Vikas Mittal

In situ Determination and Imaging of Physical Properties of Soft Organic Materials by Analytical Transmission Electron Microscopy

Analytical transmission electron microscopy (ATEM) offers great flexibility in identification of the structural-chemical organization of soft materials at the level of individual macromolecules. However, the determination of mechanical characteristics such as hardness/elasticity of the amorphous and polycrystalline organic substances by ATEM has been problematic so far. Here, we show that energy filtered TEM (EFTEM) measurements enable direct identification and study of mechanical properties in complex (bio-)polymer systems of relevance for different industrial and (bio-)medical applications. We experimentally demonstrate strong correlations between hardness/elasticity of different polymers (polycaprolactone, polylactid, polyethelene, etc.) and their volume plasmon energy. Thickness and anisotropy effects, which substantially mask the material contrast in EFTEM bulk plasmon images, can be adequately removed by normalizing the latter by carbon elemental map. EFTEM data has been validated using atomic force microscopy phase images, where phase shift related to the hardness and elastic modulus of the materials.

Self-healing anti-corrosion coatings for applications in structural and petrochemical engineering

Abstract: The chapter describes various self-healing mechanisms and approaches for achieving self-healing anti-corrosion coatings. Self-healing anti-corrosion coating systems based on polyaniline-modified ferrites, conducting polymer-modified graphene, polyaniline-modified TiO2 as well as the layer-by-layer approach are reviewed.

Polyolefin/Graphene Nanocomposite Materials

Polymer-/graphene-based nanomaterials have attracted significant scientific interest in recent years due to marked enhancement in the polymer properties at low-filler fractions. Graphene has also been reported to provide better property modifications than other nanofillers like layered silicates and nanotubes. The property enhancements are attributed commonly to the high aspect ratio of graphene platelets, filler-polymer interactions at the interface, and uniform dispersion of the platelets in the polymer matrices. Graphene also provides opportunities to tune its surface in order to achieve compatibility with the polymer matrices. Occasionally, chemical binding of the polymer matrix to the graphene surface has also been achieved. Though some challenges exist, which hinder the large-scale defect-free production and reproduction as well as large-scale commercial application, some applications have already found their way in the market. With ever-increasing knowledge and experience in synthesis, handling, surface modification, and processing of graphene, the number of applications is expected to grow steadily. This chapter briefly reviews the various synthesis and surface modification methodologies of graphene and subsequently provides examples of some recent studies on polyolefin/graphene nanocomposites.

Characterization of polyethylene-based multiphase systems containing zero- and two-dimensional nanoparticulate reinforcement materials by analytical electron and atomic force microscopy

Multiphase polymer nanomaterials with reinforcements of different structural features have immense commercial applications. Characterization of the morphological features in these nanocomposites like filler dispersion, effect of filler and compatibilizer on polymer phase morphology, interaction of filler and compatibilizer, and so on is of significant importance as these shape the composite behavior and properties. To study these aspects, polyethylene (PE) nanocomposites generated with and without compatibilizer using two different types of fillers were comprehensively characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM) including analytical TEM (e.g. energy-dispersive x-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS)). Differential scanning calorimetric analysis was performed in order to quantify thermotropical properties of the nanocomposites. The filler dispersion was poor in the absence of compatibilizer, whereas its addition enhanced the filler delamination owing to the positive interactions between the polar filler surface and polar component of the compatibilizer. The compatibilizer addition also decreased the melt enthalpy due to reduced crystallinity along with change in polymer phase morphology. The filler pullout was also observed even in the compatibilized samples leading to higher AFM height variation in these composites. The EELS and EDXS analysis was further useful in analyzing the type of filler phase as well as interactions between the filler and compatibilizer phases. The compatibilizer was also observed to concentrate near the interface with the filler as signal of oxygen atoms associated with compatibilizer chains did not enhance in matrix, but increased at organic–inorganic interface.

Optimal mechanical and gas permeation properties of polypropylene-organically modified montmorillonite (PP-OMMT) nanocomposites

Abstract This article focuses on obtaining optimal mechanical properties of polypropylene-organically modified montmorillonite (PP-OMMT) nanocomposites for different objectives using simulations. The primary objective was to minimize the cost of the PP-OMMT nanocomposites. The other aim was to obtain specific desired properties of the nanocomposite (irrespective of the nanocomposite cost). The later simulation results are useful in designing products where quality of the nanocomposite cannot be compromised (while the cost of the PP-OMMT is secondary). The properties that were optimized include Young’s modulus and oxygen permeation. Regression models were obtained and used to predict these properties as functions of corresponding compositions of the composites. Further, optimization procedures were simulated using these models along with other constraints and objective functions. All simulations were programmed using MATLAB version 7.10.0 (R2010a).

High CEC generation and surface modification in mica and vermiculite minerals

Montmorillonite layered silicate has been commonly used to reinforce polymer matrices. Due to its swelling in water, organic modification of the mineral surface is easily achieved which makes the surface compatible with polymers. Other minerals like mica and vermiculite though can also lead to high aspect ratio platelets in nanocomposites, but they do not swell in water owing to much stronger electrostatic forces of attraction holding their platelets together (layer charge density >0.5 eq · mol−1 in comparison with 0.25–0.5 eq · mol−1 for montmorillonite). In current study, milling, delamination and cation exchange processing of mica and vermiculite minerals has been reported to explore their potential as reinforcement materials. Wet grinding and subsequent sieving of the coarse minerals led to fine-sized particles suitable to perform chemical delamination in water. The delamination process resulted in Li-mica and Na-vermiculite with enhanced access to the interlayer cations, thus, higher CEC. Successful surface modification of the delaminated minerals with alkyl ammonium ions could be achieved which resulted in significant enhancements in their basal plane spacing. Peak degradation temperatures of 260°C were measured for C18 and 2C18 modified vermiculite, whereas 300°C and 275°C were observed respectively for C18 and 2C18 modified mica minerals which make them suitable for compounding with polymers at high temperature.

Modeling of tensile modulus of polyolefin-layered silicate nanocomposites: modified micro-mechanical and statistical methods

Abstract Applicability and subsequent modification of various composite models for the prediction of the relative tensile modulus of polyolefin nanocomposites has been studied. A number of models, such as the modified Halpin-Tsai, Guth, Mori-Tanaka, Hui and Shia and Takayanagi models, as well as factorial and mixture designs, were considered. Various assumptions in the models, such as uniform shape and size of filler (i.e., complete exfoliation), alignment, as well as interfacial bonding between the components, restrict their application for the prediction of the nanocomposite modulus. The modified Guth model and Halpin-Tsai model, with the ∅m concept, were developed further to incorporate the modulus reduction factors for polyolefin nanocomposites. This allowed the generation of master curves of the modulus reduction factor as a function of the aspect ratio of the filler in the composite. It was observed that the Mori Tanaka model, modified by constructing models of various representative volume elements (RVEs) of the underlying structure of the nanoclay filled polymers, matched the experimental values of the tensile modulus of polyolefin nanocomposites. The modified Hui and Shia model, incorporating the non-bonding interfacial effects, as well as the three component modified Takayanagi model, were also able to predict the tensile modulus of polyolefin nanocomposites efficiently. Factorial and mixture designs did not require the conventionally used assumptions and satisfactorily reflected the material behavior, and were specific to the particular components used to generate nanocomposites. These models were also helpful in predicting the aspect ratio of the filler in the composites, when synergistically combined with other modified models.