Feasibility Study: Statistical Modelling of Microstructural Variables in Particulate Filled Composite Materials

Particulate reinforced polymers are becoming an increasingly important class of materials particularly with the development of nanotechnology. Modern materials may be composites on many scales containing both fibres and particles. The microstructure of the particulate phase can be very varied. These variations include both changing particle size and distribution. The overall aim of this feasibility study is to explore the role of statistical modelling in defining the microstructural dependence of the mechanical properties of particulate composite materials. The microstructural parameters which will be included in this feasibility study will be particle size and particle distribution. This proposal has been inspired by work currently being undertaken. To obtain the best properties from a particle-modified polymer, it is considered that the particles should be well-dispersed, and each particle should be wetted by the polymer. If this is not the case, then the agglomerates will act as defects resulting in a reduction in performance rather than any enhancement. The material properties affected by poor dispersion include elastic properties (such as stiffness); strength; fracture behaviour, permeability and conductivity. Achieving a good dispersion is a major challenge when preparing formulations. The dispersion of particles in general, and especially nanoparticles, is difficult due to the high surface area and incompatability with the matrix polymer, and generally a surface treatment or compatabiliser is required. However, this does not guarantee that a good stable dispersion will be achieved even when ultrasonication or high-shear mixing is used. Once agglomeration occurs it is very difficult to break up the agglomerates.Assessing the degree of dispersion is very subjective, and the dispersion may vary across the length scales. For example a sample may look homogeneous at the macroscale, but electron microscopy may indicate that the particles are agglomerated at the micro- or nanoscale. What is required to remove this subjectivity is a numerical value of a parameter that quantifies the degree of dispersion. However, to the investigators' knowledge, there are no quantitative methods to assess the dispersion of particles. The qualitative methods currently used generally rely on an operator's opinion, and hence one person's 'good' dispersion is 'poor' to someone else. The ability to provide a numerical value to describe the degree of dispersion will allow faster screening of surface treatments for particles and improved process control. It will provide both academia and industry with the ability to assess and follow the evolution of agglomeration, without the subjectivity attached to current methods.