The name is absent

Figure 5.6: Excess surface free energy of the copolymer as a function of the effective film
thickness, for symmetric phases of the copolymer. For the diblock copolymer, N = 8 and
e∣kT = 0.289. For surfaces, e_w∕kT = 0.1.

able to attain their bulk equilibrium period, D_b. However, there is a slight offset from
the actual value of D;, due to packing near the wall. This offset is accounted by δ.
Thus the excess surface free energy is at minimum at integer values of H_eyʃ when the
film lamellar period is in accord with the bulk equilibrium period. The values of the
excess free energy are the same at all the integer values of H_eyy. In any lɪ phase,
the free energy is higher for H_e∕y < n when the lamella are compressed and H_eyγ > n
when the lamella are stretched than their preferred lamellar period. For H_e∫∫ > n, as
the lamella are highly stretched the copolymer undergoes the transition from lɪ to
^2(n₊ι) ph^ase to decrease the excess surface free energy.

We can also observe the anti-symmetric ʃɪ-i-i lamellar structures of the diblock
copolymer. Figure 5.7 shows the anti-symmetric segment density profiles of the two

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