Or why are good dispersion and bad distribution of filler good for electrical conductivity? Thanks in advance
An objective of producing polymeric composites is to distribute (disperse) the filler as homogeneously as possible so that the resulting mechanical properties of the polymer/filler composite will be uniform. Typically fillers are aggregated in particles composed of few to many primary filler particles. They may be in the form of layered aggregates, such as clays (for example talc and montmorillonite) or in the form of 3D clustered aggregates wherein the primary particles adhere to one another by van der Waals forces (such as calcium carbonate, titania, etc). If one can achieve separation of such aggregates into individual primary particles so that these particles are uniformly distributed throughout the polymer, one can say the filler has been completely and homogeneously dispersed. A mechanical process of mixing polymer and filler, wherein shear forces are applied to filler clusters and aggregates, is a dispersion process. If complete dispersion is obtained, and the mixture can be very effectively mixed, the resulting distribution of filler will be nearly homogeneous. If the primary filler particles differ greatly in size, and an effectively liquid state is maintained for a significant time after the dispersion process, the particles may sediment and become inhomogeneously distributed throughout the composite mixture. If you look at Fig 6 in our paper, Polymer (2010) 51:4540-4546, you can see how a uniform carbon dispersion when allowed to sediment during drying of the dispersion and binder (binder produces a polymer matrix) can produce a layered and very inhomogeneous distribution of filler particles. Such a distribution may be good or bad for electrical conductivity, depending on what you consider good or bad.
Distribution is the way the particles fill the space, whereas dispersion is the way these particles are agglomerated or not. With a good distribution, each particle is as far as possible from its nearest neighbour, so that the space is homogeneoulsy filled with particles. With a good dispersion, all particles have the same shape and size, as small as possible, as no agglomerates exist. Therefore, it is quite possible to have good distribution but poor dispersion, or poor disribution and good dispersion, see attached Figure. If particles are conducting and if you want a high conductivity, you shoud indeed prefer the situation in which particles can make a conducting path by touching each other, but agglomerates should be avoided as many particles would be useless because behaving as dead ends for the conducting path.
Alain
Fillers are adding in the polymer matrix for enhancing the properties which could be
1. mechanical strength
2. Conductivity
3. Other functional properties.
The loading of the filler is to be optimized to make it effective so that the desired properties are best and uniform ( as described by scientists in earlier remarks). It is a homogeneous system. For that the solubility limit is optimized so that it does not turn up to a non-homogeneous system. So uniform distribution is achieved.
It is also optimized for good dispersion which enhances the applicability of these materials.
Excellent particle dispersion is usually desired for maximum properties enhancement, yet a homogeneous distribution may not be necessary as some level of non-uniformity may actually enhance properties. This is described e.g. for electrical properties in: Gabriella Faiella, Vincenza Antonucci, Samuel T. Buschhorn, Luis A.S.A. Prado, Karl Schulte, Michele Giordano, Tailoring the electrical properties of MWCNT/epoxy composites controlling processing conditions, Composites Part A: Applied Science and Manufacturing, Volume 43, Issue 9, September 2012, Pages 1441-1447, ISSN 1359-835X, http://dx.doi.org/10.1016/j.compositesa.2012.04.002.
In case of polymrer clay composites, dispersion of clay layer within polymer matrix is not the only factor contributing to the properties of the composites but also the direction of clay layer dispersed (aligned) against to the surface of the compoliste films.Good barrier properties should be achieved when good dispersed clay layer aligned (the same direction) perpendicular to normal of surface of the film.Generally, good barrier properties when the composite structure is intercalated as the clay layers become obstabcle for permean molecules/gas, while good mechanical properties are achieved when the composite stucture is exfoliated.
How to achieve a uniform Distribution of particles in the polymer matrix? Please can anyone suggest regarding the experimental conditions or practices to be followed in the composite preparations to obtain a uniform Distribution of particles in the polymer matrix.
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