Polymer melt surface density profile

The quantity of primary interest in the study of nonuniform fluids is the density profile of the fluid at a surface. Dickman and Hall [28] reported the density profiles of freely jointed hard-sphere chains at hard walls. Their focus was on the equation of state of melts of hard-chain polymers, and they performed simulations of polymers at hard walls because the bulk pressure, P, can be calculated from the value of the density profile at the surface using the wall sum rule ... 

The integral equation theory is a simple means of studying the density profiles of dense polymer melts at surfaces where the structure is dominated by... 

We now turn to the question of what we can say about the structure of the polymer surface at the microscopic level. As we have seen, in addition to predicting the surface tension, square gradient theories also predict the density profile at the surface of the polymer melt. Typically, the density goes smoothly from the melt density to zero (the density of the vapour phase being vanishingly small for high polymers) over a few angstroni imits, in very much the same way as it does at the surface of a small-molecule liquid. 

However, there is not much information available about plastic properties besides density and melt flow index (MFI). Having no consistent grade or/and source of plastics, a manufacturer faces from time to time a significant variation in the flowability of a polymer that is already purchased, sometimes in amounts of rail cars. These variations lead to improper process settings for production. This in turn results in a variety of defects on the surface of extruded profiles, such as sharkskin (fish skin), surface roughness, edge tearing, and so forth, and other property inconsistency in the final product. 

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