Good Dispersion State Research Articles

Strong and conductive polybenzimidazole composites with high graphene contents

Graphene has been considered as an ideal reinforcement agent for polymer composites for a long time, however, strong and highly conductive composites have rarely been reported because of the poor dispersion that results when the loading of graphene is increased to a certain level. In this paper, by combining simple solvent-exchange and solution-casting methods, graphene oxide (GO)/polybenzimidazole composites with high GO contents (up to 40 wt%) are initially prepared. SEM and XRD results demonstrate the good dispersion state and alignment of GO in the composites. Tensile testing reveals that the modulus of the composite increases with the addition of GO as a result of the homogenous dispersion and strong interfacial interactions, while the strength shows a maximum value in the composite with 20 wt% GO. To make the composites conductive, chemical treatment with hydroiodic acid or thermal annealing at 220 °C were carried out on the samples. It was found that the chemical reduction is more effective in improving the conductivities of the composites, but slightly detrimental to the mechanical properties. Although the thermally treated composites show relatively lower conductivities, they possess a higher modulus and strength than the corresponding unreduced and chemically reduced ones. By these efforts, composites with diverse properties, but which are generally mechanically strong and conductive, are fabricated. It is expected that these high-performance composites could find applications in a broad range of technical fields.

Study of adsorption-assisted photocatalytic oxidation of benzene with TiO2/SiO2 nanocomposites

TiO2/SiO2 composite photocatalysts were prepared via a simple reflux-stir process. These composites exhibit a highly distributed state between TiO2 (P25) and fumed silica (SiO2) nanoparticles, and the SiO2 nanoparticles surround the TiO2 crystalline grains closely. The photoactivity of the composites was investigated by photocatalytic oxidation of gaseous benzene. By adjusting the Ti/Si mole ratio from 50:1 to 1:1, the photocatalytic efficiency of the TiO2/SiO2 composites ascends firstly and then decreases. The optimum Ti/Si mole ratio is 30:1, and the photocatalytic efficiency reaches 92.3% within 120min, which is 6.8 times higher than that of P25. Additionally, recycled tests which performed ten times demonstrate the nanocomposites possess a pretty good recyclability. The excellent photocatalytic performances can be chiefly attributed to the good dispersion state between TiO2 and SiO2. The special structure helps the formation of a high population of hydroxyl groups on the catalysts surface, and these hydroxyl groups greatly improve the charge separation efficiency and the reaction rate. In addition, the enhanced adsorption powers to water vapor and benzene also contribute to the high photoactivity.

Assessment of intertube interactions in different functionalized multiwalled carbon nanotubes incorporated in a phenoxy resin

AbstractIn this work, about 1 wt% of different functionalized carbon nanotubes (CNTs), namely CNTCOOH (CNT with carboxylic groups), CNTNH2 (CNT with amine groups) and CNTOH (CNT with hydroxyl groups), as well as nonfunctionalized CNTs were incorporated into a phenoxy resin via a melt mixing process. The extent of intertubes and polymer–tubes interactions and their influence on state of CNTs dispersion were assessed through determination of electrical, rheological, and morphological characteristics. CNTNH2 showed the lowest intertubes interactions followed by CNTOH and CNTCOOH. Nanocomposite made from CNTCOOH showed the poorest state of CNTs dispersion and the biggest CNTs agglomerates and it remained nonconductive. The acid‐functionalized CNTs were not able to form strong polymer–tube interactions because of their high cohesive energy and therefore in the melt rheological investigations they exhibited the lowest storage modulus and complex viscosity as well as the highest loss factor among all the studied CNTs. A good balance between intertubes and polymer–tube interactions is necessary through proper selection of CNTs functional groups for achieving a good state of CNTs dispersion and consequently obtaining enhanced electrical and viscoelastic properties. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Magnetic nanocomposites based on hydrogenated epoxy resin

A hydrogenated derivative of diglycidylether of bisphenol A (HDGEBA) has been successfully employed to prepare magnetic thermosetting nanocomposites. Magnetite nanoparticles of ≈10nm modified with oleic acid were synthesized by co-precipitation of ferric and ferrous salts in ammonium solutions. Nanocomposites with amounts up to 5% ww−1 of nanoparticles were dispersed in HDGEBA by co-solvent method and cured with m-xylilendiamine. Both the particles and nanocomposites were characterized by FTIR, DSC, TGA, XRD, TEM, DMTA and VSM. Due to the lower polarity of the hydrogenated resin, the enhanced compatibility with magnetite oleic coverage allowed obtaining good dispersions of the nanoparticles for compositions up 1% ww−1, while at higher concentration agglomerates were observed. Two behaviors in the thermal properties were obtained: for compositions below 1% ww−1 the glass transition temperature increased with the amount of nanoparticles, whereas for higher amounts the glass transition temperature decreased. Superparamagnetic behavior was observed in both the particles and the nanocomposites; the blockage temperature gradually increases with loading but it is lower than the observed for bulk magnetite nanoparticles. This fact reflects that nanoparticle–nanoparticle distances in the nanocomposites gradually decrease with loading which is in accordance with a good dispersion state for low loadings and the presence of aggregates at high loadings.

Preparation and properties of water‐absorbent composites of chloroprene rubber, starch, and sodium acrylate

AbstractThe effects of the amounts of starch, sodium acrylate (NaAA) and dicumyl peroxide (DCP) on the properties of chloroprene rubber (CR)/starch/NaAA composites prepared by melting method were investigated. The results showed that the addition of starch improved the mechanical properties, but decreased the water‐absorbing capacity of the composite, most likely due to the decrease in the local concentration of the main water‐absorbing material sodium polyacrylate and the increase in crosslinking density of the composite resulting from the reaction between starch and CR. This reaction was verified by the vulcanized curves, DSC curves, and the cut surface morphology. The as‐prepared composite demonstrated higher water‐absorbing capacity, resulting from the incorporation of NaAA. The mechanical properties decreased with increasing the DCP loading, and the water‐absorbing ratio is the maximum at 1.0 phr DCP. The tensile strength of the composite decreased significantly after water immersion, due to the absorbed water acting as a plasticizer. The extracted component from composites after water immersion is mainly sodium polyacrylate according to Fourier transform infrared (FT‐IR) spectroscopy analysis. The morphology of the composites before and after water immersion was observed by optical transmission microscopy (OTM). The results indicated that the starch exhibits a good dispersion state, and the water‐absorbing capacity results primarily from sodium polyacrylate. Copyright © 2010 John Wiley & Sons, Ltd.

Epoxy-Graphene UV-cured nanocomposites

This work presents the preparation of functionalized graphene sheets (FGS)/epoxy coatings cured by cationic photopolymerization with enhanced mechanical properties. The kinetics of the photopolymerization process for formulations up to 1.5 wt% of graphene were evaluated by means of Real-Time FTIR spectroscopy. The reinforcement of the cured coatings by the graphene was studied by measuring the dynamic-mechanical properties and the surface hardness. An increase of almost 40 °C in the Tg was obtained by adding 1.5 wt% of graphene to the epoxy matrix. A good dispersion state and interaction of the graphene with the matrix were observed by TEM and FESEM analyses.

Preparation of anatase nano‐TiO2/xanthan gum composite (NTX) and rheological study of the interior wall coatings using NTX as additive

PurposeThe purpose of this paper is to develop a kind of novel and high‐performance rheological additive, an eco‐friendly composite of anatase nano‐TiO2 particles and xanthan gum (NTX), for interior wall coatings.Design/methodology/approachNTX was prepared through heating and refluxing the mixture of TiO2 hydrosol and xanthan gum, and five interior wall coating samples were fabricated with different NTX contents. The morphology of nano‐TiO2 hydrosol and NTX were characterised with TEM, and the stability and rheological properties of these coating samples were studied.FindingsTEM images showed a core‐shell structure of NTX, and that nano‐TiO2 particles in it were encapsulated by xanthan gum, which was anticipated to weaken Van der Waals force among nano‐TiO2 particles thus preventing the aggregation of nano‐particles. All of the five coating samples were found to be non‐Newtonian pseudo‐plastic fluid, and showed excellent stability and thixotropic property.Research limitations/implicationsThis paper focused on the preparation, the characterisation of NTX additive and the study of the rheological behaviours of the coating samples with NTX. Some other aspects, such as coating durability, photocatalytic ability and film properties, will be studied in the future.Practical implicationsIt was proven that NTX was an effective eco‐friendly rheological additive for interior wall coatings. Consequently, this paper threw light on developing eco‐friendly interior wall coatings.Originality/valueA kind of novel and effective rheological additive was developed for interior wall coatings in the study reported in the paper. A method was also developed to introduce functional nano‐particles into coating in a good dispersion state.

Nanoparticle Dispersion and Aggregation in Polymer Nanocomposites: Insights from Molecular Dynamics Simulation

It is a great challenge to fully understand the microscopic dispersion and aggregation of nanoparticles (NPs) in polymer nanocomposites (PNCs) through experimental techniques. Here, coarse-grained molecular dynamics is adopted to study the dispersion and aggregation mechanisms of spherical NPs in polymer melts. By tuning the polymer-filler interaction in a wide range at both low and high filler loadings, we qualitatively sketch the phase behavior of the PNCs and structural spatial organization of the fillers mediated by the polymers, which emphasize that a homogeneous filler dispersion exists just at the intermediate interfacial interaction, in contrast with traditional viewpoints. The conclusion is in good agreement with the theoretically predicted results from Schweizer et al. Besides, to mimick the experimental coarsening process of NPs in polymer matrixes (ACS Nano 2008, 2, 1305), by grafting polymer chains on the filler surface, we obtain a good filler dispersion with a large interparticle distance. Considering the PNC system without the presence of chemical bonding between the NPs and the grafted polymer chains, the resulting good dispersion state is further used to investigate the effects of the temperature, polymer-filler interaction, and filler size on the filler aggregation process. It is found that the coarsening or aggregation process of the NPs is sensitive to the temperature, and the aggregation extent reaches the minimum in the case of moderate polymer-filler interaction, because in this case a good dispersion is obtained. That is to say, once the filler achieves a good dispersion in a polymer matrix, the properties of the PNCs will be improved significantly, because the coarsening process of the NPs will be delayed and the aging of the PNCs will be slowed.

Preparation and burning behaviors of flame retarding biodegradable poly(lactic acid) nanocomposite based on zinc aluminum layered double hydroxide

A flame retarding biodegradable polylactic acid (PLA) nanocomposite based on flame retardant composites (containing ammonium polyphosphate (APP), pentaerythritol (PER) and melamine cyanurate (MC) by controlling the weight ratio was 2:2:1) and organomodified zinc aluminum layered double hydroxide (Zn-Al-LDH) has been prepared by melt-compounding directly. The morphology and burning behaviour of nanocomposite with 2 wt% Zn-Al-LDH loadings were investigated. The extent of dispersion of LDH was quantified by wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM), illuminating the good dispersion state for ZnAl-LDH in the PLA matrix. Significant improvements in fire retardant performance were observed for the nanocomposite from microscale combustion calorimeter (MCC) and cone calorimetry (reducing both the heat release rate and the total heat released). It revealed that incorporation of FR and ZnAl-LDH was very efficient in improving the flame retardance of PLA composite.

Electrical/dielectric properties and conduction mechanism in melt processed polyamide/multi-walled carbon nanotubes composites

Abstract The electrical and dielectric properties of polyamide 6 (PA6)/multi-walled carbon nanotubes (MWCNT) nanocomposites prepared by melt mixing were investigated by employing dielectric relaxation spectroscopy in broad frequency (10−2–106 Hz) and temperature ranges (from −150 to 150 °C). Transmission electron microscopy revealed a good state of CNT dispersion in the polymeric matrix. The percolation threshold (pc) was found to be 1.7 vol.% by using the dependence of both dc conductivity and critical frequency (fc) from dc to ac transition on vol.% concentration in MWCNT. The actual aspect ratio of the nanotubes in the nanocomposites was calculated using a theoretical model (proposed by Garboczi et al.) and the obtained value was correlated with the pc value according to the excluded volume theory. Additionally, the contact resistance (Rc) between the conductive nanotubes was found to be ∼105 Ω. Investigation of the temperature dependence of conductivity revealed a charge transport which is controlled by thermal fluctuation-induced tunneling for temperatures up to the glass transition. Finally, it was shown that the addition of nanotubes has no significant influence on the relaxation mechanisms of the PA6 matrix.

Preparation and microstructure of titanate nanowire thin films by spray Layer-by-Layer assembly method

Hydrogen titanate nanowires were prepared by hydrothermal method in 10 M NaOH followed by ion-exchanging process. Titanate nanowire thin films were successfully obtained by spray Layer-by-Layer (spray LbL) method within a short time. Due to the good dispersion state of the nanowires in an aqueous suspension and their linear morphology, titanate nanowires effectively adsorbed on the glass substrate. As a reference, TiO2-anatase nanoparticle thin films were also prepared by spray LbL method.

Preparation and Microstructure of Titanate Nanotube Thin Films by Spray Layer-by-Layer Assembly Method

Hydrogen titanate nanowires were prepared by hydrothermal method in 10 M NaOH followed by ion-exchanging process. Titanate nanowire thin films were successfully obtained by spray Layer-by-Layer (spray LbL) method within a short time. Due to the good dispersion state of the nanowires in an aqueous suspension and their linear morphology, titanate nanowires effectively adsorbed on the glass substrate. As a reference, TiO2-anatase nanoparticle thin films were also prepared by spray LbL method

A facile route of polythiophene nanoparticles via Fe3+‐catalyzed oxidative polymerization in aqueous medium

AbstractWe have demonstrated that unsubstituted thiophene can be polymerized by Fe3+‐catalyzed oxidative polymerization inside nanosized thiophene monomer droplets, that is, nanoreactors, dispersed in aqueous medium, which can be performed under acidic solution conditions with anionic surfactant. Besides, we proposed a synthetic mechanism for the formation of the unsubstituted polythiophene nanoparticles in aqueous medium. This facile method includes a FeCl3/H2O2 (catalyst/oxidant) combination system, which guarantees a high conversion (ca. 99%) of thiophene monomers with only a trace of FeCl3. The average particle size was about 30 nm, within a narrow particle‐size distribution (PDI = 1.15), which resulted in a good dispersion state of the unsubstituted polythiophene nanoparticles. Hansen solubility parameters were introduced to interpret the dispersion state of the polythiophene nanoparticles with various organic solvents. The UV–Visible absorption and photoluminescence (PL) spectrum were measured to investigate the light emitting properties of the prepared unsubstituted polythiophene nanoparticle emulsions. According to non‐normalized PL analysis, the reduced total PL intensity of the polythiophene nanoparticle emulsions can be rationalized by self‐absorption in a wavelength range less than 500 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2097–2107, 2008

Synthesis of pure MgTiO3 by optimizing mixing/grinding condition of MgO+TiO2 powders

Through the dielectric materials used for the making of type I multilayer ceramic capacitors, the ilmenite magnesium titanate MgTiO 3 is of particular importance. Yet, it seems difficult to get pure MgTiO 3 with a controlled stoichiometry. In order to be able to synthesize it by solid-state reaction, we therefore studied the mixing/grinding behavior of the precursors MgO + TiO 2 . The evolution versus pH of the zeta potential values of both MgO and TiO 2 (anatase) powders shows that it is impossible to get correct pH values allowing a good dispersion state and thus an easy control of the mixing of these two species when considering only electrostatic repulsion. So, we considered to add dispersing agent in order to get a steric dispersion behavior. Rheological characterization of the slurries showed that we were able to get a good dispersion state during the process of mixing/grinding. XRD and SEM/EDX analysis shows the ability of obtaining “pure” MgTiO 3 with a controlled stoichiometry after calcination by controlling the rheological behavior of slurries during mixing/grinding.

Multiscale fiber‐reinforced composites prepared by vacuum‐assisted resin transfer molding

AbstractCarbon nanotube (CNT)/aramid fiber epoxy composites were produced using a new manufacturing method proposed in this study. The rheological and morphological experiments of the CNT/PEO nanocomposites indicates that the PEO nanocomposites have a good dispersion state of the CNTs. The flexural mechanical properties of the aramid fiber/CNT epoxy composites were measured. The CNTs dispersed in the epoxy resin between the aramid fibers were observed using field emission scanning electron miscroscope (FESEM). It was found that the flexural properties of the multiscale fiber‐reinforced composites were higher than those of aramid fiber/epoxy composites. POLYM. COMPOS., 28:458–461, 2007. © 2007 Society of Plastics Engineers.

A new processing aid for dry-pressing: A copolymer acting as dispersant and binder

PV X copolymers containing both carboxylate ( COO −) and hydroxyl groups (vinyl alcohol) are synthesized with the objective to ensure the double function of dispersant and of binder for dry-pressed green parts. Carboxylate groups are responsible for strong adsorption of copolymers onto alumina surface and can promote sufficient electrostatic repulsive forces to achieve a good state of dispersion, similar to that obtained with a classical ammonium polymethacrylate (PMA-NH 4 +) for a proportion of carboxylic groups in the copolymer larger than 35%. On the other hand, hydroxyl groups confer higher mechanical strength than PVA to the green pressed parts (4.2 MPa for 1.5 wt.% PV35 (35% COO −) versus 1.8 MPa for 1.5 wt.% PVA, with and without PEG as plasticizer, in the case of samples pressed at 120 MPa). The high density of the green parts obtained with soft PV35 copolymer and the good adsorption of this compound onto alumina surface lead to a high mechanical strength of the pressed compacts. After addition of 1.5 wt.% PV35, the amount adsorbed (0.7 wt.%) confers a high cohesion to the spray-dried granules and the non-adsorbed copolymer (0.8 wt.%) reinforces adhesion between granules through interdiffusion of the low T g polymeric films. Then, synthesized PV X copolymers have proved to be efficient dispersants for aqueous suspensions of alumina and also efficient binders for dry-pressing, even for concentrations as low as 1.5 wt.%.

Patterning of fine particles by means of supercritical CO2

A new method for positioning fine particles on surfaces has been developed. Supercritical CO2-assisted printing (SCAP) was utilized to spray and deposit the prepared particles on solid substrates. By means of masks, regular arrays of the particles were successfully created in designed patterns. Typical size of the particles employed was in the range of submicrometers to micrometers. Supercritical CO2 (sc-CO2) acted as an effective dispersion and transportation medium in this process. Good dispersion state of the particles was achieved by stirring in sc-CO2. Fabrications of fine patterns of solder particles and other ceramic powders on smooth plates were demonstrated. Under optimum operation conditions, fine structures of 30 μm in width can be formed in a minimal pitch of 60 μm. Ultra high yield of the patterning was obtained since the deposition rate could be as high as 100 μm per second. Main factors affecting the process were discussed. The research results indicate that the SCAP is a potential approach to the organization of fine particles into microstructures. Hopefully, it may find wide industrial applications where lithography is needed, such as solder printing in surface mounting technology for higher density electronics and thick film fabrication for miniature systems.

Dispersing Properties of Copolymers Able to Act as Binders

Macromolecules, containing both charged groups (COO− and SO3−), in order to ensure powder dispersion, and neutral groups (vinyl alcohol and ethyl hydroxyl acrylate), in order to obtain enough strength in the green parts, were synthesized to be used in the dry pressing process. The evaluation and the comparison of the capacity of these synthesized copolymers with disperse alumina particles in aqueous media are considered in this paper. Both COO− and SO3− ionized groups are responsible for strong adsorption onto alumina surface and can promote sufficient electrostatic repulsive forces to achieve a good state of dispersion. The role of the copolymers in the stabilization of alumina suspensions was found to be greatly affected by the nature and by the fraction of groups in the macromolecular chains. A low concentration of copolymers (0.5 wt% on alumina basis) containing 35% of carboxylic groups and 65% of vinyl alcohol groups (PV35) or containing 55% of carboxylic groups and 45% of hydroxy ethyl acrylate groups (EH2A55) leads to stable alumina suspensions with a low viscosity similar to that obtained with a classical ammonium polymethacrylate (between 10 and 20 mPa·s for 27 vol% alumina suspensions). Copolymers containing sulfonate groups are less efficient.

Dispersion of Al 2O 3 concentrated suspensions with new molecules able to act as binder

The objective is to define and synthesise molecules with a double function of dispersant and of binder. New acrylic copolymer molecules containing both carboxylic groups expected to bring a dispersant contribution and hydroxyl vinyl groups expected to bring a binder contribution were synthesised. The fraction of these two types of groups can be adjusted to balance the dispersion and the binder contributions. In a first step, the effect of these acrylic copolymer molecules on the interactions between alumina particles in aqueous suspension and on the rheology of concentrated suspensions was studied. Carboxylic groups allow adsorption of acrylic copolymers onto the alumina surface and can promote sufficient electrostatic repulsive forces to obtain a good state of dispersion. The amount of carboxylic groups controls the density of charge of the particle surface and hence, the ability of the copolymer to act as a dispersant. A low amount (0.6 wt.%) of a copolymer containing 35% of carboxylic groups, leads to stable suspensions with a critical powder leading of 80 wt.% corresponding to 50 vol.%.

Preparation of Gold Nanoparticles in Inorganic Suspension and Clay Gel Solution.

Gold nanoparticles are prepared in titania, silica and clay suspensions by chemical reduction of tetrachroloauric ions using 1,3-aceton dicarboxylic acid. The formation rates of gold nanoparticles in titania and silica suspensions were almost the same as that in an aqueous solution. Slower formation rates were obtained in a clay gel solution, becoming slower with increasing clay concentration. Although the gold nanoparticles became large and polydispersed, due to the slow diffusion rate of tetrachroloauric ions in the clay gel, the good dispersion state of gold nanoparticles was retained even after the clay gel had dried.