Various Phase Behaviors of Weakly Interacting Binary Block Copolymer Blends

Abstract

We investigated the phase behaviors of block copolymer (BCP) blends composed of the weakly interacting (with no specific interaction) polystyrene-b-poly(n-butyl methacrylate) (PS-b-PnBMA) and polystyrene-b-poly(n-hexyl methacrylate) (PS-b-PnHMA), using small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and depolarized light scattering (DPLS). A miscible phase between the PnBMA and PnHMA blocks in the BCP blends allows the various composition-dependent phase behaviors, which display a lower disorder-to-order transition (LDOT) to an order-to-disorder transition (ODT) on heating as the blend composition varies from PS-b-PnBMA to PS-b-PnHMA. In between these two extremes, intriguingly, the miscible PS-b-PnBMA/PS-b-PnHMA blends display a closed-loop phase transition consisting of a LDOT and an upper order-to-disorder transition (UODT).

Blends of Two Diblock Copolymers with Opposite Phase Behaviors

“…In closing, our work is motivated by the unique blends of PS‐b‐P( n ‐butyl MA) and PS‐b‐P( n ‐hexyl MA), which was studied by Ryu and co‐workers . The present theory supports the observed phase behaviors of their blends.…”

“…So, the morphology becomes the lamellae of A and C domains given in Figure c. The A‐b‐B/A‐b‐C blend at ϕ c2 = 0.4 exhibits the lamellae of A domains and B/C domains, which is shown in Figure b …”

“…In this case, the chosen yields the effective χ BC = –0.00063 at 450 K and at 0.1 MPa with χ H = –0.00090 and χ S = 0.00027. It is recalled that P( n ‐butyl MA) and P( n ‐hexyl MA) are miscible judging from the thermal and optical behaviors of their blends . The assumed B/C pair interactions generate a force field for them to suppress self‐assembly in both directions.…”

“…It was found by Ryu, Kim, and Russell that one of those homologous members, PS‐b‐P( n ‐pentyl MA), possesses an immiscibility loop (self‐assembly only in a certain temperature range) along with its unprecedentedly high pressure sensitivity . It was lately shown by Ryu and co‐workers that blending PS‐b‐P( n ‐butyl MA) and PS‐b‐P( n ‐hexyl MA) yielded all kinds of self‐assembly behaviors including a loop …”

Relaxation processes in a lower disorder order transition diblock copolymer

“…Similar behavior has been found in particular blends, where the difference in compressibilities produces a phase separation upon heating. 6 Extensive theoretical work has incorporated finite compressibility into the Random Phase Approximation (RPA) through effective interactions. 7,8 In that way, χ was reinterpreted as χ = χ app + χ comp , where χ app is the conventional exchange energy with proper density dependence and χ comp represents compressibility difference between constituent blocks.…”