The structure of confined polymer chains are quite different from the chains in
the bulk. The translational freedom and number of available conformations of the
chains decreases in the confined space, which induces an entropie penalty on the
polymer chains due to the confinement [254, 255]. On the other hand, there is an
energetic advantage if the polymer-surface interactions are favorable for adsorption.
At dense polymer concentrations, another entropie effect known as the packing effect
comes into play. In these systems, packing some of the molecules near the surface
increases the available free volume in rest of the fluid thereby increasing the entropy
of the fluid. As evident, polymer chain architecture plays an important role in de-
termining these entropie and enthalpic effects. For different architectures such as
linear and branched, we expect different behavior near the confining surfaces. In a
branched polymer chain, there are one or more small multi-functional units called
the branch points, which are directly linked to more than two long chains. A variety
of branched chain architectures are possible depending on the number and position
of the branch points. In star polymer, a polymer chain has only one branch point,
from which many branches of the chain (or the arms) originate. Branched polymers
with two or more branch points are called comb polymers, when a backbone and the
branches can be distinguished. If there are numerous branch points that are densely
spaced along the backbone, the highly branched polymer is called molecular bottle
brush. Recently more complex architectures such as dendrimers or cascade polymers
have been synthesized that combine a central branch point with a regular repetitive
181