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For high school students
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Ever since the days of Newton, physicists have been trying to explain natural phenomenon to enhance our understanding and to apply our knowledge to solve a multitude of challenges that face the human civilization. Today, as polymer physicists, we are following the same example. We are trying to study physical interactions of polymeric systems that have potential applications in a wide variety of areas such as medical formulations and biosensors. Layer-by-layer electrostatic self assembly is a technique that has become extremely popular to produce ultrathin films or complexes that are simple to devise and yet are very robust. To illustrate this technique, imagine a positively charged solid surface (Ex. A thin rod of charged graphite) dipped into a solution containing negatively charged materials. Due to the attraction between opposite charges, a layer of the negatively charged materials clings on to the surface reversing the net surface charge. This process can be repeated until we obtain the required number of 'multilayers' we desire. If we use materials such as DNA, proteins etc., we could possibly make a biosensor using this technique and monitor the damage caused when exposed to a harmful chemical. Thus we are mimicking the function of the biological materials in this case. The self assembled complexes have already been put to use by the living systems to sustain life. In our body, for example, the 'synovial fluids' are similar to the protein-polymeric complexes and play an important role in the lubrication of mammalian joints during the joint motion. Although we know that these assemblies are very strongly bound to each other, as physicists we would like to know the exact types of interactions that play a role in their strength. By studying these interactions, we not only gain a better understanding, but also hope to eventually come up with better designs for future applications. This can be done by deriving equations from the conventional laws of physics and testing them using modern computers. For example, in an assembly that has proteins, DNA or charged polymers, we can find out about how the interactions are influencing the biological function. The interactions of protein with DNA are central to the control of the gene expression and nucleic acid metabolism. At the simplest level, we can imagine the protein or the polymer to be made up of numerous beads interconnected through springs and can study their mechanics as well as dynamics. Thus, our attempt is to try and simulate physical models of biological structures, along with their functions. The complexity of the models we build depends on both the system under study and also the available computational resources. We use computer packages developed by leading researchers around the world and also write our own programs when building and testing our models.This is the essence of the theory and simulations that are carried on in our research group. |
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