Interpenetrating polymer networks of poly(dimethylsiloxane): 1. Preparation and characterization

Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10³ and 75 × 10³ g mol⁻¹ were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with M_n = 15 × 10³ and 75 × 10³ g mol⁻¹. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements.     

Preparation of ultra-high-strength nylon-6 fibre by a multi-step zone-annealing method

A multi-step procedure to improve the zone-annealing method was attempted to prepare a high-modulus and high-strength nylon-6 fibre. By the adoption of this procedure, the dynamic storage modulus at room temperature was markedly increased and reached 15.7 × 10¹⁰ dyne cm⁻² which is 1.5 times that obtained by the previous zone-annealing method. Tensile properties, orientation, crystallinity and mechanical dispersion were also measured. Comparing the multi-step procedure with the previous one-step procedure, the excellent effects of the multi-step procedure on mechanical properties are discussed. Further, in order to prevent selective relaxation of amorphous molecular chains on removing the applied tension after zone-annealing, heat-setting at constant length was subsequently carried out on the as-zone-annealed fibre. The mechanical properties were further improved: for example, the dynamic storage modulus at room temperature of the resulting fibre was raised to 16.9 × 10¹⁰ dyne cm⁻², which was well beyond the highest modulus available in the literature, 14 × 10¹⁰ dyne cm⁻².     

Diamond growth by carbon ion implantation of diamond

Medium energy (5–25 keV) ¹³C⁺ ion implantation into diamond (100) to a fluence ranging from 10¹⁶ cm⁻² to 10¹⁸ cm⁻² was performed for the study of diamond growth via the approach of ion beam implantation. The samples were characterized with Rutherford backscattering/channelling spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and Auger electron spectroscopy. Extended defects are formed in the cascade collision volume during bombardment at high temperatures. Carbon incorporation indeed induces a volume growth but the diamond (100) samples receiving a fluence of 4 × 10¹⁷ to 2 × 10¹⁸ at. cm⁻² (with a dose rate of 5 × 10¹⁵ at. cm⁻² s⁻¹ at 5 to 25 keV and 800 °C) showed no He-ion channelling. Common to these samples is that the top surface layer of a few nanometers has a substantial amount of graphite which can be removed by chemical etching. The rest of the grown layer is polycrystalline diamond with a very high density of extended defects.     

Estimation of the contribution of tube renewal in the terminal relaxation of linear polybutadiene

A set of low-molecular-weight (low-MW) entangled linear polybutadienes with molecular weights between 1.1 × 10⁴ and 2.5 × 10⁵ have been dilutedly embedded in a high-molecular-weight linear polybutadiene (M_w = 7.6 · 10⁵) matrix. The viscoelastic properties of these blends with 9.1% low-MW polymer have been measured. The loss moduli-frequency master curves, G^″ (Щ), contain contributions from both polymers. The contribution of the low-MW polymer is obtained by subtracting the contribution of the matrix. The maximum in G^″, G^″_m, due to the low-MW polymer occurs at a lower frequency (0.3 to 0.5 log units) than in the homopolymer. This result indicates that the longest relaxation time of the entangled linear polymer embedded in a high-molecular-weight matrix is increased by a factor of 2.0 to 3.0 because tube renewal normally operating in the homopolymer is almost completely absent in the matrix. The longest relaxation time of the polymers in the matrix depends on M^3.3₀. This is only slightly less than the dependence found in linear polymer melts (M^3.3₇). This indicates that reptation and chain-end fluctuation together contribute to the relaxation of linear polymers in permanent networks.     

Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2  of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<680 mL g⁻¹; the intrinsic viscosity, 130<[η]<550 mL g⁻¹. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000<M<240 000 g mol⁻¹. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [η] were: [η]=5.58×10⁻³ M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen k_s values for these substances is discussed.     

Pyrylium salt-photosensitised degradation of phenolic contaminants present in olive oil wastewaters with solar light: Part II. Benzoic acid derivatives

Solar light photodegradation, catalysed by a pyrylium salt, of seven benzoic acids present in olive oil mill, has been studied. Significant percentages of photodegradation (20–40%) have been achieved after 6 h of solar exposure for six of the acids, even though they were expected to be difficult to oxidise, due to the presence of an electron-withdrawing carboxylic acid group directly attached to the aromatic ring. Quenching constants for the electron-transfer process between the substrate and the excited catalyst were calculated by means of fluorescence measurements for syringic acid (66×10⁹ M⁻¹ s⁻¹), gallic acid (51×10⁹ M⁻¹ s⁻¹), veratric acid (51×10⁹ M⁻¹ s⁻¹), vanillic acid (48×10⁹ M⁻¹ s⁻¹), protocatechuic acid (37×10⁹ M⁻¹ s⁻¹) and p-hydroxybenzoic acid (15×10⁹ M⁻¹ s⁻¹); no quenching was found for benzoic acid. These photophysical measurements are in good correlation with the yields obtained in the pyrylium salt photocatalysed degradation of those phenolic acids.     

Characterization of diamond-like carbon films before and after heavy energetic ion implantations

Hydrogenated diamond-like carbon films were implanted by 110 keV Fe⁺ at doses ranging from 1 × 10¹³ to 5 × 10¹⁶ ions cm⁻². The film resistivities and the infra-red transmittances of the specimens were determined as functions of the implanted doses. Raman spectra and the infra-red transmittances of the film layers were used to characterize the structural changes of the implanted films. It was found that, when the implantation dose was higher than about 5 × 10¹⁴ or 1 × 10¹⁵ ions cm⁻², the film resistivity and the total infra-red transmittance of the specimens decreased significantly. However, when the dose was smaller than this value, the resistivity decreased firstly and then increased with dose and the measured values were higher than those of corresponding as-grown ones. The infra-red transmittance of the specimens was also improved to some extent under the lower dose range. By using structural characterization results, especially the infra-red transmittances of the film layers, we conclude that the electrical and optical property changes at doses higher than about 5 × 10¹⁴ or 1 × 10¹⁵ ions cm⁻² were due to the following changes, i.e., the decrease in the population of both sp² C-H and sp³ C-H bonds (compared with that of sp³ C-H bonds, the decrease in speed of sp² C-H bonds is smaller), the decrease of bond-angle disorder and the increased population of sp² C-C bonds. However, at doses between 1 × 10¹⁴ and 5 × 10¹⁴ or 1 × 10¹⁵ ions cm⁻², the implantation induced increase of C-H bonds was responsible for the observed property changes. Compared with the previous reports, the novelty of the present work is: the IR transmittance curves of the single film layers give us direct evidence for the changes of different C-H bonds with increasing ion dose and thus proved the transformation mechanism proposed previously.     

The elastic modulus of the poly(phosphonitrilic chloride) crystal

The Young's modulus for a crystal of poly(phosphonitrilic chloride) (poly-dichlorophosphazene) (NPCl₂)_n has been calculated using force constants derived from spectroscopy. Assuming that the molecule is a uniform helix the value of the modulus is 1.38 × 10⁹ dyne cm⁻² [dyne cm⁻² = 0.1 N m⁻²]; the result is 1.66 × 10¹⁰ dyne cm⁻² if a cis-planar structure is assumed for the molecule. Neither value is close to those obtained experimentally (1.8 × 10⁶ to 6.5 × 10⁶ dyne cm⁻²). This is because experimental values relate to the amorphous polymer whereas the calculated values are those for the crystal. There is good agreement between the values calculated for the (NPCl₂)_n crystal and those for other polymer crystals.     

Effects of oxygen concentration on the electrical properties of ZnO films

In this paper, electrical characteristics by various oxygen content in ZnO films were studied. To control the oxygen content of ZnO films, post-thermal annealing was performed in N₂ and air ambient, led to improve crystallinity and optical properties of ZnO films. The oxygen concentration was measured by Auger electron spectroscopy. The ZnO films having the deficiency of oxygen showed the electron concentrations between 10²¹ and mid 6 × 10¹⁷ cm⁻³ and resistivity at 10⁻³–10⁻¹ Ω cm. On the other hand, when the oxygen concentration of the ZnO films was up to the stoichiometry with Zn, the ZnO films showed low electron concentration at −10¹⁷ cm⁻³ and resistivity at 10 Ω cm.     

Conformation of isotactic polystyrene (IPS) in the bulk crystallized state as revealed by small-angle neutron scattering

Neutron scattering experiments have been performed on isotactic polystyrene (IPS) samples in the bulk crystallized state (T_{crystallization} = 185°C). The determination of the conformation of tagged chains ranging from 2.5 × 10⁵ to 7 × 10⁵ has been undertaken on two different hydrogenated IPS matrices. A matrix of usual molecular weight (M_w = 4 × 10⁵) leads to results which do not agree with Flory's model. In this case, measurements on radius of gyration R_g show on the one hand an important increase of this parameter (40%) with increasing crystallinity for the highest molecular weight tagged chains and on the other hand a variation with molecular weight like M^0.78. These results are interpreted with a schematic model involving a long crystalline sequence incorporated in the monocrystal along the 110 plane and two amorphous wings. Such an assumption is confirmed by the scattering behaviours in the intermediate range. On the other hand, by using an IPSH matrix of very high molecular weight (M_w = 1.75 × 10⁶), and the same tagged chains previously considered, a very weak variation of R_g with increasing crystallinity is observed. This leads to consider in this case Flory's conformation which is corroborated by data obtained in the intermediate range.     

On the possibility of the application of a radiotracer method for the in situ study of the accumulation of ions in corrosion products adhered to the surface of some steels

The sorption of ³⁶Cl labelled Cl⁻ ions into the layer of corrosion products adhered to the surface of corroding powdered steel samples has been studied as a function of the time at 1.8 × 10⁻² NaCl concentration. The effect of CrO²⁻₄ and SO₂₋₄ ions on the sorption process and the mobility of sorbed species was investigated.     

FTIR study of the adsorption of single pollutants and mixtures of pollutants onto titanium dioxide in water: oxalic and salicylic acids

The use of ATR–FTIR to probe the adsorption of oxalic and salicylic acids, and of mixtures of both, onto TiO₂ (Degussa P-25) demonstrates the potential of the technique to characterise the evolution of the catalyst with time, including surface poisoning. Under equilibrium dark conditions, three surface species are formed by oxalate, and two by salicylate. Their stabilities, described by conditional Langmuir-type equilibria involving the dissociative, electroneutral adsorption of the acids H₂L, are at pH 3.7, 2.4×10⁶, 3.0×10⁴ and 3.0×10³ mol⁻¹ dm³ for oxalic acid, and 2.9×10⁵ and 9.1×10³ mol⁻¹ dm³ for salicylic acid. The nature of the species is discussed in terms of their spectral features. The displacement of each acid from the surface by addition of the other one was followed also by ATR–FTIR. The results demonstrate that oxalate displaces totally chemisorbed salicylate, whereas salicylate displaces oxalate only partially. These results are explained by assuming competitive chemisorption onto two different surface sites, plus oxalate adsorption onto a site that exhibits negligible affinity for salicylate. Irreversible adsorption by partially oxidised products in the course of photocatalytic processes can therefore be assessed by ATR–FTIR.     

Molecular, thermal and morphological characterization of narrowly branched fractions of 1-octene LLDPE: 2. Study of the lamellar morphology by transmission electron microscopy

The lamellar morphology of a linear low density ethylene/1-octene copolymer (LLDPE A), and its fractions with short chain branching contents ranging between 3 and 28 branches per 1000 C atoms, has been investigated using transmission electron microscopy. The weight average molecular weight of the samples studied decreases from 2.7 × 10⁵ at the lowest branching content down to 4.9 × 10⁴ at the highest branching content. The branching content is the major factor determining the lamellar thickness, while the morphological structure of the lamellae depends both on the branching content and the molecular weight. In contrast to the unfractionated copolymer LLDPE A, lamellar stacks were observed in all fractions.     

Nuclear magnetic resonance approach to the characterization of siloxane-silica network-like structures

This work deals with mesh size properties of network-like structures associated with random siloxane-silica mixtures. The transverse magnetic relaxation function of protons is shown to obey a superposition property controlled by the silica concentration C_Si, in the range 0C_Si0.50 (w/w). Correspondingly, its invariant mathematical structure is governed by the average residual energy of dipole-dipole interactions only. The parameter Δ_e is given the role of a timescale shift factor; it is related to the average mesh size of a given network. Nuclear magnetic resonance measurements show that silica aggregates do not induce any strong deviation from the primary entanglement system established in a pure siloxane melt. Whether infinite siloxane-silica clusters are swollen by polymer chains or whether finite size clusters are diluted in a siloxane melt, the resulting networks are described by similar distribution functions of elementary chains connecting neighbouring entanglements; these functions are shifted towards smaller mesh sizes upon addition of silica. These properties hold for several high molecular weight samples: , 2.4 × 10⁵ and 1.6 × 10⁵, respectively.     

Compression of poly(vinyl alcohol) gels by ultracentrifugal forces

Compression due to ultracentrifugal forces was investigated for poly(vinyl alcohol) (PVA) gels. The concentration gradient profiles for the gels were obtained by experiment and were then compared with a theoretical prediction. By the application of the centrifugal forces, the concentration gradient near the bottom increases sharply whereas the gradient inside the gel remains almost constant in the region far from the bottom. Further application of the centrifugal forces enhances the peak near the bottom. These are well explained by the theory proposed in the previous paper [Urayama et al. J Chem Phys 2005;122:024906.]. The frictional coefficient f for the PVA gels, which originates from the friction between the polymer network and solvent molecules, is estimated to be 3.5×10¹⁴ N s m⁻⁴.     

Studies on the structure and formation mechanism of carbon gel in the carbon black filled polyisoprene rubber composite

The structure and formation mechanism of carbon gel in carbon black filled polyisoprene composites were studied by the pulsed NMR technique. The composites were prepared from a wide range of molecular weights by a solution blend. The carbon gels were extracted from the composites by a solvent-extraction method. The content of carbon gel was not governed by the molecular weight of rubber but was controlled by the viscosity of rubber solutions which were used for the blend. Three rubber phases, having different spin-spin relaxation times, were detected in all the carbon gels. The increase of carbon gel content in the composites was mainly from the increase of highly mobile rubber phase, and the gel became soft with the development of this phase. On the other hand, the content and structure of glassy rubber phases were not affected by the size of the carbon gel, and they showed almost a constant value despite the large change in the carbon gel content. A part of the highly mobile rubber phase in the gels could be removed by solvent extraction at high temperature. These results suggest that the formation of carbon gel is primarily governed by two factors: One is the well-known rubber-carbon black interaction, and the other is a physical crosslink between the carbon gel and unbound rubber molecules during blend. © 1996 John Wiley & Sons, Inc.     

Deformation and toughness of polymeric systems: 3. Influence of crosslink density

In part 1 of this series the phenomenon of a critical ligament thickness (ID_c) below which brittle polymers become ductile was investigated for polystyrene (PS). Using the thermoplastic polystyrene-poly(2,6-dimethyl-1,4-phenylene ether) (PS-PPE) model system, it was demonstrated in part 2 of this series that the absolute value of ID_c as well as the maximum toughness (i.e. maximum strain to break) was dependent on the network density of the polymer used. In this study the toughness and ID_c of crosslinked thermosetting polymers were investigated using epoxides based on the diglycidyl ether of bisphenol A as a model system. The crosslink density (v_c) is varied between values comparable with (v_c = 9 × 10²⁵ chains m⁻³), up to values much higher than (v_c = 235 × 10²⁵ chains m⁻³), the entanglement density in the thermoplastic PS-PPE system. The maximum macroscopic toughness proportional to the strain to break (λ_macr) or given by the slow-speed fracture toughness (G_Ic) and the notched high-speed tensile toughness (G_h) of core-shell rubber-modified epoxides uniquely increases with an increasing molecular weight between crosslinks (M_c). Only by using extreme testing conditions (notched high-speed impact testing), could the ID_c of a limited range of epoxides be determined: 0.21 μm (v_c = 9 × 10²⁵ chains m⁻³) ≤ ID_c ≤ 0.29 μm (v_c = 14 × 10²⁵ chains m⁻³). Both the experimentally determined values of ID_c and the toughness of the epoxides compare well with the values determined for the entangled thermoplastic PS-PPE model system in the same range of network densities, elucidating the principal similarity of the influence of entanglements and crosslinks on the deformation processes. Good agreement was observed between the experimentally determined values of ID_c of the epoxides and the values predicted by the simple model introduced in part 2 of this series.     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

Methacryl-terminated macromers by living polymerization as precursors of IPN polymer electrolytes

A new class of polymer electrolytes, based on the interpenetrating polymer network approach, was obtained starting from functionalised macromers, of poly-ether nature, in the presence of a lithium salt (LiBF₄, LiClO₄, LiCF₃SO₃) and propylene carbonate (PC) or tetraethyleneglycol dimethylether (TGME), as plasticizers.

The macromers were synthesised by living polymerisation employing a HI/I₂ system as the initiator. The macromer has a polymerisable end group, which can undergo radical polymerisation, attached to a monodisperse poly-vinylether, containing suitable ethylene oxide groups for ion coordination. Monomers and macromers were characterised by FTi.r., u.v.–vis, ¹H- and ¹³C-n.m.r.

Self-consistent and easily handled membranes were obtained as thin films by a dry procedure using u.v. radiation to polymerise and crosslink the network precursors, directly on suitable substrates, in the presence of the plasticizer and the lithium salt. The electrolytic membranes were studied by complex impedance and their thermal properties determined by differential scanning calorimetry analysis.

Ionic conductivities (σ) were measured for PC and TGME-based membranes at various plasticizer and salt contents as a function of T (60 to −20°C). LiClO₄/PC/PE electrolytes, with 3.8% (w/w) salt and 63% PC, have the highest σ (1.15×10⁻³ and 3.54×10⁻⁴ S cm⁻¹ at 20°C and −20°C, respectively). One order of magnitude lower conductivities are achieved with TGME; samples with 6% (w/w) LiClO₄ and 45% (w/w) TGME exhibit σ values of 2.7×10⁻⁴ and 2.45×10⁻⁵ S cm⁻¹ at 20°C and −20°C.     

Sorption kinetics of ammonia and ammonium ions on gel and macroporous sulphonic acid cation exchangers

Diffusion of ammonia and ammonium ions in sulphonic acid cation exchangers (gel Purolite SGC 100 × 10 MBH and macroporous Purolite C 160 MBH) from the solutions, representing the composition of “caustic condensate” (waste of nitrogen fertilizers production) is affected by pH of initial solution and structure of the matrix of cation exchanger. In gel matrix the effective intraparticle diffusivity (D_ef) depends greatly on the solution pH because of shrinkage in alkaline and swelling in acidic medium: on decreasing the initial concentration of ammonia from 0.214 to 0.003 and increasing that of ammonium nitrate from 0 to 0.214 mol l⁻¹ instead, the effect of ion exchange leads to a decrease in pH, resulting in swelling and increase in D_ef from 0.1 to 0.34 × 10⁻¹⁰ for gel Purolite SGC 100 × 10 MBH and variation of 0.18–0.11 × 10⁻¹⁰ m² s⁻¹ for macroporous Purolite C 160 MBH (resistant to shrinkage and swelling).

In Purolite C 160 MBH both macropore diffusivity (0.07–0.29 × 10⁻¹⁰ m² s⁻¹) and gel (solid phase) diffusivity (0.06–0.19 × 10⁻¹⁰ m² s⁻¹) are higher than micropore diffusivity (0.28–0.56 × 10⁻¹⁸ m² s⁻¹).

With respect to the effective intraparticle diffusivity, resistance to nitric acid, used for the regeneration, and high concentration of ammonium nitrate in eluate (up to 110 g l⁻¹), Purolite C 160 MBH has been installed for the conversion of ammonia and ammonium ions to ammonium nitrate reusable in the fertilizers production. This allows minimizing the economic loss and preventing the environmental contamination.