the enhancement of the monomer conversion, especially, the solvent have an obvious effect on the catalyst activity. The resulting poly(cis‐norbornene‐exo‐2,3‐dimethyl carboxylates) (PNB‐dimethyl carboxylates) show good solubility in common organic solvent and high thermal stability up to 360 °C. The glass transition temperature was detected by DMA at 331, 324, and 318 °C for acetate, propionate, and butyrate, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3391–3399, 2007     

Racemization of chiral amino alcohols III: Effect of Mg or Ca addition on the activity and stability of the Co/γ-Al2O3 catalyst

The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al₂O₃ catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield of over 83% at using the Mg modified Co/γ-Al₂O₃ catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H₂. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous for dispersing and stabilizing the active species of the Co/γ-Al₂O₃ catalyst, protecting from sintering, significantly improving its catalytic activity and stability.     

A new trend in the synergistic extraction of rare-earth(III) complexes with various β-diketones and 1,10-phenanthroline

The synergistic extraction of rare-earth (RE) [La(III), Sm(III), Tb(III) and Lu(III)] complexes, with three β-diketones (HA) [hexafluoroacetylacetone (Hhfa), pivaloyl-trifluoroacetone (Hpta) and benzoylacetone] in the presence of a bidentate ligand (S), 1,10-phenanthroline, in benzene was investigated. The general composition of the adducts formed is expressed as RE(A)₃S. RE(A)₃(S)₂ is also observed in La-Hhfa, La-Hpta and Sm-Hhfa systems. The adduct formation contains β_s,1 and β_s,2 and the synergistic extraction constants K_ex,s,1 were determined. The trend of these constants is discussed in terms of the RE(III), β-diketone, neutral bidentate ligand and organic solvent.     

Two-dimensional zero-field NMR and NQR

Corrlalations between quadrupolar frequencies in a spin I = 1 system are determined through a two-dimensional version of the zero-field NMR experiment. Results presented on a selectively deuterated polycrystalline solid illustrate this for the quadrupolar lines corresponding to inequivalent deuterium sites.     

Formation of sulfhydryl (SH) species on the clean and (2 × 2)-S covered Pt(111) surfaces by H2S decomposition

H₂S decomposition on the clean and (2 × 2)-S covered Pt(111) surfaces has been characterized using high-resolution electron energy loss (HREELS) and temperature-programmed desorption (TPD) spectroscopies. On the Pt(111)-(2 × 2)-S surface, a mixture of molecular H₂S and sulfhydryl (SH) species forms following H₂S adsorption at 110 K. The molecular H₂S desorbs at 140 K leaving a (2 × 2)-S overlayer saturated with SH; the SH is stable up to 190 K. On the clean Pt(111) surface, a mixture of atomic sulfur, SH and chemisorbed molecular H₂S is formed following H₂S adsorption at 110 K. On the clean surface, adsorbed SH decomposes near 150 K. We report here the first definitive observation of an adsorbed sulfhydryl species on a metal surface.