Boris M. Ginzburg

On the supermolecular structure of fullerene C60 solutions

Small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) techniques were used for investigation of fullerene C60 solutions in toluene and p‐xylene. On all SAXS curves, intensity decreases to some constant value of IC with increase of scattering angle. The value of IC depends on concentration non‐monotonically: it first slightly increases, then drops sharply to some minimal value, and then increases again. A qualitative explanation of such dependence is offered. It is supposed that the presence of fullerene C60 in solution suppresses thermal fluctuations of density in the solvent. In combination with the X‐ray data the results obtained for solutions of fullerene C60 by various others techniques (calorimetry, densimetry, etc.) are discussed. Possible models of a supermolecular structure of fullerene C60 solutions in good solvents are considered.

Influence of C60 Fullerene on the Oxidative Degradation of a Free Radical Poly(Methyl Methacrylate)

The results of studies of thermal and oxidative degradation of a free-radical poly(methyl methacrylate) (PMMA) and the influence of a fullerene C60 on these processes are considered. The best characteristic of the change of the thermal stability is the temperature shift of the entire thermal gravimetric (TG) curve (or the middle part of it), but not the shift of onset or the starting temperature of the mass loss. During oxidative degradation in air of PMMA, three processes occur practically simultaneously: thermal degradation, or scission of chains; oxidation, or insertion of oxygen atoms in the polymer chains and in products of the degradation; and a sublimation of degradation products. The competition between exothermic and endothermic processes results in sharp changes in the balance of heat energy in the system and the sign of the total heat effect. In accord with these changes all of the process of PMMA oxidative degradation can conditionally be divided into three stages. The introducing of small quantities of C60 in a system results in replacement of oxygen by a fullerene or to a partial avoidance of oxidation, as a result of which, at the first stage, a smaller quantity of degradation products is formed and oxidized. There is a “transfer” of degradation products and heat generation from the first, lowest temperature stage, to the third, highest one. Simultaneous application of DSC and TG techniques has shown that during oxidative degradation of PMMA, especially in the presence of a fullerene, there is a latent degradation manifested in exothermal effects on DSC curves without mass losses on the TG curves. The introducing of C60 results in narrowing of the peaks (by ∼1.5 times) on DTG and MTA curves that may be explained by the narrowing of a set of possible degradation reactions. The C60 molecules are divided during oxidative degradation of PMMA into two groups: linked (∼20%) and nonlinked with macroradicals of PMMA. The nonlinked molecules of C60, in turn, are subdivided into oxidized and volatilizing without oxidation and degradation. The inhibiting effect of C60 on the thermal oxidative degradation reduces basically to two processes: to formation of fullerene-containing chains of PMMA and to nonchain inhibition. The matrix of PMMA also has a significant influence on the thermal behavior of C60.

On the Terminology and Structural Interpretation of Stress‐Strain Curves During Uniaxial Stretching of Soft‐Chain Semicrystalline Polymers

On the basis of the literature and, in particular, the authors (BMG) experimental data about the shear deformation of low density polyethylene (LDPE), as a typical, widely used, soft‐chain amorphous‐crystalline polymer, a correlation of different parts of the most typical stress‐strain curve during uniaxial stretching, on the one hand, and corresponding structural changes, on the other, was carried out. Interpretation of different stages of deformation in terms of a shear deformation of crystallites is given; the various phenomena accompanying the deformation process, in particular, a neck formation, are discussed. The analogy of deformation curves and van der Waals isotherms for the vapor‐liquid transition is discussed. The analogy allows the explanation of a wide spectrum of experimental data that has been reported by various authors studying the deformation of oriented and nonoriented samples of semicrystalline polymers under various conditions. On the basis of the developed concepts we also speculate about the origin of deposits of minerals, in particular metals, in the Earths crust.

Thermal and tribological properties of fullerene-containing composite systems. Part 2. Formation of tribo-polymer films during boundary sliding friction in the presence of fullerene C60

The techniques of mass‐spectrometric thermal analysis, wide‐angle X‐ray diffraction, scanning and transmission electron microscopy, light microscopy, and hardness and tribological measurements were used for study of formation and properties of protective—anti‐wear and friction‐reducing—tribo‐polymer film forming on metal surfaces during sliding boundary friction, in the presence of fullerene C60 used as an additive to some mineral lubricating oils and greases. A possible mechanism of formation of tribo‐polymer film was proposed based on the idea of attachment of paraffin and naphthenic oligomers of the lubricants to C60 molecules, which in turn are polymerized and form a hard fullerene network with attached polyolefin chains. A fullerene network provides a high wear resistance while polyolefin chains provide some decrease in the friction coefficient and widening of the working intervals of friction joints.

Thermal and Tribological Properties of Fullerene‐Containing Composite Systems. Part 1. Thermal Stability of Fullerene‐Polymer Systems

Abstract The techniques of mass‐spectrometric thermal analysis, differential scanning calorimetry, differential thermogravimetry, and wide‐angle x‐ray analysis of thermal and oxidative degradation of two types of fullerene‐containing polymer systems (FCPS) were studied: 1) FCPS with covalent interaction of fullerene C60 with polymers; 2) FCPS representing mixtures of C60 with polymers in which interaction of components is realized only by means of Van‐der‐Waals forces. In both types of FCPS the electron acceptation properties of C60 are manifested. In some systems of the first type, a great decrease in thermal stability of a polymer component was observed; in systems of the second type the ability of fullerene C60 to play a role of “trap” of free radicals is especially manifested. The polymer matrix also influences the thermal behavior of fullerene C60. In particular, fullerene can serve as a specific “probe” of chemical processes that occur during thermal degradation of a polymer. Different polystyrenes and poly(methyl methacrylate)s containing 1–10 mass% C60 (FCPS) were investigated.

Construction Of The Full Phase Diagram For The System Of Poly(γ-benzyl-l-glutamate)/dimethylformamide On The Basis Of The Complex Of Literature Data

The system poly-γ-benzyl-l-glutamate—dimethylformamide (PBG/DMF) is the most-studied of the rodlike polymer-solvent systems. However, up to now there is no satisfactory experimental phase diagram (PD) for this system in the entire range of concentrations. For all studied systems only fragments of the PD are known. Some regions of these fragments agree qualitatively with the theoretical PD for an ensemble of rodlike particles in an isotropic solvent. However, most parts of the PD do not agree with the theoretical ones. A critical analysis of the corresponding experimental data was carried out and on the basis of this analysis a new PD was constructed in the enti re range of concentration. The obtained PD differs essentially from the known theoretical diagram and is very close to the diagram predicted by Papkov taking into account the formation of crystallosolvates. The peculiarities of the phase transitions in the various regions of the PD are considered. It is shown that the so-named lyotropic liquid crystals (LC), on the basis of solved rodlike polymers, are thermotropic LCs diluted by the isotropic solvent. A specific role in the PD are played by the crystallosolvates (CS), which are identified with the phase defined by Luzzati as the “complex phase.” In particular, the phase region LC-CS exists instead of the LC-LC region in the theoretical PDs. Some new concepts of the crystallosolvate defects and on the “limiting” LC phase are discussed. Consideration of the liquidus lines CS/LC and CS/(isotropic liquid) permits us to propose some explanations of the PDs at low polymer concentrations. Most parts of the real PD represent the superposition of different phase equilibria and are complicated by the processes of gelation, crystallization and crystallosolvate formation that cannot be described by the modern theories. The fragments of the PDs in the literature for some rodlike polymers in solution agree well with the general PD for PBG/DMF. Special features of the phase transitions in the different areas of the PD are discussed. On the basis of the principles used in this work for construction of the PD, critical consideration of the PDs published in the literature have been carried out; our understanding of results obtained by other authors are presented. The perspectives of further investigations are considered.

Effect of Fullerene C60 on Thermal Oxidative Degradation of Polymethyl Methacrylate Prepared by Radical Polymerization

The influence of small C60 additions on thermal and thermal oxidative degradation of polymethyl methacrylate prepared by radical polymerization was studied by differential scanning calorimetry, thermo- gravimetric analysis, differential thermogravimetric analysis, and mass spectrometry.

On the “Cold Drawing” of Semicrystalline Polymers

On the basis of the literature and the authors data, the specific features of stress‐strain curves during uniaxial stretching of semicrystalline polymers were analyzed. It was shown that the general external appearance of a deformed sample (presence or lack of neck) and character of stress‐strain curves depend not only on strain temperature, T2, but also on the temperature, T1, of previous processing (or treatment) of the sample. The definition of “cold drawing,” valid for amorphous polymers, is not applicable to semicrystalline polymers. A new definition of cold drawing for semicrystalline polymers is offered.

Structurization of a solvent interacting with fullerene C60

Solutions of fullerene C60 in toluene and p-xylene were investigated by small-angle X-ray diffraction. In all small-angle scattering curves, the scattering intensity decreases to constant value IC with an increase in the scattering angle. The value of IC nonmonotonically depends on the fullerene concentration. The radii of gyration of scattering elements were determined by constructing small-angle X-ray diffraction patterns in Guinier coordinates.

Tribological Properties of Poly(Para-Phenylene Sulfide) and its Carbon Fiber Composites with Water Lubrication

Tribological properties of poly(para-phenylene sulfide) (PPS) with different molecular mass were studied. PPS properties were compared with the same properties of its carbon fiber-filled plastics. For the interpretation of tribological test results an especial role was assigned to the load capacity of materials. The concept of load capacity permits consideration of different tribological dependencies as phase diagrams. The structure of the samples was characterized by X-ray diffraction and differential scanning calorimetry techniques.