Abstract  Colloidal GaP nanowires (NWs) were synthesized on a large scale by a surfactant-free, self-seeded solution-liquid-solid (SLS) method using triethylgallium and tris(trimethylsilyl)phosphine as precursors and a noncoordinating squalane solvent. Ga nanoscale droplets were generated in situ by thermal decomposition of the Ga precursor and subsequently promoted the NW growth. The GaP NWs were not intentionally doped and showed a positive open-circuit photovoltage based on photoelectrochemical measurements. Purified GaP NWs were used for visible-light-driven water splitting. Upon photodeposition of Pt nanoparticles on the wire surfaces, significantly enhanced hydrogen production was observed. The results indicate that colloidal surfactant-free GaP NWs combined with potent surface electrocatalysts could serve as promising photocathodes for artificial photosynthesis.

Abstract  A photophysical analysis of 10(-4) M solutions of 7-azaindole in hydrocarbon solvents including 2-methylbutane, 3-methylpentane, ethylcyclohexane, decalin, and squalane revealed that the viability of the two-proton phototautomerism in its dimer is clearly medium-dependent. However, in all media studied, a small tunneling contribution in the photoinduced double proton transfer continues to exist at low temperatures.

Abstract  All-trans-octatetraene 3,10-di(tert-butyl)-2,2,11,11-tetramethyl-3,5,7,9-dodecatetraene emits fluorescence in three different regions of the visible spectrum. Thus, it produces an extremely weak emission in the gas phase that can hardly be detected in the condensed phase; such an emission exhibits a negligible Stokes shift with respect to the 1A(g)-->1B(u) absorption transition and can, in principle, be assigned to the 1B(u)-->1A(g) emission for the compound. A second, structureless fluorescence emission, centered in the region of 525 nm, is observed in the gas phase and at somewhat higher wavelengths in the condensed phase [viz., 570 nm in 2-methylbutane (2MB) and 550 nm in squalane (SQ)]. While detectable, this emission increases significantly, with no change in spectral position, as the solution temperature is lowered; also, it is abruptly replaced by a new, strongly blueshifted emission at approximately 490 nm in 2MB and 455 mm in SQ when the viscosity of the medium exceeds a given level. The fact that the two fluorescence emissions considerably depart from the expected behavior for a 1B(u)-->1A(g) emission in an all-trans-polyene, and that one disappears while the other simultaneously appears as the medium becomes more rigid, suggests that the two emissions are produced by two different molecular structures and that the rigidity of the medium switches their production from the originally excited all-trans 1B(u) form. The observed spectral behavior is consistent with a recently proposed model [J. Catalan, Chem. Phys. 335, 69 (2007)] in which the 1B(u) excited state of octatetraene can give two distinct molecular conformers as a result of twisting about different C-C single bonds.

Abstract  The exchange of copolymer chains between 1 vol % PS-PEP (poly(styrene-b-ethylene-alt-propylene)) di-block copolymer micelles in squalane (selective for PEP) is investigated using time-resolved small-angle neutron scattering (TR-SANS) as a function of added PEP homopolymer. The solvent squalane, C30H62, is substituted in part or completely with PEP homopolymers that are the same molecular weight as the corona blocks. Polymer solutions/mixtures (1 vol % PS-PEP, plus 2, 7, or 15 vol % PEP in squalane, and 1 vol % PS-PEP in PEP) were separately prepared using normal (h-PS) or deuterated equivalent (d-PS) PS-PEP diblock copolymers. The solvent was contrast matched to a 50/50 mixed h-/d-PS micelle core, so that the scattering intensity decays with the mixing of h- and d-PS-PEP chains undergoing exchange between micelles. The chain exchange rate can therefore be assessed quantitatively. As the concentration of added homopolymer in solution increases above the overlap concentration of PEP chains, the chain exchange rate drops significantly. The results are compared to an earlier study of chain exchange between PS-PEP micelles in a 15% solution in squalane, which was also found to be significantly slower than when the solution is dilute. The primary factor in this slowing down of chain exchange is an increased screening of excluded volume interactions among the corona blocks. The role of increasing micelle aggregation number with PEP concentration is found not to be the dominant effect up to 15% added PEP but may play an increasingly important role in the PEP melt matrix, where no chain exchange could be detected in these experiments.

Abstract  The effect of temperature on the steady-shear viscosity of a soft semi-crystalline crosslinked-polyethylene microparticle suspension in squalane was studied using rotational rheometry. The results show a sharp increase in the viscosity of the system occurring at about 86 degrees C. The magnitude of this spike is dependent on the concentration of the suspension and is reproducible over multiple heating and cooling cycles. This phenomenon has been attributed to the melting of the crystalline regions within the particles, causing them to swell by soaking up squalane. The Mooney equation was used to model the viscosity data based on swelling data obtained from separate experiments. The results showed that the model is inadequate for describing the observed phenomenon, suggesting the possibility of additional interactions existing among the particles. POLYM. ENG. SCI., 48:329-335, 2008. (c) 2007 Society of Plastics Engineers.

Abstract  The kinetics have been studied for two processes whose limiting stage is the diffusion of molecular oxygen: (i) oxidation of radicals after irradiation; and (ii) quenching of phenanthrene phosphorescence. The processes were studied in glassy squalane and poly(methyl methacrylate) matrices. Comparison between the kinetic properties of these processes allowed us to conclude about predominant stabilization of radicals near structural defects of glass. In squalane this manifests itself in anomalously high value of reaction radius for oxidation of radicals and in poly(methyl methacrylate) in quantitative difference in the parameters of distribution in rate constants for processes (i) and (ii).

Abstract  Squalane is an important ingredient in the cosmetic, nutraceutical, and pharmaceutical industries. It has also been used as a model compound for the hydrocracking of crude and microalgae oil. Thus, a series of green heterogeneous metal catalysts were prepared to achieve complete hydrogenation of highly unsaturated squalene into squalane. Surface modification of the clay and metal intercalation simultaneously occurred during wet impregnation. The Pd-nanoparticles-intercalated clay with a dominating Pd(111) facet showed the highest reactivity and selectivity. The catalyst was stable with very low Pd leaching (approximate to 0.03 ppm) and was recyclable without losing any significant catalytic activity.

Abstract  Trans-azobenzene dissolved in different liquid hydrocarbons absorbs fluorescence arising from all acceptors previously used in Fluorescence Detected Magnetic Resonance (FDMR) and Optically Detected ESR (OD ESR) spectroscopy making optical detection impossible. In this report a new acceptor, rubrene, having sufficient quantum yield of fluorescence in the red band 550-620 nm, has been proven successful. OD ESR spectra of the radical-ion pair trans-azobenzene+/rubrene- were detected in liquid squalane (2,6,10,15,19,23-hexamethyl-tetracosane) solution in the temperature range 294-243 K. The experimental isotropic hyperfine splittings of the radical cation of trans-azobenzene (a(N) = 1.4 mT) have been compared with those from MNDO/INDO calculations and with those of earlier work using freon matrix studies.

Abstract  PE microgels were prepared from mechanical fragmentation and from immiscible blends of PS and PE. The surface topology of microgels obtained from mechanical fragmentation was hypothesized to consist of long linear PE chains that are capable of interparticle co-crystallization as suggested by low-strain oscillatory shear experiment results. To investigate this hypothesis, PE microgels with a smooth surface and a PS corona were prepared using immiscible blends of PE and PS, followed by removal of the PS matrix. The rheological response of suspensions of PE microgels with a PS corona in squalane was similar to suspensions of PE microgels with crystallizable surface chains whereby the system would gel and exhibit hysteresis upon a cooling and heating cycle. Suspensions of PE microgels without any surface chains, however, were reversible over multiple cooling and heating cycles. It was determined that the PS corona and the cross-link density of the microgels had an effect (p < 0.01) on the reversibility whereas the microgel concentration in the suspension did not (p = 0.82).

Abstract  Retention data obtained previously at 25 degrees C on a hexadecane capillary column by Zhang et al, and a packed hexadecane column by Abraham et al., both uncorrected for any effects due to interfacial adsorption, were compared with retention data obtained by Poole et al. on a packed squalane column at 120 degrees C, with the latter fully corrected for such effects. It is shown that for most solutes, the capillary and packed column data are equally compatible with the squalene corrected data, but for the solutes dimethyl sulfoxide, dimethylformamide and dimethylacetamide the packed column data are in much better accord with the corrected data than are the capillary column data. It is further shown that both sets of results at 25 degrees C for carboxylic acids are in error, owing to dimerization. Retention volumes on Chromosorb G AW DMCS are reported at 25 and at 93 degrees C. It is shown that at 25 degrees C, there could be some contribution to solute retention from adsorption on the support, but that this is almost impossible at 93 degrees C.

Abstract  The inverse secondary equilibrium isotope effects of Rh(I)-C2H4 and Rh(I)-C2H3D were directly measured using a gas chromatographic column of dicarbonyl-rhodium(I)-3-trifluoroacetyl-1R-camphorate in squalane solution at 283-333 K. Statistical isotope effects were also obtained from a reduced partition function using harmonic vibrational frequencies of RHC-C2H, complexes and normal-mode analysis. The observed isotope effects were in good agreement with those deduced from the reduced partition function. Thermodynamic data of the inverse isotope effect were DELTA(D.H)-DELTA-H = - 469 +/- 12 J mol -1 and DELTA(D.H)DELTA-S = - 0.975 +/- 0.017 J mol -1 K -1, where DELTA(D,H)-DELTA-H = DELTA-H(D) - DELTA-H(H) = the difference of the enthalpy changes of the deuterated and non-deuterated compounds (see refs. 1 and 22) and DELTA(D.H)-DELTA-S = DELTA-S(D) - DELTA-S(H) = the difference of the entropy changes of the deuterated and non-deuterated compounds. The detailed analysis of the force constant most affected, F(C-C) = 8.39 mdyn/angstrom, by metal complexation was closer to that of the carbon-carbon double bond (9.1 mdyn/angstrom) than to that of the carbon-carbon single bond (4.3 mdyn/angstrom).

Abstract  Oxygen diffusion in low temperature squalane glasses was studied by phenanthrene phosphorescence quenching and anthracene fluorescence quenching in geminate pairs (anthracene...O-2). The oxygen mobility can be described by continuous diffusion. Anthracene fluorescence quenching in geminate pairs allow to measure diffusion coefficients till 10(-23) cm(2)/s.

Abstract  The reaction kinetics of the three-phase CO2 methanation for a commercial Ni/SiO2 catalyst suspended in a liquid phase is studied in a continuous stirred-tank slurry reactor at a CO2 partial pressure of 1 bar and temperatures from 220 degrees C to 320 degrees C. By applying different liquids, namely squalane, octadecane, and dibenzyltoluene, showing different gas solubilities, it is found that the gas concentration in the liquid phase and not the partial pressure in the gas phase is the driving force for the CO2 methanation reaction kinetics. The liquid phase does not influence the reaction kinetics but reduces the available gas concentrations and H-2/CO2 ratio on the catalyst surface. Based on these findings, a kinetic rate equation for the three-phase CO2 methanation is developed additionally incorporating the chemical equilibrium limitations relevant in the temperature regime.

Abstract  The small amounts of chlorine dioxide that are routinely supplemented to drinking water as a disinfectant also cause a degradation of the polyolefin pipes that are used for distribution of the water. Commonly used phenolic antioxidants can extend the service life of the polymer but the expected lifetime is still much shorter than desired (50 years) due to depletion of the antioxidant in the surface zone exposed to the aqueous solution. In search for better stabilizers for the pipes, we have tested an organotellurium compound, 4-(N,N-dimethylamino)phenyl 3-phenoxypropyl telluride (1), as well as its corresponding selenium and sulphur analogues and a series of organotellurium compounds where the electron density at the heteroatom was varied. Stabilizers were dissolved in squalane, which is a liquid hydrocarbon that could serve as a model for a polyolefin. The oxidation induction time (OIT), determined after exposure of the squalane solution to an aqueous solution of 10 ppm of chlorine dioxide for various times was determined by DSC to indicate the loss of antioxidant protection. Whereas Irganox 1010 was only effective as a stabilizer for a few hours, many of the organochalcogen compounds were considerably more resistant (>91 h for compound 1) towards chlorine dioxide.

Thermogravimetric analyses of antioxidants indicated insignificant decomposition below 200 degrees C and increasing stability for the lighter chalcogen compounds (telluride < selenide < sulfide). Among organotelluriums, stability increases with increasing electron density at the heteroatom. Oxidation potentials of stabilizers as determined by cyclic voltammetry correlated fairly well with their protective effect in squalane (OIT-values). We therefore hypothesize that these compounds act primarily as electron donors towards peroxyl radicals. As determined by Te-125 NMR-spectroscopy, organotellurium compound 1 in the presence of an excess of chlorine dioxide failed to produce an oxidation product. This may be the clue to its long-lasting protective effect in the squalane-assay. (C) 2015 Elsevier Ltd. All rights reserved.

Abstract  Within this work, UV-initiated interaction mechanisms between the phenolic antioxidant Irganox 1330 and nine commercially used hindered amine light stabilizers (HALS) were successfully studied using high-performance liquid chromatography (HPLC) coupled to UV and high-resolution mass spectrometric detection (MS). An analytical evaluation of the stabilizer performances in the polypropylene-mimicking solvent squalane revealed that all investigated HALS exhibited a strong synergism when combined with the phenolic antioxidant. Up to now, the synergistic interaction was described as a result of the hydrogen transfer from a hydroxylamine derived from HALS to the oxidized form of a primary antioxidant, whereby the phenol is regenerated. Investigations on degradation products, however, indicated that the proposed interaction mechanism cannot be applied to a sterically hindered phenol such as Irganox 1330. Instead, a completely new stabilization mechanism of phenolic antioxidants in the presence of HALS, involving the formation of quinoid derivatives, was discovered and confirmed by using a model compound. (C) 2016 Elsevier Ltd. All rights reserved.

Abstract  Previously single wavelength ellipsometry has been successfully used to study the spreading of liquid polymer microdroplets on solid substrates. Extending that experimental approach, we present in this study the first experiments of spatially resolved spectroscopic ellipsometry applied to the spreading of layered microdroplets and show that it is possible to recover the experimental thickness profiles of polydimethylsiloxane and squalane on hydrophilic silicon wafers. To complement these molecular measurements, we also present new computer simulation results concerning the velocity field and the mass transfer during this spreading process. These results are in agreement with the predictions of the de Gennes-Cazabat model. (C) 1998 Elsevier Science S.A.

Abstract  The solubilities of three low-volatile liquids were measured in supercritical and liquid carbon dioxide at 7-28 MPa and 296-333 K. Solutes of different polarities were selected, namely non-polar squalane, polar glycerol, and dinonyl phthalate of medium polarity. Dynamic method of measurement with gravimetrically determined amount of the extracted solute was applied. The solubilities were correlated with density of pure carbon dioxide, using the Adachi-Lu equation. The equation represents the experimental solubilities with relative standard deviation 2-3%. (C) 1997 Elsevier Science B.V.

Abstract  A new experimental approach to the study of collisions of hydroxyl radicals with liquid surfaces is described, incorporating a molecular-beam source of OH (or, in practice, OD, for technical reasons) radicals. This allowed the collision-energy dependence of the scattering to be examined. The incident and scattered OD molecules were detected by laser-induced fluorescence. The representative branched, long-chain alkane, squalane (2,6,10,15,19,23-hexamethyltetracosane), and its partially unsaturated analogue, squalene (2,6,10,15,19,23-hexamethyl-2,6,10,14,18,22-tetracosahexaene), were compared with perfluoropolyether as an inert reference liquid. Dynamical aspects of the scattering necessary to quantify the OD survival probability, and hence its complement, the reactive sticking coefficient, were determined. Results were obtained at average laboratory-frame kinetic energies of 7.2 and 29.5 kJ mol(-1); they are compared with previous independent measurements using a photolytic source of OH with an average kinetic energy of 54 kJ mol(-1). At lower collision energies, the survival probability is significantly lower on squalene than on squalane but increases significantly with collision energy. This is consistent with a negatively activated contribution to loss of hydroxyl through addition to double-bond sites at the squalene surface. In contrast, survival on squalane surface is found to be approximately independent of collision energy across the range examined. This is surprising because it does not reflect the positively activated behavior typical of gas-phase OH + alkane reactions. We suggest that this may be explained by a higher probability of trapping dynamics at lower collision energies, enhancing the probability of reaction following migration to more reactive sites. The results have implications for the modeling of OH uptake on atmospheric aerosol surfaces as a function of chemical composition and temperature.

Abstract  The dynamics of oxygen-atom scattering from the surfaces of a series of room-temperature ionic liquids containing the 1-alkyl-3-methylimidazolium cation [C(n)mim] and the tetrafluoroborate anion [BF4] were studied by reactive-atom scattering with mass spectrometric detection of products (RAS-MS). The length of the alkyl chain was varied (n = 4, 8, 12) in order to investigate the relationship between the scattering dynamics and the density of alkyl chains on the surface and their ordering. RAS-MS uses a beam-surface scattering technique with a hyperthermal O atom beam source and a rotatable mass spectrometer detector. Time-of-flight and angular distributions were collected for inelastically scattered 0 and reactively scattered OH and H2O, enabling product flux distributions to be obtained as a function of final translational energy and scattering angle, P(E-T,theta(f)). A new analysis technique was used to separate these distributions into three distinct components, corresponding to three dynamical pathways for scattered products: fast and slow impulsive scattering and thermal desorption. The results of these experiments support previous findings that surface alkyl coverage increases with increasing alkyl chain length, but these dynamical studies provide the additional insight that the ionic liquids with alkyl chains of n = 8, 12 have smoother surfaces than the ionic liquid with n = 4 and the pure alkane liquid, squalane (2,6,10,15,19,23-hexamethyltetracosane).

Abstract  In this paper we present an extension of the statistical associating fluid theory (SAFT) for branched molecules with a Lennard-Jones dimer reference fluid (SAFTD-LJ-Branch). The theory successfully predicts how branched architecture affects the attraction and repulsion between molecules. SAFTD-LJ-Branch takes a form similar to SAFTD-LJ with an additional parameter NB introduced to account for the branching effect. We propose an approach relating NB to the number of different types of articulation segments. The theory is used to study the effect of chain architecture on the thermodynamic properties of isomeric alkanes. SAFTD-LJ-Branch accurately predicts the phase diagram of pure butane, pentane or hexane isomers. Further, vapor pressures of n-triacontane and squalane are predicted without further fitting and shown to be in semiquantitative agreement with experimental data. Finally, SAFTD-LJ-Branch is demonstrated to be well applicable to mixtures as we model the vapor-liquid coexistence of binary alkane mixtures containing different hexane isomers and recover the experimental trends.

Abstract  A simple theoretical-based correlation of the ratio of the critical temperature to the critical pressure (T-c/p(c)) as a function of the van der Waals surface area (Q,) has been previously developed based on an extensive database of critical data published prior to 1996. The final equation was the following: T-c/p(c) = 9.0673 + 0.43309(Q(w)(1.3) + Q(w)(1.95)) where T-c is the critical temperature in kelvin and p(c) is the critical pressure in bar. This correlation is further validated here based on recent experimental data for various families of organic compounds, including some heavy ones (mono- and diacids, alkenes, cyclo/phenylalkanes, and squalane). This and previous validations verify that this correlation has a much broader application range, up to (T-c/p(c)) ratios of 200, than the data used in its development (compounds with ratios up to 100). it seems that most organic compounds, including the very heavy and complex ones, follow the trend suggested by this equation. This equation can be used for testing existing group-contribution estimation methods. It is shown here that direct comparison of the Joback and Constantinou-Gani methods for two families of compounds (alkenes and carboxylic acids) is in agreement with their validation via the proposed equation. Similar results have been obtained for other compounds. Both group-contribution methods are of equal accuracy for heavy alkenes and acids, provided that experimental boiling point temperatures are available for the Joback method. If such data are not available, e.g., for heavy compounds, the Constantinou-Gani method should be preferred. The proposed correlation does not offer an alternative to group-contribution methods as it only provides a single relationship of the two critical properties. Its universal character, though, and validation for many heavy compounds offer a way to test and compare existing group-contribution methods and, finally, to select the one that best conforms with the proposed correlation. It is recommended that the proposed correlation is indeed used for high molecular weight compounds for which experimental critical properties are typically not available.

Abstract  Vapor and liquid equilibrium compositions have been measured for the hexane + hexadecane and the hexane + 1-hexadecanol systems at temperatures from 472.0 K to 623.0 K and pressures from 6.2 bar to 46.4 bar. A continuous-flow apparatus was used both to minimize possible thermal degradation and to accurately measure the lower hexadecanol concentrations in the vapor phase. Mixture critical pressures and compositions were also measured. Results indicate that the addition of the hydroxyl group to the C-16 hydrocarbon backbone significantly affects the phase behavior with hexane.