Preface

Polymer composites are made of two components: polymer or matrix (continuous phase) and filler or reinforcement (discontinuous phase) to obtain properties that cannot be achieved by a single component alone. The specific tensile properties of fiber reinforced composites are excellent because of their low density and high mechanical properties. Over the past few decades such composites have replaced metals in many applications from aerospace to sports gears, from automobiles to wind turbines, and from circuit boards to civil structures such as bridges and buildings. With composites impacting every part of our lives they have become ubiquitous. Over the past 2-3 decades the fillers or reinforcing elements used in composites have become smaller and smaller to their current nanosize. Using nanoparticles or nanofibrils in polymers or resins provides significant advantages. Hundreds of studies have shown that only a small weight percent (loading) of nanoparticles can significantly alter the stiffness, strength and fracture strain as well as electrical, thermal or other functional properties of polymers because of their high surface-to-volume ratio. However, such benefits can be derived only if the particle dispersion is uniform and no clustering occurs. It is also universally accepted that the nanoparticle/resin interface and the interphase region in nanocomposites play a critical role in enhancing their properties. With better understanding of interface and interphase characteristics it should be possible to predict as well as design polymer nanocomposites with desired properties and performance. This book brings together several experts and leading researchers in this field to present their cutting edge research in understanding, modifying and controlling interfacial interactions between various nanofillers and a host of polymer matrices.

The book is divided into two parts; Part 1: Nanocomposite Interfaces/Interphases with 6 chapters and Part 2: Techniques to Characterize/Control Nanoadhesion with 5 chapters. In chapter 1 Schadler and coworkers define and discuss the two phases of polymer nanocomposites: polymeric matrix phase and inorganic nanofiller phase. Efforts have been made to improve the intrinsic properties of both the matrix and the nanofiller to enhance the overall performance of polymer nanocomposites. Accordingly, this chapter discusses the thermodynamic mechanisms governing nanofiller dispersion. The thermodynamic matrix/filler interactions also influence the structure and properties of the interfacial region, which can be significantly different from the bulk material. Examples of such structural modifications in semicrystalline and thermoset polymer nanocomposites are presented. In chapter 2 Pegoretti and colleagues discuss engineering of interphase with nanofillers in fiber-reinforced polymer composites. The first part of the chapter surveys recent advancements in the interphase engineering of fiber-reinforced polymer composites using different nanofillers. The second part of the chapter discusses strategies followed for stress transfer improvement or adding functionality to the interphase. The chapter also includes state-of-the-art knowledge on the characterization and modelling of the interphase. In the last 'Outlook' section some challenges and perspectives in the engineering of fiber/matrix interphase are summarized. The third chapter by Kim and colleagues discusses formation and functionality of interphase, a distinct region between the two phases in polymer nanocomposites. This chapter presents fundamental issues on the formation of interphase between carbon-based nanofillers, such as carbon nanotubes, graphene, carbon black, and polymer matrices. Special emphasis is placed on illustrating the role of interphase in governing the mechanical, electrical, thermal and other functional properties of nanocomposites. Based on the progress made so far, some suggestions are proposed for designing the interphase with specific structures for intended applications of nanocomposites. In chapter 4 D'Souza and colleagues examine the effects of crystallization on the interface in polymer nanocomposites. Crystallization in polymer nanocomposites is influenced by the nature of the polymer, the percentage of nanoparticles present and their dispersion and interparticle distance. This chapter presents the effect of montmorillonite nanoclay on the interfacial crystallization in three polymers: nylon, poly (ethylene terephthalate) and poly (ethylene naphthalate). The effect of crystallization on the permeability of all three systems is also examined. Chapter 5 by Zaldivar and Kim discusses a new class of Graphite Nanoplatelets (GnPs) based nanocomposites that have unique electrical and thermal properties. To obtain the highest possible properties, the nanoparticle/resin bonding needs to be improved. The chapter discusses how the nanoparticle surface can be optimally functionalized using Split Plasma Method. The sixth and the final chapter of Part 1 by Pissis and associates is devoted to the experimental investigation of interfacial effects in polymer nanocomposites using calorimetric studies for the glass transition and dielectric techniques for the segmental dynamics. After discussing the experimental techniques briefly, the authors focus on proper evaluation of the measurements to extract maximum information from the data. The authors also present methods and equations used to evaluate the results in terms of interfacial characteristics, in particular polymer fraction in the interfacial layer (the fraction of polymer with modified properties) and thickness of the interfacial layer. The chapter provides an overview of the state-of-the-art in the field from the materials point of view simply by using various methods to characterize several selected polymer nanocomposites.

Part 2 of the book spans chapter 7 to chapter 11. In chapter 7 Liu describes the recent progress in theoretical and experimental aspects of interfacial adhesion in nanostructured carbon materials based polymer nanocomposites and summarizes the common methods utilized to characterize the interfacial properties in nanocomposites. The next chapter by Sain and colleagues discusses chemical and physical techniques for surface modification of nanocellulose reinforcements. The polarity of cellulose fibers due to the abundance of hydroxyl groups is responsible for poor wetting of natural fibers by non-polar resins. Furthermore, a large difference in surface free energy levels between resins and natural fiber reinforcements is responsible for poor interfacial bonding. The chapter discusses the most recent surface treatment techniques being employed to develop high-performance nanocomposites. In chapter 9 Park and colleagues discuss a unique electro-micromechanical technique developed as an efficient nondestructive evaluation (NDE) method for sensing and determination of micro-damage at the filler/epoxy interface in nanocomposites. This 'self-sensing' method has also been used to evaluate interfacial damage in fiber reinforced polymer matrix nanocomposites. Among the advantages of this new NDE method, compared to other evaluation methods, include better stability, lower cost and its relative simplicity. Bhattacharyya and colleague discuss particulate incorporation, interphase generation and evaluation by nanoindentation in polymeric biocomposites in chapter 10. This chapter provides an overall perspective on the development of composites containing bio-based reinforcements, e.g., biochar. The properties and governing factors of the biochar composites are explained, which is followed by a discussion of the suitability of nanoindentation technique for determining nano-sized particle/resin interfacial properties. Finally, several studies involving nanoindentation on the nano-sized interfacial regions of composites are reviewed and critically discussed. In the 11th and the final chapter Pasquinelli and colleagues demonstrate the use of molecular dynamics (MD) simulations to quantify filler-matrix adhesion and nanocomposite mechanical properties. They also illustrate how MD simulations can predict the mechanical properties of polymer nanocomposites as a function of the chemical and structural composition of these materials. Other prospects for MD simulations include calculating other physical properties, improving the structure-property prediction through advancements in hardware architecture and software development, and connecting through multiscale modeling the nanoscale/microscale details from MD simulations to the macroscale characteristics.

The book should be of interest to researchers in academia, in government research labs and R&D personnel in a host of industries (e.g. aerospace, automotive, biomedical, composites, dentistry, fibers, medical, microelectronics, packaging, plastics, textiles) who are interested in designing and improving the properties of polymers and composites by the addition of nanoparticles. Industries such as aerospace and automotive where light-weighting of each component is critical and an ongoing effort, improved properties through scientific understanding of nanocomposites could be very advantageous. Anyone working in plastics/polymers and composites industries should find this book of great interest and very useful.

It is our great pleasure to thank those who made this book possible. First and foremost, we are profusely thankful to the contributing authors for their sustained interest, enthusiasm and cooperation and for investing their valuable time in sharing their knowledge and cutting edge research (in the form of chapters) with the interested community. This book would not have been possible without their hard work. The unwavering interest and...