Colloidal liquid crystal type assemblies of spheroidal polystyrene core/polyglycidol‐rich shell particles (P[S/PGL]) formed at the liquid‐silicon‐air interface by a directed dewetting process

A method for the preparation of stripe‐like monolayers of microspheroids is described. The particles were obtained from polystyrene core/polyglycidol‐rich shell microspheres by stretching poly (vinyl alcohol) films that contain embedded particles. The stretching was performed under controlled conditions at temperatures above the T_g of the films and particles. The elongated films were dissolved in water, and the microspheroids were subsequently removed and purified from the poly (vinyl alcohol). The aspect ratio (AR) of the particles, which denotes the ratio of the lengths of the longer to shorter particle axes, was determined by the film elongation. The AR values were in the range of 2.9‐7.7. Spheroidal particles with various ARs were deposited onto silicon wafers from an ethanol (EtOH) suspension. The particle concentration and volume of the suspension were the same in each experiment. Evaporation of the EtOH yielded stripes of spherical particles packed into nematic‐type colloidal crystals and assembled into monolayers. The orientation of the stripes after ethanol evaporation was perpendicular to the triphasic (silicon‐ethanol‐air) interface along the silicon substrate. The adsorbed stripes on the wafers were characterized in terms of their interstripe distance (ID), stripe width, and crystal domain size. Nematic‐type spheroid arrangements in the stripes were the dominant structure, which enabled denser packing of the particles into colloidal crystals than that allowed by the smectic‐type arrangements. Furthermore, the number of spheroids adsorbed per surface unit of the silicon wafers was similar for all ARs, but the width and frequency of the spheroid stripes adsorbed on the wafers were different.     

Gas-Phase Synthesis of Triphenylene (C18H12)

For the last decades, the hydrogen-abstraction−acetylene-addition (HACA) mechanism has been widely invoked to rationalize the high-temperature synthesis of PAHs as detected in carbonaceous meteorites (CM) and proposed to exist in the interstellar medium (ISM). By unravelling the chemistry of the 9-phenanthrenyl radical ([C₁₄H₉]^.) with vinylacetylene (C₄H₄), we present the first compelling evidence of a barrier-less pathway leading to a prototype tetracyclic PAH – triphenylene (C₁₈H₁₂) – via an unconventional hydrogen abstraction–vinylacetylene addition (HAVA) mechanism operational at temperatures as low as 10 K. The barrier-less, exoergic nature of the reaction reveals HAVA as a versatile reaction mechanism that may drive molecular mass growth processes to PAHs and even two-dimensional, graphene-type nanostructures in cold environments in deep space thus leading to a better understanding of the carbon chemistry in our universe through the untangling of elementary reactions on the most fundamental level.     

Tailored side‐chain architecture of benzil voltage stabilizers for enhanced dielectric strength of cross‐linked polyethylene

The synthesis and physico‐chemical properties of seven benzil‐type voltage stabilizers are reported. The benzil core is substituted with alkyl chains of different length that are linked to the benzil core via an ester, ether, or tertiary amine group. All additives can be melt‐processed with low‐density polyethylene (LDPE). Fourier‐transform infrared spectroscopy confirms that benzil compounds are not affected by the LDPE cross‐linking reaction induced by dicumyl peroxide. Moreover, a combination of gel content measurements, thermal analysis, and small‐angle X‐ray scattering indicates that the presence of benzil voltage stabilizers does not significantly alter the microstructure of cross‐linked polyethylene (XLPE). Electrical tree inhibition experiments under high‐voltage alternating current conditions show that all investigated additives substantially enhance the dielectric strength of the insulating material at a concentration of only 10 mmol kg^?1. The highest improvement in dielectric strength, of more than 70% with respect to reference XLPE, is obtained with voltage stabilizers, which carry short (methyl) side chains that are linked to the benzil core via an ester or tertiary amine group. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1047–1054     

CO2 gasification of char from spent mushroom substrate in TG-MS system

Journal of Thermal Analysis and Calorimetry - Gasification of the char obtained from the spent substrate after mushroom cultivation was carried out in a thermobalance connected to a mass...     

Synthesis and X-ray structure of p-tolyl phenylthioglyoxylate

The title compound (C₁₅H₁₂O₂S) is triclinic witha=7.077(10),b=8.825(2),c=11.068(2) Å, =106.66(3)^o, Z=2, and space group P. The significant structural features lies in the two carbonyl groups of the thioglyoxylate which are oriented antiperiplanar to each other [–168.2(2)^o]. The central C(8)–C(9) bond is 1.553(3) Å. The phenyl rings are twisted with respect to the carbonyl groups. Short contacts are present between S and O(1) [2.652(2) Å] and also between S and O(2) [2.758(2) Å].     

Polynomial symplectomorphisms

Let be the field of real or complex numbers. Let (X ²ⁿ, )be a symplectic affine space. We study the group of polynomialsymplectomorphisms of X. We show that for an arbitrary k thegroup of polynomial symplectomorphisms acts k-transitively onX. Moreover, if 2 l 2n – 2 then elements of this groupcan be characterized by polynomial automorphisms which preservethe symplectic type of all algebraic l-dimensional subvarietiesof X.     

Properties of poly(styrene/alpha-tert-butoxy-omega-vinylbenzyl-polyglycidol) microspheres suspended in water. Effect of sodium chloride and temperature on particle diameters and electrophoretic mobility

Hydrodynamic and electrophoretic properties of core-shell poly(styrene/alpha- tert-butoxy-omega-vinylbenzyl-polyglycidol) (P(S/PGL)) microspheres suspended in water are described. The microspheres were obtained by surfactant-free emulsion copolymerization of styrene and alpha- tert-butoxy-omega-vinylbenzyl-polyglycidol macromonomer ( M n = 2800, M w/ M n = 1.05). The process yielded microspheres with number average diameter D n = 270 nm and with low diameter dispersity index D w/ D n = 1.01. Shells of P(S/PGL) microspheres were enriched in polyglycidol. Molar fraction of polyglycidol monomeric units in the shells (determined by X-ray photoelectron spectroscopy) was equal to 0.34, which is much higher than the average molar fraction of polyglycidol monomeric units in whole particles of 0.048. Influences of NaCl concentration and temperature on P(S/PGL) microsphere diameters and on their electrophoretic mobility were investigated. It was found that hydrodynamic diameter of P(S/PGL) microspheres, determined by photon correlation spectroscopy, decreased significantly when temperature did exceed a certain value (transition temperature, T t). It has been found that the decrease is more pronounced for higher concentrations of NaCl in the medium. For microspheres suspended in 10 (-1) M NaCl, the hydrodynamic diameter decreased by 8% whereas for the same particles in pure water the diameter decreased by 5.2%. The process of shrinkage was fully reversible. Values of T t for P(S/PGL) microspheres were lower for higher concentrations of NaCl. Adjustment of salt concentration allowed controlling T t in a range from 44.4 to 49.9 degrees C. 13C NMR relaxation time measurements (T 1) for carbon atoms in polyglycidol macromonomer revealed that T 1 did increase with increasing temperature (in temperature range from 25 to 75 degrees C) indicating higher motion of chains at higher temperature. Addition of NaCl did not induce a substantial change of T 1 in the mentioned temperature range. The swelling-deswelling properties of P(S/PGL) microspheres' interfacial layer affected adsorption of P(S/PGL) particles on modified with (3-aminopropyl)triethoxysilane mica. It was shown that the deposition of P(S/PGL) microspheres at 25 degrees C on mica led to formation of two-dimensional crystal-shape assemblies, whereas at 60 degrees C (far above T t = 49.8 degrees C in H2O) the microspheres were randomly adsorbed without formation of colloidal crystal assemblies.     

Reliability of Elastic‐Plastic Frame Structures

An effective algorithm for estimating the reliability of frame structures made of an elastic perfectly plastic material is presented. It is assumed that the structure is working in uniaxial state of stress, the material parameters and the limit values of the loads are described by random variables, all loads are acting in a static manner, the probability density functions of all random variables, which describe the structure and loads are known. As the structure reliability measure the probability of failure and corresponding reliability index are regarded. The dead (constant) load and the climatic loads are taken into account. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical conductivity of polycrystalline films of p-sexiphenyl

In this work the results of DC conductivity measurements of polycrystalline p-sexiphenyl thin films are presented. The investigations concerned the effect of temperature, film thickness and electric field on the DC conductivity mechanism. The thickness of the investigated material varied from 0.2 to 2.5 μm. The measurements were carried out for different electrode polarities of the 0 -100 V voltage and at temperatures ranging from 15 to 325 K. Thin films of p-sexiphenyl were obtained by controlled vacuum sublimation on BK-7 glass substrate with gold and aluminium electrodes. Analyzing the obtained results we conclude that injection of the charge carrier from electrodes into the investigated material proceeds by thermionic emission and field emission and it is dependent on temperature and external electric field. The charge carrier transport is controlled by localized states (traps) in the forbidden energy gap. The activation energy calculated from formula ln I = f(1/kT) varied from kT for low temperature up to 1.0 eV.     

Copolymers of 7-oxabicyclo[2.2.1] heptane with 1,3-dioxane and promesogenic telechelic oligomers thereof

Copolymers of 7-oxabicyclo[2.2.1] heptane (B) (and of its 2-methyl derivatives) with 1,3-dioxane (D) were obtained by cationic copolymerization initiated with benzoylium hexafluoroantimonate. Structure of copolymers was determined by ₁H- and ₁₃C-NMR. The proportion of the acetal bonds in copolymers was additionally confirmed in studies of the products of hydrolysis (only the acetal bonds hydrolyze). D is unable to homopolymerize for the thermodynamic reasons and therefore mostly pseudoperiodic copolymers (-DB_x-)_y are formed. Nevertheless, the reshuffling reactions are responsible for the appearance of “wrong” units. These are: the separate oxymethylene and oxy-1,3-propylene units (P, subunits of D) located between two B units. Only the acetal bonds are cleaved in the acidic hydrolysis with dilute HCl. This gives the promesogenic telechelic oligomers of mostly HO-P-B_x-OH structure. This article is the first to describe successful cationic copolymerization of a cyclic acetal with a cyclic ether. Moreover, the inability of D to homopolymerize gives the thermodynamic basis of the pseudoperiodic copolymer formation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1733–1742, 1997