ABSTRACT
CONTENTS 8.1 Introduction ........................................................................................................................ 152 8.2 Fundamentals of Rheology .............................................................................................. 153
8.2.1 Shear and Extensional Rheology for Polymer Nanocomposites .................... 153 8.3 Measurement Techniques ................................................................................................. 154
8.3.1 Dynamic Measurements ....................................................................................... 155 8.3.2 Extensional Rheological Measurements ............................................................. 156
8.3.2.1 Meissner-Type Extensional Rheometer ................................................ 156 8.3.2.2 Drawing of Molten Filament after Extrusion ...................................... 157
8.3 The Rheology of Composites ........................................................................................... 158 8.3.1 Rheology of Polymer Nanocomposites............................................................... 159
8.4 Nanocomposites with Carbon Nanotubes ..................................................................... 161 8.5 Polymer-Clay Nanocomposites ....................................................................................... 164
8.5.1 Effect of Carbon Dioxide on Nanocomposites................................................... 174 8.5.2 Rheology and Clay Structure within Nanocomposites ................................... 175 8.5.3 Rheology of Silica Particles and Clay-Based Nanocomposites:
Differences and Similarities ................................................................................. 176 8.5.3.1 Rheology of Silica-Particle-Based Nanocomposites........................... 177
8.5.4 Rheology Based on Preparation Techniques ..................................................... 180 8.5.5 Influence of Filler Shape on Rheology ................................................................ 184 8.5.6 Extensional Rheology of Filled Polymer Systems ............................................. 185
8.5.6.1 Extensional Rheology of Nanocomposites .......................................... 186 8.6 The Rheology of Colloidal Suspensions ......................................................................... 188
8.6.1 Surface Forces ......................................................................................................... 189 8.6.2 Van der Waals Attraction and Repulsion Forces ............................................... 189 8.6.3 Electrical Double Layer Formation ...................................................................... 190 8.6.4 Steric Repulsion ...................................................................................................... 190 8.6.5 Interactions in Polymer Nanocomposites .......................................................... 191
8.6.5.1 Polymer-Solvent Interactions ................................................................ 191 8.6.5.2 Polymer-Particle Interactions ................................................................ 192 8.6.5.3 Particle-Particle Interactions ................................................................. 192 8.6.5.4 Polymer-Polymer Interaction................................................................. 192
8.6.6 Difference in Rheological Behavior of Nanocomposites and Colloidal Suspensions ............................................................................................................ 193
8.7 Rheological Modeling of Polymer Nanocomposites .................................................... 194 8.7.1 Herschel-Buckley Model ....................................................................................... 194 8.7.2 Williamson-Carreau Model ................................................................................. 195
The rheological characterization of polymeric materials is important with respect to the processing of polymeric materials. Polymeric materials, unlike other materials, exhibit liquid-solid (viscoelasticity) behavior in the melt phase and this leads to added complications in processing. The morphological evolution and the final properties of the polymeric system to a large extent depend on the processing technique used and also on the melt-phase properties of the polymeric material. The rheology of polymeric materials often provides clear insight into the molecular structure of the polymer under varied conditions and thus helps in controlling the desired final properties of the materials after processing.1-4
Most polymers are amorphous and possess less crystallinity. It is well known that the addition of small amounts of fillers, even in amorphous polymers, leads to substantial improvement in overall properties, such as an increase in viscosity, and good thermal and mechanical properties. The concept of inherent free volume in polymeric materials resulted in the development of filled polymer systems. It was believed that if the free volume within the polymeric system could be filled, then there would be improvement in the thermomechanical properties of the polymeric materials. This proposition led to a significant amount of research in the area of filled polymer systems, finally leading to the advent of polymer nanocomposites technology.
