Comparison of Solid-Liquid and Liquid-Liquid Mass Transfer

Abstract

Mass transfer from solutions of m-acetotoluide, phenacetin and salicylamide into a stationary solvent, water, was studied. A sharp concentration jump was found at the leading solute front for all three liquid-liquid systmes. A comparison was made between the mass transferred in solid-liquid and liquid-liquid systems. The dissolution of m-acetotoluide, phenacetin and salicylamide was compared with mass transfer of solute from solutions with concentrations C_i, 2C_i and C_s into the pure solvent. In all cases, the amount dissolved from the solid was approximated by the C_i or the 2C_i-solvent system with the amount transferred in the C_s-solvent system approximately 100 fold greater than was dissolved from the solid. It was concluded that a concentration much less than saturation exists at the solid-liquid interface and that dissolution of the three compounds studied is controlled by the rate of solvent interaction at the solid surface.     

Solubility of Fullerenes C60 and C70 in Seven Normal Alcohols and Their Deduced Solubility in Water

Abstract

The solubilities of C₆₀ and C₇₀ at 25°C in seven normal alcohols obey the relationship InY = a + bX + cX², where Y is solubility and X is the Hildebrand solubility parameter of the solvent. Extrapolation to the solubility parameter of water yields solubilities in water of 1.3′10^?11 (C₆₀) and 1.3′10^?10(C₇₀) ng/ml with an uncertainty of one order of magnitude.     

Effects of Intense Ultrasound Treatment of C60 Solutions

Abstract

C₆₀ was treated at room temperature, in air with intense ultrasound in the following solvents; decalin, tetralin. cyclohexane and CCl₄. It is shown by UV-VIS and FT-IR spectroscopy that in decalin and in tetralin the dominant reaction seems to be a sono-oxidation, although more complex reactions involving the solvent take place. In CC1₄ sono-oxidation is accompanied by an extensive sono-polymerization. Products in CCl₄ are C₆₀O, C₆₀O₂ and others; the sonopolymer collected from sonicated CCl₄ was easily identified by FT-IR spectroscopy. Sonopolymerization occurs also in decalin and tetralin and is promoted by free radicals as in the case of CCl₄. No reactions are observed in cyclohexane due to the very low solubility of C₆₀ in this solvent and the poor cavitation ability of cyclohexane under the action of ultrasound.     

Electrochemical Doping of Tetramethylammonium Ions into C60 Film

Abstract

The electrochemical properties of C₆₀ films were studied by cyclic voltammetry and electrochemical quartz crystal microbalance technique in organic electrolyte solution. Tetramethylammonium perchlorate was used as a supporting electrolyte in acetonitrile solution. Thin films are prepared by solvent quickly evaporated method on a preheated glassy carbon electrode. The electrochemical response of C₆₀ films is consistent with a reduction mechanism that is dominated by ion transport to form contact ion pair. In the proposed mechanism, swelling of the film with solvent and intercalation of cations into the film proceed parallelly. The stability of the film with respect to successive redox cycles was also interpreted.     

Nonlinear Stern-Volmer Fluorescence Quenching of Pyrene by C60/70

Abstract

The Stern-Volmer plot of fluorescence quenching of pyrene by C₆₀ (or C₇₀) is upward, and non linearly proportional to the fullerene concentration. Electronic absorption measurements show that pyrene and C₆₀ do not form static complexes under the experimental condition. a novel “inner filter effect” model is proposed to rationalize the observed non linear upward Stern Volmer behavior. At a given C₆₀ concentration, increasing either solvent polarity or temperature (T > 280 K) causes diminishment in the I₀/I ratio. the data strongly suggest that even at concentrations far below saturation, fullerenes form aggregates in organic solvents.     

Esr Study of C60 N- Anion Radicals in DMSO Solution

Abstract

With the aim to stabilize reduced C₆₀ molecules of solid fulleride as free anion radicals in solution, Na_xC₆₀ (x=l, 10) was dissolved in DMSO. The Na_xC₆₀ was chosen among the other alkali-metal fullerides due to the possibility to increase a number of intercalated Na atoms in a fee. lattice of C₆₀ A sufficiently high concentration of C₆₀ anion radicals of an order of magnitude larger than that usually achieved in solution by an electrochemical reduction was obtained. The sharp resonances with the linewidths of order of 0.1 G and with g=2.0004(6) ?2.0012(8) of the room temperature ESR spectra of fluid solution were assigned from mono- to pentaanions of C₆₀. An appearance of additional sharp peaks at g=2.0016–2.0019 in the spectra of solution of nominal Na₁₀C₆₀, but Na₁C₆₀, tentatively related to C₆₀ ^n- with n>6. The results of this study showed a simple approach in an accomplishment of highly concentrated solutions of free anion radicals C₆₀ ^n-, as well as in stabilization of the anion radicals with increased n. In this way a homogeneity of alkali metal intercalation and characteristics of the solvent will be important.     

Bromination of [60]Fullerene. II. Crystal and Molecular Structure of [60]Fullerene Bromides,C60Br6, C60Br8, and C60Br24

Abstract

The crystal and molecular structures of the bromofullerene solvates C₆₀Br₆·0.5C₆H₅Cl·0.5Br₂, C₆₀Br₈·1.5(o‐C₆H₄Cl₂), C₆₀Br₈·Br₂, C₆₀Br₈·0.5C₆H₅Br·0.5Br₂, and C₆₀Br₂₄·2Br₂ have been determined by single crystal X‐ray diffraction. The molecular species C₆₀Br₆, C₆₀Br₈, and C₆₀Br₂₄ which have idealized C _s , C _2v  , and T _h symmetries, respectively, have several different types of C?Br and C?C bonds. A comparison between different solvates of the same bromofullerenes revealed a larger stability of the packing modes for the C₆₀Br₆ and C₆₀Br₂₄ solvates, whereas the C₆₀Br₈ solvates showed different packing motifs dependent on the nature and amount of the solvent molecules.     

Thermal Reactions of C60 with Siliranes: Carbosilylation and Silylene Addition of Fullerenes

Thermal reactions of C₆₀ with siliranes (1a, b) afforded carbosilylated C₆₀ derivatives. When a bicyclic fused silirane (1c) was employed instead of 1a and 1b, a silylene adduct and its hydrolyzed compound were obtained through thermal extrusion of silylenes from 1c. These products were determined to be 1,2-adducts at 6,6-junctions of C₆₀ by MS, UV, and NMR analyses. These results provide a complementary method to the photochemical addition of reactive silicon compounds, which have been long employed for silylation of C₆₀. Electrochemical analyses revealed the redox properties of the silylated products, indicating the perturbation caused by silyl groups introduced on the C₆₀ cage. Theoretical calculations were also conducted for understanding of the electronic property of the silylated product.     

Laser Photolysis Study on Mechanism and Efficiency of Electron Transfer Between Fullerenes (C60 and C70) and Tetraselenafulvalenes

Abstract

Efficient electron-transfer reactions from three kind of tetraselenafulvalenes (TSeF's) to photoexcited triplet state of C₆₀ or C₇₀ in polar solvents have been confirmed by transient absorption spectroscopy observing the decay of ³C₆₀*/³C₇₀* and rise of C₆₀ ^??/C₇₀ ^??. Growth of single crystal seems to be stimulated by laser irradiation of the solution containing C₆₀ and bis(ethylenedithio)tetraselena-fulvalene (BEDT-TSeF), in which C₆₀ ^?? was effectively formed.     

Dynamics and pattern formation in thermally induced phase separation of polymer–solvent system

In this paper, the characteristic dynamics and pattern formation of polymer–solvent system, undergoing thermal induced phase separation (spinodal decomposition), have been studied using non-linear simulations. The modified Cahn–Hilliard equation with the incorporation of the Flory–Huggins free energy model is used. The development of a wide variety of initial and intermediate stage morphology is feasible either by introducing sharp/continuous spatial temperature variation or by altering the initial mean solvent concentration (C_o) in the vicinity of the minima (C_m) of the spinodal parameter (second derivative of excess Gibbs free energy w.r.t concentration). For C_o < C_m initial stage of phase separation proceeds by the formation of columns/island of the solvent rich phase dispersed in polymer rich continuous phase. On the contrary, C_o > C_m, phase separation leads to formation of holes of polymer rich phase dispersed in the continuous solvent rich phase. For an intermediate mean concentration very close to C_m inter-connecting structures are evolved. A continuous variation of spatial temperature leads to the directional (rather than random) evolution of phase separated pattern. The initial stage of evolution always propagates from the lowest to the highest temperature regime. A spatial step variation of temperature leads to formation of localized novel phase separated patterns. For a flow system, the dynamics and pattern formation can be controlled by tuning the different timescales: timescale of convection, de-mixing and coalescence.     

Gelation theory for solutions of polymers with loci of strong interaction

This paper presents a statistical mechanical analysis of gelation in certain solutions ofA/B copolymers. Repeat unitsA, the major units, must constitute about 90 mole% or more of the copolymer, and are compatible with the solvent. Repeat unitsB, the minor units, must be totally incompatible with the solvent and represent loci of strong interaction between the macromolecular chains. If these interactions are sufficiently strong they can lead to gelation of the mixture. The following simplifications of the model afford results that can be expressed in simple, closed form: (1) TheB units are uniformly distributed along the chain backbone. (2) Polymer concentration must be greater then that for chain overlap. (3)B–B interactions lead to dimerization ofB units only. Examples include: (1) Any aqueous polymer solution where theA repeat units are hydrophilic and theB repeat units are hydrophobic;B–B interactions are thus by hydrophobic bonding. (2) Neutralized acrylic acid/acrylamide copolymers where theB are acrylamide repeat units which associate by hydrogen bonds. (3) Ionomer solutions whereB–B bonding is by dipole-dipole interaction. The results show that there is a critical copolymer concentration for gel formation, C _c . It turns out that C _c decreases withB content for low dimerization energies and increases withB content for higher dimerization energies. At intermediate dimerization energies, C _c is insensitive to theB content. The two extreme regimes of behavior are similar to contradictory predictions of previously published theories. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000     

Direct and Catalytic Hydrogenation of Buckminsterfullerene C60

Abstract

C₆₀H₁₈ was obtained by direct hydrogenation of C₆₀ at 400 C and 80 atm C₆₀ was hydrogenated to C₆₀H₃₆ as a main product in the presence of Pd/C catalyst at 180C and 30–70 atm. C₆₀H₃₆ is unstable in dichloromethane and some other organic solvents.     

Solubilities of ethylene,ethane, and carbon dioxide in mixed solvents consisting of methanol,acetone, and water

The amount of gas absorbed in a liquid solvent or solvent mixture is measured with a high-precision gas burette. Solubility coefficients (Henry and Ostwald coefficients) of C₂H₄ and C₂H₆ are determined at ambient temperature and atmospheric pressure (1) in the pure solvents C₃H₆O, CH₃OH, and H₂O; (2) in the three binary mixtures of the solvents as a function of the composition of the solvent mixture; and (3) in several ternary mixtures of arbitrary composition. The experimental data are presented in diagrams and tables.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Intermolecular Interaction of [60]Fullerene with Tröger's Base Analogues

Tröger's base (TB, 1) and its analogues were synthesized and were subject to the titration experiments to evaluate their ability of supramolecular complexation with C₆₀. Results demonstrate clearly that the fluorene-based TB analogue (2) and the bioctylfluorene-based TB analogue (3) show 1:1 binding with C₆₀ to form the corresponding complexes while TB 1 does not. Titration experiments exhibited that the association constant (K_ass) of 3/C₆₀ (48.1 ± 7.9 M ^?1) was larger than that of 2/C₆₀ (13.7 ± 1.4 M ^?1)_. The formation of the 1:1 binding complexes 2/C₆₀ and 3/C₆₀ was also confirmed by MALDI-TOF mass spectrometry. Theoretical calculations suggest that 2 and 3 have appropriate cavities to embrace C₆₀. These findings indicate that not only the π/π interaction between the fluorene moieties and the C₆₀ surface but also the CH/π interaction between the octyl groups and the C₆₀ surface serve efficiently in the supramolecular complexation with C₆₀.     

Theoretical Study of Decachlorocorannulene and its Congeners C20X10 and C20Z5

Abstract

The electronic structure of C₂₀Cl₁₀ synthesized by arc discharge has been studied using ab initio calculation at MP2/3-21G theory level. Theoretical studies of C₂₀F₁₀ and C₂₀O₅, C₂₀S₅, C₂₀P₅ have been carried out using the same method.     

Crystal Structure of C60 and C70 Compounds

Abstract

Fullerene intercalated compounds are the most intensively examined molecular materials to exhibit superconducting, ferromagnetic, optical non-linear and other properties. the fullerene C₆₀ or C₇₀ serve usually as electron acceptors in these materials. Although the electron acceptor properties of the fullerene are similar to those of the weak organic acceptors, the fullerene forms various C₆₀-based materials, namely clathrates, charge-transfer complexes and weak, molecular complexes. the search for cation species for fullerene-based materials is one of the routes towards progress in the design of materials with interesting physical properties.

Physical properties of the fullerene-derived molecular compounds are determined mainly by their crystal structure packing. Relatively large cavities in the fullerene solid can easily accommodate small units like solvent molecules or electron-donor organic compounds. An intercalation with these species is usually accompanied either by a lowering in crystal symmetry or by a change in the stacking arrangement of the C₆₀ spheres. These factors influence the interactions between fullerene (host) and an organic molecule (guest). Charge transfer between the electron donor molecule and the fullerene is usually weak and is hindered by unfavourable steric factors; it does not correlate with the ionization potential of the donor.

In this paper we present characteristic structures of one-, two-, and three-component fullerene compounds or else the structures of fullerene clathrates, neutral (van der Waals) complexes and ionic charge-transfer complexes. One can conclude that the stability and properties of the fullerene-based derivatives are defined by the steric compatibility between the three-dimensional donor and the spherical or elongated fullerene.     

New Developments on the Photochlorination of C60 and C70 Fullerene and Preparation of Fullerene Derivatives: Polyfluorofullerenes and Polyfullerols.

Abstract

Improved methods for photochlorination of C₆₀ and C₇₀ are described. The photoproducts fit respectively the average formulae C₆₀ Cl₄₀ and C₇₀ Cl₄₇. It is also shown that these photoproducts can be easily fluorinated by means of KF to give fluorofullerenes.

Polyhydroxyfullerene (fullerol) can be easily produced by the action of a methanolic solution of alkali over C₆₀ Cl₄₀.     

Size control for fullerene C60 nanocrystals during the high temperature and high pressure fluid crystallization process

The preparation and size control for mono-dispersed fullerene C₆₀ fine particles was successfully achieved during the high temperature and high pressure fluid (HTPL) crystallization process, in which acetone was used as the HTPL solvent and pure water or the mixture of acetone and water as the cooling solvent. The prepared fullerene C₆₀ particles had spherical shape and narrow size distribution with the average size ranging from 44 nm to 110 nm depending on the various experimental conditions, such as fluid temperature, solvent flow rate, system pressure and the ratio of acetone and water in cooling solvent. The products were characterized by using X-ray powder diffraction (XRD), scan electron microscopy (SEM), dynamic light scattering technique (DLS) and UV–VIS spectrum, respectively. And the size effect of such fullerene C₆₀ nanocrystals was confirmed.     

Determination of C60 and/or C70 Concentrations

Abstract

Two methods of quantitative analyses of the fullerenes C₆₀ and C₇₀ are described. Quantitative Infrared Spectroscopy permits the determination of the concentrations of pure and mixed compositions of C₆₀ and C₇₀ in carbondisulfide solutions. Alternatively, the ratio of C₆₀/C₇₀ is analyzed by evaluating the lattice parameters of a solid solution of the fullerene species and cyclohexane according to Vegard's Law. Both methods show high accuracy and are suited for calibration of mass spectrometric analyses of fullerene samples.     

13C and Alkali NMR Studies of Electronic and Structural Properties of Alkali Fullerides

Abstract

Extensive NMR experiments have been performed both on the ¹³C and the alkali NMR in A_nC₆₀. In the superconducting A₃C₆₀. evidences for uniaxial molecular rotations of the C₆₀ and for a low T structural anomaly will be given. The linear chain structure of A₁C₆₀ is revealed by Magic Angle Spinning NMR, while its magnetic properties are studied by ¹³C and ⁸⁷Rb wideband NMR.