Rheological characterization of polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol graft copolymer (Soluplus®) water dispersions

Soluplus® is a graft copolymer, with PEG and vinylcaprolactam/vinyl acetate side chains, recently available as excipient used to promote fast drug release in pharmaceutical dosage forms and as solubility enhancer. Despite this copolymer is reported to be able to act as a thickening additive and even as gelling agent as a function of temperature, there is a lack of information about the physical–chemical properties of its water dispersions. Thus, the aim of this paper is to investigate the influence of Soluplus® concentration and experimental temperature on the modification of the rheological properties of Soluplus® water dispersions. The results clearly indicated the influence of both the studied parameters and of their interactions on the Soluplus® thickening ability. Although some systems appear gel by human perception at 37 °C, the mechanical spectra demonstrated the lack of the formation of a tridimensional network structure. Overall, in all the analyzed temperatures and concentrations, the systems always behave as a “rheological” dilute or semidilute polymer solution.     

Thermal stability of high density polyethylene–fumed silica nanocomposites

High-density polyethylene-based nanocomposites were prepared through a melt compounding process by using surface functionalized fumed silica nanoparticles in various amounts, in order to investigate their capability to improve both mechanical properties and resistance to thermal degradation. The fine dispersion of silica aggregates led to noticeable improvements of both the elastic modulus and of the stress at yield proportionally to the filler content, while the tensile properties at break were not impaired even at elevated filler content. Thermogravimetric analysis showed that the selected nanoparticles were extremely effective both in increasing the decomposition temperature and in decreasing the mass loss rate, even at relatively low filler loadings. The formation of a char enriched layer, limiting the diffusion of the oxygen through the nanofilled samples, was responsible of noticeable improvements of the limiting oxygen index, especially at elevated silica loadings. In contrast with commonly reported literature results, cone calorimeter tests also revealed the efficacy of functionalized nanoparticles in delaying the time to ignition and in decreasing the heat release rate values. Therefore, the addition of functionalized fumed silica nanoparticles could represent an effective way to enhance the flammability properties of polyolefin matrices even at low filler concentrations.     

Preparation of polystyrene/silica nanocomposites by radical copolymerization of styrene with silica macromonomer

A two-stage process has been developed to generate the silica-based macromonomer through surface-modification of silica with polymerizable vinyl groups. The silica surfaces were treated with excess 2,4-toluene diisocynate (TDI), after which the residual isocyanate groups were converted into polymerizable vinyl groups by reaction with hydroxypropylacrylate (HPA). Thus, polystyrene/silica nanocomposites were prepared by conventional radical copolymerization of styrene with silica macromonomer. The main effecting factors, such as ratios of styrene to the macromonomer, together with polymerization time on the copolymerization were studied in detail. FTIR, DSC and TGA were utilized to characterize the nanocomposites. Experimental results revealed that the silica nanoparticles act as cross-linking points in the polystytene/silica nanocomposites, and the glass transition temperatures of the nanocomposites are higher than that of the corresponding pure polystyrene. The glass transition temperatures of nanocomposites increased with the increasing of silica contents, which were further ascertained by DSC.     

Photochemical degradation study of polyvinyl acetate paints used in artworks by Py–GC/MS

Photochemical degradation of commercial polyvinyl acetate (PVAc) homopolymer and PVAc paints mixed with burnt umber, cobalt blue, cadmium red dark, nickel azo yellow and titanium white commonly used for artworks were studied by pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Py–GC/MS with single-shot technique was used for the characterization of the thermal degradation of PVAc at different temperatures, while the double-shot technique of Py–GC/MS was used to reveal the differences in the specimens before and after UV ageing, including the changes of detectable amounts of deacetylation product – acetic acid and plasticizers such as diethyl phthalate (DEP). Furthermore, the relative concentration of the pyrolysis products of the paint samples could be measured and compared in the second step of the double-shot Py–GC/MS, which are highly dependent on the presence of pigments and the ageing status of PVAc paints.     

The temperature effect on electrokinetic properties of the silica–polyvinyl alcohol (PVA) system

The influence of polyvinyl alcohol (PVA) adsorption on the structure of the diffuse layer of silica (SiO₂) in the temperature range 15–35 °C was examined. The microelectrophoresis method was used in the experiments to determine the zeta potential of the solid particles in the absence and presence of the polymer. The adsorption of PVA macromolecules causes the zeta potential decrease in all investigated SiO₂ systems. Moreover this, decrease is the most pronounced at the highest examined temperature. Obtained results indicate that the conformational changes of adsorbed polymer chains are responsible for changes in electrokinetic properties of silica particles. Moreover, the structure of diffuse layer on the solid surface with adsorbed polymer results from the following effects: the presence of acetate groups in PVA chains, the blockade of silica surface groups by adsorbed polymer and the shift of slipping plane due to macromolecules adsorption.     

Dynamics of the surface layer in cyanobiphenyl–aerosil nanocomposites with a high silica density

Composites were prepared from an aerosil and 4-n-alkyl-4′cyanobiphenyls with five to eight carbon atoms in the alkyl chain. Their high silica density of ～7?g aerosil in 1?cm³ of liquid crystal (LC) allows the observation of the behaviour of a thin cyanobiphenyl layer (having nearly a monolayer structure) on the silica particles. The systems are investigated by dielectric spectroscopy (10^?2–10⁹?Hz) in a large temperature range (220–370?K). All the composites show a (main) relaxation process at frequencies much lower than the processes observed for the bulk LC that was assigned to the dynamics of the molecules in the surface layer. The temperature dependence of its characteristic frequencies obeys the Vogel–Fulcher–Tammann law, which is found to be typical for glass-forming liquids. The quasi two-dimensional character of the glass transition in the surface layer is discussed for the first time. At the nematic-to-isotropic transition temperature of the bulk, the composites show a continuous decrease of the characteristic frequencies as a function of the alkyl chain length, while the bulk LCs show the well known odd–even behaviour. The magnitude and temperature dependence of the slow relaxation process in the composites (molecules on an outer surface) agree with those of the same molecules confined to the nanopores of molecular sieves (internal surface).     

Polypropylene wax (PPw)/silica hybrid by in situ non-aqueous sol–gel process for preparation of PP/silica nanocomposites

This paper presented a novel approach to prepare PP/silica nanocomposites. First, PPw-g-KH570 (γ-methacryloxypropyl trimethoxysilane) was obtained by pre-irradiation grafting method and characterized by FTIR and TGA. Then the non-aqueous sol–gel gelation kinetics of TEOS (tetraethoxysilane)-formic acid system in xylene was researched. Subsequently PPw/silica hybrid was obtained by in situ non-aqueous sol–gel reaction of TEOS in the presence of PPw-g-KH570 solution in xylene. Finally PP/silica nanocomposites were prepared by blending of PP matrix and PPw/silica hybrid. The mechanism of in situ formed PPw/silica hybrid was proposed. The morphology of PPw/silica hybrid and microstructures of PP/silica nanocomposites were characterized by TEM and SEM. The mechanical and thermal properties of PP/silica nanocomposites were also well studied by tensile tests and DSC. It was showed that the nanosilica particles were well dispersed in PPw/silica hybrid with the aid of grafting KH570 due to co-condensation by grafted KH570 and TEOS. PPw/silica hybrid was well dispersed in PP matrix with good compatibility and strong interactions. The resulted PP/silica nanocomposites possessed better performance than that of pure PP matrix.     

Quiescent hydrothermal synthesis of reduced graphene oxide–periodic mesoporous silica sandwich nanocomposites with perpendicular mesochannel alignments

Quiescent hydrothermal conditions were applied to synthesis of the sandwich nanocomposites of reduced graphite oxide (rGO) and periodic mesoporous silica (PMS) with vertically aligned mesochannels. It was found that the formation of the PMS–rGO–PMS sandwich structure is very sensitive to the surface and synthesis conditions. Although a higher temperature hydrothermal condition promotes reduction of GO and formation of bulky mesoporous nanoparticles, quiescent hydrothermal condition can serve as an alternative approach to obtain the unusual nanocomposites and slightly promote the structural stability of PMS on the surface of rGO.     

Preparation and characterization of polyacrylamide–silver nanocomposites

Polyacrylamide–silver nanocomposites are successfully prepared by irradiating the aqueous solution of AgNO₃ and acrylamide monomer with ⁶⁰Co γ-ray. The composites are found to contain nanometer silver particles with a narrow size distribution and a homogeneous dispersion. The existing of isopropanol (as a hydroxyl radical scavenger and chain transfer agent) in system affects the properties of both the dispersed phase and matrix of the nanocomposites. The fast-formed polymer chains probably play a key role in preventing the aggregation of silver particles which are reduced later.     

Poly (ether amide) and silica nanocomposites derived from sol–gel process

The sol–gel derived chemically combined organic–inorganic nanocomposites were synthesized from poly(etheramide) and tetraethoxysilane. Reaction of a mixture of 4-aminophenyl ether and 1,3-phenyldiamine with terephthaloyl chloride (TPC) in dimethylacetamide (DMAc) produced the amide chains. These chains were modified with carbonyl chloride end groups using a slight excess of diacid chloride and were then reacted with aminophenyl trimethoxysilane (APTMOS), where the amine group reacted with carbonyl chloride end groups. Hydrolysis/condensation of tetraethoxysilane (TEOS) and alkoxy groups present in APTMOS developed bonding between the polyamide chains and inorganic silica network generated in situ. By changing the relative proportions of the polymer solution and the amount of TEOS, the composition of hybrid films was varied. Thin hybrid films with various concentrations of silica network obtained after evaporation of the solvent were subjected to mechanical, dynamic mechanical thermal and morphological measurements. The results indicate a gradual increase in the modulus (3.84 GPa) and tensile strength (121 MPa) up to 15-wt.% silica relative to the pure polyamide. The elongation at break point and toughness gradually decrease with addition of silica content. These hybrids were found to be thermally stable up to a temperature of 500 °C. The weight retained above 800 °C was roughly proportional to amount of silica in the matrix. The glass transition temperature and the storage moduli increased with increasing silica concentration. The maximum increase in the T _g value (358 °C) was observed with 15-wt.% silica. Scanning electron micrographs indicated the uniform distribution of silica in the composites with an average particle size ranging from 9 to 47 nm.     

Characterisation of nickel–zinc ferrite/silica nanocomposites with low ferrite concentration obtained by an improved modified sol–gel method

The paper presents a study regarding the structure, morphology and magnetic behaviour of x% (Ni_0.65Zn_0.35Fe₂O₄)/(100 − x)% SiO₂ ferrimagnetic nanocomposites for low Ni–Zn ferrite concentration (x = 5, 10, 15, 20 and 30 mass percent) obtained by an improved modified sol–gel method. The obtained gels and nanocomposites have been characterized by fast Fourier transform-infrared (FT-IR) spectrometry, X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurements (MM). The addition of a supplementary quantity of diol in the synthesis, corresponding to a molar ratio EG : TEOS = 1:1, and the control of the thermal treatment applied to the precursor xerogels tetraethylortosilicate (TEOS)–metal nitrates (MN)–ethylene glycol (EG) leads to fine (~2–9 nm), almost spherical Ni–Zn ferrite nanoparticles homogenously dispersed inside the amorphous SiO₂ matrix. TEM images reveal the fine nature and the narrow size distribution of the ferrite nanoparticles. Nanoparticles diameter increases with the ferrite concentration and with the annealing temperature. For all concentrations of ferrite in SiO₂ and all annealing temperature, we have obtained Ni_0.65Zn_0.35Fe₂O₄ ferrite as single phase (proven by XRD) in the amorphous silica matrix, only after a pre-treatment of synthesized gels, at 573 K, for 3 h. The magnetic behaviour of ferrite nanoparticles in quasi-static magnetic fields is very particular, depending on the annealing temperature and the ferrite content in silica matrix. We have obtained superparamagnetic behaviour for the nanocomposites, for a concentration of 30% ferrite in SiO₂ at high annealing temperature, of 1,273 K.     

Enthalpic interaction coefficients of NaI–alkanediol pairs in methanol and in water

The dissolution enthalpies of NaI in the mixtures of methanol with 1,2-alkanediols (1,2-propanediol, 1,2-butanediol, 1,2-pentanediol) and with ??,??-alkanediols (1,3-propanediol, 1,4-butanediol, 1,5-pentanediol), as well NaI in the mixtures of water with 1,3-propanediol and 1,2-pentanediol, were determined at 298.15?K. The energetic effect of interactions between the investigated alkanediols and NaI in methanol and in water was calculated using the enthalpic pair interaction coefficients (h _xy ) model. These results along with the other data concerning the NaI?Cnon-electrolyte pairs taken from our earlier reports and from the literature were analyzed with respect to the effect of the non-electrolyte properties on the variations of the h _xy values. The group contributions illustrating the interactions of NaI with selected functional groups in non-electrolyte (alkanediol and alkanol) molecules, namely: CH₂ and OH groups were calculated and discussed.     

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO₂ [P(St-BA-AA)/SiO₂] nanocomposites by in situ formation of SiO₂ nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Sol–gel synthesis of iron oxide–silica composite microstructures

Spherical silica particles doped with iron oxide have been synthesized via base-catalyzed one-pot sol?Cgel process using tetraethoxysilane (TEOS) and iron(III) ethoxide (ITE) as co-precursors. In the modified St?ber process adopted, depending on the concentration of ITE in the starting composition, materials of various morphologies were observed under a scanning electron microscope and an atomic force microscope. The presence of ITE significantly affected the formation process of particulate silica; the spherical particles were formed accompanied by the co-presence of irregular-shaped finer aggregates. The fraction of the aggregates with rough surfaces increased with an increase of the ITE content in the reaction mixture. Both the spherical particles and irregular-shaped aggregates contained iron hydroxide and they exhibited paramagnetic behavior. The chemical composition and physicochemical properties of the materials were determined using various complementary spectroscopic methods.     

Effect of POSS on thermomechanical properties of epoxy–POSS nanocomposites

The epoxy–POSS hybrid networks with POSS bound as pendant cages or with untethered POSS dispersed in the matrix were prepared and their structure was controlled. Formation of the hybrid network was followed by chemorheology. In situ development of physical crosslinks in the pregel stage of the network build-up was observed in case of the hybrids with tethered POSS. The complex effect of POSS on mechanical properties is manifested by either increase or decrease in rubbery modulus of different hybrids. This behavior reflects (a) reinforcement due to POSS hard aggregates, (b) diminishing of crosslinking density of the epoxy network by tethered monofunctional POSS and (c) physical crosslinking via POSS domains. Theories of network formation and rubbery elasticity as well as the model of mechanical behavior of particulate composites were applied to interpret the mechanical properties of the hybrids.     

Polybenzoxazine–silica (PBZ–SiO2) hybrid nanocomposites through in situ sol–gel method

New type of Polybenzoxazine–silica (PBZ–SiO₂) hybrid nanocomposites was prepared through in situ sol–gel method. Benzoxazine was synthesized using bisphenol-A, trans-4-aminocyclohexanol hydrochloride and formaldehyde solution through Mannich condensation reaction and was characterized by FT-IR, ¹HNMR and ¹³CNMR spectroscopy. The methodology adopted in the present study involves to formation of hydrogen bond interaction between the benzoxazine monomer and the silica matrix, followed by the ring opening polymerization of benzoxazine monomer through thermal curing to obtain a red brown transparent PBZ–SiO₂ hybrid. The formation of hybrid nanocomposites was confirmed by FT-IR. Thermal and morphological properties of the hybrid materials were investigated by the differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM). The PBZ–SiO₂ hybrids show improved thermal properties and glass transition (Tg) temperature. The nitrogen porosimetry study was carried out to confirm the nanometer level integration of polybenzoxazine in the PBZ–SiO₂ hybrid nanocomposites.     

Novel structural behaviour of iron in alkali–alkaline-earth–silica glasses

The combined effect of alkali and alkaline-earth ions on the redox, distribution, co-ordination and environment of Fe ions in alkali–alkaline-earth–silica glasses has been studied using a multi-technique approach. Wet chemical analysis and Mössbauer, electron spin resonance (ESR), optical absorption and photoluminescence spectroscopies were utilised. Behaviour generally falls into two categories, which we have termed ‘collective’ and ‘selective’. Collective behaviour occurs when alkali and alkaline-earth ions have similar effects on a property and the overall effect is cumulative. This is characterised by a linear relationship with optical basicity of the glass. Some parameters associated with the environment of Fe²⁺ ions fall into this category. Selective behaviour occurs when alkali and alkaline-earth ions have opposing effects on a property, suggesting competition or selectivity. This is characterised by a linear relationship with the alkali/alkaline-earth ionic radius ratio, cation field-strength ratio or oxide-basicity ratio. The Fe²⁺/ΣFe ratio and several parameters associated with the distribution, coordination and environment of Fe³⁺ ions fall into this category. These results have implications for the local structure surrounding Fe species. A relationship has been suggested linking coordination and distribution of Fe³⁺ ions.     

Dehydration of glycerol with silica–phosphate-supported copper catalyst

Research on Chemical Intermediates - Silica–phosphate-supported copper catalyst was prepared by neutralization of sodium silicate with orthophosphoric acid followed by the addition of copper...     

Thermal stability and flammability of butadiene–styrene rubber nanocomposites

Heterobimetallic oxalato complex precursors, manganese(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate (MnOLa), cobalt(II)pentaaquatris(oxalato)lanthanate(III)trihydrate (CoOLa), nickel(II)pentaaquatris(oxalato)lanthanate(III)hexahydrate (NiOLa) and copper(II)diaaquatris(oxalato)lanthanate(III)monohydrate (CuOLa) of the type, M₃[La(C₂O₄)₃(H₂O) _m ]₂·nH₂O have been synthesized in aqueous medium. The precursors were characterized by elemental analysis, IR, electronic spectral and powder X-ray diffraction studies. The good crystalline nature with monoclinic structures predominates in MnOLa and NiOLa whereas triclinic structures were found in CoOLa and CuOLa. The solid-state thermal behaviour of the precursors was explored using TG, DTG and DTA in air. The MnOLa generated a mixture species consisting mainly of MnO₂, Mn₃O₄, Mn₅O₈, La₂O₃ and LaMn₇O₁₂ at 1000 °C through the formation of several intermediate species at 380 and 570 °C. The studies revealed that CoOLa led mainly to LaCoO₃ and La₂CoO₄ along with some oxides of both the cobalt and lanthanum at 1000 °C. In case of nickel analogue the mixture species identified at 1000 °C are mainly of La₂NiO₄, La₂O₃, Ni₂O₃ and NiO_2. In case of CuOLa the product at 1000 °C consisted of La₂CuO₄, La₂Cu₂O₅ and oxides of copper and lanthanum. The nature of decomposition of the precursors in nitrogen were seen from DSC study and the kinetic parameters i.e., E ^* , lnk ₀, ΔH ^# , ΔS ^# and order of reaction of all the steps were evaluated and discussed.     

Characterization and electrochemical study of hemoglobin–carbon nanoparticles–polyvinyl alcohol nanoporous hybrid film

A hybrid film is fabricated by casting hemoglobin (Hb)–carbon nanoparticles (CNPs)–polyvinyl alcohol (PVA) suspension on glassy carbon electrode (GCE). The resulting film shows a three-dimensional nanoporous structure. In the hybrid film, the ultraviolet visible (UV–Vis) absorption spectra of Hb keep almost unchanged. The organic–inorganic hybrid material can promote the direct electron transfer of Hb. A pair of well-defined and quasireversible peaks with a formal potential of −0.348 V (vs saturated calomel electrode) is obtained, which is caused by the electrochemical reaction of the Fe(III)/Fe(II) couple of Hb. The electron transfer rate constant (k _s) is estimated to be 3.9 s⁻¹. The immobilized Hb exhibits high stability and excellent electrochemical catalysis to the reduction of oxygen (O₂), hydrogen peroxide (H₂O₂), and nitrite (). The catalytic currents are linear to the concentrations of H₂O₂ and from 1.96 to 112 μM and from 0.2 to 1.8 mM, respectively. Therefore, the hybrid film may be a good matrix for protein immobilization and biosensor fabrication.