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A domain structure resembling lamellae pierced by an ordered array of perforations. It is distinct from an unperforated lamellar phase and from a double gyroid.

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 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.^[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.

The starting point is in the lamellar region. Preferential swelling of polystyrene makes polyisoprene the increasingly small minority domain, so the relevant effective composition moves left from $f_{PI}^{\mathrm{eff}}=0.45$.

If segregation stayed near $\chi N=35$, following the horizontal path in the supplied diagram would give lamellae → hexagonally perforated layers → hexagonally arranged PI cylinders → PI spheres, before sufficient asymmetry reaches the disordered region. The perforated-layer interval is narrow, around $f_{PI}\simeq 0.36$–$0.40$ at this segregation strength; precise boundaries should not be read more accurately than the figure allows.

Solvent also changes effective segregation, so the actual trajectory need not be horizontal. If it passes closer to the order-disorder boundary, it can enter the narrow double gyroid region instead of, or after, the hexagonally perforated layer phase. Greater dilution can cause disorder before all the ordered morphologies appear. Thus a plausible alternative is lamellae → gyroid → cylinders → disorder.

The robust prediction is the change toward minority-PI curved structures, not a guarantee that every named phase occurs. A solvent partition coefficient and a concentration-dependent interaction model would be needed to locate the actual path quantitatively; applying a dry-melt diagram to a swollen material is an effective approximation.