Flexible Nanocomposites Research Articles

Synthesis and thermal studies of flexible polyurethane nanocomposite foams obtained using nanoclay modified with flame retardant compound

This work presents thermal studies of nanocomposites based on the flexible polyurethane (PU) matrix and filled using montmorillonite organically modified with organophosphorus flame retardant compound. Flexible PU nanocomposite foams were prepared in the reaction carried out between reactive alcoholic hydroxyl and isocyanate groups with the ratio of NCO to OH groups equal to 1.05. The amount of an organoclay ranging from 3 to 9 vol% was added to the polyol component of the resin before mixing with isocyanate. The apparent density of PU foams was ranging from 0.066 to 0.077 g cm−1. Thermal properties of the flexible PU nanocomposite foams were investigated by thermogravimetry and dynamical mechanical analysis. Glass transition temperatures (T g) were defined as maximum peak on tanδ curve. Thermal decomposition was observed at 310–320 °C (calculated from the onset of TG curve). Tensile strength of the PU foams was determined using mechanical test. The microstructure of the nanoparticles and the composites was investigated by X-ray diffraction. Finally, it was confirmed that the thermal and mechanical properties of flexible PU nanocomposite depend on the amount of nanoclay.

Flexible and flame resistant poly(lactic acid)/organomontmorillonite nanocomposites

ABSTRACTThe PLA/OMMT nanocomposites were produced using a melt compounding technique with isopropylated triaryl phosphate ester flame retardant (FR; 10–30 parts per 100 resin). The flammability of the PLA/OMMT composites was evaluated with an Underwriter Laboratory (UL‐94) vertical burning test, and their char morphology was studied using scanning electron microscopy (SEM). The thermal properties of the PLA/OMMT were characterized with a thermogravimetric analyzer (TGA) and a differential scanning calorimeter (DSC). The thermal analyses showed that adding FR reduced the decomposition onset temperature (To) of PLA/OMMT. Both PLA/OMMT/FR20 and PLA/OMMT/FR30 showed excellent flame retardant abilities, earning a V‐0 rating during the UL‐94 vertical burning test. A compact, coherent and continuous protective char layer was formed in the PLA/OMMT/FR nanocomposites. Additionally, the DSC results indicated that the flexibility of the PLA/OMMT composites increased after adding FR due to the FR‐induced plasticization. The impact strength of PLA/OMMT was greatly increased by the addition of FR. Flexible PLA nanocomposites with high flame resistance were successfully produced. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41253.

Hydrogen peroxide biosensor based on microperoxidase-11 immobilized on flexible MWCNTs-BC nanocomposite film

In the present work, we report on an experimental study of flexible nanocomposite film for electrochemical detection of hydrogen peroxide (H2O2) based on bacterial cellulose (BC) and multi-walled carbon nanotubes (MWCNTs) in combination with microperoxidase-11 (MP-11). MWCNTs are used to functionalize BC and provide a flexible conductive film. On the other hand, BC can improve MWCNTs׳ biocompatibility. The investigation shows that MP-11 immobilized on the flexible film of MWCNTs–BC can easily present a pair of well-defined and quasi-reversible redox peaks, revealing a direct electrochemistry of MP-11 on the nanocomposite film. The apparent heterogeneous electron-transfer rate constant ks is estimated to be 11.5s−1. The resulting flexible electrode presents appreciated catalytic properties for electrochemical detection of H2O2, comparing to traditional electrodes (such as gold, glassy carbon electrode) modified with MP-11. The proposed biosensor exhibits a low detection limit of 0.1µM (at a signal-to-noise ratio of 3) with a linear range of 0.1–257.6µM, and acquires a satisfactory stability.

Flexible-capron toughened epoxy/graphene nanocomposites for high k dielectric and ultraviolet radiation-resistant applications

In the present work, flexible hybrid nanocomposites with high k dielectric and UV resistant behaviour have been developed and studied using capron-toughened epoxy resin with different weight percentages (wt%) of graphene oxide (GO). Among the wt% of GO, 0.7 wt% nanocomposite possesses the highest value of dielectric constant. 1 wt% GO nanocomposite has the highest retention of tensile strength (93.35%) with graphene morphology, even after 168 h UV exposure, proving that its 2D graphene network serves as a passive protective layer against UV radiation. High dielectric behaviour and efficient retention of strength properties suggest that the flexible and light-weight hybrid nanocomposite material developed in the present work can be used as potential capacitors in microelectronics for satellites operating at low earth orbit.

Effect of carbon nanotubes shape on the properties of multiwall carbon nanotubes/polyethylene flexible transparent conductive films

Transparent conductive material is used in a wide range of applications and is particularly interesting. In the present work, a series of multiwall carbon nanotubes/low density polyethylene nanocomposites with different carbon nanotubes were prepared via solution casting method. The optical transparency, morphology, and resistivity of transparent conductive films have been characterized by using UV–Vis Spectrophotometer, Field emission scanning electron microscope and Multimeter, respectively. Their electrically conductive and optically transparent properties were studied and compared. The result showed that thinner and longer multiwall carbon nanotubes were more suitable for the fabrication of flexible transparent conductive nanocomposites. The sample filled with 1 wt% of T.1 (outside diameter <8 nm, length 10–30 μm) had good transparent conductive properties (volume conductivity of 3.12 × 10−3 S m−1 and optical transmittance of 62.8 % at the light wavelength of 600 nm). The high volume conductivity and optical transparency demonstrated that such kind of nanocomposite films had favorable potential in the applications from electromagnetic interference shielding to transparent electrodes.

Flexible and Transparent Nanocomposite of Reduced Graphene Oxide and P(VDF‐TrFE) Copolymer for High Thermal Responsivity in a Field‐Effect Transistor

A new class of temperature‐sensing materials is demonstrated along with their integration into transparent and flexible field‐effect transistor (FET) temperature sensors with high thermal responsivity, stability, and reproducibility. The novelty of this particular type of temperature sensor is the incorporation of an R‐GO/P(VDF‐TrFE) nanocomposite channel as a sensing layer that is highly responsive to temperature, and is optically transparent and mechanically flexible. Furthermore, the nanocomposite sensing layer is easily coated onto flexible substrates for the fabrication of transparent and flexible FETs using a simple spin‐coating method. The transparent and flexible nanocomposite FETs are capable of detecting an extremely small temperature change as small as 0.1 °C and are highly responsive to human body temperature. Temperature responsivity and optical transmittance of transparent nanocomposite FETs were adjustable and tuneable by changing the thickness and R‐GO concentration of the nanocomposite.

Fluoro-polymer functionalized graphene for flexible ferroelectric polymer-based high-k nanocomposites with suppressed dielectric loss and low percolation threshold.

Flexible nanodielectric materials with high dielectric constant and low dielectric loss have huge potential applications in the modern electronic and electric industry. Graphene sheets (GS) and reduced-graphene oxide (RGO) are promising fillers for preparing flexible polymer-based nanodielectric materials because of their unique two-dimensional structure and excellent electrical and mechanical properties. However, the easy aggregation of GS/RGO significantly limits the potential of graphene in enhancing the dielectric constant of polymer composites. In addition, the poor filler/matrix nanoscale interfacial adhesion also causes difficulties in suppressing the dielectric loss of the composites. In this work, using a facile and environmentally friendly approach, polydopamine coated RGO (PDA-RGO) and fluoro-polymer functionalized RGO (PF-PDA-RGO) were prepared. Compared with the RGO prepared by the conventional methods [i.e. hydrazine reduced-graphene oxide (H-RGO)] and PDA-RGO, the resulting PF-PDA-RGO nanosheets exhibit excellent dispersion in the ferroelectric polymer matrix [i.e. poly(vinylidene fluoride-co-hexafluoro propylene), P(VDF-HFP)] and strong interfacial adhesion with the matrix, leading to a low percolation threshold (fc = 1.06 vol%) and excellent flexibility for the corresponding nanocomposites. Among the three nanocomposites, the P(VDF-HFP)/PF-PDA-RGO nanocomposites exhibited the optimum performance (i.e. simultaneously having high dielectric constant and low dielectric loss). For instance, at 1000 Hz, the P(VDF-HFP) nanocomposite sample with 1.0 vol% PF-PDA-RGO has a dielectric constant of 107.9 and a dielectric loss of 0.070, showing good potential for dielectric applications. Our strategy provides a new pathway to prepare high performance flexible nanodielectric materials.

Development of Stretchable PZT/PDMS Nanocomposite Film with CNT Electrode

The piezoelectric composite film of ferroelectric PZT ceramic (PbZrxTi1-xO3) and polymer (PDMS, Polydimethylsiloxane) was prepared to improve the flexibility of piezoelectric material. The bar coating method was applied to fabricate flexible nanocomposite film with large surface area by low cost process. In the case of using metal electrode on the composite film, although there is no problem by bending process, the electrode is usually broken away from the film by stretching process. However, the well-attached, flexible CNT electrode on PZT/PDMS film improved flexibility, especially stretchability. PZT particles was usually settled down into polymer matrix due to gravity of the weighty particle, so to improve the dispersion of PZT powder in polymer matrix, small amount of additives (CNT powder, Carbon nanotube powder) was physically mixed with the matrix. By stretching the film, an output voltage of PZT(70 wt%)/PDMS with CNT (0.5 wt%) was measured.

Preparation and characterization of flexible polyurethane foam nanocomposites reinforced by magnetic core-shell Fe3O4@APTS nanoparticles

Novel magnetic polyurethane flexible foam nanocomposites were synthesized by incorporation of aminopropyltriethoxysilane (APTS) functionalized magnetite nanoparticles (MNPs) via one-shot method. The functionalized MNPs (Fe3O4@APTS) were synthesized by co-precipitation of the Fe2+ and Fe3+ with NH4OH and further functionalization with APTS onto the surface of MNPs by sol–gel method. The magnetic core-shell NPs were used up to 3.0 % in the foam formulation and the magnetic nanocomposites prepared successfully. The results of thermogravimetric analysis (TGA) showed an increasing in thermal stability of polyurethane nanocomposite foam at initial, 5 and 10 %, and maximum thermal decomposition temperatures by incorporation of Fe3O4@APTS. In addition SEM images revealed the uniformity of the foam structures and decreasing in pore sizes. Furthermore, VSM result showed super paramagnetic behavior for Fe3O4@APTS-PU nanocomposites.

Preparation, Characterization and Properties of Flexible Magnetic Nanocomposites of NiFe2O4-polybenzoxazine-LLDPE

A simple method for the preparation of magnetic nanocomposites consisting of NiFe2O4 nanoparticles, polybenzoxazine (PB), linear low-density polyethylene (LLDPE) and LLDPE-g- Maleic anhydride (LgM) is described. Composites were prepared by forming benzoxazine- NiFe2O4 nanocomposites followed by melt blending with LLDPE and thermal curing of benzoxazine. The composites were characterized by XRD, DSC and TGA, FT-IR, SEM, UTM and VSM. The saturation magnetization of the composites containing 33.25 wt% NiFe2O4 was 7.72 emu/g and it decreased with decreasing amount of NiFe2O4 in the composite. The composite films exhibited mechanical flexibility as well as magnetic properties.

Synthesis and investigation of PMMA films with homogeneously dispersed multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWNT) modified by 2.2′-azoiso-butyronitrile (AIBN) were incorporated into methyl methacrylate (MMA) by sonochemistry method, resulting in homogenous dispersion of MWNT, which makes possible to obtain flexible conductive polymer-matrix nanocomposites films of PMMA, with MWNT concentrations ranging from 0 to 0.5 wt%. Modified MWNT (AIBN-MWNT) were studied by Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and through visual observations in order to compare the dispersion in 2-propanone and toluene with that of pristine MWNT. Synthesized PMMA-AIBN-MWNT films were studied by FT-IR and Raman spectroscopy. Using FT-IR for the AIBN-MWNT it was not possible to identify any group or groups attached to the nanotubes. Raman spectroscopy shows a small modification in the Lorentzian peaks ratio ID/G of AIBN-MWNT, meanwhile XPS showed that atomic compositions does not change for AIBN-MWNT compared to the pristine nanotubes. Also by impedance it was analyzed the conductivity of PMMA-MWNT films and the results showed a threshold percolation at 0.5 wt%. FT-IR and Raman analyses for PMMA-AIBN-MWNT composite indicate a covalent bonding between PMMA and MWNT due to the opening of π-bonds of the nanotubes, which is related with a possible proposed reaction scheme.

Force and slip detection with direct-write compliant tactile sensors using multi-walled carbon nanotube/polymer composites

A mechanically compliant tactile sensor has been developed through direct-write (DW) deposition of a flexible conductive nanocomposite embedded between flexible polyurethane materials. Dispersion of multi-walled carbon nanotubes (MWCNTs) in a flexible and photocurable monomer introduced electrical and piezoresistive properties to the polymer which was used for the flexible conductive nanocomposite. Dispensing experiments were performed using the developed DW system to precisely create and embed the sensor elements between polyurethane substrates. From the experimental results, several flexible sensors including highly stretchable sensor elements (wires) were fabricated. Experiments were also performed to show that the sensor could detect applied forces at distinct locations on the surface. Slip was detected by examining the frequency content of the signals; sliding contact was characterized by a greater presence of high frequency power spectral density caused by mechanical vibrations that occur during slip. A Chebyshev band pass filter was developed to amplify these vibrations to distinguish between slip and nonslip tactile events. Finally, it is concluded that the study demonstrated in this work provides compelling evidence that the suggested materials, and methods of fabrication and characterization are promising for compliant tactile sensors.

Properties of magnetron-sputtered moisture barrier layer on transparent polyimide/graphene nanocomposite film

Colorless polyimides (PIs) have been considered as potential substrates for flexible displays due to their excellent transparency, thermal stability, mechanical strength and flexibility. However, high water vapor transmission rate (WVTR) of PI films limits the lifetime of electronic devices using PI films as substrates. Two approaches were applied to reduce the WVTR of PI films. Graphene (RG), which is thermally reduced graphene oxide (GO), was blended with a nearly colorless PI solution synthesized from an alicyclic tetracarboxylic dianhydride and aromatic diamine in cosolvent to obtain PI/RG nanocomposites. Subsequently, a barrier thin film was deposited on those PI nanocomposites by radio frequency magnetron sputtering from a Si3N4 target. The deposited barrier layer was amorphous and its composition along the thickness was homogeneous based on the X-ray diffraction patterns and the depth profile by X-ray photoelectron spectroscopy. An optimum deposition thickness of the barrier layer is 30nm to obtain a close-packed, smooth and continuous barrier film on PI. The presence of a 30nm-thick barrier layer on PI/RG-0.1 nanocomposite film capably reduces the WVTR to 0.17g/m2-day compared to 181g/m2-day for pure PI and 13g/m2-day for PI/RG-0.1. The surface of PI/RG is more hydrophobic and the capacity of moisture absorption by PI/RG is lower than PI/GO indicating the water resistance by RG is superior to that by GO. This flexible nanocomposite film remains high optical clarity and simultaneously shows excellent water barrier performance, enhanced dimensional stability and sufficient mechanical strength for advanced electronic applications.

Observation of large magnetodielectric and direct magnetoelectric behavior in LCMO/PVDF 0-3 nanocomposites

A two-phase multifunctional La2CoMnO6 (LCMO)/Poly-vinylidene fluoride 0–3 flexible nanocomposite (NCOMP) thick films have been prepared. Interestingly, this NCOMP shows linear increase of magnetoelectric voltage coefficient (MVC) with applied dc magnetic-bias fields up to 5 kOe, exhibiting no sign of hysteresis. For the typical LCMO concentration, fLCMO = 0.15, the maximum MVC measured is 1.45 mV cm−1 Oe−1 (using 50 kHz resonant signal). This low dielectric loss (∼0.12) NCOMP also showed intriguing high magnetodielectric effect (∼10%) around the ferromagnetic transition temperature (Tc ∼ 230 K) with minimal leakage current. Such results make the present nanocomposite significantly important for the development of magnetic field tuned electronic devices. At the request of the authors, this article is being retracted effective 9 December 2014.

Highly luminescent, flexible and biocompatible cadmium-based nanocomposites

Polydimethylsiloxane doped with colloidal CdSe/CdS nanocrystals is proposed as high-luminescent and biocompatible nanocomposite. A physical mixing procedure has been adopted to realize the optically active material and spectral and time-resolved optical analysis has been carried out in order to proof that nanocrystals quantum properties are preserved into the polymeric host matrix. Biocompatibility tests have shown no cadmium release in water ambient and no differences have been observed in cell viability cultured on pure PDMS substrates and on nanocomposite films. The obtained results let us envision possible applications of the proposed material as luminescent substrate for label-free cell imaging compatible with the most common optical microscopy techniques.

Largely enhanced energy density in flexible P(VDF-TrFE) nanocomposites by surface-modified electrospun BaSrTiO3fibers

By using Bi2O3-doped Ba0.3Sr0.7TiO3 (BSBT) fibers prepared via electrospinning and modified by dopamine as dielectric fillers, BSBT/P(VDF-TrFE) flexible nanocomposites are fabricated by solution casting. A low loading of BSBT nanofibers leads to a large increase in the dielectric constant and breakdown strength. In particular, the discharged energy density of the nanocomposites is significantly enhanced several times in comparison with the pure polymer matrix. The enhanced breakdown strength and discharged energy density could be attributed to the combined effects of the surface modification, large aspect ratio and paraelectric polarization behavior of the BSBT fibers. The present work indicates the enhancing potential of energy density on the polymer–ceramic composite by the paraelectric nanofiber fillers.

Full elastic constitutive relation of non-isotropic aligned-CNT/PDMS flexible nanocomposites

The elastic response of vertically aligned-carbon nanotube/polydimethylsiloxane (A-CNT/PDMS) nanocomposites is presented in this study and related to the underlying aligned-CNT morphology. Multiwalled carbon nanotubes (MWCNTs) at 1% Vf are embedded in a flexible substrate of PDMS to create a flexible polymer nanocomposite (PNC). The PNC properties are evaluated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile mechanical tests, and the full linearly elastic constitutive relation is established for such a PNC. The results suggest that the CNTs retain the alignment after wetting and curing of PDMS. PDMS is significantly modified by the reinforcing aligned-CNT fibers, demonstrating non-isotropic (as opposed to the isotropic neat PDMS) elastic properties all different from PDMS (Young's modulus of 0.8 MPa), including an anisotropy ratio of 4.8 and increases in the modulus of A-CNT/PDMS over PDMS by more than 900% and 100%, in the CNT longitudinal and transverse directions, respectively. This study reports the first full constitutive relation that may be useful in modeling PNCs as composites or as elements of hierarchical nanoengineered composites, particularly PDMS-CNT PNCs are envisioned as elements in biomedical devices such as pressure transducers and energy harvesters.

Flexible hierarchical nanocomposites based on MnO2nanowires/CoAl hydrotalcite/carbon fibers for high-performance supercapacitors

A hierarchical nanocomposite based on MnO2 nanowire/CoAl layered double hydroxide/carbon fibers is fabricated by a facile two-step method as a high-performance supercapacitor. The CoAl-LDH nanocrystals grown on flexible carbon fibers were prepared via an in situ hydrothermal method, followed by loading of MnO2 nanowires through a direct redox reaction between the Co2+ species and MnO4−. The hierarchical MnO2/LDH/CFs electrode as a supercapacitor displays a high specific capacitance (944 F g−1 at 1 A g−1) and rate capability, good stability and excellent long-term cycling life.

Graphene-crosslinked polyurethane block copolymer nanocomposites with enhanced mechanical, electrical, and shape memory properties

Highly flexible, conductive, and shape memory polyurethane nanocomposites were prepared using a robust and fast process. Functionalized graphene sheets were incorporated as crosslinkers in the prepolymer, prepared from a reaction of 4,4′-methylene bis(phenyl isocyanate) and poly(e-caprolactone)diol. The covalently bonded graphene sheets were homogeneously dispersed in the polymer matrix. In comparison to pristine polyurethane and carbon nanotube-crosslinked polyurethane, the graphene-crosslinked polyurethane composite exhibited higher modulus and breaking stress, and exceptional elongation-at-break. The resulting composite exhibited 97% shape recovery, 95% shape retention, enhanced shape recovery force, and fast electroactive shape recovery rate, thus it could be a promising material for the fabrication of graphene-based actuating devices.

Flexible PVDF-BaTiO3 Nanocomposites as Potential Materials for Pressure Sensors

In this work, PVDF–BaTiO3 composites were prepared using cryogenic high-energy ball milling (HEBM) and subsequent hot pressing. PVDF-BaTiO3 mixtures with different weight fractions of submicrometric BaTiO3 particles were subjected to 1 h of active milling. By applying pressure at 200°C the resulting powder was molded in the form of thin discs. This processing method allowed us to obtain an extraordinary uniform dispersion of the BaTiO3 particles within the PVDF polymer matrix. A morphological and structural characterization of the materials was done using conventional techniques (DSC, FTIR, XRD, SEM). Piezoelectric characterization of the specimens was also carried out by two different tests for inducing output voltage signals in the materials: i) single impact by ball free fall; and ii) macroscopic tapping. It was found that the output voltage decreases in both cases with the amount of BaTiO3 particles. The origin of this observation does not seem to be due to changes in the crystalline structure or morphology of the PVDF induced by the presence of BaTiO3. Rather, it can be explained taking into account that the constituents of the composites under study, BaTiO3 and PVDF, have opposite piezoelectric effects.