Differential thermogravimetric analysis of the products of radiation-chemical telomerization of tetrafluoroethylene in acetone

Differential thermogravimetric (DTG) curves of the products of radiation-chemical telomerization of tetrafluoroethylene solutions in acetone with concentrations (c) of 0.06 to 2.0 mol/l were measured in the temperature range 20–600°C. The pattern of the DTG curves was determined by evaporation of telomers at c < 0.2 mol/l and their thermal degradation at c > 0.2 mol/l. Acetone-soluble telomers with an average chain length of less than 5 units prevail at c < 0.1 mol/l, whereas telomers with a chain length up to 15 units, which form colloid particles, dominate at higher c values. It was shown by means of atomic-force microscopy that such colloid solutions form coatings composed of submicron-sized particles.     

Study of fluoroalkylsilanes,a new class of amphiphilic oligomers: Determination of end groups and chain length

Radiation-initiated polymerization of tetrafluoroethylene (TFE) in the liquid alkylsilanes Si(CH₃)₄ (I), C₂H₅Si(CH₃)₃ (II), and ClSi(CH₃)₃ (III) produces fluoroalkylsilane oligomers with the general formula R(C₂F₄) _n X, where X = H or Cl in I, II, and III and R is one of the radicals generated by the abstraction of H from the methyl and ethyl groups in I and II or Cl detachment from III. The nature of R has been determined using an NMR technique, and the molecular mass distribution (MMD) has been found from abundances in anion progressions in mass spectra and from DTG and GPC data. At initial TFE concentrations (C ₀) changed from 0.4, 1, and 0.13 to 1, 2.7, and 0.7 mol/L in I, II and III, respectively, the average chain length 〈n〉 increases from 4–5 to 10–12 and the MMD changes from the unimodal to the bimodal pattern in which the proportion of oligomers with n < 6 decreases with increasing C ₀. As 〈n〉 increases and the MMD changes, the homogeneous solution becomes colloidal and then turns into a gel. The colloidal particles are largely composed of long oligomers, and the number of solvent molecules per C₂F₄ unit decreases with an increase in C ₀ and is 4–7 in the gel.     

Non-Isothermal Crystallization Behavior of β-Nucleated Isotactic Polypropylene/Multi-Walled Carbon Nanotube Composites with Different Melt Structures

In this study, the melt structure status of isotactic polypropylene/multi-walled carbon nanotubes composites (iPP/MWCNTs) nucleated with β-NA was tuned by changing the fusion temperature T _f . The non-isothermal crystallization behavior and subsequent melting behavior of the sample were studied in detail. The results showed that under different cooling rates (2, 5, 10, 20 and 40 deg/min), the crystallization temperature increased gradually with the decrease of T _f , meanwhile, when T _f was in the temperature range of 166–174°C where ordered structures survived in the melt (named Region II), the crystallization activation energy was significantly lower compared with the case T _f > 174°C or T _f < 166°C. On the subsequent melting curves, the occurrence of the melt structure can be observed at all the cooling rates studied; the location of the Region II was constant, which did not show dependency on the cooling rates; low cooling rate and relative low T _f within 166–174°C encouraged the formation of more β-phase triggered by melt structure.     

Peroxy radicals as motional probes at the end of isolated polystyrene chains and on the cellulose surfaces in vacuum

The isolated polystyrene chains spin-labeled with peroxide radical at the free end (IPSOO) in which the chain roots were covalently bonded to the surface of microcrystalline cellulose (MCC) powder were produced by mechanochemical polymerization of styrene initiated by MCC mechanoradicals. The IPSOO was used as motional probes at the ends of isolated polystyrene chains tethered on the surface of MCC powder. Two modes for the molecular motion of IPSOO were observed. One was a tumbling motion of IPSOO on the MCC surface, defined as a train state, and another was a free rotational motion of IPSOO protruding out from the MCC surface, defined as a tail state. The temperature of tumbling motion (T _tum ) of IPSOO at the train state was at 90 K with anisotropic correlation times. T _tum (90 K) is extremely low compared to the glass transition temperature (T _g ^b ; 373 K) of polystyrene in the bulk. At temperatures above 219 K, the IPSOO was protruded out from the MCC surface, and freely rotated at the tail state. The train–tail transition temperature (T _train–tail ) was estimated to be 222 K. T _tum (90 K) and T _train–tail (222 K) are due to the extremely low chain segmental density of IPSOO on the MCC surface under vacuum. The interaction between IPSOO and the MCC surface is a minor contributing factor in the mobility of IPSOO on the surface under vacuum. It was found that peroxy radicals are useful probes to characterize the chain mobility reflecting their environmental conditions.     

Quantum Chemical Study of Niobium and Tantalum M<Subscript>4</Subscript>O<Subscript>10</Subscript> Oxide Clusters and M<Subscript>4</Subscript>O<Stack><Subscript>10</Subscript><Superscript>–</Superscript></Stack> Anions

Structural parameters and vibrational frequencies of the clusters (T_d)–Nb₄O₁₀, (C_3v)-TaNb₃O₁₀, (D_2d)-Nb₄O ₁₀ ^– , and (C_s)-TaNb₃O ₁₀ ^– were calculated. According to the (U)DFT/SDD calculations with BLYP, B3LYP, and PBE0 functionals magnetization of the anion (D_2d)-Nb₄O ₁₀ ^– is distributed equally among four niobium atoms. In the anion (C_s)-TaNb₃O ₁₀ ^– unpaired electron presumably occupies niobium atoms. The distinction in contributions from Nb atoms in the magnetization of the tantalum-containing cluster grows with the exchange component of the DFT functional in the series of functionals BLYP < B3LYP < PBE0 < UHF.     

Thermodynamic properties of triphenylantimony dibenzoate

The temperature dependence of the heat capacity of triphenylantimony dibenzoate Ph₃Sb(OC(O)Ph)₂ is studied in the range of 6–480 K by means of precision adiabatic vacuum calorimetry and differential scanning calorimetry. The melting of the compound is observed in this temperature range, and its standard thermodynamic characteristics are identified and analyzed. Ph₃Sb(OC(O)Ph)₂ is obtained in a metastable amorphous state in a calorimeter. The standard thermodynamic functions of Ph₃Sb(OC(O)Ph)₂ in the crystalline and liquid states are calculated from the obtained experimental data: C_p^°(T), H°(T)–H°(0), S°(T), and G°(T)–H°(0) for the region from T → 0 to 480 K. The standard entropy of formation of the compound in the crystalline state at T = 298.15 K is determined. Multifractal processing of the low-temperature (T < 50 K) heat capacity of the compound is performed. It is concluded that the structure of the compound has a planar chain topology.     

Molecular orientation ordering in surface layers of polymer films

The spontaneous ordering of fragments of chain molecules near the surface in polymer films is described in terms of the multichain model that allows for local intra-and interchain orientational interactions of chain segments and for transverse fluctuation of their orientation in the approximation of strong planar-orientation order in the layers. Chain packing in the plane-ordered state is impossible unless the interchain interaction parameter has a value of b = 2K ₂/k _B T > b _c. The value of b _c decreases with a growth in chain rigidity (parameter a = 2K ₁/k _B T). The calculated dependence of the limiting values of the quadrupole orientation order parameter S ₀ on the length of the Kuhn statistical segment A = 2a reasonably well describes the experimental data obtained in a study of polymer-homolog (polysaccharide) films by means of the tilted polarized-beam technique at an interchain interaction parameter of b = 1.75. The monolayer thickness (d ? 10 mn) is films of some polysaccharides was calculated from the fit of the theoretical to the experimental dependences of the orientational order parameter and the birefringence on the number of layers.     

Method for calculating the sizes of nucleation centers upon homogeneous crystallization from a supercooled liquid

An alternative approach to calculating critical sizes l_k of nucleation centers and work A_k of their formation upon crystallization from a supercooled melt by analyzing the variation in the Gibbs energy during the phase transformation is considered. Unlike the classical variant, it is proposed that the transformation entropy be associated not with melting temperature T_L but with temperature T < T_L at which the nucleation of crystals occurs. New equations for l_k and A_k are derived. Based on the results from calculating these quantities for a series of compounds, it is shown that this approach is unbiased and it is possible to eliminate known conflicts in analyzing these parameters in the classical interpretation.     

Similarity examination of truncated virial equation of state correspondence to linear isothermal regularity (LIR) by applying square-well (SW) potential

Linear isotherm regularity works very well for fluids at high densities, and it has been shown that it is compatible with the EOSs based on statistical–mechanical theory. On the other hand, at low densities, the first few terms of virial EOS have the most contribution to express the deviations from ideal behavior. For finding similarities between dense and dilute states, experimental p–v–T data of 14 fluids (He, Ne, Ar, Kr, H₂, O₂, N₂, CO, NH₃, CH₃OH, CH₄, C₂H₄, C₂H₆ and C₃H₈) are examined. Comparing the thermal dependencies of the attraction and repulsion terms (A and B) of the LIR with the second and third virial coefficients (B ₂ and B ₃) in liquid and supercritical regions (0.7 < T _r < 3.0) shows a remarkable similarity. Square-well potential is applied to examination and comparison of theoretical results with experimental results. It is shown that in liquid and supercritical regions, (1) the short-range potential governs among particles in dense fluids, and the long-range interactions become important in the less dense fluid, (2) similar to Boyle temperature, T _B, in dilute state, there is a temperature as T′_B (in dense fluids) that the attractive forces and the repulsive forces acting on the dense-fluid particles balance out; thus, probably there is a maximum σ (molecular diameter) at nearly 2T _c (T′_B), and (3) in the liquid and supercritical regions (0.7 < T _r < 3.0), in the first-order approximation, there are no significant interactions higher than triple interactions in dense-fluid particles.     

Evaporation of Plasticizer from NEPE Type Propellant

Using the method of dynamic thermogravimetry and differential scanning calorimetry in the heating rate range 0.46–10.0 deg^–1 min^–1, evaporation of the plasticizer from propellant samples of the NEPE type was investigated. The experiments were carried out in an open system in a flow of pure argon at atmospheric pressure. Nitroglycerin is the main mass fraction of the plasticizer. The activation energy E of the gross evaporation–diffusion process is determined by various methods. Heat of evaporation of the plasticizer ΔH_v is estimated. It is shown that in the early stage of evaporation the values of E and ΔH_v practically coincide. At a temperature of 298.15 K ΔH_v = 89 ± 4 kJ mol^–1, which is in satisfactory agreement with the literature data for heat of evaporation of pure nitroglycerin. With any way of preventing free removal of the plasticizer from the surface of the samples on the DSC thermograms successive exothermic peaks of the thermal decomposition of the plasticizer and the octogen are observed, which are not realized in the open system for the indicated heating rates at T < 190°C.     

A Search for a Direct Relationship Between Chromatographic and Adsorption Data

Shifts of chromatographic peak maxima and centres of gravity have been investigated for different amounts of propane injected on to a chromatographic column in ideal, non-linear chromatography. Specific retention volumes (V _{g (273)}, corrected to the standard temperature, 273.15 K), propane adsorption isotherms, and the first and second derivatives of the isotherms, (da/dp) _T and (d²a/dp²) _T , were determined for samples of active carbon and for different amounts of propane injected on column. Relationships between specific retention volume and the molar differential work of adsorption, A, were calculated on the basis of the propane isotherms and using the retention times of the peak maxima and the centres of gravity of the peaks. The equations obtained, ln V _{g (273)}=f₁(A) and(dW/dA) _{T, F c} = f₂(ln V _{g (273)}), have been used to explain the relationships between (i) chromatographic peak profiles and (ii) the distribution function of pore volumes filled with propane and the molar differential work of adsorption at different column temperatures (303–318 K).     

The structural organization of liquid low-molecular-weight epoxy oligomers

The possibility of the existence and the behavior of molecular aggregates in low-molecular-weight epoxy resins were studied. The globular morphology of all liquid resins was determined using transmission electron microscopy. The lamellar morphology of crystallized ED24 was established by additionally using atomic-force microscopy. The thermal behavior of oligomeric epoxides was studied over the temperature range ?100–100°C. The T _g and T _ll transitions were recorded for liquid resins by differential scanning calorimetry. For solid ED24, the T _m peak of resin melting situated between T _g and T _ll was observed. The existence of the T _ll transition was substantiated by positron annihilation measurements. The morphological picture was thermally unstable and became completely degenerate at T _ll. The morphology and thermophysical parameters of the resins changed substantially after their vibrational treatment. The morphology of oligomers was shown to be “hereditarily” (genetically) related to that of the corresponding network polymers.     

Thermal polymerization of styrene: New data on the conversion dependence of the initiation rate

With the aid of new acceptors of free radicals usable at high temperatures (T > 100°C), the rate of initiation w _i has been measured experimentally for the thermal polymerization of styrene at 122.5°C in a wide range of conversions C = 0–80%. It has been shown that the value of w _i tends to increase in the course of polymerization transformation in agreement with the w _i = f(C) relationship calculated from the kinetic data on the thermal polymerization of styrene in the absence of counters of free radicals. Hypothetical reasons for this non-trivial tendency have been formulated. The experimental dependence w _i = f(C) has been measured for the first time and has been invoked to refine currently available mathematical models for the thermal polymerization of styrene that assume that w _i remains invariable in the course of polymerization transformation.     

Spin-lattice relaxations study of water mobility in natural natrolite

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀?2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T₁ and T_1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T_1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.     

Mesophilic Acidogenesis of Food Waste-Recycling Wastewater: Effects of Hydraulic Retention Time,pH, and Temperature

The effects of hydraulic retention time (HRT), pH, and operating temperature (T _OP) on the degradation of food waste-recycling wastewater (FRW) were investigated in laboratory-scale hydrolysis/acidogenesis reactors. Response surface analysis was used to approximate the production of volatile organic acids and degradation of volatile suspended solids (VSS), carbohydrate, protein, and lipid with regard to the independent variables (1?≤?HRT?≤?3 days, 4?≤?pH?≤?6, 25?≤?T _OP?≤?45 °C). Partial cubic models adequately approximated the corresponding response surfaces at α?<?5 %. The physiological conditions for maximum acidification (0.4 g TVFA?+?EtOH/g VS_added) and the maximal degradation of VSS (47.5 %), carbohydrate (92.0 %), protein (17.7 %), and lipid (73.7 %) were different. Analysis of variance suggested that pH had a great effect on the responses in most cases, while T _OP and HRT, and their interaction, were significant in some cases. Denaturing gradient gel electrophoresis analysis revealed that Sporanaerobacter acetigenes, Lactobacillus sp., and Eubacterium pyruvivorans-like microorganisms might be main contributors to the hydrolysis and acidogenesis of FRW. Biochemical methane potential test confirmed higher methane yield (538.2 mL CH₄/g VS_added) from an acidogenic effluent than from raw FRW.     

Density,Viscosity, and Glass Transition of an Ethylenediamine–Ethylene Glycol Binary System

Densities ρ and viscosities η were measured for the binary mixtures of ethylenediamine (EDA) and ethylene glycol (EG) in the temperature range 288.15–323.15 K for ρ and at 273.15–323.15 K for η, both of which are broader temperature ranges than those reported previously. The value of ρ monotonously decreases against the mole fraction of EDA, x _EDA, and increasing temperature. The concentration dependence of η exhibits a maximum in the intermediate concentration range at all temperatures measured. The glass transition temperature, T _g, for samples with x _EDA < 0.7 was measured using differential scanning calorimetry. The measured T _g values show a peak in the intermediate concentration range, which is a behavior similar to that of η; however, the peak concentrations for η and T _g did not precisely align because of a deviation in the maximum hydrogen-bond density. The partial molar volumes for EDA and EG and the thermal expansivities, α, were obtained from ρ. Results in the present study are discussed in terms of the extensively increasing hydrogen-bond density for polyamine–polyhydric alcohol systems.     

The thermodynamic properties of 5-vinyltetrazole and poly-5-vinyltetrazole over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependences of the heat capacities of 5-vinyltetrazole and poly-5-vinyltetrazole were measured by adiabatic vacuum calorimetry over the temperature range 6-(350–370) K with errors of ～0.2%. The results were used to calculate the thermodynamic functions of the compounds, C _p ^° , H ^°(T) - H ^°(0), S ^°(T), and G ^°(T) - H ^°(0), over the temperature range from T → 0 to 350–370 K. The energy of combustion of 5-vinyltetrazole and poly-5-vinyltetrazole was measured in an isothermic-shell static bomb calorimeter. The standard enthalpies of combustion Δ _c H ^° and thermodynamic characteristics of formation Δ_f H ^°, Δ_f S ^°, and Δ_f G ^° at 298.15 K and p = 0.1 MPa were calculated. The results were used to determine the thermodynamic characteristics of polymerization of 5-vinyltetrazole over the temperature range from T → 0 to 350 K.     

Diffusion and Relaxation Dynamics of Supercooled Polymer Melts

The dynamic properties of polymer melts are investigated in the range of normal liquid regime to the supercooled liquid regime. The polymer is modeled as a coarse-grained bead-spring model with chain length ranging from 5 to 160. The mean squared displacement and non-Gaussian parameter are used to describe the self diffusion of polymer beads. We find slow dynamics with decreasing temperature and increasing chain length. The time evolution of non-Gaussian parameters shows two peaks(or one peak one shoulder) in the α-relaxation time, τα, regime and sub-diffusion time regime, respectively, where the first primary peak indicates the dynamic heterogeneity stemmed from the motion of beads, and the secondary peak is the result of correlated motion along a polymer chain. Moreover, the relaxation of polymer beads shows clear two-step decay in supercooled melts and the dynamics shows growing heterogeneity with decreasing temperature. As chain length is increased, a peak of the dynamic susceptibility occurs, and the peak height,χ*4, increases and then reaches a plateau. The curves of the height of the first peak of α_2, α _2~*, versus τ and the curves of χ_4~*α versus τα follow two master curves for different chain lengths. Our results indicate the similarity of dynamic heterogeneity dominated by the motion of single bead even the chain length is different. It is interesting to find that the Stokes-Einstein(SE) relation between τα and diffusion coefficient D, D~τ-1 q, is highly length-scale dependent. The SE relation breaks down in both normal melts regime and supercooled regime at large magnitude of wave vectors, attributed to the non-Brownian motion arising from the chain connectivity and growing heterogeneity due to supercooling. However, the SE relation is reconstructed when the probing length scale is large(at small magnitude of wave vectors). Our results show a hierarchical physical picture of the supercooled polymeric dynamics.     

An XPS and STM Study of Oxidized Platinum Particles Formed by the Interaction between Pt/HOPG with NO<Subscript>2</Subscript>

X-ray photoelectron spectroscopy (XPS) (with AlK_α and AgL_α radiations) and scanning tunneling microscopy (STM) were used to study the interaction of two model samples prepared by vacuum evaporation of platinum on highly oriented pyrolytic graphite (HOPG) with NO₂ at room temperature. According to STM data, platinum evaporation on the graphite surface produced particles of a flattened shape. In the Pt/HOPGS1 sample with a lower concentration of platinum, the average diameter of particles d and the height-to-diameter ratio h/d were 2.8 nm and 0.29, respectively. In the Pt/HOPG-S2 sample with a higher concentration of platinum, the average values of d and h/d were 5.1 nm and 0.32. When the samples interacted with NO₂ (P ≈ 3 × 10^–6 mbar), the particles of metallic platinum completely converted to the particles of PtO_2· Upon oxidation, the shape of larger platinum particles in the Pt/HOPG-S2 sample did not change, although for the dispersed particles in the Pt/HOPG-S1 samples under these conditions, the h/d ratio increases. The reduction of oxide to metal particles on heating the Pt/HOPG-S1 sample in vacuum at 460°С is accompanied by an increase in the size of particles. Their shape became more round compared to the initial one. It was found that X-ray radiation affects the state of platinum in the oxidized sample by reducing the surface layer of PtO₂ to PtO.