Nanoindentation in polymer nanocomposites

This article reviews recent literature on polymer nanocomposites using advanced indentation techniques to evaluate the surface mechanical properties down to the nanoscale level. Special emphasis is placed on nanocomposites incorporating carbon-based (nanotubes, graphene, nanodiamond) or inorganic (nanoclays, spherical nanoparticles) nanofillers. The current literature on instrumented indentation provides apparently conflicting information on the synergistic effect of polymer nanocomposites on mechanical properties. An effort has been done to gather information from different sources to offer a clear picture of the state-of-the-art in the field. Nanoindentation is a most valuable tool for the evaluation of the modulus, hardness and creep enhancements upon incorporation of the filler. It is shown that thermoset, glassy and semicrystalline matrices can exhibit distinct reinforcing mechanisms. The improvement of mechanical properties is found to mainly depend on the nature of the filler and the dispersion and interaction with the matrix. Other factors such as shape, dimensions and degree of orientation of the nanofiller, as well as matrix morphology are discussed. A comparison between nanoindentation results and macroscopic properties is offered. Finally, indentation size effects are also critically examined. Challenges and future perspectives in the application of depth-sensing instrumentation to characterize mechanical properties of polymer nanocomposite materials are suggested.     

Numerical characterisation of fullerene based polymer nanocomposites considering interface effects

In this investigation, the effective mechanical properties of fullerene nanocomposites considering interface effects were characterised. Load transfer in nanocomposite materials is achieved through the fullerene/matrix interface. Thus, to determine nanocomposite mechanical properties, the interface behaviour must be determined. A single fullerene and the surrounding polymer matrix are modelled. Two cases of perfect bonding and an elastic interface are considered. Two models are suggested for elastic interface. The first elastic interface model consists of a thin layer of an elastic material surrounding the fullerene. In the second elastic interface model, a series of spring elements are used as the fullerene/matrix interface. The results of numerical models indicate the importance of adequate interface bonding for a more effective strengthening of polymer matrix by fullerene. Also, Young’s modulus prediction for fullerene in epoxy matrix is compared to experimental data investigated by Rafiee et al. (2011), and good agreement is observed.     

Molecular theories of polymer nanocomposites

Significant progress towards the development of microscopic predictive theories of the equilibrium structure, polymer-mediated interactions, and phase behavior of polymer nanocomposites has been made recently based on liquid state integral equation, density functional, and self-consistent mean field approaches. The basics of these three theoretical frameworks are summarized, and selected highlights of their recent applications discussed for spherical, nonspherical, and polymer-grafted nanoparticles dissolved in athermal and adsorbing concentrated solutions and homopolymer melts. The role of nanoparticle size, volume fraction, and interfacial cohesive interactions is emphasized, especially with regards to their influence on filler dispersion and spatial ordering via entropic depletion attraction, polymer adsorption-mediated steric stabilization, and local bridging of nanoparticles. Some of the many remaining theoretical challenges and open fundamental questions are summarized.     

Cyclic fatigue of polymer nanocomposites

This paper presents an experimental study on cyclic fatigue of two polymer nanocomposites in two common failure modes: mechanical failure in epoxy nanocomposites and thermal softening in polyamide (PA, nylon) 6 nanocomposites. For epoxy nanocomposites, the effects of hard (silica) and soft (rubber) nano-particles on un-notched samples under constant cyclic stress amplitude fatigue were studied. Hard particles were shown to increase but soft particles decrease the fatigue life of nanocomposites compared to unmodified epoxy. At the same stress amplitude, the extent of fatigue crack growth prior to fast fracture was largest in rubber nanocomposites and least in pure epoxy, reflecting the differences in their fracture toughness values. Ternary nanocomposites with both hard and soft (silica and rubber) particles were also investigated and their fatigue performances were compared to the binary nanocomposites. Further, the stress (σ_a) versus life (N_r) test data of pure epoxy and its binary and ternary nanocomposites are well described by Basquin’s law.PA6 nanocomposites exhibited fatigue failure due to thermal softening when the maximum local temperature of the specimens subjected to cyclic loading reached the glass transition temperature, T_g, of the material. Critical stress (σ_a) versus frequency (ω) envelopes for design against thermal failure were obtained for PA6/organoclay, PA6/POE-g-MA and PA6/pristine clay. Experimental results compared favorably with theoretical predictions.     

Optical properties of polymer nanocomposites

Nanomaterials have emerged as an area of interest motivated by potential applications of these materials in light emitting diodes, solar cells, polarizers, light-stable colour filters, optical sensors, optical data communication and optical data storage. Nanomaterials are of particular interest as they combine the properties of two or more different materials with the possibility of possessing novel mechanical, electronic or chemical behaviour. Understanding and tuning such effects could lead to hybrid devices based on these nanocomposites with improved optical properties. We have prepared polymer nanocomposites of well-defined compositions and studied the optical properties of powders and their thin films. UV-vis absorption spectroscopy on nanocomposite powders and spectroscopic ellipsometry measurements on thin films was used to study the effect of interfacial morphology, interparticle spacing and finite size effects on optical properties of nanocomposites. Systematic shift in the imaginary part of the dielectric function can be seen with variation in size and fraction of the gold nanoparticle. The thickness of the film also plays a significant role in the tunability of the optical spectra.     

Supercritical fluid applications in polymer nanocomposites

Supercritical fluids have been used to synthesize and foam a variety of polymer nanocomposite materials. There have been significant advances in developing and characterizing nanoscale structures and using supercritical fluids to alter properties at the nanoscale. In this work we summarize these advances and discuss foam properties generated using supercritical carbon dioxide as well as relevant fundamental properties of the system.     

聚合物/粘土纳米复合材料研究进展

聚合物/粘土纳米复合材料(PCN)是近几年纳米材料领域中的研究热点.综述了聚合物/粘土纳米复合材料的几种制备方法及研究进展,并将纳米复合材料与普通材料的物理性能相比较,得知纳米复合材料有优良的物理性能.总结了这一领域尚待解决的问题.     

Quantified stereological macrodispersion analysis of polymer nanocomposites

A quantified stereological characterization approach for polymer nanocomposite macrodispersion is presented. Three differently dispersed 1.0 wt.% polycarbonate/carbon nanofiber composites are studied with the analysis tool to quantitatively describe the differences in the nanocomposite microstructures. Strong trends were found describing the differences with observed agglomeration states. Established stereological functions were used with the observed agglomerate data to estimate the bulk macrodispersion states of the different systems. Error analysis was performed on the estimated bulk agglomeration states which revealed accurate or increased accuracy compared to observed data for the poor and medium dispersion systems studied. Through this characterization approach, a better understanding of nanocomposite macrodispersion states can be realized creating more effective property correlation and material behavior prediction.     

Molecular interactions alter clay and polymer structure in polymer clay nanocomposites.

In this work, using photoacoustic Fourier transform infrared spectroscopy (FTIR) we have studied the structural distortion of clay crystal structure in organically modified montmorillonite (OMMT) and polymer clay nanocomposites (PCN). To study the effect of organic modifiers on the distortion of crystal structure of clay, we have synthesized OMMTs and PCNs containing same polymer and clay but with three different organic modifiers (12-aminolauric acid, n-dodecylamine, and 1,12-diaminododecane), and conducted the FTIR study on these PCNs. Our previous molecular dynamics (MD) study on these PCNs reveals that significant nonbonded interactions (van der Waals, electrostatic interactions) exist between the different constituents (polymer, organic modifier, and clay) of nanocomposites. Previous work based on X-ray diffraction (XRD) and differential scanning calorimetry (DSC) on the same set of PCNs shows that crystallinity of polymer in PCNs have changed significantly in comparison to those in pristine polymer; and, the nonbonded interactions between different constituents of PCN are responsible for the change in crystal structure of polymer in PCN. In this work to evaluate the structural distortion of crystal structure of clay in OMMTs and PCNs, the positions of bands corresponding to different modes of vibration of Si-O bonds are determined from the deconvolution of broad Si-O bands in OMMTs and PCNs obtained from FTIR spectra. Intensity and area under the Si-O bands are indicative of orientation of clay crystal structures in OMMTs and PCNs. Significant changes in the Si-O bands are observed from each vibration mode in OMMTs and PCNs containing three different organic modifiers indicating that organic modifiers influence the structural orientation of silica tetrahedra in OMMTs and PCNs. Deconvolution of Si-O bands in OMMTs indicate a band at approximately 1200 cm(-1) that is orientation-dependent Si-O band. The specific changes in intensity and area under this band for OMMTs with three different organic modifiers further confirm the change in structural orientation of silica tetrahedra of OMMTs by organic modifiers. Thus, from our work it is evident that organic modifiers have significant influence on the structure of polymer and clay in PCNs. It appears that in nanocomposites, in addition to strong interactions at interfaces between constituents, the structure of different phases (clay and polymer) of PCN are also altered, which does not occur in conventional composite materials. Thus, the mechanisms governing composite action in nanocomposites are quite different from that of conventional macro composites.     

Properties of tin/plasma polymer nanocomposites

Thin composite layers (tin in plasma polymer matrix) were prepared in a stainless steel vacuum chamber. An RF powered magnetron with tin target was used to excite the discharge and to activate the monomer species (n-hexane). The gas mixture introduced comprised Ar and n-hexane vapours. The properties of the films and chemical composition were characterized by AFM (surface morphology), TEM and Electron tomography (bulk structure characterization), XPS and FTIR spectroscopy (chemical composition analyses). Current-voltage characteristics were measured to examine the electrical properties of the layers and their dependence on the deposition parameters.     

聚合物/MMT纳米复合材料的结晶性能

综述了尼龙/MMT、PP/MMT、PET/MMT等代表性的结晶性聚合物/MMT纳米复合材料结晶行为,分析了MMT的加入对聚合物结晶的影响,提出建立聚合物/MMT纳米复合材料宏观性能和微观结构之间的关系,并展望了未来的发展方向.     

New advances in polymer/layered silicate nanocomposites

This review discusses some recent advances in polymer silicate nanocomposites. In particular, we highlight the properties of specific nanocomposites while emphasizing the lack of properties trade-offs in these systems. We also present our work on the structure and dynamics of the polymer/nanofiller interface and attempt to relate them to macroscopic nanocomposite properties.     

Time-resolved luminescence in conducting polymer/antidot nanocomposites

We report modification of the structure and properties of conjugated polymers through controlled embedding wide-gap nanocrystals (antidots) within the polymer matrix. Investigations were carried out by means of stationary and time-resolved photoluminescence. Antidots strongly modify the luminescence spectrum of poly(p-phenylene vinylene) but have almost no influence on the spectrum of poly(2-(6-cyano-6'-methylheptyloxy)-1, 4-phenylene. We explain this observation with respect to the different chain structure and electron density distribution in these two materials. The temporal evolution of luminescence spectra in polymer/antidot composites contains a series of characteristic times. The shortest of these (0.35-0.6 ns) are independent of antidot material and characterize processes in the polymer matrix. Larger times considerably exceeding 1 ns are composition-sensitive and attributable to carrier capture by nanocrystals. The qualitative character of the modification of luminescence spectra associated with the inclusion of antidots depends strongly on the characteristics of the polymer matrices and more weakly on the antidot material. This suggests that the predominant effect of the nanocrystals relates to the modification of the matrix near the polymer-inorganic interface.     

Thermoplastic polymer nanocomposites for applications in optical devices

Polymer optical fibres (POF) have superior properties compared to glass fibres like e.g. high flexural strength, uncomplicated mechanical machining and inexpensive mass production. Dispersion of nanoscaled ceramic fillers in polymers allows the modification of the refractive index depending on the ceramic used and the aspired application. Current work deals with the development of a process chain to tailor the refractive index of PMMA using a UV-curable reactive resin and ceramic nanopowders as well as with the ageing behaviour of polymer nanocomposites. Improved dispersion techniques applying high shear forces to deagglomerate the ceramic powders lead to a refractive index shift depending on the ceramic fillers maintaining a transparency of resulting polymer nanocomposites sufficient for optical applications in the visible (633 nm) and in the infrared (1550 nm) regime. Optical devices were obtained using reaction moulding of the modified polymer nanocomposites as rapid prototyping method.     

碳纳米管增强聚合物复合材料的研究进展

论述了碳纳米管/聚合物纳米复合材料的各种制备方法和最新进展。详细讨论了碳纳米管/聚合物纳米复合材料的结构和性能,并对今后的研究方向进行了展望。     

Optimisation of hybridisation effect in graphene reinforced polymer nanocomposites

This article focuses on the optimisation of electrical and mechanical properties of hybrid blends of polyoxymethylene (POM) as primary thermoplastic matrix, polypyrrole (PPY) as secondary conducting polymer and graphene (G) as reinforcement. An initial Taguchi analysis was performed with a focus on improving electrical conductivity (σ) and tensile strength. A mixture analysis using ‘simplex’ statistical design was applied to develop an experimental subset that identified an optimal combination in weight-percentage. Both electrical and mechanical properties were improved by the addition of PPY and graphene particles due to hybridisation mechanism as well as double percolation threshold. The maximum electrical conductivity of 0.95 S cm^?1 was achieved with POM reinforced with 3 wt.% of G and 2.5 wt.% of PPY loading. The mechanical properties were found to be increased with increase in addition of both G and PPY.     

聚合物/有机改性蒙脱土纳米复合材料的制备方法研究进展

聚合物/蒙脱土纳米复合材料因具有独特的结构,以及较常规聚合物基复合材料更优异的性能,而展现出诱人的开发和应用前景。聚合物/蒙脱土纳米复合材料的制备也因此成为探索高性能复合材料的途径之一,受到新材料科学研究领域的普遍关注。本文综述了近年来在蒙脱土的有机改性、聚合物/蒙脱土纳米复合材料的制备方法方面的研究进展。     

Simulation of interphase percolation and gradients in polymer nanocomposites

Experimental data suggests that well dispersed nanoparticles within a polymer matrix induce a significant interphase zone of altered polymer mobility surrounding each nanoparticle, which can lead to a percolating interphase network inside of the composite. To investigate this concept and the nature of the interphase, a two-dimensional finite element model is developed to study the impact of interphase zones on the overall properties of the composite. Thirty non-overlapping identical circular inclusions are randomly distributed in the matrix with layers of interphase surrounding the inclusions. The simulation results clearly show that the loss moduli of composites are either broadened or shifted corresponding to the absence or presence of a geometrically percolating interphase network. Our numerical study correlates well with experimental data showing broadening of loss peaks for unfunctionalized composites and a large shift of the loss modulus for functionalized nanotube polymer composites. Further, our results indicate the existence of a gradient in properties of the interphase layer and that incorporating this gradient into modeling is critical to reflect the behavior of polymer nanocomposites.     

Quantum confinement effect of CdS nanoparticles dispersed within PVP/PVA nanocomposites

Nanocomposite films of CdS nanoparticles within PVP/PVA blend were prepared. The prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The amount of Cd⁺ used strongly influenced the size of the CdS nanoparticles, which was confirmed by XRD, UV–vis absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher content of cadmium. The results of XRD indicate that CdS nanoparticles were formed with hexagonal phase in the polymeric matrix. PL and UV–vis spectra reveal that nanocomposite films shows quantum confinement effect. Optical band gap and particle size were calculated and is in agreement with the results obtained from TEM data. The direct energy band gap was increased up to 2.86 eV.