Home About us Contact
|
Home About us Contact | ||
|
|
||
Molecular Dimensions (molecular + dimension)
Selected AbstractsExperimental Study on the Molecular Dimension and Configuration of Polymer and Its Flow Characteristics from Electrolyte EffectCHINESE JOURNAL OF CHEMISTRY, Issue 4 2009Xiangguo LU Abstract Molecular clew dimension and configuration of polymer, and flow characteristics of polymer solution were studied from electrolyte effect, by making use of dynamic light scattering (DLS), scanning electron microscopy (SEM), apparent viscosity method and core flow experiment. It can be observed that with the electrolyte concentration increasing, there exists a variation trend of "decreasing, increasing and decreasing again" to the molecular clew dimension of the polymer. The compression action of Ca2+ or Mg2+ to the double electrode layer of polymer molecules is more powerful by comparison against Na+, which results in that Ca2+ and Mg2+ have a more extensive effect on the viscosity of polymer solution, and clew dimensions and their distribution. With the electrolyte concentration increasing, the polymer molecular configuration of multi-layer stereoscopic random reticulation transformed into a dendritic one. During the succeeding water flooding, the variation degree of injection pressure of core was mainly determined by the swelling extent of molecular clew of retained polymer and the produced amount of polymer. And the bigger the molecular weight of polymer is, the stronger the compression or swelling action of electrolyte to the molecule clews is, and the greater the increasing degree of injection pressure during succeeding water flooding is. The greater difference of electrolyte concentrations in used water between polymer flooding and succeeding water flooding can result in greater increasing degree of injection pressure during the succeeding water flooding. So, an advisable increasing in difference of electrolyte concentrations in used water between the polymer flooding and succeeding water flooding was proposed when designing the polymer flooding performance in oilfields, which has promising result for improving effect of polymer flooding. [source] Precise Control over Molecular Dimensions of Block-Copolymer Domains Using the Interfacial Energy of Chemically Nanopatterned Substrates,ADVANCED MATERIALS, Issue 15 2004W. Edwards Epitaxial assembly of block-copolymer films (see Figure) onto chemically nanopatterned substrates results in arrays of nanoscopic domains that are defect-free, oriented, and registered with the underlying substrate. The range of dimensions of features (or periodicity of structures) that can be patterned with perfection and registration strongly depends on the interfacial energy between the substrate and the polymer film. [source] Nanotube Membrane Based BiosensorsELECTROANALYSIS, Issue 1-2 2004Punit Kohli Abstract We review highly sensitive detection based on electrochemical methods. These methods are based on monodisperse gold and alumina nanotubule membranes with inside diameter approaching molecular dimensions. The analyte species can be detected by measuring a change in trans-membrane current when the analyte is added to the nanotubule-based cell. The second method entails the use of a concentration change based on the nanotubule membrane. Biomemtic ion-gated channels micropore and nanotubule membrane sensors are also reviewed. These synthetic ion channels can be switched from an "off" state to an "on" state in response to an external chemical stimulus. Using these methods, we have achieved detection limits as low as 10,pM. Potential applications for these biosensors are in fields such as bioanalytical, biomedical, pharmaceutical and drug discovery. [source] Embryonic States of Fluorapatite,Gelatine Nanocomposites and Their Intrinsic Electric-Field-Driven Morphogenesis: The Missing Link on the Way from Atomistic Simulations to Pattern Formation on the MesoscaleADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Paul Simon Abstract The shape development of fluorapatite (FAP),gelatine nanocomposites is revealed by means of HRTEM investigations starting from molecular dimensions up to the formation of mesoscaled (elongated) hexagonal prisms. The composite nature of the aggregates is proved by IR spectroscopy and by chemical analyses on all states of shape development. The initial states are characterized by triple-helical fiber protein bundles, which are mineralized step-by-step forming and fixing nanoplatelets of FAP in a mosaic arrangement. After being fully mineralized the bundles form elongated composite nanoboards. In the next step of the growth process the boards aggregate to bundles of boards which are in a more or less parallel alignment with respect to each other. By adding up more and more composite nanoboards a critical size is reached and an electric field is developed, which takes over control and directs the further development of the aggregates. This kind of electric-field-directed growth of the elongated polar nanoboards additionally leads to the formation and inclusion of protein nanofibrils into the growing composite aggregate. By this method, cone-like nanofibril structures develop along the long axis of the aggregates accompanied by more perfect parallel alignment of the composite boards within the aggregates. Further shape development is characterized by adding up composite nanoboards, in particular to increase the third dimension in volume. This thickening process preferably takes place in the middle part of the elongated aggregates and finally proceeds to their basal ends until a perfect hexagonal prismatic seed is formed, which then is ready for further shape development on the micrometer scale. [source] Nanorod-Driven Orientational Control of Liquid Crystal for Polarization-Tailored Electro-Optic DevicesADVANCED MATERIALS, Issue 9 2009Somobrata Acharya Dispersion of ultranarrow ZnS nanorods of molecular dimensions encapsulated by a fluid-like soft organic layer in the nematic liquid crystal (LC ZLI-4792) results in a novel soft-matter-type blend with previously unachieved electro-optic properties. The local ordering of the nanorods significantly affects the global ordering of the blend, allowing a more rapid response. [source] Capacity of activated carbon derived from pistachio shells by H3PO4 in the removal of dyes and phenolicsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2003Amina A Attia Abstract Two activated carbons were obtained from pistachio shells by impregnation with H3PO4 under standard conditions of acid concentration (50 wt%) and heat treatment at 773 K for 2 h. The soaking time was 24 and 72 h for the two samples before thermal pyrolysis. Analysis of the N2/77 K adsorption isotherms proved that both were highly adsorbing carbons with considerable microporosity, and that the prolonged contact with activant enhanced total porosity (surface area and pore volume) and increased the amount of mesoporosity. Adsorption isotherms of probe molecules, viz methylene blue (MB), rhodamine B (RB), phenol (P) and p -nitrophenol (PNP), were determined at room temperature, from aqueous solutions. Both the Langmuir and Freundlich model adsorption equations show satisfactory fit to experimental data. Both carbons exhibit similar adsorption parameters irrespective of their porosity characteristics. The sequence of uptake per unit weight was: PNP > MB > RB > P. Low affinity towards phenol may be associated with its competition with water molecules which are more favourably attracted to the acid surface which has a high oxygen functionality. Preferred adsorption in the order PNP > MB > RB is proposed to be a function of carbon porosity, related to the increased molecular dimensions of the solutes. Adsorption from a binary mixture of equal concentrations of MB and RB showed reduced uptake for both sorbates in comparison to the single component experiments. RB removal surpasses that of MB in the binary test and may be attributed to lower water solubility and higher molecular dimensions. Copyright © 2003 Society of Chemical Industry [source] Hydrodynamic modeling of diffusion tensor properties of flexible moleculesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2009Vincenzo Barone Abstract We present a computationally efficient implementation of hydrodynamic modeling for the evaluation of diffusion tensors of molecules with internal degrees of freedom, adapted to take into account information from linear scaling computations of solvent accessible surfaces implemented in the framework of last generation continuum solvent models. Torsional angles are taken also explicitly into account, while retaining correct hydrodynamic interactions. A comparison with literature data is presented to prove the effectiveness of the approach for a wide range of molecular dimensions and solvent environments. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Spatial arrangement of molecules in homomolecular Z' = 2 structuresACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2006Elna Pidcock The Box Model of crystal packing describes unit cells in terms of a limited number of arrangements of molecular building blocks. An analysis of Z,, 1 structures has shown that cell dimensions are related to molecular dimensions in a systematic way and that the spatial arrangement of molecules in crystal structures is very similar, irrespective of Z or space group. In this paper it is shown that the spatial arrangement of molecules in Z, = 2 structures are, within the context of the Box Model, very similar to that found for Z,, 1 structures. The absence of crystallographic symmetry does not appear to affect correlations between molecular dimensions and cell dimensions, or between the packing patterns and the positions of molecules in the unit cell, established from the analysis of Z,, 1 structures. The preference shown by Z, = 2 structures for low surface-area packing patterns and the observation that strong energetic interactions are most often found between the large faces of the independent molecules reaffirms the importance of molecular shape in crystal packing. [source] 3,3,6,6,9,9-Hexaethyl-1,2,4,5,7,8-hexaoxacyclononane at 296 KACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009Jorge Cerna The title molecule (diethyl ketone triperoxide, DEKTP), C15H30O6, is a cyclic triperoxide closely related to triacetone triperoxide (TATP), one of the most unstable explosives known. However, the stability of DEKTP is ca 20,50 times greater than that of TATP. DEKTP crystallizes with two molecules in the asymmetric unit, with virtually identical geometry. The cyclononane core is stabilized in a twisted boat,chair conformation (approximate D3 symmetry), very close to that previously described for TATP. The explanation for the safe thermal behaviour of DEKTP compared with TATP should thus not be sought in the molecular dimensions, but rather in the thermal decomposition kinetics. [source] 11-Methyl-2,3-benzodipyrrin-1-oneACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2004Raymond Bonnett The title compound {alternative names: 11-methyl-2,3-benzopyrromethenone and 3-[(1-methylpyrrol-2-yl)methylidene]-2,3-dihydro-1H -isoindol-1-one}, C14H12N2O, was prepared by the base-catalysed condensation of phthalimidine with 2-formyl-1-methylpyrrole; yellow orthorhombic crystals, space group Pbca, were obtained from ethanol. The molecule is almost planar, having Z(,)antiperiplanar geometry. The molecules are arranged in pairs with intermolecular hydrogen bonding between lactam functions. Comparison with literature values for polyalkyldipyrrin-1-ones shows that, apart from the local constraints of the benzene ring, the fused benzo ring has little effect on the molecular dimensions of the dipyrrin-1-one skeleton. [source] Camouflaged Carborarods Derived from B -Permethyl-1,12-diethynyl- para - and B -Octamethyl-1,7-diethylnyl- meta -carborane ModulesCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2005Axel Herzog Dr. Abstract Rigid camouflaged carborarods constructed from the corresponding C,C,-diethynyl derivatives of B -decamethyl-1,12-dicarbadodecaborane(12) (6) and B -octamethyl-1,7-dicarbadodecaborane(12) (48) have been synthesized by largely conventional organic transformations. These carborarods are the longest discrete rod species available by this method in which B-methylated p -carborane and m- carborane cages are linked through their carbon vertices by using butadiynylene moieties. They exhibit enhanced solubility in common organic solvents relative to all other presently known carborane-based rigid-rod molecules. The oxidative coupling of bis(ethynyl) derivatives of 6 generates oligomers containing, on average, 16 carborane modules. The structural characterization of the corresponding dimeric species revealed that the carborarods possess a sinusoidal chain distortion in the solid state. The stereoelectronic properties of these and related model carborarods were evaluated by using molecular dimensions as a monitor for the comparison of computational and experimental methods. In addition, the effect of exhaustive B-methylation of 12- and 10-vertex para -carborane cages in a series of model C,C,-diethynyl derivatives was similarly investigated by computational and structural studies. As expected, a correlation of intercage CC bond lengths with cage size was observed and was attributed to hybridization effects. B-Permethylation had no significant structural effect with either 10- or 12-vertex cage derivatives. Relative to unsubstituted compounds, thermal and chemical stabilities of B-permethylated derivatives were increased through the operation of a steric "bumper-car" process, and solubilities in organic solvents were enhanced. The formation of linear, sterically encumbered platina,carborarods using ethynyl derivatives of 6 as precursors is described. [source] | |||||||||||||||||||||||||