Reptation is the snake-like motion of a long polymer through the constraints imposed by neighboring chains or a fixed porous matrix. A tube model restricts large transverse motion while allowing curvilinear motion along the chain contour. For a flexible chain with additive segment friction, contour diffusion scales as and the time to renew a contour of length proportional to scales as . With coil size squared proportional to , this gives a centre-of-mass diffusion coefficient proportional to . Applying this tube picture to weak-field DNA gel electrophoresis gives an inverse-length mobility over its appropriate regime; field-induced orientation and trapping can invalidate that simple law.
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Reptation is a term used in the context of polymer physics and materials science to describe a process by which polymer chains move or "crawl" through a medium, typically by undergoing a series of localized motions that allow them to gradually change position. This movement is somewhat analogous to the way a snake slithers, hence the name "reptation.