Optimizing the Synthesis and Thermal Properties of Conducting Polymer–Montmorillonite Clay Nanocomposites

Given the availability of a wide range of properties not possessed by individual materials, nanocomposites based on conducting polymers and inorganic materials have attracted much deserved attention. However, there has been little attempt to optimize the synthesis and thermal properties of polyaniline–clay nanocomposites. In this study, the synthesis and thermal properties of polyaniline (PANi) and polyaniline–clay nanocomposites (PACN) were performed by systematically varying the feed composition. Both PANi and polyaniline–montmorillonite (MMT) nanocomposites were prepared by using ammonium persulfate (APS) as the oxidant. The chemical structure of the nanocomposites was studied by Fourier transform infrared spectroscopy (FTIR). FTIR spectra confirmed the presence of clay in the nanocomposites and the existence of mainly the emiraldine form of PANi. Thermal analysis was performed by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The morphology and structure of PANi and PACN were studied by scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM). Our results confirm the intercalation and partial exfoliation of clay. This study also showed that increasing the oxidant concentration resulted in decreasing thermal stability and melting temperature of PANi. The reinforcement of PANi with MMT resulted in increased thermal stability and increased melting point of PANi. It was also shown that the addition of only about 0.1 wt% of APS resulted in an optimal thermal stability and melting point for PANi.

The Effect of Dielectric Polarization Rate Difference of Filler and Matrix on the Electrorheological Responses of Poly(ionic liquid)/Polyaniline Composite Particles

By using different conductivity of polyaniline as filler, a kind of poly(ionic liquid)/polyaniline composite particles was synthesized to investigate the influence of dielectric polarization rate difference between filler and matrix on the electrorheological response and flow stability of composite-based electrorheological fluids under simultaneous effect of shear and electric fields. The composite particles were prepared by a post ion-exchange procedure and then treated by ammonia or hydrazine to obtain different conductivity of polyaniline. Their electrorheological response was measured by dispersing these composite particles in insulating carrier liquid under electric fields. It showed that the composite particles treated by ammonia had the strongest electrorheological response and most stable flow behavior in a broad shear rate region from 0.5 s⁻¹ to 1000 s⁻¹. By using dielectric spectroscopy, it found that the enhanced electrorheological response with stable flow depended on the matching degree of the dielectric polarization rates between poly(ionic liquid) matrix and polyaniline filler. The closer their polarization rates are, the more stable the flow curves are. These results are helpful to design optimal composite-based electrorheological materials with enhanced and stable ER performance.

Electro-response of MoS2 Nanosheets-Based Smart Fluid with Tailorable Electrical Conductivity

The correlation between electrical conductivity and electro-responsive behavior is identified by introducing few-layer molybdenum disulfide (MoS2) nanosheets to electrorheological (ER) fluid. Few-layer MoS2 nanosheets are successfully fabricated, with a high yield of above 60%, using a straightforward method, and applied to an electro-responsive smart fluid. The electrical conductivity of MoS2 is easily tunable by adjusting the annealing temperature because of its semiconducting behavior. From an in-depth study on the conductivity-dependent ER behavior of few-layer MoS2 nanosheets, it can be verified that an optimum value of the electrical conductivity exists for the electro-responsive material, corresponding to the Wagner model. To the best of our knowledge, this is the first report on the potential of a transition-metal dichalcogenide as a candidate material for an ER fluid. This study may provide promising approaches for the performance improvement of electro-responsive smart fluids.

Facile synthesis of polyaniline nanotubes and their enhanced stimuli-response under electric fields

Polyaniline (PANI) nanotubes were fabricated successfully using a micelle soft-template method in the presence of oxalic acid as a dopant and applied as the dispersed phase of an electrorheological (ER) fluid.

Pickering emulsion polymerized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/polystyrene composite particles and their electric stimuli-response

We report a facile synthesis of Pickering emulsion polymerized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/polystyrene composite particles and their electrorheology.

Synthesis and characterization of SiO2/polyaniline/Ag core–shell particles and studies of their electrical and hemolytic properties: multifunctional core–shell particles

Three layers of conducting core–shell nanocomposite particles composed of SiO₂/polyaniline (PAni)/Ag were prepared in the presence of silicon dioxide (SiO₂) in an aqueous solution containing sodium dodecyl benzenesulfonate (SDBS) as a surfactant.

Electrorheology of nanofiber suspensions

Electrorheological (ER) fluid, which can be transformed rapidly from a fluid-like state to a solid-like state under an external electric field, is considered to be one of the most important smart fluids. However, conventional ER fluids based on microparticles are subjected to challenges in practical applications due to the lack of versatile performances. Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances. In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers. Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

Probing the Properties of Nanocomposites Synthesized from Aramid and Surface-Modified Clay

Nanocomposites were prepared by the inclusion of layered silicates into the aramid matrix via a solution intercalation technique. Polyamide was synthesized by reacting 4,4′-oxydianiline with isophthaloyl chloride and then end-capping with carbonyl chloride end groups using excess diacid chloride. The compatibility between the two phases was obtained through surface modification of montmorillonite with long-chain alkyl diamine. The nanocomposites were characterized with regard to structural, morphological, mechanical, thermal, and water absorption measurements. These investigations confirmed the formation of delaminated and disordered intercalated nanostructures at different clay loadings. Mechanical properties were significantly enhanced relative to pristine polyamide, even with the addition of only 2 wt-% of nanoclay. Thermal decomposition temperatures of the nanocomposites were in the range 300–450°C. Glass transition temperature data exhibited improvement (123°C) up to 16 wt-% addition of organoclay. Water absorption of the neat aramid was rather high (5.7%), but decreased with augmenting clay content.

Preparation of montmorillonite/titania nanocomposite and enhanced electrorheological activity

We prepared a new type of electrorheological particle composed of TiO2 nanocrystallites-coated montmorillonite (MMT/TiO2) nanocomposite by the sol-gel technique. The characterizations including TGA, XRD, TEM, SEM, EDS, and FTIR showed that TiO2 was deposited on the surface of the MMT flakes with anatase nanocrystallite. An obviously enhanced ER effect was found in the MMT/TiO2 nanocomposites based ER fluids compared with pure MMT and TiO2. Furthermore, the temperature and sedimentation stabilities of the MMT/TiO2 ER fluids had also been improved greatly. Interestingly, the content of TiO2 was demonstrated to have an important influence on the ER effect. When the content of TiO2 was about 20 wt%, the ER effect of MMT/TiO2 ER fluid reached its maximum, which was about 5 times that of pure MMT ER fluid and 27 times that of pure TiO2 ER fluid. Based on dielectric analysis, the significant ER enhancement by formation nanocrystallites-coated montmorillonite was attributed to the enhanced interfacial polarization in this nanocomposite particle due to the effective limitation of the long-range drift of active ions in montmorillonite particles.

A new approach of enhancing the shear stress of electrorheological fluids of montmorillonite nanocomposite by emulsion intercalation of poly-N-methaniline

Poly-N-methaniline/montmorillonite (PNMA-MMT) nanocomposite particles with high dielectric constant as well as suitable conductivity were synthesized by an emulsion intercalation method and characterized by FT-IR, XRD, and TEM spectrometry, respectively. The electrorheological (ER) properties of the suspensions of PNMA-MMT particles in silicone oil (20 wt%) were investigated under DC electric fields. It was found that the shear stress of poly-N-methaniline/montmorillonite electrorheological fluid (ERF) is 6.0 kPa in 3 kV/mm (74.5 s(-1)), which is 3.6 times that of electrorheological fluid at zero field, and also much higher than that of pure poly-N-methaniline (PNMA) and montmorillonite (MMT). In the range of 10-90 degrees C, the shear stress changes slightly with the temperature. The sedimentation ratio of PNMA-MMT ERF was about 97% after 60 days. Furthermore, the dielectric constant of PNMA-MMT nanocomposite was increased 3.74 times that of PNMA and 1.99 times that of MMT at 1000 Hz, the dielectric loss tangent also increased about 1.58 times that of PNMA. It is apparent that the notable ER effect of PNMA-MMT ER fluid was attributed to the prominent dielectric property of the poly-N-methaniline/montmorillonite nanocomposite particles.