The effect of high curing temperature on the reaction kinetics in MK/lime and MK-blended cement matrices at 60 °C

It is well known that the pozzolanic reaction between metakaolin (MK) and calcium hydroxide produces CSH, C₂ASH₈ (stratlingite), C₄AH₁₃ and C₃ASH₆ (hydrogarnet). However, the presence or absence of these hydrated phases depends on different parameters, such as curing temperature, matrix used, etc. This paper shows the results of a study in order to know the effect of high curing temperature (60 °C) on the kinetics of the pozzolanic reaction in different matrices. MK/lime (calcium hydroxide) and MK-blended cement matrices were studied in samples stored and cured at 60 °C and up to 123 days of hydration. The nature, sequence and crystallinity of the hydrated phases were analysed using differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques.Results showed that the sequence and formation of the hydrated phases was different in both matrices cured at 60 °C. In an MK/lime matrix, C₂ASH₈, C₄AH₁₃ and C₃ASH₆ were the main hydrated phases; while in an MK-blended cement, stratlingite was the sole hydrated phase issued from pozzolanic reaction. The DTA and XRD data also reveal an important fact: there is no evidence of the presence of hydrogarnet in blended cements.     

The effect of temperature on the hydration rate and stability of the hydration phases of metakaolin-lime-water systems

The paper presents the results of a study carried out to determine the effect of curing temperature on the kinetics of reaction of a metakaolin (MK)/lime mixture. MK and analytical grade Ca(OH)₂ were mixed in a ratio of 1:1 by weight and with a water/binder ratio of 2.37. Specimens were cured at 20 and 60 °C. In the first case, the curing time varied from 2 h up to 180 days and, in the second case, from 2 h up to 123 days. A mathematical model was applied to calculate the rate constant for the hydration reaction. The identity and the amount of the phases present were determined from thermal analysis (TG and DTA) data. The results showed that the rate constant for the samples cured at 60 °C was 68 times greater than the rate constant at 20 °C for the same curing period (up to 9 days). At 20 °C, the sequence of appearance of the hydrated phases was C-S-H, C₂ASH₈ and C₄AH₁₃; while at 60 °C, the sequence was C-S-H, C₂ASH₈, C₄AH₁₃ and hydrogarnet (C₃ASH₆). There is no evidence of further C₂ASH₈ and C₄AH₁₃ transformation into hydrogarnet in the mixture studied for 123 days at 60 °C.     

Evolution of Mineralogical Phases by 27Al and 29Si NMR in MK‐Ca(OH)2 System Cured at 60°C

The evolution of the metastable phases in metakaolin/Ca(OH)₂ systems cured at high temperatures, remains mostly unknown, newer techniques may now help to establish both the kinetic mechanism of the pozzolanic reaction and the thermodynamic stability of the main hydrated hexagonal phases: Stratlingite (C₂ASH₈) and tetra calcium aluminate hydrate (C₄AH₁₃). For this reason this work examines the kinetics of the pozzolanic reaction in the MK/Ca(OH)₂ system over 123 d at 60°C using nuclear magnetic resonance spectroscopy (²⁷Al and ²⁹Si NMR). The results obtained by ²⁷Al and ²⁹Si NMR show that during the first 30 h, the metastable phases C₂ASH₈ and C₄AH₁₃, coexist with the cubic phase (C₃ASH₆) obtained directly from the pozzolanic reaction. The gel C–S–H is clearly identified after 21 h of reaction, whereas at shorter times the C–S–H bands overlap those with the unreacted metakaolin ones. After 123 d of pozzolanic reaction, the first signs of the cubic phase are detected, a consequence of the conversion reaction of the metastable phases, and a phenomenon not previously identified.     

The rheological,thermostable, and mechanical properties of polypropylene/fullerene C60 nanocomposites with improved interfacial interaction

Polypropylene (PP)/C₆₀ nanocomposites with improved interfacial interaction were prepared via in situ melt radical reaction. It was found that the relaxation time of PP/C₆₀ nanocomposites containing peroxide increased due to the reaction between C₆₀ and PP macroradicals and the formation of long chain branched or crosslinking structure. Thermogravimetric analysis (TGA) results showed that the thermal stability of PP/C₆₀ nanocomposites was enhanced. The initial decomposition temperatures and activation energy of PP/C₆₀ nancomposites were strongly influenced by the content of unreacted C₆₀. Because of the improved interfacial interaction, PP/C₆₀ nanocomposites containing peroxide showed obvious increase in tensile strength, Young' modulus, flexural strength, flexural modulus, and impact strength, compared to PP/C₆₀ nanocomposites (without peroxide) containing the same content of C₆₀. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Researches on the photoconductivity and UV-visible absorption spectra of the first C60-chemically modified poly(N-vinylcarbazole)

Summary Addition of C₆₀ moiety, a powerful electron acceptor to poly(N-vinylcarbazole) by chemical reaction results in the marked enhancement in photoconductivity relative to pure PVK and C₆₀ /PVK mixtures (C₆₀-doped PVK). The photoinduced discharge rates for pure PVK, C₆₀-chemically modified PVK(C₆₀-PVK copolymer) and C₆₀-doped PVK under the same experimental conditions are found in the following order: C₆₀-PVK copolymer>C₆₀-doped PVK>pure PVK. The photoconductive performance in C₆₀-PVK copolymer is closely related to fullerene level. The C₆₀-PVK copolymer, which has a visibly earthy yellow cast when compared with the unreacted polymer, has a new structure in the UV-Vis absorption spectrum with the active range extending from about 280 to 870 nm. A qualitative comparison of the submicro-morphological structures for PVK, C₆₀, C₆₀-PVK and C₆₀-doped PVK is given.     

Acceleration of the Diels-Alder Reaction between 9-Functionalized Anthracenes and C60/C70 in the Cavity of a Water Soluble Subphthalocyanine Cage

Herein we report on the acceleration of the Diels-Alder reaction between a series of 9-functionalized anthracenes and C₆₀/C₇₀ encapsulated in a water-soluble metallo-organic Pd(II)-subphthalocyanine cage ( SubPc-cage ), which performs as a catalytic molecular reactor that provides a beneficial hydrophobic environment. Negatively and positively charged anthracenes do not react either with C₆₀ or C₇₀, due to a favored solvation in water medium and/or to detrimental interactions with positively-charged Pd(II) corners of SubPc-cage . Experiments with C₆₀ and C₇₀ rendered parallel results, although C₇₀ proved more reactive, leading to anthracene cycloadducts by reaction in the α bonds. All the results have been rationalized by theoretical calculations at the GFN2-xTB level.     

Influence of metastable hydrated phases on the pore size distribution and degree of hydration of MK-blended cements cured at 60 °C

When MK reacts with calcium hydroxide, cementitious products are formed. It has been reported that CSH, C₂ASH₈ and C₄AH₁₃ are the most important hydrated phases formed. These phases are stable at 20 °C. However, some of them (C₂ASH₈ and C₄AH₁₃) are metastable phases, converting to hydrogarnet (C₃ASH₆) for long curing times at elevated temperatures. The partial or total conversion reaction could produce a negative effect on the performance and durability of blended cements, due to a volume decrease associated with the process of transformation.Due to the influence that this conversion could have on the microstructure and durability of a cement paste containing MK, the current paper presents the results of a research programme carried out on blended cements containing 10%, 20% and 25% of MK, cured at 60 °C up to 124 days of hydration.The total, partial porosity and average pore diameter evolution vs. time is determined using mercury intrusion porosimetry (MIP). An estimated degree of hydration of MK-blended cements cured at 60 °C is proposed.The results show that there is no increase in porosity values and average pore diameters with time. Therefore, the hydrated phases produced in MK-blended cements under the test conditions used do not have a negative effect on the microporosity. A suitable correlation between porosity and degree of hydration has been found.     

Functionalization of C60 with gold nanoparticles

Gold nanoparticles (GNPs) with attached C₆₀ molecules (C₆₀-GNPs) were prepared through the amination reaction of fullerene C₆₀ with peripheral amino groups located on the surface of gold. Molecules of 4-aminobenzenethiol/1-hexanethiol containing amino groups were introduced onto the surface of gold by the reduction of a gold salt (HAuCl₄) with sodium borohydride (NaBH₄) in a one-pot way, which was accompanied by anchoring of the targeted thiol mixture on the gold cluster by Au-S bonds. This simple system avoids many difficult reactions and purification processes and does not involve a complicated chemical modification of C₆₀ and exchange reactions of GNPs.     

Fluorination of pressure-polymerized C60 phases

The reactivity of O-, T- and R-phases of the high pressure-high temperature (HPHT) polymerized C₆₀ towards gaseous fluorine in the temperature range of 50-250 °C was investigated. The reaction products were characterized by FTIR, powder X-ray diffraction, SEM, EDX, and VTP-EIMS to determine the bulk stoichiometries, bonding patterns, phase compositions, crystalline structures and thermal decomposition behavior of the fluorinated polymers. At 1 h isothermal treatment duration, fluorinated products with various bulk stoichiometries were obtained from different polymer phases with the R-phase showing the highest fluorine uptake. At 250 °C, all C₆₀ polymers showed partial decomposition to unfluorinated C₆₀ monomer under fluorine atmosphere. At 200 °C, the fluorination of R-phase yielded a pure fluoropolymer most likely having a {C₆₀F_x}_n (x = 36-44) composition. The same fluoropolymer was presumably obtained from O- and T-phases in lower yields. The linear chain structure was suggested for this new fluorocarbon polymer in agreement with the molecular mechanics modeling calculations.     

Preparation and spectroscopic properties of chlorofullerenes C60Cl24, C60Cl28, and C60Cl30

We report easy preparation of recently discovered highly chlorinated fullerenes T_h-C₆₀Cl₂₄, C₁-C₆₀Cl₂₈, and D_3d-C₆₀Cl₃₀ in high-temperature reactions of C₆₀ with PCl₅ and ICl. Formation and interconversion of chlorofullerenes was investigated in details for C₆₀-ICl system. C₆₀Cl₂₈ is the least stable chlorofullerene that undergoes rearrangement (accompanied by partial chlorine elimination) into more stable T_h-C₆₀Cl₂₄ under more drastic reaction conditions (increased temperature and time of chlorination). T_h-C₆₀Cl₂₄ yields D_3d-C₆₀Cl₃₀ at temperatures above 220 °C via a sequence of rearrangements and further addition of chlorine. In contrast to the fullerene reaction with ICl, interaction of C₆₀ with PCl₅ is very selective with respect to formation of C₆₀Cl₂₄ in a wide temperature range. Solid-state electronic (UV-Vis) and vibrational (IR) spectra of chlorinated fullerenes C₆₀Cl₂₄, C₆₀Cl₂₈, C₆₀Cl₃₀ and fluorinated fullerenes C₆₀F₁₈ and C₆₀F₃₆ were recorded in the spectral range between 30 and 45,000 cm⁻¹. Raman spectra were also acquired for all investigated compounds. Moreover, molecular geometry of the C₆₀Cl₂₄ and its theoretical IR-absorption spectrum were calculated using B3LYP/STO-3G chemistry model.     

Relative stability of polymerized phases of C60: Depolymerization of a tetragonal phase

Differential scanning calorimetry and IR-spectroscopy have been used to study the depolymerization of the 2D tetragonal (T) polymerized phase of C₆₀ at p = 1 atm. The depolymerization enthalpy obtained was 17.7 ± 1.7 kJ per mole of C₆₀. Experimental enthalpies of depolymerization along with the lattice energies calculated by the atom-atom potential method were combined into the thermochemical cycles to account for the trends in the relative stability of the polymerized phases of C₆₀. Surprisingly low depolymerization enthalpy of 2D rhombohedral (R) phase compared to 1D orthorhombic (O) and 2D T-phases was explained by the unfavorable packing energy of the isolated rhombohedral layers into R-crystal lattice, though the averaged C₆₀ = C₆₀ bond energy was also lower for R- than for O- and T- phases, being 31, 42 and 43 kJ/mol, respectively. Results of DFT quantum chemical calculations of the energetics of C₆₀ polymers were in qualitative agreement with this trend. The mechanism of depolymerization appeared to be significantly different for R-phase compared to other polymers. While decomposition of O- and T-phases occurred in one step without any IR-detectable intermediate species, depolymerization of R-phase was found to be at least a two-step process. Comparison of experimental and DFT simulated IR-spectra suggested that intermediate species were cyclic trimers or similar oligomers.     

Synthesis of C60 end-capped poly(4-diphenylaminostyrene): Addition of poly(4-diphenylaminostyryl)lithium to C60

The covalent modification of fullerene-C₆₀ (C₆₀) with poly(4-diphenylaminostyrene) (PDAS) was examined to explore the possibility of preparing new materials for effective photovoltaic cells. The high nucleophilicity and small steric hindrance of the PDAS carbanion is a very important factor in the addition of poly(4-diphenylaminostyryl)lithium (PDASLi) to C₆₀. C₆₀ end-capped PDAS (C₆₀-PDAS), consisting of one PDAS molecule bonded to one C₆₀ molecule at the polymer chain-end, was successfully prepared from the PDASLi/N,N,N’,N’-tetramethylethylenediamine system and C₆₀. UV/vis and photoluminescence spectra suggest that C₆₀-PDAS has considerable potential for the preparation of effective photovoltaic cells.     

Synthesis and characterization of polyethylene/C<Subscript>60</Subscript> fullerene structures by photoluminescence

Fullerene C₆₀ has attracted attention due to its special chemical and physical properties. However, its poor solubility and processability arise difficulties in practical applications. These problems may be surpassed by grafting C₆₀ on polymers. This study presents the synthesis of the polyethylene/maleic anhydride copolymers and C₆₀ structures and their characterization by photoluminescence. The synthesis of the material is based upon the reaction of fullerene C₆₀ with amino groups containing in the polymer chains. In the first step, some polyethylene (PE)/maleic anhydride (MA) copolymers having 1, 3, 6 and 10 wt.% anhydride groups were reacted with an amine compound. The following step consists in the reaction of C₆₀ with the amine groups. A proof that the structures synthesized contain C₆₀ is given by the photoluminescence spectra.     

High-pressure solubility of fullerene C60 in toluene

The solubility of fullerene C₆₀ in toluene was measured at temperatures between 278.2 and 308.2 K and pressures up to 340 MPa, and also at temperatures between 258.2 and 298.2 K under atmospheric pressure. The solubility increased with increasing pressure, and then decreased with a sharp maximum, suggesting a transition between solid phases. A thermodynamic analysis of the solubility supported the proposal of Korobov, et al. that the two solids correspond to C₆₀ (fcc) and C₆₀ · 2 (toluene) solvate. The solubility enhancement of C₆₀ by pressure in a low-pressure region is an unusual phenomenon when compared with the decrease in solubility of nonpolar molecular solids generally observed with rises in pressure.     

Development of [60] fullerene supported on silica catalysts for the photo-oxidation of alkenes

Simple or successive incipient wetness impregnation followed by heating at 180 °C is proved an efficient preparation method for dispersing effectively onto the silica surface various amounts of C₆₀ in the range 1–4% (w/w). BET, XRD, DRS, TGA, microelectrophoresis and photoluminescence have been used to characterize the photocatalysts prepared. A high dispersion was obtained for the quite stable supported C₆₀ phase, comprised mainly from relatively small or medium size C₆₀ clusters/aggregates. The photocatalytic activity was assessed in the singlet oxygen oxidation of alkenes by examining the photo-oxygenation of 2-methyl-2-heptene as a probe reaction. The catalytic tests were carried out at 0–5 °C in CH₃CN, under oxygen atmosphere and using a 300 W xenon lamp as the light source. The heterogeneous catalysts obtained were proved to be active in the photocatalytic oxidation of olefins via a ¹O₂ ene reaction. The catalysts exhibited significant conversion, turnover number and turnover frequency values, substantially higher than those achieved over the unsupported C₆₀. The conversion increases with the amount of the supported C₆₀ up to a value equal to 3% (w/w) and then it decreases whereas turnover number and turnover frequency decreases monotonically as the amount of the supported C₆₀ increases. The easy separation of these solid catalysts from the reaction mixture, the high activity and stability as well as the retained activity in subsequent catalytic cycles, make these supported catalysts suitable for a small-scale synthesis of fine chemicals.     

C60 affects DNA replication in vitro by decreasing the melting temperature of DNA templates

The effect of C₆₀ on DNA replication in vitro was studied by a quantitative real-time polymerase chain reaction (QPCR) system using a designed 110bp single-stranded DNA as the template. The results indicated that the efficiency of QPCR can be dramatically enhanced by C₆₀ at the beginning of the exponential phase, and that QPCR production can be significantly inhibited by C₆₀ at later cycles or at the plateau, which is the period represented by an interesting inverted U-shaped time response curve. Two different sized double-stranded DNA fragments (110bp and 60bp) were used to investigate the possible interaction between C₆₀ and DNA. The melting curve results showed that C₆₀ significantly decreased the melting temperatures (Tm) of the DNA fragments. By changing the concentrations of the initial DNA templates or C₆₀ in the QPCR system, we found that the decreased Tm value of DNA templates by C₆₀ is the primary reason for the increased QPCR efficiency. Our findings are consistent with the conclusions of other studies that C₆₀ can disrupt DNA replication in vitro by binding to DNA and changing the conformation of DNA templates.     

Synthesis of functionalized fullerene‐C60 by the living anionic polymerization technique

The synthesis of functionalized fullerene‐C₆₀ (C₆₀) was performed using living anionic polymerization. The metalation of the benzylic hydrogen atom on toluene or p‐substituted toluene was conducted with the alkyllithium/amine system, and examined by living anionic polymerization of 1,3‐cyclohexadiene. The number of carbanions bonded onto C₆₀ was estimated by the grafting reaction of living polymer onto C₆₀. The tert‐butyllithium/N,N,N′,N′‐tetramethylethylenediamine system was an effective metalation reagent, and toluene‐, p‐xylene‐, 4‐methyltriphenylamine‐functionalized C₆₀s having good solubility were successfully synthesized. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanistic investigation and selectivity of the grafting onto C60 of macroradicals prepared by cobalt-mediated radical polymerization

The grafting mechanism of poly(vinyl acetate) macroradicals prepared by cobalt-mediated radical polymerization onto C₆₀ is investigated. The experimental conditions directly impact the nature and stability of the PVAc/C₆₀ adducts. In the presence of residual initiating radicals that can compete with PVAc° macroradicals for addition onto C₆₀, mixtures of PVAc/C₆₀ adducts having between one and eight polymer chains per C₆₀ are formed. PVAc/C₆₀ adducts prepared with low [PVAc]:[C₆₀] ratios may contain weak C₆₀–C₆₀ bonds that further dissociate and account for the instability of the products. The formation of such dimers can be lessened by increasing the temperature from 30 °C to 100 °C. The temperature increase also allows a complete dissociation of the PVAc-Co dormant species into PVAc° macroradicals and an almost quantitative grafting of eight PVAc chains onto C₆₀, leading to well-defined C₆₀(PVAc)₈ octa-adducts. These results might shed new light on the grafting onto C₆₀ of macroradicals prepared by other CRP techniques.     

Solution-phase synthesis of dumbbell-shaped C120 by FeCl3-mediated dimerization of C60

In the presence of FeCl₃, C₆₀ in 1,1,2,2-tetrachloroethane reacted at 150 °C to produce a dumbbell-shaped dimer C₁₂₀. We propose a reaction mechanism that includes FeCl₃-mediated generation of an intermediate C₆₀ radical cation, which reacts with C₆₀ to form the dimer. The respectable chemical yield (21%) and quantity (106 mg) of the product will open new possibilities for investigating solution-phase polymerization of fullerenes as well as for conducting applied research on C₁₂₀.     

Fullerene (C60)–transitional metal (Ti) composites: Structural and biological properties of the thin films

Thin films of the binary C₆₀/Ti composites (with various phase ratios) were deposited on the Si(001) wafers and microscopic glass coverslips in continuous and micropatterned forms. The composites acquired a nanogranular structure with granules of about 50 nm in size. The RBS inspection confirmed homogeneous distribution of the phases and also the presence of oxygen. The Raman study suggested polymerization of the C₆₀/Ti composites into polymeric structures. The hybrid substrates were tested on biocompatibility—the films were seeded with human osteoblast-like MG 63 cells, and their proliferation was analyzed for 7 days. It has been found that the C₆₀/Ti composites can be counted as good supports for the adhesion of the selected MG 63 cells. The composites exhibited similar biocompatibility as the mix of amorphous carbon and titanium, but different than fullerene (C₆₀) solids.