Extensional rheology of a shear-thickening cornstarch and water suspension

A filament-stretching rheometer is used to measure the extensional viscosity of a shear-thickening suspension of cornstarch in water. The experiments are performed at a concentration of 55 wt.%. The shear rheology of these suspensions demonstrates a strong shear-thickening behavior. The extensional rheology of the suspensions demonstrates a Newtonian response at low extension rates. At moderate strain rates, the fluid strain hardens. The speed of the strain hardening and the extensional viscosity achieved increase quickly with increasing extension rate. Above a critical extension rate, the extensional viscosity goes through a maximum and the fluid filaments fail through a brittle fracture at a constant tensile stress. The glassy response of the suspension is likely the result of jamming of particles or clusters of particles at these high extension rates. This same mechanism is responsible for the shear thickening of these suspensions. In capillary breakup extensional rheometry, measurement of these suspensions demonstrates a divergence in the extensional viscosity as the fluid stops draining after a modest strain is accumulated.     

7Li NMR as probe for solvent–cellulose interactions in cellulose dissolution

Molten salt hydrates proved to be alternative solvents to cellulose. Toinvestigate the reasons for this dissolving ability, information about thesolvent–cellulose interactions is essential. As well as ¹³CHR NMR, ⁷Li NMR was used to obtain further insight into thisproblem.After comparing several molten salt hydrates, the ⁷Li NMR spectrarevealed a smaller shielding of the lithium cation for not dissolving than fordissolving and swelling cellulose systems. In most solvent systems theshieldingat the ⁷Li nuclei increases with the cellulose concentration. 2D⁷Li-¹H HOESY NMR was successfully applied to verify thepresence of cellobiose, used as a model compound for cellulose, in the firstco-ordination sphere of the lithium cation.     

Configurational assignments of the diastereomers of 3,3′‐(1,2‐ethanediyl)bis[2‐(3‐fluorophenyl)‐5‐methyl‐4‐thiazolidinone] derivative with four stereogenic centers

Diastereomers of antiinflammatory/analgesic and antihistaminic 3,3′[(1,2‐ethanediyl)bis(2‐aryl‐4‐thiazo‐lidinone)] derivatives possessing two stereogenic centers (indicated as BIS 2*C) have been widely investigated in recent years. The 5,5′‐dimethyl analogues (BIS 4*C), now reported, have been synthesized by reaction of (±) α‐mercaptopropionic acid and N,N'‐di(3‐fluorobenzyliden)ethylenediamine. Because the 2 and 2′carbons bear the same groups and similarly the 5 and 5′ carbons, and the latter groups are different from the former, four enantiomeric pairs and two meso forms exist in this situation. These diastereomers were identified by the concerted use of nmr spectroscopy and hplc on chiral stationary phase.     

Carbon dioxide hydrogenation: Efficient catalysis by an NHC-amidate Pd(II) complex

The utilization of carbon dioxide as a carbon source has long been a challenge in modern organic chemistry due to its low reactivity, yet high abundance. Herein we demonstrate the highly efficient hydrogenation of carbon dioxide into formic acid in the presence of an NHC-amidate Pd(II) complex. Excellent turnover number was observed when the catalyst was used under heterolytic conditions. This catalytic system provides a new and efficient carbon dioxide hydrogenation method.     

Direct visualization of a self-organized multilayer film of low T(g) diblock copolymer micelles

The first in situ proof of the presence of true nanoscale micelle structure within alternating layers of a self-assembled cationic and anionic diblock copolymer micelle-micelle multilayer film is presented using atomic force microscopy. Apparently similar layer morphologies are distinguished by the interaction force curves normal to each layer. The three-dimensional order in these low Tg diblock copolymer films, together with their mechanical resilience and strongly hydrated nature, suggests many new technological applications.     

Green solvents from ionic liquids and deep eutectic solvents to natural deep eutectic solvents

Natural deep eutectic solvents (NADESs) are defined as mixtures of certain molar ratios of natural compounds such as sugars, organic acids, amino acids, and organic bases that are abundant in organisms. The melting points of these mixtures are considerably lower than those of their individual ingredients and far below ambient temperature. The first publications on the NADES concept in 2011 created a great expectation regarding their potential as green solvents that could replace conventional organic solvents in a wide range of applications. This was largely because many of the drawbacks of conventional synthetic ionic liquids (ILs) and deep eutectic solvents (DESs), particularly their toxicity and environmental hazards, could be solved using NADESs. Throughout the last 7 years, the interest in NADESs has increased enormously as reflected by the exponential growth of the number of related publications. The research on NADESs has rapidly expanded particularly into the evaluation of the feasibility of their application in diverse fields such as the extraction of (targeted) bioactive compounds from natural sources, as media for enzymatic or chemical reactions, preservatives of labile compounds, or as vehicles of non–water-soluble compounds for pharmaceutical purposes. Along with the exploration of these potential applications, there have been a large number of other studies related to their physicochemical features, the search for new NADESs, the research into the interactions between NADES components or with solutes, the recovery of solutes from NADES solutions, and the ways of circumventing inherent problems of NADESs such as their high viscosity and the consequent difficulties in handling them. This article contains a review of the applications of NADESs as extraction solvents, reaction media, and preservative, providing also a perspective of their future.     

Chaotic and fractal patterns for interacting nonlinear waves

Using an appropriate reduction method, a quite general new integrable system of equations 2 + 1 dimensions can be derived from the dispersive long-wave equation. Various soliton and dromion solutions are obtaining by selecting some types of solutions appropriately. The interaction between the localized solutions is completely elastic, because they pass through each other and preserve their shapes and velocities, the only change being a phase shift. The arbitrariness of the functions included in the general solution implies that approximate lower dimensional chaotic patterns such as chaotic–chaotic patterns, periodic–chaotic patterns, chaotic line soliton patterns and chaotic dromion patterns can appear in the solution. In a similar way, fractal dromion patterns and stochastic fractal excitations also exist for appropriate choices of the boundary conditions and/or initial conditions.     

Ionic Dissociation of SiCl4: Formation of [SiL6]Cl4 with L=Dimethylphosphinic Acid

Reactions of SiCl₄ with R₂PO(OH) (R=Me, Cl) yield compounds with six-fold coordinated silicon atoms. Whereas R=Me afforded the hexacoordinated tetra-cationic silicon complex [Si(Me₂PO(OH))₆]⁴⁺ with chloride counter-ions, R=Cl caused release of HCl with formation of a cyclic dimeric silicon complex [Si(Cl₂PO(OH))(Cl₂PO₂)₃(μ-Cl₂PO₂)]₂ with bridging bidentate dichlorophosphates.     

Cylindrical cellular automata

A one-dimensional cellular automaton with periodic boundary conditions may be viewed as a lattice of sites on a cylinder evolving according to a local interaction rule. A technique is described for finding analytically the set of attractors for such an automaton. Given any one-dimensional automaton rule, a matrixA is defined such that the number of fixed points on an arbitrary cylinder size is given by the trace ofA ⁿ , where the powern depends linearly on the cylinder size. More generally, the number of strings of arbitrary length that appear in limit cycles of any fixed period is found as the solution of a linear recurrence relation derived from the characteristic equation of an associated matrix. The technique thus makes it possible, for any rule, to compute the number of limit cycles of any period on any cylinder size. To illustrate the technique, closed-form expressions are provided for the complete attractor structure of all two-neighbor rules. The analysis of attractors also identifies shifts as a basic mechanism underlying periodic behavior. Every limit cycle can be equivalently defined as a set of strings on which the action of the rule is a shift of sizes/h; i.e., each string cyclically shifts bys sites inh iterations of the rule. The study of shifts provides detailed information on the structure and number of limit cycles for one-dimensional automata.