Amphiphilic compounds such as lipids and surfactants are fundamental building blocks of soft matter. We describe experiments with poly(1,2-butadiene-b-ethylene oxide) (PB-PEO) diblock copolymers, which form Y-junctions and three-dimensional networks in water at weight fractions of PEOintermediate to those associated with vesicle and wormlike micelle morphologies. Fragmentation of the network produces a nonergodic array of complex reticulated particles that have been imaged by cryogenic transmission electron microscopy. Data obtained with two sets of PB-PEOcompounds indicate that this type of self-assembly appears above a critical molecular weight. These block copolymers represent versatile amphiphiles, mimicking certain low molecular weight three-component (surfactant/water/oil) microemulsions, without addition of a separate hydrophobe.

Aqueous micellar dispersions of poly(ethylene oxide)-poly(butadiene) (PEO-PB) diblock copolymers were investigated using cryogenic transmission electron microscopy (cryo-TEM). A variety of binary blends were prepared by premixing (before dispersion) and postmixing (after dispersion) diblocks with varying composition and molecular weight. Cryo-TEM results establish there is no perceptible exchange of macromolecules between aggregates resulting in a nonergodic state, where overall equilibrium is never achieved. However, analysis of many microscopic images leads to the conclusion that these nonergodic micelles relax to a state of local equilibrium through the redistribution of block copolymers within the topological framework established during dispersion. Different average compositions and molecular weights exhibit varying degrees of structural complexity, which appears to peak in the vicinity of network formation. Away from this condition the micelle morphology is relatively insensitive to core or corona polydispersity. However, at compositions where the monomodal and nearly monodisperse amphiphiles produce branched wormlike micelles and a network, bimodal mixtures displayed intramicellar segregation leading to cylindrical undulations and octopus-like aggregates with cylindrical micelles emanating from a single bilayer core. These findings are discussed in the context of interfacial curvature and surfactancy.

An asymmetric poly(styrene-b-isoprene) diblock copolymer with block molecular weights of 13 000 and 71 000 g/mol, respectively, was dissolved at 1 vol % in a series of solvents with varying selectivity for styrene: dibuthyl phthalate (DBP), diethyl phthalate (DEP), and dimethyl phthalate (DMP). The degree of solvent selectivity was adjusted by mixing DBP/DEP and DEP/DMP in various proportions. With increasing solvent selectivity, the predominant micellar shape changes from spheres to cylinders to vesicles, reflecting the changing interfacial curvature. The detailed micellar morphologies were characterized by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). Recently developed form factors were used to characterize the micellar structures in detail, and a vesicle form factor was derived for this system. From the core dimensions, the packing properties, such as the interfacial area per chain and the core chain stretching, were determined. The cryo-TEM results demonstrate the suitability of the technique for these glass-forming solvents and gave micellar core dimensions in quantitative agreement with those from SAXS. The universality of the shape sequence sphere/cylinder/vesicle, well-established for aqueous solutions of surfactants and block copolymers, is thus confirmed for organic systems.

The phase behavior of 44 poly(isoprene-b-styrene-b-ethylene oxide) (ISO) linear triblock copolymer melts was investigated at weak to intermediate segregation strengths and spanning a comprehensive range of compositions. Phases were characterized by a combination of experimental techniques, including small-angle X-ray scattering, dynamic mechanical spectroscopy, transmission electron microscopy, and birefringence measurements. Combined with our previous results, six different stable ordered state symmetries have been identified: lamellae (LAM), Fddd orthorhombic network (O 70 ), double gyroid (Q 230 ), alternating gyroid (Q 214 ), hexagonal (HEX), and body-centered cubic (BCC). The phase map of ISO specimens was found to be somewhat asymmetric around the f I ) f O isopleth. This work provides a guide for theoretical studies and gives insight into the intricate effects of various parameters on the self-assembly of ABC triblock copolymers. Experimental SAXS data evaluated with a simple scattering intensity model show that local mixing varies continuously across the phase map between states of two-and three-domain segregation. IntroductionMore than four decades of research has established quantitative and predictive theoretical tools for anticipating the phase behavior of AB diblock copolymers, which complement a rich collection of experimental data. 1-7 Addition of a third chemically distinct C block to an AB diblock expands the phase complexity and the number of experimentally adjustable parameters, resulting in a fascinating, yet largely unpredictable, array of morphologies. Nearly three dozen ordered phases have been discovered in ABC triblocks 2,8-23 compared to just four well-established equilibrium phases in AB diblocks. This expanded scope is both stimulating and intimidating. Three different polymer blocks offers desirable features such as increased molecular design opportunities and increased functionality. However, additional blocks imply additional variables, with a geometrically expanding degree of complexity with each new element.Self-assembly of block copolymers in the bulk liquid state is governed by three sets of parameters: composition, interfacial tension, and sequencing. (The block statistical segment lengths constitute a fourth, less critical, set of variables.) For AB diblocks there is one composition variable, f A ) 1 -f B , one segment-segment interaction parameter, AB , and one sequence. Linear ABC triblocks are governed by two independent composition variables, three ij 's, and three distinct sequences. Choosing among these parameters in order to target a specific morphology for a particular application represents a daunting task, complicated by a lack of theoretical guidance and relatively few comprehensive experimental phase portraits.Different types of ABC triblock copolymers (specifically referring to those in linear architectures and in the bulk liquid state) have been investigated by a host of research groups, such as Hashimoto et al., 29,30 Matsushita et al.,15,16,31,32 Stadler et al...

Hydration of poly(butadiene-b-ethylene oxide) diblock copolymers leads to various ordered and disordered phases, analogous to the aqueous phase behavior of surfactants and lipids. Small-angle x-ray scattering measurements corroborated by cryogenic scanning electron microscopy imaging reveal a random network (N) morphology at polymer compositions and water content intermediate to those associated with ordered cylinders (H1) and lamellae (L). This sequence of self-assembled structures is strikingly similar to the phase behavior of certain water-oil-surfactant microemulsions.