Holographic polymer‐dispersed liquid crystal fabrication under electric field

The transmission mode of holographic polymer‐dispersed liquid crystals (HPDLCs) was developed an under electric field. It is reported that orientation of LC molecules under an electric field induces orientation of oligomer molecules giving rise to low off‐state diffraction and small grating shrinkage. Copyright © 2005 Society of Chemical Industry     

Preparation and characterization of Pani and Pani‐Ag nanocomposites via interfacial polymerization

Polyaniline (Pani) and Polyaniline‐silver nanocomposites (Pani‐Ag) were prepared by employing interfacial polymerization using ammonium persulphate as an oxidizing agent. During the polymerization, the Ag+ is reduced to Ag⁰, and the formations of regular nanocomposite materials were studied by Fourier transform infrared spectroscopy and UV–visible spectroscopy techniques. Scanning electron microscopy and transmission electron microscopy images were conducted to characterize the morphology. Thermogravimetric and differential thermal analysis were carried out to study the thermal stability of the resulting composites. Formation of conducting emeraldine salt form was concluded by electrical conductivity. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The production of large scale ultrathin aligned CNT films by combining AC electric field with liquid flow

We report a simple and versatile technique combining the use of an AC electric field with a liquid shear force to prepare ultrathin aligned CNT films on solid substrates. Multiwalled carbon nanotubes (MWCNTs), which were synthesized by a template method and acid-treated single walled carbon nanotubes (SWCNTs) were dispersed in water and used for the ultrathin film fabrication. A solid substrate was immersed in the CNT dispersions and withdrawn at constant speed under AC electric field. SEM images of the substrate showed that CNTs were aligned with the AC electric field and the withdrawal direction and formed uniform films with a thickness around 10 nm for SWCNTs and 90 nm for MWCNTs. Repeating the deposition process increases the density and size of the film while also maintaining nanometer-scale thickness. Unidirectional alignment of CNTs was also confirmed by Raman spectra and electric conductivity measurements. It was found that ultrathin films of aligned SWCNTs exhibited very high anisotropic electrical conductivity with conductivity measured parallel to the alignment direction 3.3 × 10⁵ times higher than that measured in the perpendicular direction. We demonstrate that use of the aligned ultrathin SWCNT film for a unidirectional alignment of liquid crystal.     

Synthesis and characterization of chlorine‐containing flame‐retardant polyurethane nanocomposites via in situ polymerization

We have developed flame‐retardant polyurethanes (FRPUs) and polyurethane (PU) nanocomposites via in situ polymerization. Three series of thermoplastic elastomeric PUs were synthesized to investigate the effect of incorporating 3‐chloro‐1,2‐propanediol (CPD) and nanoclay on mechanical, thermal properties, and also resistance to burning. PU soft segments were based on poly(propylene glycol). Hard segments were based on either CPD or 1,4‐buthane diol (BDO) in combination with methyl phenyl di‐isocyanate named PU or FRPU, respectively. In the third series, CPD was used as chain extender also nanoclay (1% wt) and incorporated and named as flame‐retardant polyurethane nanocomposites (FRPUN). Mechanical properties and LOI of PUs and nanocomposites have been evaluated. Results showed that increasing the hard segment (chlorine content) leads to the increase in flame retardancy and burning time. Addition of nanoclay to CPD‐containing PUs leads to obtain self‐extinguish PUs using lower CPD contents, higher Young's modulus, and strength without any noticeable decrease in elongation at break. Investigation of the TGA results showed that copresence of nanoclay and chlorine structure in the PU backbone can change thermal degradation pattern and improve nanocomposite thermal stability. X‐ray diffraction and transmission electron microscopy studies confirmed that exfoliation and intercalation have been well done. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fabrication of ZrO2/rGO nanocomposites by flash sintering under AC electric fields

Ceramic matrix nanocomposites containing graphene possess superior mechanical properties. However, these nanocomposites are very difficult to be prepared using the conventional methods due to severe grain growth and simultaneous degradation of the graphene at high sintering temperatures and long dwell time. Herein, the dense ZrO₂/rGO (reduced graphene oxide) nanocomposites are successfully fabricated by flash sintering of the green compacts consisting of ZrO₂ nanoparticles and graphene oxide (GO) at 893–951℃ in merely 5 seconds under the alternating current (AC) electric fields of 130–150 V cm⁻¹. The GO can be in situ thermal reduced during the flash sintering. The as-prepared ZrO₂/rGO nanocomposites exhibit excellent mechanical properties. This study presents a green and simple approach to fabricate the dense ceramic matrix nanocomposites reinforced with graphene at low temperatures in a short time.     

Tribological behaviors of aligned carbon nanotube/fullerene‐epoxy nanocomposites

The tribological properties of aligned CNT/fullerene‐epoxy nanocomposites were studied by nanoscratch, nanowear, and nano‐indentation tests. Compared with neat epoxy, aligned CNT/fullerene‐epoxy nanocomposites showed lower friction coefficient in scratch tests, a reduction of 38.1 and 26.2%, respectively. In addition, the aligned CNT‐epoxy composite showed better wear resistance and its hardness and Young's modulus increased by 29.4 and 16.8%, respectively. In contrast, for a fullerene‐epoxy nanocomposite with 10 wt% fullerenes, the hardness decreased by 50% and the Young's modulus decreased by more than 60% when compared with the neat epoxy. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Microemulsion route to fabrication of silver and platinum‐polymer nanocomposites

Polymethylmethacrylate (PMMA)‐platinum and PMMA‐silver nanocomposites have been produced using polymerization of W/O microemulsions. MMA monomer was used as the oil or continues phase of the microemulsion system and polymerized following formation of Pt and Ag nanoparticles in the fluid medium. The UV‐vis absorption spectra have been used to trace the growth process of the nanoparticles in the microemulsion system. Scanning electron microscopy and transmission electron microscopy (TEM) have been used to determine the morphology and particle size of the Pt and Ag particles in the synthesized nanocomposites. Image analyses of TEM micrographs confirm that the Pt and Ag particles in the synthesized nanocomposites have a narrow size distribution. Meanwhile, Fourier‐transform infrared spectroscopy was used to verify polymer‐nanoparticles interaction in nanocomposite bulk. POLYM. COMPOS., 35:2023–2028, 2014. © 2014 Society of Plastics Engineers     

Effects of pores on dielectric breakdown of alumina ceramics under AC electric field

The relationship between pores and dielectric breakdown strength of alumina ceramics has been investigated. Alumina specimens with different internal pores in size and quantity were obtained with polyvinyl alcohol (PVA) granules additives being removed after sintering. Pores inside the ceramic samples were characterized by density measurement and micro computed tomography (Micro CT) analysis. We tested the breakdown strength of different alumina sheets under AC electric field, with the same electrodes and voltage loading methods being adopted. The experimental results indicated that the dielectric breakdown strength of alumina specimens decreased with the increment of their thickness. Interestingly, a great deal of large pores influences the breakdown strength significantly. And the breakdown channel passes through the large hole when there is a large hole in the sample. Small pores have little effects on the insulating properties. Further discussion and analysis reveal that the measured results of breakdown strength conform to the Weibull distribution. In addition, the experimental results can be well explained by space charge injection models and electric field simulation.     

Amino‐functionalization of graphene sheets and the fabrication of their nanocomposites

Expandable graphite oxide (EGO) was functionalized with different amine groups after sequential steps as thermal expansion, oxidation, acylation, and amidation. Three types of amino‐functionalized graphenes (a‐Gphs) were prepared by exfoliating amino functionalized EGOs(a‐EGO) through controlled ultrasonication. Fourier transform infrared spectroscopy, elementary analysis, X‐ray diffraction, and thermogravimetric analysis separately confirmed the chemical structure of a‐EGO. The effect of ultrasonic power on the particle sizes of exfoliated a‐EGOs was estimated by dynamic light scattering. Single layered graphene (0.43 nm) was achieved after ultrasonicating at 500 W for 20 min, which was affirmed by the results of atomic force microscopy and transmission electron microscopy. Ultra violet–visible spectroscopy also indicates the good dispersion properties of a‐Gphs in these solvents. The thermal properties of composites are obviously increased by adding a‐Gphs and a‐EGOs as nanofillers. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Preparation and characterization of polyhydroxyurethane/silica nanocomposites via in situ surface‐initiated polymerization

The polyhydroxyurethane/silica nanocomposite (PHU/SN) was prepared by the in situ surface‐initiated polymerization of a five‐membered cyclic carbonate, 2,2‐bis[p‐(1,3‐dioxolan‐2‐one‐4‐yl‐methoxy)phenyl]propane (B5CC) and hexamethylene diamine, from the surfaces of the aminopropyl silica nanoparticles (APSN) for the first time. The percentage of grafting (PG%) and the grafting efficiency (GE%) of 27% and 19% were calculated from the results of thermogravimetric analysis (TGA), respectively, after the free polyhydroxyurethane was washed off. The chemical grafting of the polymer was also confirmed using Fourier transform infrared (FTIR) and the morphology of the silica nanoparticles in the nanocomposite was characterized by transmission electron microscope (TEM). POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Synthesis and characteristics of polystyrene–clay nanocomposites via in situ intercalative polymerization in a direct current electric field

Polystyrene (PS)/montmorillonite nanocomposites were prepared by the free‐radical polymerization of styrene‐containing dispersed clay in a direct current electric field. The intercalation spacing in the nanocomposites, the dispersion, and the orientation of these composites were investigated. The nanocomposites had higher T_g and better thermal stability when compared with the virgin PS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dynamics of single-walled carbon nanotube (SWNT)/polyisoprene (PI) nanocomposites in electric and mechanical fields

Relaxation dynamics of single-walled carbon nanotube (SWNT)/polyisoprene (PI) nanocomposites were examined by dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS) over a wide range of frequency and temperature. Both functionalized (SWNT-f) and pristine (SWNT-p) nanotubes were used and their effect on dynamics compared. Functionalized (PISF) nanocomposites were characterized by an increase in the time scale of the normal mode process as a consequence of the strong surface interactions between the polymer matrix and the nanotubes. The exact opposite is seen in pristine (PISP) nanocomposites where a decrease in the time scale of the normal mode relaxation is observed and attributed to weaker surface interactions and the effect of confinement on dynamics. The segmental process in PISF or PISP is not affected by the presence of nanotubes. The temperature dependence of the average relaxation time for normal and segmental modes is of the Vogel-Fulcher-Tammann (VFT) type. A good agreement is observed in the time scale of processes measured by DRS and DMS in PISF nanocomposites. In PISP nanocomposites, however, the time scales obtained from DRS and DMS measurements are not in consistently good agreement and an explanation is offered in terms of confinement.     

Synthesis and characterization of CTAB‐intercalated graphene/polyaniline nanocomposites via in situ oxidative polymerization

Polyaniline/graphene (PANI/GN) nanocomposites were fabricated via in‐situ oxidative polymerization of aniline in the presence of cetyltrimethylammonium bromide (CTAB) modified graphene (CGN) in 1M hydrochloric acid (HCl) solution. The morphology and structure of PANI/GN samples were investigated by Fourier transform infrared spectrum, X‐ray diffraction, ultraviolet and visible spectrum, thermogravimetric analysis, field‐emission scanning microscope (FE‐SEM), and transmitting electron microscopy (TEM). The conductivities of the PANI/GN nanocomposites were measured using four‐probe electrical conductivity measurement. The results indicated that the GN sheets disperse into the form of monolayer or stack few layers in PANI matrix. The GN sheets serve as a support material for PANI particles and the structure of GN covered with PANI nanoparticles were confirmed by FE‐SEM and TEM. The electrical conductivities of the PANI/GN samples have been improved compared with pure PANI prepared in the similar condition. POLYM. COMPOS., 36:1767–1774, 2015. © 2014 Society of Plastics Engineers     

Synthesis and characterization of linseed oil‐based nanocomposites

The nanocomposites from conjugated linseed oil, acrylic acid, and divinylbenzene are synthesized using modified montmorillonite clay and characterized for thermal properties. The wide angle X‐ray diffraction results clearly show the distortion of the platy nanolayers of the nanofiller in the polymer matrix as the peak due to the clay disappears in the nanocomposite samples. The dynamic mechanical analysis results show the enhanced storage modulus and transition temperature compared with the pristine polymer. At the glass transition temperature, the storage modulus of nanocomposites is in the range of 17–79 MPa, whereas the pristine polymer shows a storage modulus of 2.1 MPa. The melting peak temperature ranges from 230 to 260°C, which is further confirmed by thermogravimetric analysis (TGA) results. The samples are stable up to 200°C and show a two‐stage degradation. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Thermomechanical and electrical characterization of epoxy‐organoclay nanocomposites

The effect of amount of clay content on the thermomechanical and electrical properties of epoxy/organoclay nanocomposites is investigated in the present research. An organoclay, cloisite 30B (C30B), was dispersed in the epoxy resin and was cured with an amine curing agent. The morphology of the nanocomposite examined by X‐ray diffraction shows exfoliation for nanocomposites with lesser clay content and intercalation for nanocomposites with higher clay content. The storage modulus (E′) of the nanocomposites increases monotonously with the increase in the amount of clay. The short time alternating current breakdown strength of the nanocomposites increases by the addition of C30B up to a certain clay content and then show a decrease. The space charge measured by pulsed electroacoustic method shows that the nanocomposite accumulate a very less amount of space charge and the charge decay in the nanocomposites are quicker than in the pure polymer. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Densification of Y2O3 by flash sintering under an AC electric field

Frequency dependence of the densification behavior of undoped Y₂O₃ sintered by the AC-flash sintering was systematically investigated at 500 V·cm^?1 over a frequency range from 0.05 Hz to 1 kHz. The Y₂O₃ bodies sintered under an AC field showed a uniform microstructure, without an asymmetric grain size distribution between the electrodes. Almost fully-densified Y₂O₃ body was consolidated at 1 kHz exhibited a relative density greater than 99 % and an average grain size of 1.6 μm. The almost full densification probably resulted from the high input power at the relatively high onset temperature of 1300 °C at this frequency. The temperature dependence of the power dissipation during the AC-flash sintering experiments can be ascribed to the periodic fluctuations of the specimen temperature at low frequencies and to the phase shift between the applied field and the specimen current at high frequencies.     

Synthesis and characterization of resol‐layered silicate nanocomposites

Resol‐layered silicate nanocomposites were synthesized by intercalative polymerization of phenol and formaldehyde using layered clays such as an aminoacid‐modified montmorillonite (MMT) and a commercial modified MMT (Cloisite 30B). The composites were prepared by a sequential process in which one of the reactives of the phenolic resin was reacted with the organosilicate and subsequently cured with triethylamine. The nanocomposites were studied by means of X‐ray diffraction, atomic force microscopy, and thermogravimetric analysis. Results show a strong clay composition dependence on the intercalation state. The composite of resol with 2 wt % aminoacid‐modified MMT content has the best dispersion of clay layers. Thermal stability of nanocomposites was slightly increased in comparison with the neat resol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and characterization of coaxial mullite/polypyrrole fibrous nanocomposites via self‐assembling and in situ surface‐initiated polymerization

After mullite fibers particles (MFPs) were surface modified, conductive polypyrrole (PPy) layer was chemically grafted on the surface of the self‐assembled monolayer (SAM) coated MFPs, via in situ surface‐initiated polymerization, resulting in SAM‐MFPs/PPy composites. The composites possess high electrical conductivity at room temperature, weakly temperature dependence of the conductivity. The nanocomposite electrochemical properties displayed nearly symmetric charge–discharge characteristics and an ideal rectangular cyclic voltammogram. X‐ray diffraction analysis confirmed that the main peaks of SAM‐MFPs/PPy composites are similar to the SAM‐MFPs, which reveal that the crystal structure of SAM‐MFPs is well‐maintained after the coating process under polymerization reaction conditions and exhibit semicrystalline behavior. Thermogravimetric analysis shows that the thermal stability of SAM‐MFPs/PPy composites was enhanced and these can be attributed to the retardation effect of amine functionalized MFPs as barriers for the degradation of PPy. The morphology of SAM‐MFPs/PPy composites showed the coaxial fibrous structure. POLYM. COMPOS., 35:892–899, 2014. © 2013 Society of Plastics Engineers     

In situ synthesis and characterization of ZnS/epoxy nanocomposites via gas‐liquid state reaction method

In this article, the ZnS/epoxy nanocomposites were successfully prepared by the reaction of zinc acetate and H₂S gas via a simple step. Epoxy resin acted as the matrix for the formation of ZnS nanoparticles (10–20 nm) in the reaction system and kept them from agglomerating. The structure, composition, and mechanical properties of the resultant products were successfully investigated by powder X‐ray diffraction, transmission electron microscope, field emission scanning electron microscope, energy dispersive X‐ray fluorescence, and universal testing machine. Meanwhile, by employing differential scanning calorimetry (DSC) we had studied, under nonisothermal condition, the kinetic analysis of the cure reaction which was performed using two classic models: Kissinger and Flynn‐Wall‐Ozawa. The activation energy of curing reaction was 74.63 kJ/mol and 77.57 kJ/mol, respectively, by Kissinger's and Flynn‐Wall‐Ozawa's methods. The possible mechanism of preparation of ZnS/epoxy composites was discussed in this article. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Epoxy‐montmorillonite clay nanocomposites: Synthesis and characterization

Nanocomposites of epoxy resin with montmorillonite clay were synthesized by swelling of different proportions of the clay in a diglycidyl ether of bisphenol‐A followed by in situ polymerization with aromatic diamine as a curing agent. The montmorillonite was modified with octadecylamine and made organophilic. The organoclay was found to be intercalated easily by incorporation of the epoxy precursor and the clay galleries were simultaneously expanded. However, Na‐montmorillonite clay could not be intercalated during the mixing or through the curing process. Curing temperature was found to provide a balance between the reaction rate of the epoxy precursor and the diffusion rate of the curing agent into the clay galleries. The cure kinetics were studied by differential scanning calorimetry. The exfoliation behavior of the organoclay system was investigated by X‐ray diffraction. Thermogravimetric analysis was used to determine the thermal stability, which was correlated with the ionic exchange between the organic species and the silicate layers. The morphology of the nanocomposites was evaluated by scanning electron microscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2201–2210, 2004