Formation of two-dimensional structures by tuning the driving force of chemical reactions: an interpretation of kinetic control

Understanding shape control during wet chemical synthesis is important for rational synthesis of nanostructures. Here, we show that two-dimensional metal structures can be obtained from metal salts by reducing the driving force of the reduction reaction that directly translates to the growth of the metal taking place by the two-dimensional nucleation (layer-by-layer growth) mechanism. Experimental evidence is provided for Au, Ag, Pt and Pd systems by choosing appropriate reaction conditions without using any external surfactant. The results are analyzed in terms of the calculations of driving force under different conditions. The results show that surfactants may not be important for producing shape control for the case of 2-D structures while they are required to obtain size control. It is shown that the regime of low driving force is also one where the kinetics of the process is slow and thus a new interpretation of the kinetic control hypothesis is provided.     

Kinetic compensation effect in the thermal degradation of polymers

The kinetic study of thermal degradation takes into account the validity of the Arrhenius equation. From TG data, the activation energy,E _a and pre-exponential factor,A, are evaluated. These results are interpreted by using the kinetic compensation effect as basis. A linear correlation between In(A) andE _a is obtained in all cases studied. However, in a plot of the logarithm of the rate constant as a function of reciprocal temperature for the same series of reactions, the thermal oxidative degradations of Nylon-6 and PVC display a point of concurrence and one isokinetic temperature, whereas those of HIPS and PC do not. Therefore, in the thermal oxidative degradations of Nylon-6 and PVC a true compensation effect occurs, which could be related to the bulk properties of metal oxides, such as different valence states, whereas for other polymers it displays only an apparent compensation effect. This means that degradation is largely independent of the bulk properties of oxides, but may be related to the distribution of different kinds of active links in the polymer surface having different activation energies.     

Copper(II) acetate promoted intramolecular diamination of unactivated olefins

A concise method for the synthesis of cyclic sulfamides and vicinal diamines is presented. This method is enabled by Cu(OAc)2 and demonstrates a new transformation for this metal. Both five- and six-membered vicinal diamine-containing heterocycles have been synthesized in good to excellent yields, and substrate-based asymmetric induction has been achieved. This is the first reported example of intramolecular diamination of olefins.     

Photoinduced phase separation and miscibility in the condensed phase of a mixed Langmuir monolayer

We report our studies on the mixed Langmuir monolayer of mesogenic molecules, p-(ethoxy)-p-phenylazo phenyl hexanoate (EPPH) and octyl cyano biphenyl (8CB), employing the techniques of surface manometry and Brewster angle microscopy. Our studies show that the mixed monolayer exhibits higher collapse pressures for certain mole fractions of EPPH in 8CB as compared to individual monolayers. Also, a considerable reduction in the area per molecule is seen in the mixed monolayer, indicating a condensed phase. We have also studied the photostability of the mixed monolayer at different initial surface pressures. The mixed monolayer, under alternate cycles of UV and visible illumination, exhibits changes in surface pressures. This is due to the photoinduced transformation of EPPH isomers in the mixed monolayer. Our in-situ Brewster angle microscope studies for 0.5 mole fraction of EPPH in 8CB show a phase separation in the UV and a miscible phase in the visible, at low surface pressures ( approximately 5 mN/m). At higher surface pressures ( approximately 10 mN/m), under UV illumination, we find a phase separation which does not revert to a miscible phase under visible illumination.     

Effect of Metal Oxides on the Thermal Degradation of High Impact Polystyrene

The kinetic parameters for the thermal degradation of high impact polystyrene (HIPS) in presence of some metal oxides exhibit reaction rate compensation effect. In thermal degradation of HIPS in presence of transition metal oxides different active centers act simultaneously as reaction sites and macroradicals are formed through random chain scission, disproportion or cyclization. Some oxides retard the polymer degradation through crosslinking and cyclization by the interaction of macroradicals with the double bond in butadiene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simple conditions for the use of ferroin indicator in cerimetric titrations of antimony(III) alone and in mixtures with arsenic(III)

The titration of antimony(III) with cerium(V) sulphate in the presence of ferroin indicator at room temperature is entirely satisfactory in media consisting of 50% ($\text{v}\text{v}$) acetic acid and 1–3 M hydrochloric acid. In the absence of acetic acid, ferroin reacts with the antimony(V) formed in the very early stages, to give a sparingly soluble red complex, which remains in suspension and resists oxidation by cerium(IV). This titration provides a rational method for sequential visual titrations of antimony(III) and arsenic(III). The composition of the ferroin-antimony(V) complex is discussed. Titrations of antimony(III) in 0.5–1 M sulphuric acid medium do not require acetic acid but need iodine monochloride catalyst.     

Hydrogen spillover effects in the reduction of iron oxide

Freshly formed metal accelerates the rate of reduction of ferric oxide in the presence of water vapour. This effect is explained on the basis of the spillover of hydrogen from the metal sites to the oxide phase through portholes of water.

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