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【求助】 多分散性指数(polydispersity index)的意义，以及计算方法？谢谢
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多分散性指数(polydispersity index)的意义，以及计算方法？谢谢 [ Last edited by yogidan on 2009-3-10 at 10:33 ] |
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In organic chemistry, the polydispersity index (PDI), is a measure of the distribution of molecular mass in a given polymer sample. The PDI calculated is the weight average molecular weight divided by the number average molecular weight. It indicates the distribution of individual molecular masses in a batch of polymers. The PDI has a value always greater than 1, but as the polymer chains approach uniform chain length, the PDI approaches unity (1). For some natural polymers PDI is almost taken as unity. The PDI from polymerization is often denoted as: PDI=Mw/Mn A polymer material is denoted by the term polydisperse if its chain lengths vary over a wide range of molecular masses. This is characteristic of man-made polymers.. Natural organic matter produced by the decomposition of plants and wood debris in soils (humic substances) has also a pronounced polydispersed character. It is the case of humic acids and fulvic acids, natural polyelectrolyte substances having respectively higher and lower molecular weights. |
2楼2009-03-10 21:43:58
