Photocrosslinkable Polymeric Bicontinuous Microemulsions

Effect of equilibration time on the structural gradient in the vertical direction for bicontinuous microemulsions in Winsor-III and -IV systems

Bicontinuous microemulsions (BMEs), self-assembly systems consisting of oil and water nanodomains separated by surfactant monolayers, have many applications. However, changes in structure and properties of BMEs in the vertical direction can affect BMEs' utility. This study's objective was to determine the effect of equilibration time (τeq) on structural changes in the vertical direction for bicontinuous phases of Winsor-III (WIII) systems in situ or after being isolated, for D2O + H2O/1-dodecane/sodium dodecyl sulfate (SDS)/1-pentanol/NaCl at 22 °C. Small-angle neutron scattering (SANS) measurements were performed using a vertical stage sample environment that precisely aligned samples in the neutron beam. SANS data were fitted by the Teubner-Strey (TS) model and changes in TS-derived parameter values were observed. For 10 min ≤ τeq ≤ 4 h, the effective activity of the bicontinuous phase's surfactant monolayers increased with time at all vertical positions. At short equilibration (τeq = 10 min), small but significant amounts of water and oil were transiently emulsified near the WIII upper liquid-liquid interface. WIII systems underwent a relaxation process after being transferred to narrow 1 mm pathlength cells, resulting in a decrease of surfactant activity for the top half of the bicontinuous phase. For isolated bicontinuous phases, results suggest that SDS was desorbed from the BMEs by quartz near the bottom, while near the top, the water concentration near was relatively high. The results suggest that WIII systems should equilibrate for at least 4 hours after being prepared and transferred to a container that differs in cross sectional area and surfactant behavior in BMEs can change near interfaces.

Bicontinuous microemulsion in binary blends of complementary diblock copolymers

The phase behavior of binary blends of AB diblock copolymers of compositions f and 1 - f is examined using field-theoretic simulations. Highly asymmetric compositions (i.e., f ≈ 0) behave like homopolymer blends macrophase separating into coexisting A- and B-rich phases as the segregation is increased, whereas more symmetric diblocks (i.e., f ≈ 0.5) microphase separate into an ordered lamellar phase. In self-consistent field theory, these behaviors are separated by a Lifshitz critical point at f = 0.2113. However, its lower critical dimension is believed to be four, which implies that the Lifshitz point should be destroyed by fluctuations. Consistent with this, it is found to transform into a tricritical point. Furthermore, the highly swollen lamellar phase near the mean-field Lifshitz point disorders into a bicontinuous microemulsion (BμE), consisting of large interpenetrating A- and B-rich microdomains. BμE has been previously reported in ternary blends of AB diblock copolymer with its parent A- and B-type homopolymers, but in that system the homopolymers have a tendency to macrophase separate. Our alternative system for creating BμE is free of this macrophase separation.