Rheology and Crystallization Dynamics of Polymer– clay Nanocomposites

               

This purpose of this project is to examine the rheological behavior, along with both flow-induced and quiescent crystallization dynamics of polypropylene-nanoclay systems.  Incorporating nanoscale clay into polymers has recently drawn widespread attention in the materials community for its remarkable ability to significantly improve the thermal, mechanical, and barrier properties of many common plastics.

Our key objective is to study the fundamental chemistry and physics of these materials, by employing tools such as rheology, transmission electron microscopy (TEM), and x-ray diffraction (XRD) to probe the impact of various synthesis methods (i.e. melt extrusion ) on morphology and dispersion of the clay.  We also aim to examine the impact that nanoclay fillers play on the crystallization dynamics and structure, by utilizing common tools such as differential scanning calorimetry (DSC) and optical microscopy (OM).  Furthermore, we employ an in-house, tailor-made mini-extruder shear device -equipped with laser and polarizers for birefringence measurements- to elucidate the role that the fillers have on the flow-induced microstructure and crystallization dynamics.  In this work, we explore the impact of clay loading, dispersion state (i.e. exfoliated, intercalated domains), and system chemistry on the crystallization and rheological properties.  Polymer nanocomposite materials systems are foreseen to significantly impact the automobile, food packaging, and electronics industries in the near future.  It is believed the knowledge base of information, built from research efforts such as this, will aid substantially in rapidly developing and commercializing these novel materials.

 

 Polymer/Nanotubes Interaction Dynamics

               

This project involves synthesizing and characterizing a poly(isoprene)-nanotube nanocomposite.  A solution blending technique is used to form the nanocomposite.  Presumably, the solution behavior, or amount of dispersion of the nanotubes in the solvent is intimately connected with the precipitated form of the composite.  Light scattering techniques are employed to confirm this assumption.  Nanotube loadings for the composites made are on the order of 0.1 weight percent.  Samples are made from multi-wall and single-wall nanotubes, respectively.  Small amplitude oscillatory shear experiments are used to elucidate network dynamics -mechanical percolation- via rheology.  And also a modulated DSC method is employed to probe thermal percolation by calculating thermal conductivities for the nanocomposite material.  Below is a cartoon depicting the broad spectrum of nanofillers, of which nanotubes are a unique part.

Carbon nanotubes have generated such an intense interest among researchers because of their extraordinary thermal, mechanical and optical properties.  Their material properties are incredible with very high strength[~100GPa], stiffness[~1000 GPa], and failure to strain [up to 0.4].  Carbon nanotubes can have diameters as small as 1 nm and lengths up to microns, resulting in aspect ratios of up to 1,000.   There is great appeal in a nanotube-polymer composite system derived from the extreme flexibility of the nanotubes and the large interfacial areas afforded between the nanotubes and the host polymer.  It is the goal of this current project to exploit and better understand the unique syncretistic relation between carbon nanotubes and their polymer matrix.

 

SEM micrograph of carbon nanotube filaments.

 

 

Advanced Nanostructured Fluids and Polymer Processing

Oberhauser Research Group

 Rheo-Optical Studies of Polymer-Clay Nanocomposites Solutions                                                

 

Over the past decade, polymer-clay nanocomposites (PCNs) have attracted intense research and commercial interest due to profound improvements in material properties (e.g., increased tensile strength, modulus, and heat resistance and reduced gas permeability) achieved with only modest clay loading.

 

As in fiber-reinforced polymeric materials, it is likely that many of the improved material properties derive from the microstructure formed by the highly anisotropic clay platelets and the polymer matrix.  Since traditional polymer processing applications (e.g., injection molding, extrusion, blow molding) involve complex flows that strongly affect the microstructure and rheology of polymer melts and suspensions, a detailed understanding of the relationship between the clay microstructure and macroscopic properties in flow is essential to economically and reliably manufacturing products from these materials. 

Therefore, our research interests focus on the rheology behavior and the network structure of the organoclay dispersions in organic solvent (p-xylene is used currently) with polymer (polystyrene is used currently) resin dissolving in. Particularly, three questions are anticipated to be clarified via our research: (1) How does the surface chemistry between the clay silicate layers and the polymer matrix influence clay silicate dispersion? (2) How does the deformation introduced by various flow types influence the polymer-clay dispersion?  (3) What’s the relationship between the rheological behavior and the microstructure of the clay silicate dispersions? The experimental techniques we are using to achieve our goals include a controlled-stress rheometer, cryogenic transmission electron microscopy (Cryo-TEM), scanning electron microscopy (SEM) (here, we are using a novel technique called wet-SEM (Quantomix) which allows direct imaging of dispersions, for details CLICK HERE), x-ray diffraction, thermogravimetric analysis (TGA) for characterization, and a custom-built simultaneous birefringence-dichroism apparatus and a custom-built precisely controlled Couette flow cell.

 

Current Research Projects

 Rheo-Optical Studies of Polymer-Clay Nanocomposites Solutions

 Rheology and Crystallization Dynamics of Polymer Clay Nanocomposites

 Polymer/Nanotubes Interaction Dynamics