Polymers

Advancement of polymer science is one of the most significant contributions of Chemistry for the welfare of humankind in the last century. From disposable wrappers to the artificial heart; polymer touches our lives as does no other class of material, with no end to new uses and improved products in sight. Now-a-days it is almost impossible to imagine a world without polymers. Polymers or macromolecules or high polymers or giant molecules are high-molecular-weight materials composed of repeating subunits called monomers. These materials may be organic, inorganic or organometallic and synthetic or natural in origin. Polymers are essential materials for almost every industry as adhesives, building materials, paper, cloths, fibers, coatings, plastics, ceramics, concretes, liquid crystals, photo resists coatings etc. They are also major components in plant and animal body. They are important in nutrition, engineering, biology, medicine, computers, space exploration, healthcare and the environment. The first synthetic polymer was produced in 1909; called Bakelite which could be moulded at a high temperature and it would retain its shape once cooled. But it wasn't until the World War I that significant changes took place in the polymer industry. Synthetic polymers have found wide spread application because of their low density, low cost and better performance. The term nanocomposites means to distribute as much as possible amounts of nanoparticles in a polymer matrix. It has been shown that, when using fiberreinforced polymers, the maximum amount of fibers in the matrix is about 70 vol.%. Actually, the fiber volume fraction in these materials varies between 20 and 60%. Figure 1 summarizes the values to be achieved for various fillers used in composites. In a volume element of 1 cm3, it was assumed that we have continuous fibers with a diameter of 10 pm, particles (e.g., talcum) with a diameter of 1 pm, and nanotubes with a diameter of 10 nm. The aspect ratios should be 20, 100, and 1000, respectively. If we further assume a volume content of 30% for both the fibers and the particles, and only 3% for the nanotubes, we already have quite interesting results: The filler element numbers are -106fibers, -10l0 particles, and -lOI5 nanotubes, respectively. The surface area amounts to -0.1 m2 for the fibers, -1 m2 for the particles, and -100 m2 for the nanotubes. There is another important aspect to be found, and that is the distance between the filler elements. For the fibers we calculated a distance of -10 pm, for the particles -1 pm, and for the nanotubes -100 nm.