In this article, several applications of nanomaterials in food packaging and food safety are reviewed, including: polymer/clay nanocomposites as high barrier packaging materials, silver nanoparticles as potent antimicrobial agents, and nanosensors and nanomaterial-based assays for the detection of food-relevant analytes (gasses, small organic molecules and food-borne pathogens). In addition to covering the technical aspects of these topics, the current commercial status and understanding of health implications of these technologies are also discussed. These applications were chosen because they do not involve direct addition of nanoparticles to consumed foods, and thus are more likely to be marketed to the public in the short term.

Applications of nanotechnology in food packaging and food safety: Barrier materials, antimicrobials and sensors

Study of flexible nanodielectric materials (FNDMs) with high permittivity is one of the most active academic research areas in advanced functional materials. FNDMs with excellent dielectric properties are demonstrated to show great promise as energy-storage dielectric layers in high-performance capacitors. These materials, in common, consist of nanoscale particles dispersed into a flexible polymer matrix so that both the physical/chemical characteristics of the nanoparticles and the interaction between the nanoparticles and the polymers have crucial effects on the microstructures and final properties. This review first outlines the crucial issues in the nanodielectric field and then focuses on recent remarkable research developments in the fabrication of FNDMs with special constitutents, molecular structures, and microstructures. Possible reasons for several persistent issues are analyzed and the general strategies to realize FNDMs with excellent integral properties are summarized. The review further highlights some exciting examples of these FNDMs for power-energy-storage applications.

Flexible Nanodielectric Materials with High Permittivity for Power Energy Storage

The development of high-performance capacitive energy storage devices is of critical importance to address an ever-increasing electricity need. The energy density of a film capacitor is determined by the dielectric constant and breakdown strength of dielectric materials. With the highest dielectric constant among the known polymers, poly(vinylidene fluoride)-based ferroelectric terpolymers are of great potential for high energy density capacitors. However, their energy storage capability has long been limited by the relatively low breakdown strength. Here we demonstrate remarkable improvements in the energy density and charge–discharge efficiency of the ferroelectric terpolymers upon the incorporation of ultra-thin boron nitride nanosheets (BNNSs). It is found that BNNSs function as a robust scaffold to hamper the onset of electromechanical failure and simultaneously as an efficient insulating barrier against electrical conduction in the resulting polymer nanocomposites, resulting in greatly enhanced breakdown strength. Of particular note is the improved thermal conductivity of the terpolymer with the introduction of BNNSs; this is anticipated to benefit the stability and lifetime of polymer capacitors. This work establishes a facile, yet efficient approach to solution-processable dielectric materials with performance comparable or even superior to those achieved in the traditionally melt-extruded ultra-thin films.

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Solution-processed ferroelectric terpolymer nanocomposites with high breakdown strength and energy density utilizing boron nitride nanosheets

Atomic-scale interface engineering in BaTiO3@TO2 nanofibers (TiO2 nano-fibers embedded with BaTiO3 nano-particles) leads to concurrent enhancement of electric displacement and breakdown strength in poly(vinylidene fluoride) (PVDF)-based nanocomposites. An ultrahigh energy density of ≈20 J cm(-3) is achieved with only 3 vol% nanofibers, which is by far the highest discharged energy density of PVDF-based nanocomposites.

Ultrahigh Energy Density of Polymer Nanocomposites Containing BaTiO3@TiO2 Nanofibers by Atomic‐Scale Interface Engineering

Polymer film capacitors are critical components in many high-power electrical systems. Because of the low energy density of conventional polymer dielectrics, these capacitors currently occupy significant volume in the entire electrical system. This article reviews recent progress made in the development of polymer dielectrics with high energy storage density, which can potentially lead to significant weight and volume reduction in polymer film capacitors. The increase in energy density is achieved through two approaches, namely (a) the development of novel polymers with high electric polarization and optimized dielectric responses and (b) the development of nanocomposites containing polymer matrixes with high breakdown strength and inorganic nanofillers with high polarization. Promising progress has been made through both strategies, resulting in a maximum energy density of >30 J/cm3, which is at least 5 times higher than those of conventional polymer dielectrics. The state-of-the-art manufacturing method...

Polymer-Based Dielectrics with High Energy Storage Density

Processable, low-cost, high-performance hybrid dielectrics are enablers for a vast array of green technologies, including high-temperature electrical insulation and pulsed power capacitors for all-electric transportation vehicles. Maximizing the dielectric breakdown field (E(BD)), in conjunction with minimization of leakage current, directly impacts system performance because of the field's quadratic relationship with electrostatic energy storage density. On the basis of the extreme internal interfacial area and ultrafine morphology, polymer-inorganic nanocomposites (PNCs) have demonstrated modest increases in E(BD) at very low inorganic loadings, but because of insufficient control of the hierarchal morphology of the blend, have yielded a precipitous decline in E(BD) at intermediate and high inorganic volume fractions. Here in, we demonstrate that E(BD) can be increased up to these intermediate inorganic volume fractions by creating uniform one-dimensional nanocomposites (nanolaminates) rather than blends of spherical inorganic nanoparticles and polymers. Free standing nanolaminates of highly aligned and dispersed montmorillonite in polyvinyl butyral exhibited enhancements in E(BD) up to 30 vol % inorganic (70 wt % organically modified montmorillonite). These relative enhancements extend up to five times the inorganic fraction observed for random nanoparticle dispersions, and are anywhere from two to four times greater than observed at comparable volume fraction of nanoparticles. The breakdown characteristics of this model system suggested a trade-off between increased path tortuosity and polymer-deficient structural defects. This implies that an idealized PNC morphology to retard the breakdown cascade perpendicular to the electrodes will occur at intermediate volume fractions and resemble a discotic nematic phase where highly aligned, high-aspect ratio nanometer thick plates are uniformly surrounded by nanoscopic regions of polymer.

Nanolaminates: increasing dielectric breakdown strength of composites.

Studies of the barrier properties of polymer/layered silicate nanocomposites have traditionally focused on systems with low organoclay contents, with very little work comparing theory and experiment over broad composition ranges. As a result, in spite of many reports of promising enhancements in barrier properties, the envelope of applicability nanocomposite barrier models is generally unknown, making predictive modeling and materials design difficult if not impossible. In this work, model polystyrene (PS)/dimethyl ditallow modified montmorillonite (DMDT-MMT) nanocomposites are produced via a novel spray casting technique capable of creating homogeneous, free-standing nanocomposite films. This approach provides a single experimental methodology for producing films of pure polymer, pure organoclay, or any intermediate composition, with consistently high levels of layer orientation in all cases. The results of oxygen permeation analysis (OPA) performed on these model materials (0−100 vol % organoclay in 10%...

Effects of Composition, Orientation and Temperature on the O2 Permeability of Model Polymer/Clay Nanocomposites

Structure and dynamic mechanical properties of highly oriented PS/clay nanolaminates over the entire composition range

In spite of significant interest in 2D nanofillers, the effect of polymer intercalation on properties remains poorly understood. We use automated spray deposition to form two families of well-aligned polymer/clay nanolaminates that differ by one methyl group in the clay modifier; this difference results in intercalation in one instance and no intercalation in the other. Dynamic mechanical properties and gas permeability are reported alongside micromechanical and barrier models and a detailed description of the structures and phases present. Observed variations in modulus cannot be explained by micromechanical models often applied to polymer nanocomposites. In contrast with “effective particle” arguments, barrier properties are dominated by single layer aspect ratios. These findings have relevance for all manner of “bricks and mortar” hybrids. Additionally, these systems represent the macroscopic equivalent of the multilayer stacks found in practically all nanocomposites, with wide-ranging implications for...

Understanding the Consequences of Intercalation Using Model Polymer Nanolaminates

Polymer nanocomposites represent a key addition to the palette of advanced polymeric materials available to us in the context of additive manufacturing. However, our understanding of their properties, and thus our ability to predict them and to design parts based on them, remains limited. With this in mind, nanolaminates have been formed via an additive process developed in our group and referred to as automated spray deposition; these materials have been characterized with the express purpose of better understanding the composition-structure-properties relations critical to our ability to create high performance polymeric materials by design via additive techniques. Here we present a preliminary comparison of the dynamic mechanical properties of two families of nanolaminates, essentially identical except for the polarity of the polymer phase and the strength of polymer / nanofiller interactions, with the aim of better understanding the mechanical response of such materials.

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Erik Dunkerley

Papers

Nanolaminates: increasing dielectric breakdown strength of composites.

Effects of Composition, Orientation and Temperature on the O2 Permeability of Model Polymer/Clay Nanocomposites

Structure and dynamic mechanical properties of highly oriented PS/clay nanolaminates over the entire composition range

Understanding the Consequences of Intercalation Using Model Polymer Nanolaminates

The additive manufacturing of model polymer nanolaminates via automated spray deposition