A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-block-poly(ethylene oxide) (PS-b-PEO) bottlebrush block copolymers (BBCP) upon varying PEO volume fraction ( f PEO ) from 22% to 81%. A series of PS-b-PEO BBCPs with different PEO side chain lengths were prepared using ring-opening metathesis polymerization (ROMP) of PEO−norbornene (PEO-NB) (M n ∼ 0.75, 2.0, or 5.0 kg/mol) and PS−norbornene (PS-NB) (M n ∼ 3.5 kg/mol) macromonomers (MM). A map of f PEO versus side chain asymmetry (M n (PEO-NB)/ M n (PS-NB)) was constructed to describe the BBCP phase behavior. Symmetric and asymmetric lamellar morphologies were observed in the BBCPs over an exceptionally wide range of f PEO from 28% to 72%. At high f PEO , crystallization of PEO was evident. Temperaturecontrolled SAXS and WAXS revealed the presence of high order reflections arising from phase segregation above the PEO melting point. A microphase transition temperature T MST was observed over a temperature range of 150−180 °C. This temperature was relatively insensitive to both side chain length and volume fraction variations. The findings in this study provide insight into the rich phase behavior of this relatively new class of macromolecules and may lay the groundwork for their use as templates directing the fabrication of functional materials.

We report the microphase-separated morphologies of model bottlebrush block copolymers (BBCPs) over a wide range of architectural design parameters. Densely grafted polystyrene-block-poly­(dimethylsiloxane) (PS-b-PDMS) BBCPs rapidly self-assemble into ordered lamellar, cylindrical, and deformed spherical morphologies depending on the volume fraction (f), side chain length (N sc), and overall backbone length (N bb). The microstructure was characterized by using electron microscopy and X-ray scattering. An experimental phase map is constructed, describing the dependence of morphologies and order–order transitions with respect to the design parameters. A lamellar morphology is primarily observed at symmetric f, while ordered cylindrical and deformed spherical morphologies appear at asymmetric f. The relative flexibility of the PS-b-PDMS backbone facilitates the accessibility of morphologies with curved interfaces and exceptionally large domain spacing. We also find that the breadth of the lamellar window decreases with increasing backbone length and side-chain asymmetry. These findings provide a comprehensive experimental description of the PS-b-PDMS BBCPs and provide insight into the rich phase behavior of this class of macromolecules.

We investigate the linear viscoelastic behavior of poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) AB diblock brush copolymer materials over a range of volume fractions and with side-chain lengths below entanglement molecular weight (PS M n ∼ 3.5 kg/mol and PEO M n ∼ 5 kg/ mol). The high chain mobility of the brush architecture results in rapid microphase segregation of the brush copolymer segments, which occurred after mild thermal annealing. Master curves of the dynamic moduli were obtained by time− temperature superposition (tTS). The reduced degree of chain entanglements leads to a unique liquid-like rheology similar to that of bottlebrush (BB) homopolymers, even in the microphasesegregated state. The microphase-segregated domains were found to align at exceptionally low strain amplitudes (γ = 0.01) and mild processing temperatures as confirmed by small-angle X-ray scattering (SAXS). Domain/grain orientation occurred readily at strains within the linear viscoelastic regime (LVR) without noticeable effect on the dynamic moduli. This interplay of high molecular mobility and rapid phase segregation contrasts the viscoelasticity of brush block copolymers (BBCP) compared to conventional linear block copolymer (LBCP) analogues and opens up new processing possibilities of BBCP materials for a wide range of nanotechnology applications.

We have performed small-angle X-ray scattering (SAXS) measurements to study the evolution of length-scale-dependent nanoparticle (NP) correlations over a wide range of loadings in miscible silica–poly­(2-vinylpyridine) polymer nanocomposites (PNC) characterized by strong interfacial attraction. The local cage and intermediate-scale correlations evolve in a commonly observed manner with increasing silica concentration, while long-wavelength concentration fluctuations exhibit a complex behavior. Higher-loading PNCs show a nonmonotonic change in the structure factor amplitude with wavevector because of an upturn on the longest length scales, which is the most intense for the highest NP concentration sample. These observations suggest that the PNC is approaching a spinodal demixing transition of an unusual polymer bridging-induced network type. PRISM integral equation theory is quantitatively applied, captures the key features of the SAXS data, and provides a theoretical basis for a network-like phase separation analogous to polyelectrolyte coacervation. The theory with validated parameters is then used to make predictions of real-space pair correlation functions between all species, the small- and large-wavevector collective polymer structure factor, spatially resolved NP coordination numbers, the interfacial cohesive energy density, and a measure of an enlarged effective NP radius because of polymer adsorption. With increasing NP loading, intensification of tight secondary bridged NP configurations, but weakening of interpolymer and polymer–NP correlations due to packing frustration, is predicted. This local reorganization of the polymer structure coexists with macro- and microphase separation such as features at low wavevectors which vary distinctively with NP loading. The predictions for the collective polymer structure are potentially testable using scattering experiments. Our results provide an important starting point for building an understanding of collective NP dynamics.

Lyotropic chromonic liquid crystals (LCLCs) represent aqueous dispersions of organic disk-like molecules that form cylindrical aggregates. Despite the growing interest in these materials, their flow behavior is poorly understood. Here,...