= Solution
The <Flory interaction parameter> $\chi_{AB}$ measures the effective <free energy> penalty for unlike A–B contacts relative to like contacts, and $N$ is the total number of statistical segments per chain. Their product is the segregation strength: contact-energy preference competes with the <conformational entropy> cost of separating covalently joined blocks. $N$ does not grow during <solvent> evaporation. For an approximately nonselective <solvent>, increasing <polymer> <concentration> instead increases the effective importance of A–B contacts, so a roughly fixed-composition path moves from weak toward stronger effective segregation.
The diagram's labels are \b[DIS: disordered; S: <block-copolymer sphere phase>; H: <hexagonal cylinder block-copolymer phase>; G: <double gyroid>; L: <lamellar microphase>]. At $f_A=0.15$, A is the minority component and B forms the continuous matrix. Reading the supplied diagram vertically at this composition gives disorder initially, a sphere region when segregation first becomes sufficient, and a cylinder region if sufficiently strong segregation is reached within the displayed range. The thin gyroid and central lamellar regions are not the <thermodynamic equilibrium> path at this composition. The dry endpoint cannot be fixed numerically without the final $\chi_{AB}N$ value. The cited theoretical calculation determines <thermodynamic equilibrium> phase stability, not a universal evaporation trajectory.<Stability of the Gyroid Phase in Diblock Copolymers at Strong Segregation by Eric W. Cochran and others>[Macromolecules 39 (2006), pp. 2449–2451, equilibrium diblock phase stability]{ref}
Crucially, at least one block is glassy at room <temperature>. <Solvent> can initially plasticize it, but <solvent> loss can raise its effective glass-transition <temperature> above the processing <temperature>. Chain relaxation then becomes too slow to equilibrate. Even slow evaporation can therefore freeze disorder, spheres, cylinders or another transient morphology before the <thermodynamic equilibrium> dry state is reached. <Solvent> <concentration>, <annealing> time and segmental mobility must be followed alongside the <phase diagram>.
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