Effect of postgrafted alkyl chains on the wettability of hydrophilic poly(amidoamine)-grafted nano-sized silica

In order to control the surface wettability of hyperbranched hydrophilic poly(amidoamine) (PAMAM)-grafted nano-sized silica, hydrophilic alkyl chain (C _n H_2n+1) with different chain lengths (n = 4, 8, 15) were postgrafted onto PAMAM-grafted silica by the reaction of terminal amino groups of PAMAM grafted on the silica surface with alkyl acid chlorides (C _n H_2n+1-COCl). The postgrafting of C _n H_2n+1-COCl increased with increasing PAMAM grafting and alkyl chain length of C _n H_2n+1-COCl. However, the terminal amino groups of PAMAM-grafted silica used for the postgrafting of C _n H_2n+1-COCl decreased with increasing chain length. This may be due to the steric hindrance between terminal amino groups of PAMAM-grafted silica and C _n H_2n+1-COCl: the steric hindrance is considered to increase with increasing chain length of C _n H_2n+1-COCl. The surface wettability was estimated by contact angle measurement for water and methanol wettability. As a result, it was found that contact angle and methanol wettability increased with increasing alkyl chain length of postgrafted C _n H_2n+1-COCl. The hyperbranched PAMAM-grafted silica readily dispersed in water and methanol because of the hydrophilic nature of grafted PAMAM, but it lost dispersibility in water and methanol due to postgrafting of hydrophobic chains.     

Theory of two-phonon absorption processes in liquid paraffins

Calculated absorption spectra are given for linear C₈H₁₈, C₁₀H₂₂, C₁₆H₃₄ and C₂₀H₄₂ chains, based on the assumption of a two-phonon absorption mechanism. In the present work the normal modes of vibration of different finite chains are computed directly, without recourse to the Pitzer sampling approximation and without the assumption of strict k-selection rules. The calculated spectra are found to be much more sensitive to chain length than the experimental spectra. A possible explanation of the relative insensitivity of the observed spectra is suggested in terms of a characteristic chain segment length common to all the chains. Ironically, the apparent importance of chain segmentation in the two-phonon absorption suggests that one-phonon transitions may also play a significant rôle in the absorption process.     

An examination of the longitudinal acoustic mode of polyethylene crystals

Chain lengths have been calculated from the peak positions of the longitudinal acoustic modes (LAM) of polyethylene single crystals grown at several different temperatures. The data are consistent with other experimental results when the crystalline elastic modulus is taken to be 3.6 × 10¹² dyn/cm². However, this is true only if the vibrations of the crystalline chain segments are unaffected by the presence of folds and cilia on the crystal surface. The LAMs of several crystal preparations were also deconvoluted with the first-order LAM of C₉₄H₁₉₀ in order to remove instrumental broadening. The band shapes of the deconvoluted spectra are consistent with the idea that the LAM of polyethylene crystals is composed of two contributions: One due to chain stems in 110 sectors and a second due to chains in 200 sectors.     

SEMICRYSTALLINE AND SUPERLATTICE STRUCTURES IN BINARY MIXTURE OF LONG CHAIN n-ALKANES C194H390 AND C294H590

Binary mixtures of long chain n-alkanes from C₁₂₂H₂₄₆ to C₂₉₄H₅₉₀ have been found to form solid solutions despite their large chain length differences [Zeng and Ungar. Novel Layered Superstructures in Mixed Ultralong n-Alkanes. Phys. Rev. Lett. 2001, 86, 4875–4978]. In this article we describe a study of the binary mixture of C₁₉₄H₃₉₀+C₂₉₄H₅₉₀ (50:50 w/w) using small angle x-ray scattering. The molecular chain length difference between the two components is 100 C-atoms, the largest so far studied. In accordance with the findings on some other binary mixtures, two types of lamellar structures are found: the semicrystalline form (SCF) at high temperatures (>105°C) and the triple-layer superlattice at low temperatures (<95°C). The SCF consists of alternating crystalline and amorphous layers: C₁₉₄H₃₉₀ molecules are fully crystallized in the crystalline layer while C₂₉₄H₅₉₀ molecules traverse the crystalline layer and are only partially crystalline; their protruding tails, or cilia, constitute the amorphous layer. The superlattice is a periodic 1-D array of triple-layer units: the two outer layers in the unit contain a mixture of C₁₉₄H₃₉₀ and C₂₉₄H₅₉₀ while the surplus tails of C₂₉₄H₅₉₀ coalesce and interdigitate in the center and form the third, thinner crystalline layer. In the superlattice form, the unusual diffraction order dependence of the linewidth is interpreted in terms of a particular type of stacking faults.     

Vibrational and optical properties of a one‐dimensional organic–inorganic crystal [C6H14N]PbI3

Self‐assembled organic–inorganic [C₆H₁₄N]PbI₃ crystals were synthesized. The crystal structure consists of one‐dimensional semiconductor chains formed by infinite PbI₆ face‐sharing octahedra aligned along the a‐axis. The organic cations are linked to the inorganic chains by N H· · ·I hydrogen bonds and act as insulator barriers. The vibrational properties of [C₆H₁₄N]PbI₃ were studied using polarized Raman scattering and infrared (IR) absorption. The observed Raman and IR spectral features were identified by comparison with the vibrational properties of homologous compounds and with the vibrational wavenumbers calculated using the ab initio PM3 method. Moreover, the photoluminescence and diffuse reflectance of [C₆H₁₄N]PbI₃ single crystals, along with the UV‐Vis absorption of spin‐ coated films, were measured. A strong green‐blue luminescence due to radiative recombinations of 1D excitons is observed. The Stokes shift is estimated at 70 meV. Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of the hydrogen fluoride chain on the aromaticity of C6H6 in the C6H6···(HF)1–4 complexes

The effect of the hydrogen fluoride chain ((HF)_n) on the aromaticity and π character of C–C bonds of C₆H₆ in the C₆H₆···(HF)_n (n = 1–4) complexes were investigated using density functional theory employing RM05 functional. It was found that the binding energy between C₆H₆ and different (HF)_n chains showed a maximum at n = 3 (C₆H₆···(HF)₃). Also, the π–hydrogen interaction (πHI) and the bifurcated fluorine interaction (BFI) increased and decreased the π character of the C–C bond of C₆H₆, respectively. In addition, the change of aromaticity of the C₆H₆ due to the interaction with the HF chains was also studied using three different aspects such as aromatic fluctuation index (FLU), average two centre index (ATI) and proton nuclear magnetic resonance (HNMR) spectrum. The most change in the aromaticity happens when the C₆H₆ interacts with (HF)₃ chain. The variation of aromaticity with the binding energy and the summation of two-body terms were investigated and very good linear correlations were observed.     

Diamagnetic susceptibility of solid and liquid paraffins

Experimental values for the diamagnetic susceptibility of a series of mono-disperse n-paraffins ranging between 6 and 50 carbon atoms in the solid (melt and solution crystallized) and in the liquid state are reported. From the dependence of the molecular susceptibility, ScHM, on the molecular weight, information about the intermolecular interactions between adjacent chain molecules and on the arrangement of the methyl end-groups is obtained. The ScHM values of melt- and solution-crystallized paraffins are, within experimental error, indistinguishable from each other. For C₁₂H₂₆ and C₄₄H₉₀ the specific susceptibility ScHM /M rises at the melting point within a few °C and reaches a plateau which characterizes the liquid state II. For the paraffin C₂₄H₅₀ an intermediate plateau between the melting point and the final true liquid state is observed and is called liquid state I. After cooling below the melting point TM, the ScHM value of the equilibrium state can be obtained after a short time only from liquid state I, while from liquid state II days and weeks are needed for this. By combining this information with the observed ScHM values, it is concluded that in liquid state I a higher or smectic-like order exists similar to mesophases, well-known in liquid crystals, while in the real liquid state II this order is lost.     

Luminescence quenching of [Ru(bpy)3] by ruthenium(II) tetraphosphite complexes with different phosphite ligands

The luminescence quenching of excited Tris(2,2-bipyridine)ruthenium(II) ions by trans-[RuCl₂{P(OR)₃}₄] complexes with different alkyl chain ligands (R=C₂H₅, C₂H₅Cl, ⁿC₄H₉, ⁱC₃H₇ o-tolyl and ^tC₄H₉) was investigated. None of the acceptor Ru(II) phosphite complexes were luminescent, and the rate constants of the bimolecular system were determined within the range of 1.15 and 0.28×10⁸ M⁻¹ s⁻¹ for R=C₂H₅ and ^tC₄H₉, respectively. The results indicate a direct effect of the alkyl chains in the rate constants, showing a decrease of k_q as a function of increased of the alkyl chains (R) in the ruthenium(II) tetraphosphite complexes. The greater the R group content in the phosphite ligand, the more difficult the electron transfer is.     

Surface chemistry of Zn3P3 single crystals studied by XPS

X-ray photoemission spectroscopy (XPS) has been used to study the surface reaction of Zn₃P₂ single crystals.The spectra of crystals exposed to H₂, O₂, CO₂, O₂+H₂O or CO₂+H₂O during a four week period were compared to the spectra of as-grown or in UHV scraped samples. For samples contaminated with the wet gases O₂+H₂O and CO₂+H₂O additional phosphorus core levels together with a shift of the zinc core levels were observed. For crystals exposed to atmosphere during several months no phosphorus could be detected on the gasgrown surface, whereas the stochiometry of Zn₃P₂ was maintained within the bulk. Crystals with scraped surfaces showed no moisture sensitivity. No surface contamination was also detected for Zn₃P₂ crystals deposited with up to 1000 L H₂O or exposed to atmosphere during 30 min.     

On the Relationship Between Microhardness and Crystal Perfection of Chain-Extended Polyethylene

Abstract

The crystal hardness-crystal perfection correlation of polyethylene (PE) samples crystallized at high pressure from the melt (chain extended) has been studied and compared to melt crystallized samples at atmospheric pressure (chain folded). For this purpose the chain extended PE samples were analyzed by WAXS and the paracrystalline lattice distortion parameter values, g ₁₁₀, were calculated. Results are discussed in the light of structural and thermodynamical predictions. Analysis of data confirm the close existing correlation, previously found for chain-folded crystals, between the crystal hardness and g ₁₁₀, including now both the values for chain-folded and chain-extended crystals.     

Solution-grown single crystals of random terpolymer liquid crystal polymers: Chain folding,morphology, and effect of annealing

Thin (100–150 Å thick) single crystals of large lateral dimensions have been grown from dilute solution in xylene of random terpolymer, thermotropic, liquid crystal polymers containing approximately equimolar amounts of C₆ or C₇ flexible segments, oxybenzoate, and dioxyphenyl. With both polymers having molecular lengths of 800 Å or longer, electron diffraction patterns indicate chain folding. The crystal structure, hexagonal, is less perfect than found previously for thin films of the C₇ (and C₅) polymer crystallized from the nematic state by slow cooling (orthorhombic). Annealing of the crystals below the crystal-liquid crystal transition results in merging of overgrowths and rough crystal edges into the main crystal and a surface roughening, followed, at longer times and/or higher temperatures, by lamella thickening. Annealing in the nematic state results in the development of rosettes of lamellae. Implications of the results for crystallization mechanisms and morphology of the nematic state are discussed.     

Solvatochromic properties of long alkyl chain π* indicators: comparison of N,N‐dialkyl‐4‐nitroanilines and alkyl 4‐nitrophenyl ethers

Hydrophobic forms of the N,N‐dialkyl‐4‐nitroaniline (DNAP) (p‐O₂NC₆H₄NR₂) ( 1a–f ) and alkyl‐4‐nitrophenyl ether (p‐O₂NC₆H₄OR) ( 2a–c ) solvatochromic π* indicators have been characterized and compared with respect to: (a) solvatochromic bandshape, (b) sensitivity expressed as ?s , ( / d π * ), and (c) trends in ? s with increasing length of alkyl chain(s) on the probe molecule. ? Octyl 4‐nitrophenyl ether (p‐O₂NC₆H₄OC₈H₁₇) ( 2b ) and ? decyl 4‐nitrophenyl ether (p‐O₂N C₆H₄ OC₁₀H₂₁) ( 2c ) were synthesized and their solvatochromic UV/Vis absorption bands were found to maintain a Gausso‐Lorentzian bandshape for the indicators in non‐polar and alkyl substituted aromatic solvents, for example, hexane(s) and mesitylene. Corresponding absorption bands for 1a–f display increasing deviation from a Gausso‐Lorentzian shape in the same solvents as the alkyl chains on the indicator are increased in length all the way to C₁₀ and C₁₂, for example, N,N‐didecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₀H₂₁)₂) and N,N‐didodecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₂H₂₅)₂) ( 1d–f ). A plot of ? s versus C_n follows a 1st order decay for the DNAP indicators but is linear for the alkyl 4‐nitrophenyl ethers. A discussion of how the long alkyl chains on the two types of indicators affect the orientation and overlap of n and π * orbitals, and resulting solvatochromic bands is presented. For DNAP, overextending the alkyl chains to obtain greater hydrophobic character may cause the alkane component to dominate solute‐solvation processes at the expense of the probe's fundamental solvatochromic character. Copyright © 2007 John Wiley & Sons, Ltd.     

Rovibrational constants for the ground state and ν8 = 1 state of ethylene-d3 (C2HD3) by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the ν₈ fundamental band of ethylene-d₃ (C₂HD₃) was recorded with a unapodized resolution of 0.0063 cm⁻¹ in the wavenumber region of 840–980 cm⁻¹. By assigning and fitting a total of 738 infrared transitions using a Watson’s A-reduced Hamiltonian in the I^r representation, rovibrational constants for the upper state (ν₈ = 1) up to all five quartic centrifugal distortion terms were derived for the first time. The root-mean-square (rms) deviation of the fit was 0.00076 cm⁻¹. The ground state rovibrational constants of C₂HD₃ were also determined for the first time by a fit of 450 combination-differences from the present infrared measurements, with rms deviation of 0.00075 cm⁻¹. Local frequency perturbations were not detected in the C-type ν₈ band of C₂HD₃ which is centred at 918.73199 ± 0.00007 cm⁻¹.     

IUPAC critical evaluation of the rotational-vibrational spectra of water vapor. Part II: Energy levels and transition wavenumbers for HDO, HDO, and HDO

This is the second of a series of articles reporting critically evaluated rotational-vibrational line positions, transition intensities, pressure dependences, and energy levels, with associated critically reviewed assignments and uncertainties, for all the main isotopologues of water. This article presents energy levels and line positions of the following singly deuterated isotopologues of water: HD¹⁶O, HD¹⁷O, and HD¹⁸O. The MARVEL (measured active rotational-vibrational energy levels) procedure is used to determine the levels, the lines, and their self-consistent uncertainties for the spectral regions 0-22 708, 0-1674, and 0-12 105 cm⁻¹ for HD¹⁶O, HD¹⁷O, and HD¹⁸O, respectively. For HD¹⁶O, 54 740 transitions were analyzed from 76 sources, the lines come from spectra recorded both at room temperature and from hot samples. These lines correspond to 36 690 distinct assignments and 8818 energy levels. For HD¹⁷O, only 485 transitions could be analyzed from three sources; the lines correspond to 162 MARVEL energy levels. For HD¹⁸O, 8729 transitions were analyzed from 11 sources and these lines correspond to 1864 energy levels. The energy levels are checked against ones determined from accurate variational nuclear motion computations employing exact kinetic energy operators. This comparison shows that the measured transitions account for about 86% of the anticipated absorbance of HD¹⁶O at 296 K and that the transitions predicted by the MARVEL energy levels account for essentially all the remaining absorbance. The extensive list of MARVEL lines and levels obtained are given in the Supplementary Material of this article, as well as in a distributed information system applied to water, W@DIS, where they can easily be retrieved. In addition, the transition and energy level information for H₂¹⁷O and H₂¹⁸O, given in the first paper of this series [Tennyson, et al. J Quant Spectr Rad Transfer 2009;110:573-96], has been updated.     

Mesomorphic behaviors of a series of heterocyclic benzothiazole-imine-ester-based liquid crystals

A series of new calamitic liquid crystals, 2-[4-(4-alkoxybenzoyloxy)benzylidenamino]benzothiazoles comprising a heterocyclic (benzothiazole) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were prepared and characterized. This series comprises eight members wherein the members vary by the length of alkoxy chain (C_nH_2n+1O-, where n?=?4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in conformity with the expected structure. Their thermotropic behaviors were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first member of the series (n?=?4). As the alkoxy chain increased to n?=?6, 8, 10, 12, 14, the nematic phase appeared together with an additional SmA phase. When moving from n?=?16 until the highest member (n?=?18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA).     

Phase transitions at high pressure in the fullerene C60 molecular donor-acceptor complex {Hg(dedtc)2}2 · C60

Raman spectra of crystals of the molecular fullerene C₆₀ donor-acceptor complex {Hg(dedtc)₂}₂ · C₆₀ (fullerene with mercury diethyldithiocarbamate) have been measured at a pressure up to 8.4 GPa and at room temperature. A phase transition has been revealed in the pressure range of 1.2–2.0 GPa, which is accompanied by a splitting of the degenerate intramolecular phonon modes H _g (1)-H _g (4) and H _g (7)-H _g (8), as well as by a softening of the H _g (2) mode of the fullerene C₆₀. As the pressure further increases to the maximum value, the intensity of the bands varies smoothly. A decrease in the pressure leads to the reverse transition to the initial state at 1.2 GPa. The splitting of the degenerate modes H _g (1)-H _g (8) and the softening of the H _g (2) modes resemble their behavior in the formation of dimers in fullerite crystals and indicate the possible formation of dimers in two-dimensional fullerene layers under hydrostatic compression of the {Hg(dedtc)₂}₂ · C₆₀ complex.     

An electron spin resonance study of the soy bean phosphatidylcholine-based reversed micelles

The ESR spectra of l-palmitoyl-2-stearoyl-(n-doxyl)-glycero-3-phosphocholine spin label positional isomers (n = 5, 7, 10, 12 and 16) have been studied in soy bean phosphatidylcholine (SPC)-based microemulsions with various volume fractions of disperse phase over the wide temperature range. The maximum hyperfine splitting 2A _max and the order parametersS were taken as indices of the rotational mobility and the motion spatial restrictions of the labeled lipid chain segments. It is found that the temperaturesT _tr at which sharp enhancements of2A _max andS occur depend on concentration and size of the reversed micelles in solutions. To explain this, a plausible model, taking into account capability of the SPC molecule hydrocarbon chains to change a tilt angle with respect to the surface of a polar head group as temperature varies, is proposed. The estimations of the correlation times τ_sl obtained from the lineshape characteristics of the ESR spectra provided the possibility to suggest that these correlation times characterize the reorientations of the SPC chain axis about the normal to the surface of a polar head group of a reversed micelle.     

Factor group theoretical analysis of fundamental vibrations of the H2AsO 4? anion in (C6H9N2)H2AsO4 single crystal

Fundamental (lattice, rotational, and intermolecular) vibrations of the H₂AsO₄⁻ anion in (C₆H₉N₂)H₂AsO₄ crystal are calculated using the correlation theorem based on the group theory. The correlation between anionic site of symmetry C _s and the factor group D _2h of the crystal yields 12 modes for both lattice and rotational vibrations. The infrared and Raman spectra of these modes do not coincide. Addition of two hydrogen atoms to AsO₄⁻ ion yields two As-OH bonds in the H₂AsO₄⁻ anion. As a result, the molecular symmetry is reduced from T _d to C _2υ . The free H₂AsO₄⁻ anion having C _2υ symmetry gives in total 15 fundamental normal vibrations. Under the crystal field splitting effects, the number of intermolecular vibrations for the anion in infrared and Raman spectra is calculated to be 56 active vibrations. The calculated fundamental vibrationsmanifest themselves as the main features in an experimental infrared spectrum.     

Structure of the methyl radical

Carbon-13 hyperfine splittings equal to 41±3 gauss have been observed in the paramagnetic resonance of a mixture of C¹²H₃ and C¹³H₃ radicals produced by x-irradiation of CH₃I at 77°k. The observed splitting provides strong evidence that CH₃ is a planar molecule.     

Construction of novel quantum-confined structure with lead halide/gemini surfactant hybrids

Novel organic–inorganic hybrid compounds, C₁₆H₄₄N₄Pb₃I₁₀ and C₁₄H₃₄N₂Pb₂I₆, were synthesized by solvent diffusion recrystallization from the dimethylsulfoxide solution containing PbI₂ and gemini ammonium surfactants with different head groups. The results of single crystal X-ray structural analysis showed that the inorganic region of C₁₆H₄₄N₄Pb₃I₁₀ has quasi one-dimensional chains of [Pb₃I₁₀]^4? units, whereas that of C₁₂H₃₀N₂Pb₂I₆ has one-dimensional chains of face-sharing PbI₆ octahedra. The absorption and fluorescence spectra of these compounds also indicate the formation of one-dimensional inorganic chains and quantum-confined structures.