Lattice dynamics of carbon chain inside a carbon nanotube

Based on the density functional theory, we obtain the optimum geometry of carbon chain inside a carbon nanotube. The phonon spectrum and specific heat of such a chain and nanotube hybrid system are calculated in terms of lattice dynamics theory. Some new phonon branches that have been obtained come from the coupling vibrations of the nanotube and the chain. The bending and stretching modes of the chain appear at about 520 cm(-1)and 1935 cm(-1) at Gamma point, respectively. It is found that the softening of G modes results mainly from the chain induced variations in the bond length on nanotube, independent of van der Waals interaction, while the stiffening of radial breathing mode is developed by the competition between the two factors. In the low-frequency region, the vibrational density of states are very different from that of the bare nanotube. Its specific heat implies the underlying quantized phonon structures and much large thermal conductivity in the hybrid system. In addition, the chain-length dependent vibration modes are calculated, from which it is expected that a finite chain of about 14 carbon atoms in the nanotube may produce the experimental Raman peak at about 1850 cm(-1).     

Photo-oxidation of polymers—I: A quantitative study of the chemical reactions resulting from irradiation of polystyrene at 253.7 nm in the presence of oxygen

The photo-oxidation of polystyrene irradiated at 253.7 nm at a pressure of 600 Torr oxygen has been studied quantitatively. Quantum yields have been measured for most chemical reactions observed. It has thus been shown that only about 4% of the oxygen absorbed ultimately results in chain scissions. These occur with formation of an acetophenone-type end-group and an unsaturated chain-end simultaneously. Unsaturated chain-ends are then starting points for the building of sequences of conjugated double bonds (polyenes). About 30% of the absorbed oxygen is transformed into carbon dioxide without any permanent chain scission. Since energy is absorbed almost exclusively by the phenyl chromophores of the polymer, most of the observed reactions occur only because of energy transfer to photo-reactive products.     

Physico-chemical transformations in swift heavy ion modified poly(ethyleneterephthalate)

Thin films of poly(ethyleneterephthalate) (PET) were exposed to different radiation dose brought about by 80 MeV carbon and 98 MeV silicon ion beam. The UV-vis absorption studies reveal that there is decrease in optical band gap energy to the extent of ∼29.3 and 42.1%. The X-ray diffraction analyses have shown that crystallite size decreased by ∼18.6 and 52.6%, indicating amorphization of PET. The colour of PET films change from colourless to light yellowish followed by light brown as radiation dose is increased. The colour formation has been ascribed to an increase in conjugation in the carbon chain. In the case of PET irradiated with carbon ion, the electrical conductivity increased with frequency beyond a threshold value of 1 kHz. The increase in conductivity of PET films on irradiation is due to formation of defects and carbon clusters as a result of polymer chain scission. The thermal study further confirmed the increase in amorphous nature with increase in radiation dose. The results indicate that radiation dose brings about significant physicochemical transformations in PET.     

Membrane disordering induced by chloroform and carbon tetrachloride

We studied effects of chloroform and carbon tetrachloride on bilayer membranes of dimyristoyl-phosphatidylcholine (DMPC) and egg yolk phosphatidylcholine (Egg-PC) by birefringence, dynamic light scattering and fluorescence methods. It is shown that interference light due to the membrane birefringence considerably decreases by addition of the organohalogen compounds for both lipid membranes, indicating a significant decrease in membrane order. In addition, results of dynamic light scattering and turbidity measurements show a rupture of multilamellar DMPC vesicles induced by addition of chloroform at concentrations above 0.2 v/v%. No rupture of the vesicles is observed within the limit of solubility of carbon tetrachloride in water, but excessive addition of carbon tetrachloride (above 0.2 v/v%) induces the vesicle rupture. Chain orientational order was estimated from the interference light intensity at low concentrations of the organohalogen compounds without the occurrence of the vesicle rupture. The estimation shows a monotonic decrease in the chain order with increasing the concentration. The decreases in DMPC chain order by chloroform and by carbon tetrachloride are about 17% at 0.2 v/v% and 23% at 0.05 v/v%, respectively. The reduction in the chain order is correlated with an increase in the membrane fluidity observed by excimer fluorescence of pyrene incorporated to the membrane. Behavior of membrane disordering of Egg-PC is approximately similar with that of DMPC. This implies the strong interaction between the organohalogen compounds and the lipid chains, whether or not the bilayer has the vacancy resulted from unsaturated double bonds and different chains in length. The results of this work suggest that damages of biological membranes by chloroform and tetrachloride are not only induced by a direct attack on proteins but also by a significant membrane disorder.     

固体渗硼提高多孔炭抗氧化性能的研究

空气中多孔炭在高温下极易被氧化,极大地限制了其在催化领域的应用。为了提高多孔炭在高温下的抗氧化能力,以KOH化学活化法制备的多孔炭为原料,通过固体渗硼对多孔炭进行热处理。结果表明,渗硼后多孔炭表面的活性点数量明显减少,抑制了氧化性气体与多孔炭的反应,从而提高了多孔炭的抗氧化能力。并且渗剂在多孔炭中的质量分数为10%、渗剂中B4C的质量分数为25%、热处理5h时,与多孔炭原料相比,渗硼后600℃多孔炭氧化失重率由70%左右降低到20%左右,比表面积降低10%～20%,多孔炭材料的微反活性仍可达到70.25。     

Carbon-13 NMR spectra of DDT,its analogues and related compounds

Carbon-13 NMR spectra of mono- and disubstituted aromatic compounds including DDT, its analogues, homologues, derivatives and certain model compounds have been studied. The Savitsky scheme of carbon chemical shifts in disubstituted benzenes is applicable to these compounds. The data obtained show that in mono- and disubstituted aromatic compounds containing two different substituents in the α- and β-positions of the side chain, the substituted ring carbon atom shifts follow the additivity rule and can be calculated from substituent increments. Mutual effects of substituents in the ring and in the side chains are analysed. The chlorine atoms in α-position to the phenyl ring give rise to an additive α-effect of about 25 ppm, as in perchloroalkanes. The influence of a β-chlorine atom in the side chain on the substituted carbon atom in the ring is, however, only 3 ppm as against the usual value of about 10 ppm for the β-effect in alkyl chains. Moreover, the first β-chlorine substituent has no noticeable influence on the substituted ring carbon chemical shift: the effect of 3 ppm is transferred to the para-carbon atom almost without attenuation. The ring substituted carbon atom signal shifts caused by the γ-effect of chlorine in the side chain are similar to those observed in aliphatic chains. The ortho-chlorine substituents shift the side chain α-carbon atom signal by 3.6-5.2 ppm to high field compared to para-chlorophenyl compounds. This is similar to the chlorine γ-effect in aliphatic chains.     

CATALYTIC CRACKING OF LIGHT ALKANES IN THE PRESENCE OF O_2 AND SELECTIVE CONTROL OF OLEFIN PRODUCTS

lntroductionThesmallolefinslikeethylene,propeneandbutenearethec0mmerciallydesirablepetrochemicalfeedstocksandarefoundincreasingusageinchemicalindustry.Theyareusuallyobtainedfromthepyrolysis0fpetroleumhydrocarb0nswithsteaInatveryhightemPeratUreandarealsoavailablefromFCCprocess.TheimProvedFCCcatalystforeIhancingtheolefinproducthasbeenreportedll].However,FCCisalrnostimPossiblefortheshortchainalkanefeedstockscutfrompetroleum0robtuinedfromrefinerygasornatUralgassincecrackingofhydrocarbonsbeco…     

Theoretical study on the spin-state energy splittings and local spin in cationic [Re]-Cn-[Re] complexes

Total spin-state energy splittings are calculated for mono- and dications of the formula {[Re]-Cn-[Re]}z+ where [Re] = eta5-(C5Me5)Re(NO)(PPh3). Cn is an even-numbered carbon chain with n ranging from 4 to 20, and z is 1 or 2. These complexes are experimentally known, and their potential role as molecular electronic devices initiated this work. We have considered the different total spin states monocation/doublet, monocation/quartet, dication/singlet, and dication/triplet. Data obtained for two density functionals BP86 and B3LYP were compared to verify the internal consistency of the results. In both ionization states, the low-spin state is the ground state, but the spin-state splittings decrease as the chain gets longer. For the dications, the splitting reaches a nearly constant value of about 10 kJ/mol with BP86 and about 4 kJ/mol with B3LYP when there are at least 14 carbon atoms in the chain, whereas for the monocations, no constant value appears to be reached asymptotically, not even if 20 carbon atoms are in the chain. For monocations, the splittings range from 138 kJ/mol (n = 4) to 68 kJ/mol (n = 20) with BP86 and from 134 kJ/mol (n = 4) to 73 kJ/mol (n = 20) with B3LYP and are thus considerably higher than those of the dications. The spin-state splittings are qualitatively mirrored by the energy splitting between the highest-occupied molecular orbital with beta spin (HOMObeta) and the lowest-unoccupied molecular orbital with alpha spin (LUMOalpha) as obtained in the low-spin state. Furthermore, the HOMOalpha-LUMOalpha gaps decrease as the carbon chain lengthens. In addition, the local distribution of the ?z expectation value is analyzed for the monocation/doublet, the monocation/quartet, and the dication/triplet state using a modified L?wdin partitioning scheme. In the monocation/doublet and the dication/triplet state, the electron spin is distributed mainly on the metal centers and slightly delocalized onto the carbon chain. In the monocation/quartet state for chain lengths of more than 8 carbon atoms, the electron spin is mainly localized on selected atoms of the chain and not on the metal centers. In all cases, the spin delocalization onto the chain increases as the chain gets longer.     

Effects of carbon nanotubes on polymer physics

A single carbon nanotube has many similarities with an individual polymer chain including the fact that the end‐to‐end length of both are often about the same and the diameter of the chain is about the same (for single‐walled nanotubes) or only ～10 to 20 times larger (for multiwalled nanotubes). The combination of the solid surface and the similarity of the two materials means that polymer physics are altered in manners not seen with any other type of commonly used filler. The purpose of this review is to update a chapter that appears in a recent tome by Grady (2011) and describe how polymer physics is altered in composites that contain carbon nanotubes. Subjects that will be discussed include chain configuration, glass transition, polymer diffusion, unit cells and crystalline superstructure (lamellae, spherulites and shish‐kebabs), and crystallization kinetics. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Conformational order of n-alkyl modified silica gels as evaluated by Fourier transform infrared spectroscopy

The conformational behaviour of non-deuterated and selectively deuterated alkyl modified silica gels in the dry state is examined by variable temperature FT IR spectroscopy. In the present study, three systems are considered, which are distinguished by the length of the tethered alkyl chains (C9Hl9-, C18H37-, C22H45-). The desired information is obtained by the analysis of various conformational-sensitive IR bands, including CH2 wagging, CD2 stretching and CD2 rocking bands. The analysis of the CH2 wagging bands provides the relative amounts (i.e., integral numbers over the whole chain) of the kink/gauche-trans-gauche, double-gauche and end-gauche conformers in the tethered alkyl chains. From the analysis of the CD2 stretching and CD2 rocking bands information about the conformational order at a specific deuterated methylene segment is available. Here, the CD2 rocking band data are used to determine the amount of gauche conformers at the deuterated carbon positions C-4 and C-6, and C-12. It is found that the conformational order critically depends on the actual alkyl chain length, chain position and sample temperature. Particular emphasis is given to the impact of the external pressure during sample preparation on the alkyl chain conformations, about which so far no information is available. It is observed that the samples prepared as KBr pellets, which experienced a pressure of about 10 kbar, are characterised by a lower amount of gauche conformers. This substantial increase of conformational order is attributed to better alkyl chain packing along with a gain of intermolecular chain interactions.     

不同链长正构烷烃在Pt/SAPO-11催化剂上的临氢转化规律研究

采用SAPO-11分子筛制备的双功能催化剂,以碳链长度为10-14的正构烷烃为模型化合物,探索了不同碳数的长链正构烷烃临氢转化反应规律。结果表明,低温下不同碳数的正构烃都表现出较高的异构化选择性,改变反应温度使反应转化率控制在85%以下时,正构烷烃的异构化选择性可以达到90%左右;随着碳数和温度升高,正构烷烃由于发生明显的裂化反应导致转化率提高和异构化选择性降低。采用SAPO-11分子筛催化材料的双功能催化剂具有明显的产物择形异构效应,异构化产物以甲基位于端位和碳链中心的单侧链异构体为主,双(多)支链产物较少。长链正构烷烃在Pt/SAPO-11催化剂上的裂化反应在低转化率以加氢裂化为主,裂化产物的碳数呈均匀分布;在高转化率下以酸催化裂化为主,裂化产物的碳数分布呈现明显的不对称分布特征。     

The kinetics of tobacco pyrolysis

When tobacco is pyrolysed under non-isothermal flow conditions in an inert atmosphere, variation of the inert gas or its space velocity has only a minor effect on the profiles of formation rate versus temperature for seven product gases. Thus, mass transfer processes between the tobacco surface and the gas phase are very rapid, and the products are formed at an overall rate which is determined entirely by that of the chemical reactions.The effect of radical chain inhibitors (nitrogen oxides) on the pyrolysis is complex because of the resultant oxidation. Nevertheless, no evidence was found for the occurrence of radical chain reactions in the gas phase. A small proportion (less than 10%) of all the gases monitored are formed by homogeneous decomposition of volatile and semi-volatile intermediate products, in the furnace used.At temperatures above about 600°C the reduction of carbon dioxide to carbon monoxide by the carbonaceous tobacco residue becomes increasingly important. However, when tobacco is pyrolysed in an inert atmosphere, only a small amount of carbon dioxide is produced above 600°C and consequently its reduction to carbon monoxide contributes only a small proportion to the total carbon monoxide formed above that temperature. The rate of the tobacco/carbon dioxide reaction is controlled by chemical kinetic rather than mass transfer effects. Carbon monoxide reacts with tobacco to a small extent.When the tobacco is pyrolysed in an atmosphere containing oxygen (9–21% v/v), some oxidation occurs at 200°C. At 250°C the combustion rate is controlled jointly by both kinetic and mass transfer processes, but mass transfer of oxygen in the gas phase becomes increasingly important as the temperature is increased, and it is dominant above 400°C. About 8% of the total carbon monoxide formed by combustion is lost by its further oxidation.The results imply that inside the combustion coal of a burning cigarette the actual reactions occurring are of secondary importance, the rate of supply of oxygen being the dominant factor in determining the combustion rate and heat generation. In contrast, in the region immediately behind the coal, where a large proportion of the products which enter mainstream smoke are formed by thermal decomposition of tobacco constituents, the chemistry of the tobacco substrate is critical, since the decomposition kinetics are controlled by chemical rather than mass transfer effects. tobacco substrate is critical. In addition, the heat release or absorption due to the pyrolytic reactions occurring behind the coal will depend on the chemical composition of the substrate. Thus, together with the differing thermal properties of the tobacco, the temperature gradient behind the coal should depend on the nature of the tobacco.     

Enantiomeric separation of 5-alkyl-5methylhydantion derivatives by capillary gas chromatography on permethylated β-cyclodextrin and molecular modeling

Permethylated β-cyclodextrin (hereafter designated perMe-β-CD), dililuted or not in polysiloxane, is an efficient chiral discriminant for native, 3-methylated, and 1,3-dimethylated series of 5-methyl-5-(C_nH_{2n + 1})hydantoins. From thermodynamic data obtained with pure perMe-β-CD and with the aid of molecular modeling, it is concluded that: (i) For native hydantoin derivatives having a carbon chain at the 5-position varying from ethyl to nonyl (2?n?9), the retention time is related to their H-bonding capability. The resolution is poor for derivatives with n?4. For n?5, the resolution is considerably improved and this increase in resolution is attributed to the long alkyl chain being capable of being buried inside the cyclodextrin cavity. (ii) For 1,3-dimethylhydantion derivatives having a carbon chain at the 5-position varying from ethyl to hexyl(2?n?6), the retention time is mainly determined by a steric fit between the solute and the inner volume of the macrocyclic cavity. For n = 2, a particular behavior is observed, consistent with a total inclusion of the solutes inside the cavity. By contrast with the native hydantoins, the selectively is high for light derivatives. Thus, the selectivity does not correlate with a strong docking energy (such as the presence of H-bonds postulated with native derivatives). (iii) For 3-methylhydantoin derivatives having a carbon chain at the 5-position varying from ethyl to octyl (2?n?8), as expected, retension time and selectivity are intermediate between that of native hydantoins and 1,3-dimethylhydantoins. For all three series, where n?5, the increase in chain length (n) does not bring about substantial changes in the chromatographic results. Therefore, for these long alkyl chain derivatives, similar dominant interactions with perMe-β-CD are postulated.     

Prediction of gas chromatographic retention times of esters of long chain alcohols and fatty acids

The linear free energy of solution (DeltaG) relationship (DeltaG=DeltaGo+zdeltaG) for compounds of different carbon atoms (z) in the same homologous series is expanded and modified to cover compounds with two different hydrocarbon side chains. The expanded equation is successfully used to predict the retention times (tR) of standard esters of long chain alcohols and fatty acids of different chain lengths in both isothermal and temperature-programmed gas chromatography (TPGC). Approximately 90% of the 125 predicted tR values have a difference of less than 1.00% from the actual tR and the highest difference is 1.26%. Two different temperature gradients in TPGC are tested. The expanded equation can be used to forecast the tR of TPGC with good accuracy. The highest difference is +/-1.40% and +/-1.00% for the temperature gradients of 2 degrees C and 4 degrees C/min, respectively. However, the increments in free energy per carbon atom (zdeltaG) of the alcohol and acid are approximately equal but have slightly different temperature sensitivities. Therefore, it is very difficult to separate esters of different acid and alcohol chain length but with the same total carbon numbers. Furthermore, the difference in temperature sensitivities for the acid and alcohol side chains renders them to be inversely eluted at different temperatures.     

Stability and properties of oligomeric organoboron structures with six-coordinate carbon atoms at centers of hydrocarbon frameworks

Quantum chemical B3LYP/6-311G** calculations revealed that oligomers of a system containing a six-coordinate carbon atom at the center of a carbon framework composed of three 3,6-diboracyclohexa-1,4-diene rings annelated at double bonds remain energetically stable as the number of monomer units increases up to four. All oligomers have triplet ground states, the singlet states lying about 20 kcal mol^?1 higher in energy. Similar systems with B-B groups replaced by unsaturated (C=C) and saturated (HC-CH) hydrocarbon fragments lose their stability as the length of the oligomer chain increases.     

Partial phase behavior and micellar properties of tetrabutylammonium salts of fatty acids: unusual solubility in water and formation of unexpectedly small micelles

The tetrabutylammonium (TBA) salts of fatty acids, from dodecanoic acid (C12) to octacosanoic acid (C28), have been prepared by direct neutralization of the fatty acid by TBA hydroxide. Unexpectedly, all of these surfactants have been found to be soluble in water under the form of micelles at a sufficiently high temperature. For instance, the solubility of TBA octacosanoate in water is of about 7 wt % at 46 degrees C. Starting from TBA docosanoate, the aqueous solutions of the surfactants gelled below a certain temperature. The gelling temperature increased linearly with the fatty acid carbon number. Upon increasing temperature, the TBA octocosanoate showed a relatively complex phase behavior that has been investigated. The micellar solutions of these surfactants did not cloud at high temperatures, up to 98 degrees C, contrary to TBA alkylsulfates. The aggregation numbers of micelles of the various TBA alkylcarboxylates have been measured and found to be smaller than those for the maximum spherical micelle that a surfactant with the same alkyl chain length can form. The micelle micropolarity and microviscosity (as sensed by fluorescent probes) decreased and increased, respectively, with the fatty acid carbon number.     

有机相中蚕丝固定化脂肪酶催化酯化反应性能研究

研究了有机相中蚕丝固定化脂肪酶催化酶化反应的催化活性。考究了有机溶剂,底物、反应温度,ＰＨ值和体系含水量等因素对固定化脂肪酶催化活性的影响。结果表明,以异辛烷为有机溶剂,在反应温度为５０℃ＰＨ值为７．４时,酶催化活性最好。     

Polymerization of vinyl chloride in the presence of modified Ziegler–Natta catalysts comprising long chain organoaluminum compounds

Polymerization of vinyl chloride in the presence of systems containing a transition metal compound/Lewis base and an organoaluminum compound of a different length of carbon chain have been carried out. The influence of the structure and the concentrations of particular components on the polymerization yield and molecular weight of the products has been determined. The polymerization of vinyl chloride proceeds according to the free radical mechanism, and the effectiveness of such types of initiators decreases with an increase in the length of the substituent chain in the organoaluminum chain. When using ethyl derivatives, the maximum degree of vinyl chloride conversion is about 75%, and for polystyryl or polyisoprenylaluminum of an average polymerization degree of 50–100, the conversion did not exceed 0.5%. The maximum polymerization degree of vinyl chloride in block copolymers containing polyisoprenyl or polystyryl units was 90–300.     

Changes in the mechanical properties of compression moulded samples of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) degraded by Streptomyces omiyaensis SSM 5670

Streptomyces omiyaensis SSM 5670 was characterized by its ability to use compression moulded samples of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as its sole carbon source. Biodegradation of PHBV in liquid mineral salts medium was investigated using scanning electron microscopy, gravimetric measurements, capillary viscometry, tensile testing and wide angle X-ray spectroscopy. The biodegradation of PHBV proceeds via surface erosion mechanism, resulting in the formation of pits by microbial attack. PHBV specimens lost about 45% of their original weight after 45 days of exposure. During the degradation process the elastic modulus reduces less than 10%. The formation of pores and microcracks initiated at the degraded pits determines the reduction of the elongation and stress at break. However, the true stress at break is practically independent of the degradation time. No significant changes of PHBV molecular weight or crystallinity were observed during biodegradation. The polymer chain cleavage occurred only at the specimen surface and does not discriminate between crystalline and amorphous states.     

Diffusion of small molecules through modified poly(vinyl chloride) membranes

The transport properties of a set of four copolymers based on poly(vinyl chloride) (PVC) have been studied. The nucleophilic substitution of chlorine atoms with 4‐mercaptophenol sodium salt, 2‐thionaphthalene, 4‐(1‐adamantyl) thiophenol, and thiophenolate sodium salt as the nucleophiles has been performed, from low conversion levels (3%) to high levels (40%), and the permeability, solubility, and diffusivity of oxygen, nitrogen, carbon dioxide, and methane have been measured. The introduction of bulky groups to the PVC chain leads to chain separation and results in large increases in the free volume at conversions up to 10%. This brings about a 5‐fold increase in the diffusion coefficients that is almost independent of the bulkiness of the substituent. Solubility is little affected and instead tends to decrease as substitution progresses. The substitution of more than 10% of the chlorine atoms does not result in an improvement in the transport properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 964–971, 2002