Solution properties of an aqueous poly(methacryl oxyethyl trimethylammonium chloride) and its poly(oxyethylene) grafted analog

Cationic poly(methacryl oxyethyl trimethylammonium chloride), PMOTAC, and its poly(oxyethylene), POE, grafted analog have been synthesised. The molar mass of the POE grafts was M_w = 200 g/mol, and the grafting degrees of the synthesised copolymers were 2, 5, and 15 mol %. The effect of the POE grafts on the solution properties and the conformation of the polycation has been investigated in aqueous NaNO₃ by means of dynamic and static light scattering, viscometry, and Raman spectroscopy. It was found that the polyelectrolyte properties are more pronounced for the homopolymer than for the POE‐grafted copolymers. The increase of the POE‐grafting degree dramatically decreases the hydrodynamic radius of individual macromolecules and causes intermolecular association. It also suppresses the conformational response of the copolymers upon changing the ionic strength with respect to that of the homopolymer. DFT calculations have been used to estimate a possible mechanism of interaction between the POE grafts and the MOTAC repeating units. It has been revealed that the POE grafts are capable of forming intramolecular hydrogen bonds with the MOTAC groups. The latter was confirmed experimentally; addition of free POE chains to a solution of PMOTAC results in formation of intermolecular PMOTAC/POE complexes. Increasing the POE concentration decreases the solution viscosity. At the same time, the bimodal distributions of the hydrodynamic radius, which are typical for polyelectrolytes in salt‐free solutions, become monomodal representing the PMOTAC/POE complexes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 547–557, 2008     

A class of methods for linear programming

A class of methods is presented for solving standard linear programming problems. Like the simplex method, these methods move from one feasible solution to another at each iteration, improving the objective function as they go. Each such feasible solution is also associated with a basis. However, this feasible solution need not be an extreme point and the basic solution corresponding to the associated basis need not be feasible. Nevertheless, an optimal solution, if one exists, is found in a finite number of iterations (under nondegeneracy). An important example of a method in the class is the reduced gradient method with a slight modification regarding selection of the entering variable.     

A modification of the Zinoviev lower bound for constant weight codes

In [3] Zinoviev presented a new method to get lower bounds for constant weight codes. In this note we show that a simple modification of the Zinoviev method gives further improvements.     

Core level studies of calcite and dolomite

Conventional X‐ray photoelectron spectroscopy (XPS) and synchrotron‐based X‐ray photoelectron spectroscopy (HRXPS) have been used to study Iceland spar calcite (CaCO₃) and dolomite (CaMg(CO₃)₂). The obtained full widths at half maximum (FWHMs) are mostly narrower than in the previous results, which together with the symmetry of the fitted peaks indicate effective neutralisation of surface charging. Some previously unidentified features observed in the Ca 2p, C 1s and O 1s spectra of calcite have been suggested to be bulk plasmons. Also, surface core level shifts in Ca 2p (in calcite) and Mg 2p (in dolomite) spectra have been obtained and found to be consistent between XPS and HRXPS measurements. A peak attributed to carbide (CaC₂) has been suggested to indicate beam‐assisted interaction with hydrocarbons found on the surface. Copyright © 2014 John Wiley & Sons, Ltd.     

New octahedral Ta(V) hydrazido-substituted compounds for atomic layer deposition: Syntheses,X-ray diffraction structures of TaCl(NMe2)3[N(TMS)NMe2] and Ta(NMe2)4[N(TMS)NMe2], and fluxional behavior of the amido and hydrazido ligands in solution

The synthesis and structural characterization of new tantalum(V) compounds containing a single hydrazido(I) ligand are reported. Hydrazinolysis of TaCl(NMe₂)₄ using trimethylsilyl(dimethyl)hydrazine affords the compound TaCl(NMe₂)₃[N(TMS)NMe₂] in essentially quantitative yield. Metathetical replacement of the chloride ligand in TaCl(NMe₂)₃[N(TMS)NMe₂] by LiNMe₂ gives the all-nitrogen coordinated compound Ta(NMe₂)₄[N(TMS)NMe₂]. VT ¹H NMR studies support the existence of low-energy pathways involving rotation about the Ta–N bonds of the ancillary amido and hydrazido ligands in both hydrazido-substituted compounds. X-ray crystallographic analyses confirm the octahedral disposition about the tantalum metal in TaCl(NMe₂)₃[N(TMS)NMe₂] and Ta(NMe₂)₄[N(TMS)NMe₂] and the presence of an η²-hydrazido(I) ligand. Preliminary data using Ta(NMe₂)₄[N(TMS)NMe₂] as an ALD precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.     

The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium

Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons.     

HXeCCH in Ar and Kr matrices

HXeCCH molecule is prepared in Ar and Kr matrices and characterized by IR absorption spectroscopy. The experiments show that HXeCCH can be made in another host than the polarizable Xe environment. The H-Xe stretching absorption of HXeCCH in Ar and Kr is blueshifted from the value measured in solid Xe. The maximum blueshifts are +44.9 and +32.3 cm(-1) in Ar and Kr, respectively, indicating stabilization of the H-Xe bond. HXeCCH has a doublet H-Xe stretching absorption measured in Xe, Kr, and Ar matrices with a splitting of 5.7, 13, and 14 cm(-1), respectively. Ab initio calculations for the 1:1 HXeCCHcdots, three dots, centeredNg complexes (Ng = Ar, Kr, or Xe) are used to analyze the interaction of the hosts with the embedded molecule. These calculations support the matrix-site model where the band splitting observed experimentally is caused by specific interactions of the HXeCCH molecule with noble-gas atoms in certain local morphologies. However, the 1:1 complexation is unable to explain the observed blueshifts of the H-Xe stretching band in Ar and Kr matrices compared to a Xe matrix. More sophisticated computational approach is needed to account in detail the effects of solid environment.