Capillary, chain confinement

Note that while the two previous examples correspond to chains confined by cylindrical capillaries, this example is reminiscent of a chain confined to a slit. The adsorption behavior of star polymers may be analyzed in terms of such adsorption blobs. ... 

This picture, of a chain confined to a capillary, is of great utility. As we shall discuss, it guides the generalization of the blob picture to non-planar geometries and the analysis of dynamical properties. Before we address this issues, it is useful to consider the structure of a brush immersed in a poor solvent. 

The Alexander model allows a simple approach to this problem. Within this model, each tethered chain is, in effect, confined within a cylindrical capillary of diameter d. Combining Eq. 5 and 7, we can express the stretching energy as ... 

Several research groups used another interesting column technology as an alternative to the modification of the capillary surface. This method is inherited from the field of electrophoresis of nucleic acids and involves capillaries filled with solutions of linear polymers. In contrast to the monolithic columns that will be discussed later in this review, the preparation of these pseudostationary phases need not be performed within the confines of the capillary. These materials, typically specifically designed copolymers [85-88] and modified den-drimers [89], exist as physically entangled polymer chains that effectively resemble highly swollen, chemically crosslinked gels. 

Qualitative understanding of the origin of the normal stress phenomenon is not difficult. We learned in the previous chapters that a polymer melt resembles a transient network of entangled polymers. High shear rates, as they are encountered in a capillary, result in a deformation of the chains and, therefore, also of the formed network. As a consequence, a tension builds up along the lines of flow and draws the extrudate back when the confinement... 

Within the Alexander model, a chain in a brush behaves as if confined to a cylindrical capillary of cross section cf and height L (Figure 1). Blobologically, this is an especially important point since the diameter of this virtual capillary, (7 /, sets the blob size, In terms of our preceding discussion this follows because at equilibrium F / F nf or In turn, this leads to F and... 

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