Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

Nanodiamonds have excellent mechanical and optical properties, high surface areas and tunable surface structures. They are also non-toxic, which makes them well suited to biomedical applications. Here we review the synthesis, structure, properties, surface chemistry and phase transformations of individual nanodiamonds and clusters of nanodiamonds. In particular we discuss the rational control of the mechanical, chemical, electronic and optical properties of nanodiamonds through surface doping, interior doping and the introduction of functional groups. These little gems have a wide range of potential applications in tribology, drug delivery, bioimaging and tissue engineering, and also as protein mimics and a filler material for nanocomposites.

The properties and applications of nanodiamonds

A review on polymer–layered silicate nanocomposites

5. In Situ Polymerization 3907 5.1. General Polymerization 3907 5.2. Photopolymerization 3910 5.3. Surface-Initiated Polymerization 3912 5.4. Other Methods 3913 6. Colloidal Nanocomposites 3913 6.1. Sol-Gel Process 3914 6.2. In Situ Polymerization 3916 6.2.1. Emulsion Polymerization 3917 6.2.2. Emulsifier-Free Emulsion Polymerization 3919 6.2.3. Miniemulsion Polymerization 3920 6.2.4. Dispersion Polymerization 3921 6.2.5. Other Polymerization Methods 3923 6.2.6. Conducting Nanocomposites 3924 6.3. Self Assembly 3926 7. Other Preparative Methods 3926 8. Characterization and Properties 3928 8.1. Chemical Structure 3928 8.2. Microstructure and Morphology 3929 8.3. Mechanical Properties 3933 8.3.1. Tensile, Impact, and Flexural Properties 3933 8.3.2. Hardness 3936 8.3.3. Fracture Toughness 3937 8.3.4. Friction and Wear Properties 3937 8.4. Thermal Properties 3938 8.5. Flame-Retardant Properties 3941 8.6. Optical Properties 3942 8.7. Gas Transport Properties 3943 8.8. Rheological Properties 3945 8.9. Electrical Properties 3945 8.10. Other Characterization Techniques 3946 9. Applications 3947 9.1. Coatings 3947 9.2. Proton Exchange Membranes 3948 9.3. Pervaporation Membranes 3948 9.4. Encapsulation of Organic Light-Emitting Devices 3948

Polymer/Silica Nanocomposites: Preparation, Characterization, Properties, and Applications

This paper presents a review of the principal developments in functionally graded materials (FGMs) with an emphasis on the recent work published since 2000. Diverse areas relevant to various aspects of theory and applications of FGM are reflected in this paper. They include homogenization of particulate FGM, heat transfer issues, stress, stability and dynamic analyses, testing, manufacturing and design, applications, and fracture. The critical areas where further research is needed for a successful implementation of FGM in design are outlined in the conclusions. DOI: 10.1115/1.2777164

https://web.mst.edu/~vbirman/papers/Modeling%20and%20Analysis%20of%20FGM_Review_2007.pdf

Modeling and Analysis of Functionally Graded Materials and Structures

Nylon 11 coatings filled with nominal 0–15 vol % of nanosized silica or carbon black were produced using the high velocity oxy-fuel combustion spray process. The scratch and sliding wear resistance, mechanical, and barrier properties of nanocomposite coatings were measured. The effect of powder initial size, filler content, filler chemistry, coating microstructure, and morphology were evaluated. Improvements of up to 35% in scratch and 67% in wear resistance were obtained for coatings with nominal 15 vol % contents of hydrophobic silica or carbon black, respectively, relative to unfilled coatings. This increase appeared to be primarily attributable to filler addition and increased matrix crystallinity. Particle surface chemistry, distribution, and dispersion also contributed to the differences in coating scratch and wear performance. Reinforcement of the polymer matrix resulted in increases of up to 205% in the glass storage modulus of nanocomposite coatings. This increase was shown to be a function of both the surface chemistry and amount of reinforcement. The storage modulus of nanocomposite coatings at temperatures above the glass transition temperature was higher than that of unfilled coatings by up to 195%, depending primarily on the particle size of the starting polymer powder. Results also showed that the water vapor transmission rate through nanoreinforced coatings decreased by up to 50% compared with pure polymer coatings. The aqueous permeability of coatings produced from smaller particle size polymers (D-30) was lower than the permeability of coatings produced from larger particles because of the lower porosities and higher densities achieved in D-30 coatings. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2272–2289, 2000

Nylon 11/silica nanocomposite coatings applied by the HVOF process. II. Mechanical and barrier properties

Thermally sprayed functionally graded coatings based on a polyimide matrix filled with varying volume fractions of WC–Co have been investigated to improve the erosion and oxidation resistance of polymer matrix composites. A study of the coatings' effectiveness as erosion barriers was accomplished through a statistical analysis of the results of solid particle erosion testing of coated and uncoated polymer matrix composite (PMC) samples using a design of experiments (DoE) approach. Two coating systems and a control sample were evaluated in a randomized test matrix. The coatings were tested at room temperature and 250 °C, using an alumina erodent impacting the coatings at a speed of 100 m/s at angles of 20° and 90°. In general, as the angle of incidence of the eroding material increased from 20° to 90° the volume loss increased. Erosion volume loss at 250 °C was approximately twice that at room temperature.

Solid particle erosion resistance of thermally sprayed functionally graded coatings for polymer matrix composites

High-velocity oxyfuel (HVOF) sprayed polyimide/WC-Co functionally graded (FGM) coatings with flame-sprayed WC-Co topcoats have been investigated as solutions to improve the solid-particle erosion and oxidation resistance of polymer matrix composites (PMCs) in the gas flow path of advanced turbine engines. Porosity, coating thickness, and volume fraction of the WC-Co phase retained in the graded coating architecture were determined using standard metallographic techniques and computer image analysis. The adhesive bond strength of three different types of coatings was evaluated according to ASTM D 4541. Adhesive/cohesive strengths of the FGM coating were measured and compared with those of pure polyimide and polyimide/WC-Co composite coatings and also related to the tensile strength of the uncoated PMC substrate perpendicular to the thickness. The FGM coatings exhibited lower adhesive bond strengths (∼6.2 MPa) than pure polyimide coatings (∼8.4 MPa), and in all cases these values were lower than the tensile strength (∼17.6 MPa) of the reference uncoated PMC substrate. The nature and locus of the failures were characterized according to the percent adhesive and/or cohesive failure, and the interfaces tested and layers involved were analyzed by scanning electron microscopy.

Adhesive/cohesive properties of thermally sprayed functionally graded coatings for polymer matrix composites

Nylon 11 coatings filled with nanosized silica and carbon black have been produced using the high velocity oxy-fuel (HVOF) combustion spray process. The physical properties and microstructure of coatings produced from nylon 11 powders with starting particle sizes of 30 and 60 μm have been evaluated as a function of the filler content, filler chemistry, and processing conditions. The nominal filler content was varied from 5 to 20 vol %. Co-milling of the nano-sized fillers with the polymer powders produced an embedded 4–8 μm thick filler layer on the surfaces of the polymer particles. Optimization of the HVOF processing parameters based on an assessment of the degree of splatting of polymer particles was accomplished by varying the jet temperature (via hydrogen/oxygen ratio). Gas mixtures with low hydrogen contents minimized polymer particle degradation. The filler was found to be agglomerated at the splat boundaries in the final coating microstructures. Aggregates of silanated silica and carbon black were of the order of 50 nm in size, whereas the aggregates of untreated silica and hydrophilic silica were of the order of 100 nm. The morphology of the polymer and the microstructure of the coatings depended on the filler surface chemistry and the volume fraction of the filler, as well as the initial nylon 11 particle size. Although all filled coatings had higher crystallinities than pure nylon 11 coatings, coatings produced from a smaller starting polymer particle size exhibited improved spatial distribution of the silica in the matrix and lower crystallinity. In addition, coatings prepared from smaller polymer particles had a higher density and lower porosity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1684–1699, 2000

Richard Knight

Papers

Nylon 11/silica nanocomposite coatings applied by the HVOF process. II. Mechanical and barrier properties

Solid particle erosion resistance of thermally sprayed functionally graded coatings for polymer matrix composites

Adhesive/cohesive properties of thermally sprayed functionally graded coatings for polymer matrix composites

Nylon 11/silica nanocomposite coatings applied by the HVOF process. I. Microstructure and morphology

3D predictions of thermally sprayed polymer splats: Modeling particle acceleration, heating and deformation on impact with a flat substrate