Example—chain confined in a box

As an example of the application of the Green function, let us consider a polymer confined in a box of volume V = L LyL (Fig. 2.6). The confinement is expressed by an external potential which is infinite outside the box and zero inside the box. Alternatively the effect is expressed by the boundary condition 

Therefore, in this case is not equal to Py and P (unless Lg = Ly = L ), i.e., the force acting on the wall is not isotropic. Later it will be shown that this anisotropy in the pressure due to the anisotropic confinement is responsible for a variety of mechanical properties peculiar to polymers. 

The Green function method has been applied in various problems 

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