Thermal conductivity of a polymer composite filled with mixtures of particles

A new thermal conduction model is proposed for a polymer system filled with a mixture of several types of particles. Predicted values by the new model are compared with experimental data. The model is derived by extending a model that was previously proposed for a two-phase system. The following equation is derived from the new model: log λ = V · (X₂ · C₂ · log λ₂ + X₃ · C₃ · log λ₃ + (1 ? V) log (C₁ · λ₁. When the thermal conductivities of polymer and particles (λ₁, λ₂, λ₃, …) and a mixing ratio of particles (X₂, X₃, …) are known, thermal conductivity of the filled polymer (λ) with several types of particles can be estimated from the equation, with any volume content of particles (V). Furthermore, from each polymer–filler composite (two-phase system) data, the thermal conductivity of a composite filled with different filler particles can be estimated.     

Thermal conductivity and thermal expansivity of in situ composites of a liquid crystalline polymer and polycarbonate

The thermal conductivity and thermal expansivity of extruded blends of a liquid crystalline polymer (LCP) and polycarbonate (PC) with volume fraction (V_f) of LCP between 0.09 and 0.8 have been measured as functions of draw ratios λ ranging from 1.3 to 15. At V_f < 0.3, the LCP domains are dispersed in a PC matrix and the aspect ratio of the domains increases with increasing λ. At V_f > 0.55, phase inversion has occurred and the LCP becomes the continuous phase. The axial thermal conductivity K_∥ increases while the axial expansivity α_∥ decreases sharply with increasing λ, as a result of the higher aspect ratio of the LCP fibrils and the improved molecular orientation within the fibrils. Since the transverse thermal conductivity and expansivity are little affected by drawing, the blends exhibit strong anisotropy in the thermal conduction and expansion behavior at high λ. At V_f < 0.3, the behavior of K_∥ is reasonably modeled by the Halpin-Tsai equation for short fiber composites. At high draw ratio (λ = 15), all the blends behave like unidirectional continuous fiber composites, so K_∥ and α_∥ follow the rule of mixtures and the Schapery equation, respectively.     

3D Supramolecular Polymer Constructed from Agostic, Polyhapto and Thallophillic Interactions: A New Precursor for Preparation of Tl2O3 Nanoflowers

A new thallium(I) supramolecular polymer, [Tl₄(μ₃-2,4-cfp)₄] _n (1) [2,4-Hcfp = 2-chloro-4-fluorophenol] (1) with disordered cubic cage structural unit has been synthesized and characterized. The single-crystal X-ray data of 1 shows four types of Tl^I ions in the tetranuclear cubic cage unit with a coordination number three. In addition to an intra-cage thallophillic interaction, an inter-cage thallophillic interaction also exists and results in formation of 1D supramolecular polymer. Short contacts, Tl···H and Tl···C, make 1 a 3D supramolecular polymer. Short Tl···F and Tl···Cl secondary interactions also exist. Finally the Tl-ions attain O₃Tl1···C₆Tl₂, O₃Tl2···TlClF, O₃Tl3···Tl₂ and O₃Tl4···C₂TlH coordination spheres with a stereochemically ‘active’ electron lone pair of electrons on the metal ions. The thermal stability of 1 was studied by thermogravimetric and differential thermal analyses. Nanostructures of thallium(III) oxide were prepared from calcination of fine powders of 1 at 570 and 630 °C. These nanostructures were characterized by X-ray powder diffraction and scanning electron microscopy .     

Entanglement networks of 1,2-polybutadiene crosslinked in states of strain. IV. States of ease and stress–strain behavior

Linear 1,2-polybutadiene, glass transition temperature (T_g) ?18°C, is crosslinked at ?10°C, to ?20°C by γ irradiation while strained in simple extension, with extension, ratios (λ₀) from 1.2 to 2.7. After release, the sample retracts to a state of ease (λ_s) at room temperature. From equilibrium stress–strain measurements up to a stretch ratio relative to the state of ease (Λ) of 1.2, together with λ₀ and λ_s, the concentration of network strands terminated by trapped entanglements (νN) is calculated. For this purpose, a three-constant Mooney–Rivlin formulation is used, in which the entanglement network is described by Mooney–Rivlin coefficients C_1N and C_2N, whereas the crosslink networks is described by the coefficient C_1x only. The ratio ψ_N = C_2N/(C_1N + C_2N) is estimated from parallel studies of nonlinear stress relaxation of the uncrosslinked polymer, taking into account the thermal history before and during irradiation. For substantial degrees of crosslinking, i.e., for R_0′ = ν_x/ν_N > 0.4 (where ν_N is the concentration of network strands terminated by crosslinks), and for λ₀ < 1.8, C_2N agrees rather well with the value obtained from stress relaxation of the uncrosslinked polymer in the range of time scale where it is nearly independent of time (1.87 X 10⁵ pascals). The corresponding value of ν_N is 2.3 × 10^?4 moles/cm³, in good agreement with that obtained from viscoelastic measurements of the uncrosslinked polymer in the plateau zone (2.5 × 10^?4). However, for R_0′ ? 0.2, smaller values of C_2N and ν_N are obtained, indicating that for low degrees of crosslinking the entanglements are not completely trapped. Also, for higher values of λ₀, C_2N and ν_N turn out to be somewhat smaller. Similar, less extensive results were obtained previously on a 1,2-polybutadiene with somewhat higher vinyl content and a higher T_g. Crosslinked samples of both these polymers were subjected to equilibrium stress–strain measurements in simple elongation from the state of ease at higher strains up to Λ = 1.7. The results agreed closely with calculations from the three-constant Mooney–Rivlin theory.     

Degradation of the mechanical properties of composite vulcanizates loaded with paraffin wax

A composite of Styrene Butadiene Rubber (SBR) and Natural Rubber (NR) loaded with 40 phr of High Abrasion Furnace (HAF) carbon black is loaded with different concentrations of paraffin wax. From the stress–strain curves, Young's modulus was found to decrease with increasing the amount of added paraffin wax. The modified Mooney-Revlin equation was used to calculate the parameters C₁ and C₂. A plot between the true tensile stress as a function of (λ² − λ⁻¹) was used to calculate two parameters σ₀ and G, and then both the average molecular weight between crosslinks and the number of effective plastic chains per unit volume were also calculated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2265–2270, 2001     

Effect of thermal hysteresis on melting of syndiotacticity-rich poly(vinyl alcohol) hydrogel

The melting temperatures (T_M) of hydrogels prepared by chilling aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) at 0°C were measured rising temperature of gels from the initiative temperature (T_I) of 0–70°C (every 10°C). The apparent enthalpies of fusion of a junction ΔH's were estimated from the relation between the logarithm of polymer concentration (log C) and 1/T_M. ΔH depended on T_I, showing that the melting point of gels depended on a thermal hysteresis. The highest polymer concentration C_H in those of the gels which have no melting point above an initiative temperature was determined and ΔH was estimated from the relation between log C_H and the reciprocal melting point of the gels with C_H, 1/T_IM. The ΔH was 15.1 kJ/mol in the range of higher polymer concentrations and 43.9 kJ/mol in the range of lower concentrations.     

Effect of filler size distribution on the mechanical and physical properties of alumina‐filled silicone rubber

The properties of silicone rubber filled with three kinds of binary mixtures of alumina particles with different size distribution (i.e., 30 μm + 0.5 μm, 10 μm + 0.5 μm, and 5 μm + 0.5 μm) were investigated as a function of relative volume fraction of the 0.5 μm particles in the hybrid alumina (V_s) at a fixed total filler content of 55 vol%. The results indicate that each binary mixture of alumina‐filled silicone rubber exhibited improved thermal conductivity and tensile strength, and decreased dielectric constant, compared to a single particle size filler‐reinforced one, and the maximum improvements were obtained at the V_s ranging from 0.2 to 0.35; the coefficient of thermal expansion (CTE) of filled silicone rubber obviously reduced with increase in the V_s, whereas the elongation at break slightly decreased. At V_s = 0, the larger particles‐filled silicone rubber showed higher thermal conductivity, CTE, dielectric constant, and elongation at break, and lower tensile strength compared with the those of the smaller particles‐filled one. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

A New Metal–Organic ZnII Supramolecular Assembled via Hydrogen Bonds and N···N Interactions as a New Precursor for Preparation Zinc(II) Oxide Nanoparticles, Thermal, Spectroscopic and Structural Studies

A new 1D supramolecular involving two different ligands, {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O (GB = 2-guanidinobenzimidazole and bpe = 1,2-bis(4-pyridyl)ethylene, has been synthesised, characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy. The thermal stability of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O was studied by thermal gravimetric and differential thermal analyses. The single crystal X-ray analysis shows that the complex is a one-dimensional polymer involving macrocycle rings as a result of non-covalent bridging bpe ligands via N–H···N and N···N interactions, N–H···bpe···bpe···H–N, with the basic repeating {[Zn(GB)₂](μ-bpe)₃}(ClO₄)₂·H₂O units and by connecting [Zn(GB)₂]²⁺ nodes. ZnO nanoparticles were obtained by calcination of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O at 500 °C in air. The nanoparticles were characterized by X-ray diffraction and scanning electron microscopy.     

Thermal conductivity of a polymer composite

A prediction equation for thermal conductivity of polymer composites reported in our previous papers has been revised in terms of two view points: (1) estimation of thermal conductivity of a composite using an idea of reduced thermal conductivity; and (2) the effect of ease in forming conductive filler chains on thermal conductivity is related to the CVF value in electric conductivity of the composite. The new equation was confirmed to be adaptable to thermal conductivities of varieties of polymer composite systems filled with spherical or irregular fillers. The equation was also considered to explain thermal conductivity of polymer composites filled with fibers. Further, it was found that thermal conductivities of fiber composites can be estimated by introducing a factor of the CVF value or aspect ratio (L/D) into the new equation. © 1993 John Wiley & Sons, Inc.     

Development of a correlation between the non-polar solubility parameter,refractive index and molecular structure. I. Aliphatic hydrocarbons

For non-polar liquids (e.g. the alkanes) the cohesion energy density (λ²) can be shown to be a function of the refractive index (nD ), molal volume (V) and molecular structure according to: where Δ is the non-polar solubility parameter and the increments g_ij are determined from molecular structure. The difference between values of Δ calculated by this formula and experimental data is <0.1% for the C₅–C₁₆ n-alkanes and <0.8% for the C₅–C₈ branched isomers. The main object of this correlation was to provide a method for estimating the London dispersion force contribution to the cohesive energy of branched polar liquids.     

Fabrication of Silver Nanoparticles and 3D Interpenetrated Coordination Polymer Nanorods from the Same Initial Reagents

Nanorods of the three-dimensional coordination polymer, [Ag₂(μ ₂-py-4-c)₂] _n (1) [py-4-c⁻ = pyridine-4-carboxylate], have been synthesized by sonochemical process. The single-crystal X-ray data of compound 1 shows the formation of a 3D interpenetrated silver(I) coordination polymer, which has agostic interactions around the silver(I) ions and two types of Ag^I ions with O₂NAg1···O₂H, N₂ Ag2···O₂H₂ coordination spheres. Silver nanoparticles were fabricated from thermal decomposition of 1 nanorods. These nanostructures were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The thermal stability of 1 was studied by thermo gravimetric (TG) and differential thermal (DT) analysis.     

Diffusivity of alkanes in polystyrene

Gravimetry is used to study the diffusivity of a homologous series of linear alkanes (C_n, with n = 8, 10, 12, 14 and 16) in amorphous polystyrene at temperatures ranging from 45 °C to 145 °C, i.e. both below and above the polymer glass transition temperature (100 °C). All the mass uptake results obtained are well described by a simple Fickian model (for t < t_1/2) and are used to calculate the corresponding diffusion coefficients (D) using the thin-film approximation of the Fickian equation. For all the alkanes considered, the temperature dependency of the diffusion coefficients is non-Arrhenius in character, over the broad temperature intervals considered. For any particular temperature log(D) varies linearly (R² > 0.993, for all temperatures) with respect to the number of carbon atoms (n) in the alkyl chain, log(D) decreasing when n increases. For each liquid penetrant, over the temperature intervals considered, its log(D) also increases linearly (R² > 0.996 for all the systems) with the decrease in the penetrant’s liquid viscosity.     

Preparation and characterisation of BaTiO3 based PTC ceramics with high performance

Abstract

The nanocrystalline BaTiO₃ based PTC powders had been prepared by a simple sol–gel method starting from comparatively cheap raw materials. The powders and ceramics were characterised by thermogravimetry–differential scanning calorimetry, X-ray diffraction and scanning electron microscopy, while electronic properties of the ceramics were also studied. The good material electronic properties were obtained, including a Curie temperature (T _C) of 100°C, a resistivity at room temperature (ρ _25°C) of 18 Ω cm, a high resistivity step ratio (ρ _max/ρ _min) of 1·2×10⁶, a temperature coefficient of resistivity (α ₃₀) of 17% °C^?1 and a withstand voltage intensity (V _b) of 196 V mm^?1.     

Synthesis of Lead(II) Minoxidil Coordination Polymer: A New Precursor for Lead(II) Oxide and Lead(II) Hydroxyl Bromide

A new lead(II) coordination polymer, [PbBr₂(C₉H₁₅N₅O)]_n (1), where C₉H₁₅N₅O is (2,4-diamino-6-piperidine-1-yl) pyrimidine N-oxide (minoxidil) is synthesized and characterized. Polymer 1 is synthesized in methanol by sonochemical and hydrothermal methods from lead(II) acetate, KBr and the minoxidil ligand. The crystal structure of [PbBr₂(C₉H₁₅N₅O)]_n indicates a syndiotactic coordination polymer. The Pb(II) atom lies on a mirror plane; the mirror plane is perpendicular to the pyrimidine ring bisecting the piperidine ring. N–H···O intramolecular and C–H···Br, N–H···N strong intermolecular interactions were observed. Micro-rods of PbO and nano-plates of PbOHBr were prepared by thermal decomposition of the nano-structured [PbBr₂(C₉H₁₅N₅O)]_n as a precursor. Characterization of the products was carried out using X-ray crystallography, elemental analysis, FTIR spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and thermal analysis. The sonochemical method resulted in a significant reduction of reaction time, reaction temperature and particle sizes of the products.     

A luminous efficiency function,VD65* (λ), for daylight adaptation: A correction

We recently proposed a 2° photopic luminosity function, V_D65*(λ) [J Vis 2005;5:948–968], which improves upon the original CIE 1924 V(λ) function and its modifications, while being consistent with a linear combination of the Stockman and Sharpe [Vis Res 2000;40:1711–1737] long‐ and middle‐wavelength‐sensitive cone fundamentals [L(λ) and M(λ), respectively]. Its derivation was based on 25‐Hz heterochromatic flicker photometric (HFP) data obtained from 40 observers of known genotype on a 1000 troland white (D65) background. However, as a result of an analysis of new luminous efficiency data obtained on an series of chromatic backgrounds [J Vis 2008;8:1–26], we now recognize that the 25‐Hz flickering targets, though near‐flicker‐threshold, altered the mean chromaticity of the adapting background. Consequently, we have revised the original analysis, taking into account the changes in mean adapting chromaticity with target wavelength. Our reanalysis of the individual and mean data shows that the V_D65*(λ) function for a D65 background should be redefined as 1.89L(λ) + M(λ) in quantal terms and as 1.98L(λ) + M(λ) in energy terms. The change in the L‐cone weighting factor represents a change in luminous efficiency across the spectrum of ～0.04 log unit. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Removal of 1,1′-Dimethyl-4,4′bipyridyl Dichloride from Aqueous Solution by Natural and Activated Bentonite

The sorption of 1,1′-dimethyl-4,4′bipyridilium dichloride (paraquat) on bentonite desiccated at 110°C untreated, and acid-treated with H₂SO₄ solutions over a concentration range between 0·25 M and 1·00 M , from aqueous solution at 30°C has been studied by using batch experiments. In addition, column experiments were carried out with the bentonite sample treated with the 1·00 M H₂SO₄ solution [B-A(1·00)] by using two aqueous solutions of paraquat of different concentrations (C = 29·40 mg dm⁻³ and C = 65·38 mg dm⁻³). The experimental data points have been fitted to the Langmuir equation in order to calculate the sorption capacities (X_m) of the samples; X_m values range from 1·35×10⁵ mg kg⁻¹ for the sample acid-treated with 0·375 M H₂SO₄ [B-A(0·375)] up to 1·96×10⁵ mg kg⁻¹ for the untreated bentonite [B-N]. The removal efficiency (R) has also been calculated; R values ranging from 44·61% for the [B-A(0·375)] sample up to 67·23% for B-N. The batch experiments show that the natural bentonite is more effective than the acid-treated bentonite in relation to sorption of paraquat. The column experiments show that the B-A(1·00) sample might be reasonably used in removing paraquat, the column efficiency increasing from 37·55% for the C = 65·38 mg dm⁻³ aqueous solution of paraquat up to 66·58% for the C = 29·40 mg dm⁻³ one. © 1997 SCI.     

Elastic constants and thermal expansivity of gel-spun polyethylene fiber and its composites

The five independent stiffness constants, C₁₁, C₃₃, C₄₄, C₆₆, and C₁₃, and the axial and transverse thermal expansivity of unidirectional gel-spun polyethylene fiber reinforced composites have been measured as functions of fiber volume fraction V_f. The axial extensional modulus C₃₃ and axial Poisson's ratio v₁₃ follow the rule of mixtures, while the axial shear modulus C₄₄, transverse shear modulus C₆₆, and transverse plane-strain bulk modulus C_t ( = C₁₁ − C₆₆) obey the Halpin-Tsai equation. Extrapolation to V_f = 1 gives the five stiffness constants of gel-spun polyethylene fiber. The tensile property of the fiber is highly anisotropic, with the axial Young's modulus about 40 times higher than the transverse Young's modulus. In contrast, the axial shear modulus exceeds the transverse shear modulus by only 5%. A similar treatment of the thermal expansivity data in terms of the Schapery equations gives an axial thermal expansivity of −1.25 × 10⁻⁵ K⁻¹ and a transverse thermal expansivity of 11.7 × 10⁻⁵ K⁻¹ for the fiber.     

Estimation of thermal conductivity of polymer multiphase composites

The thermal conductivities of a medium density polyethylene composites filled separately with two different thermal conductive fillers including graphite, cuprum, and aluminum oxide (Al₂O₃), an epoxy composites filled respectively with two different thermal conductive fillers including silicon nitride, aluminum hydroxide, Al₂O₃ and aluminum nitride, and a polypropylene composites filled with aluminum hydroxide and magnesium hydroxide were estimated using a thermal conductivity equation of polymer multiphase composites. This equation was based on a new heat transfer model, and the parameters were easily determined. It was found that the estimated thermal conductivities of the three composites systems were approximately close to the experimental measured data reported in literature. In addition, the predictions were roughly close to the estimations from the Agari model. POLYM. ENG. SCI., 57:965–972, 2017. © 2016 Society of Plastics Engineers