The name is absent

that of the linear polymer. The density of the mid-segments (for both linear and star
polymer) at distances of 1 - 2σ are higher than that in the bulk. Hence, although
the packing effects pushes the all the segments of the chains towards the surface, the
conformational restrictions on the mid-segments prevent them from approaching it.

Figure 7.5b shows the average segment density profile of the articulation segment
and the arm segments of the same 4-arm star polymer fluid (m = 5 at η_aυg = 0.3 and
H = 10 σ). Again, severe conformational constraint on the articulation segment of
the chains leads to its depletion near the surface.

To further study the effects of molecular topology on confined (athermal) poly-
mers, two cases are analyzed. The first case compares the segment density profiles of
smaller 4-segment linear and 3-arm star (m = 1) polymer fluids while the second case
compares the density profiles of larger 25-segment linear, 3-arm star (m — 8), and
4-arm star (m = 6) polymer fluids confined between two hard walls separated by H
= 10 σ at average fluid packing fractions of 0.1 and 0.3. Figure 7.6a shows the total
segment density profiles for 4-segment linear and 3-arm star polymers. The profiles
are similar at both the packing fractions. This is the case even for star polymers with
different number of arms as shown in fig. 7.6b for 25-segment linear, 3-arm star and
4-arm star polymers. Infact, the profiles for the 3-arm star and 4-arm star polymers
almost overlap each other. Hence, the total segment density profiles of confined ather-
mal polymers are not very sensitive to the molecular topology. However, the profiles
of the individual segments depend upon the molecular topology as shown in fig. 7.7.

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