New insights on fumed colloidal rheology—shear thickening and vorticity-aligned structures in flocculating dispersions

We investigate the rheology of dilute dispersions of fumed colloidal particles with attractive interactions in hydrocarbon liquids. Surprisingly, these systems display shear thickening due to the breakdown of densified flocs and a concomitant increase in the effective volume fraction of the fractal particles in the fluid. We show that this shear thickening is controlled by a critical stress and accompanied by a positive increase in the first normal stress difference, N ₁, at the shear thickening transition. This is in contrast to the well-known hydrocluster mechanism of shear thickening in concentrated hard-sphere and repulsive systems. Gel elasticity depends strongly on the stress applied to suspensions in preshear, scaling roughly as \(G'\sim\sigma_{\text{preshear}}^{2}\). We propose a simple model to account for these results in terms of the cluster number density determined by the preshear stress. At low shear rates, vorticity-aligned aggregates are present at \(\dot\gamma\approx 10^0 {\rm{s}}^{-1}\) . In this regime, the system displays a small but noticeable increase in viscosity on increasing shear rate. We investigate the effect of tool roughness and find that wall slip is not responsible for the observed phenomena. Instead, the increase in the apparent viscosity results from increased flow resistance due to the presence of gap-spanning log-like flocs in rolling flow.     

Preparation, characterization and non-linear optical properties of pristine m-nitroaniline (m-NA) and its recycled polystyrene (Re-PS) coated single crystals

Meta-nitroaniline (m-NA) is one of the organic single crystals extensively studied due to its high non-linear effect. m-NA is also known to exhibit comparable or even better non-linear optical (NLO) properties than known inorganic materials. In this paper, we report development of m-NA single crystals by solution growth technique using different solvent systems. The size of the single crystal varies depending on solvent. The highest average crystal size acquired was 10 mm×5 mm×5 mm using methyl ethyl ketone and acetone as solvent. These single crystals were characterized using various physico-chemical techniques such as XRD and scanning electron microscopy (SEM). The developed crystals were subsequently coated with recycled polystyrene (Re-PS) (1, 2, 5 and 10 wt% concentrations) to study the effect of polymer coating on the second harmonic generation (SHG) properties of the single crystals. The purpose of polymer coating on m-NA single crystal is to improve surface morphology of crystal (i.e. it makes surface smooth) and to enhance power handling capacity for pulse laser of a crystal which, in turn, improves the SHG intensity. The optimum percentage of coating was determined for the m-NA single crystals obtained from different solvent systems. Furthermore, the polymer coating also plays key role in preventing the degradation of the m-NA crystal (well-known as highly sublime material) and ultimately increasing the shelf life of the crystal for its device application.     

Tetrad effect in mixed-ligand lanthanide chelates. Part II: Lanthanide. CDTA/DTPA. orcinol/resorcinol/phloroglucinol ternary systems

The variation profiles of certain properties of the lanthanide [Ln(III)] series show discontinuities at or around Gd(III) (4f⁷ stage), Nd (IH)-Pm(III) (4f³−4f⁴ stage) and Ho (III)-Er (III) (4f¹⁰−4f¹¹ stage) due to the presence of a tetrad effect. In the present work the occurrence of the tetradic phenomenon has been studied for the formation constants, log K _MAL ^MA of the mixed-ligand Ln (III) chelates of the type [Ln(III).A.L], where Ln(III) = La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb (III) or Dy(III); A = CDTA or DTPA; L = orcinol, resorcinol or phloroglucinol. The presence of the tetrad effect in log K _MAL ^MA values has been tested with the help of the straight line approximation method, differential plot method and inclined-W hypothesis. The magnitude of the effect has been found to lie in the sequence f⁷ > f³ −f⁴.     

Bridgehead Nitrogen Heterocycles: Facile Synthesis of Imidazo [2,1-b]-1,3,4-Thiadiazoles Using Hypervalent Iodine

2,6-Diarylimidazo [2,1-b]-1,3,4-thiadiazoles (3) were synthesized by reactions of either α-haloketones with 2-aminothiadiazoles (1) or directly with acetophenones in the presence of [hydroxy(p-tosyloxy)iodo]benzene. The latter method is convenient and versatile.     

Selective reductions. 59. Effective intramolecular asymmetric reductions of alpha-, beta-, and gamma-keto acids with diisopinocampheylborane and intermolecular asymmetric reductions of the corresponding esters with B-chlorodiisopinocampheylborane

A comparison of the stereochemistry of the products obtained from the intramolecular asymmetric reduction of a series of keto acids with (-)-diisopinocampheylborane and intermolecular asymmetric reduction of the corresponding series of keto esters with (-)-B-chlorodiisopinocampheylborane ((-)-DIP-Chloride) has been made. The stereochemistry of the hydroxy acids from the reduction of keto acids is dependent only on the enantiomer of the reagent used. The stereochemistry of the products from the reduction of keto esters is also consistent, except those of aliphatic alpha-keto esters. alpha-, beta-, and gamma-keto acids provide the corresponding hydroxy acids in 77-98% ee, and the alpha- and gamma- keto esters afford the hydroxy esters in 82->or=99% ee. beta-Keto esters do not undergo reduction. Although the reduction of delta-keto acids does not proceed under the same reaction conditions, the reduction of delta-keto esters is facile. All of the products from the reduction of gamma-keto acids and esters and delta-keto esters were converted to the corresponding lactones. This study revealed that DIP-Chloride is an efficient reagent for the reduction of alpha-keto esters at low temperatures.     

An efficient synthesis of fluorine-containing substituted spiro[piperidine-4,4′-pyrano[3,2-c]quinoline]-3′-carbonitrile by nonconventional methods

A series of fluorine-containing substituted spiro[piperidine-4,4′-pyrano[3,2-c]quinolines] were synthesized through a rapid one-pot multi-component reaction under microwave irradiation and sonication. The method has the advantages of excellent yields (80-96%) and short reaction time (3-10 min). We provide a series of fluorinated quinoline derivatives interesting for biological screening tests.     

Re(III)Cl(3)] core complexes with bifunctional single amino acid chelates

The reactions of the Re(V) starting material [ReO(PPh(3))(2)Cl(3)] with ligands of the type XN(Y)Z [X = Y = 2-pyridylmethyl, Z = -CH(2)CO(2)Et (L(1)Et), -CH(2)CH(2)CO(2)Et (L(2)Et), -CH(2)CH(2)CH(2)CH(2)CH(NHCO(2)Bu(t))CO(2)H (L(3)H); X = 2-pyridylmethyl, Y = 2-(1-methylimidazolyl)methyl, Z = -CH(2)CO(2)Et (L(4)Et)] yielded the Re(III) trichloride complexes of the type [ReCl(3)(L(n)R)]. The complexes are mononuclear, paramagnetic species with a facial geometry of the chloride ligands. The nitrogen donors of the tridentate L(n)()R ligands complete the distorted octahedral coordination spheres of the complexes. Crystal data: [ReCl(3)(L(1)Et)] (1), monoclinic, C2/m, a = 16.088(3) A, b = 9.980(2) A, c = 12.829(2) A, beta = 91.384(3) degrees, Z = 4, D(calc) = 1.967 g/cm(-)(3); [ReCl(3)(L(4)Et)] (4), monoclinic, C2/c, a = 22.880(1) A, b = 7.4926(4) A, c = 22.560(1) A, beta = 94.186(1) degrees, Z = 8, D(calc) = 2.001 g/cm(-3).     

Synergic extraction of thorium by beta-isopropyltropolone-neutral donor combinations

The extraction of thorium by benzene solutions of HIPT in presence of different neutral extractants (S) was studied using perchloric, hydrochloric and sulphuric acids as aqueous media. With TBP as the donor the effect of the diluents CCl₄, benzene and CHCl₃ on the extraction was studied. The synergism observed was attributed to the formation of the extractable adduct Th(IPT)₄ · S and, in some cases, to the extraction of additional mixed adducts involving the participation of the anion of the aqueous medium used for extraction. The adduct formation constants for the formation of Th(IPT)₄ ·S were evaluated and the formation of this adduct was independently confirmed by spectrophotometric measurements. The aqueous complexing of thorium by IPT was investigated spectrophotometrically as these data were required for the quantitative interpretation of the extraction data.     

Photo- and electropatterning of hydrogel-encapsulated living cell arrays

Living cells have the potential to serve as sensors, naturally integrating the response to stimuli to generate predictions about cell fate (e.g., differentiation, migration, proliferation, apoptosis). Miniaturized arrays of living cells further offer the capability to interrogate many cells in parallel and thereby enable high-throughput and/or combinatorial assays. However, the interface between living cells and synthetic chip platforms is a critical one wherein the cellular phenotype must be preserved to generate useful signals. While some cell types retain tissue-specific features on a flat (2-D) surface, it has become increasingly apparent that a 3-D physical environment will be required for others. In this paper, we present two independent methods for creating living cell arrays that are encapsulated within a poly(ethylene glycol)-based hydrogel to create a local 3-D microenvironment. First, 'photopatterning' selectively crosslinks hydrogel microstructures containing living cells with approximately 100 microm feature size. Second, 'electropatterning' utilizes dielectrophoretic forces to position cells within a prepolymer solution prior to crosslinking, forming cell patterns with micron resolution. We further combine these methods to obtain hierarchical control of cell positioning over length scales ranging from microns to centimeters. This level of microenvironmental control should enable the fabrication of next-generation cellular microarrays in which robust 3-D cultures of cells are presented with appropriate physical and chemical cues and, consequently, report on cellular responses that resemble in vivo behavior.