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We describe the phase behavior of a cylinder-forming block copolymer (BCP)/homopolymer blend and the generation of aligned nanopores by a combination of magnetic field alignment and selective removal of the minority-block-miscible homopolymer. Alignment is achieved by cooling through the order–disorder transition temperature (Todt) in a 6 T field. The system is a blend of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) and poly(ethylene glycol) (PEG). PEG is miscible with P4VP and partitions preferentially into the cylindrical microdomains. Calorimetry and X-ray scattering show that Todt decreases linearly with PEG concentration until the onset of macrophase separation, inferred by PEG crystallization. Beyond this point, Todt is invariant with PEG content. Increasing PEG molar mass decreases the concentration at which macrophase separation is observed. Nanopore formation is confirmed by dye uptake experiments that show a clear dependence of dye uptake on PEG content before removal. We anticipate that this...

Recent experiments have highlighted the intrinsic magnetic anisotropy in coil–coil diblock copolymers, specifically in poly(styrene-block-4-vinylpyridine) (PS-b-P4VP), that enables magnetic field alignment at field strengths of a few tesla. We consider here the alignment response of two low molecular weight (MW) lamallae-forming PS-b-P4VP systems. Cooling across the disorder–order transition temperature (Todt) results in strong alignment for the higher MW sample (5.5K), whereas little alignment is discernible for the lower MW system (3.6K). This disparity under otherwise identical conditions of field strength and cooling rate suggests that different average grain sizes are produced during slow cooling of these materials, with larger grains formed in the higher MW material. Blending the block copolymers results in homogeneous samples which display Todt, d-spacings, and grain sizes that are intermediate between the two neat diblocks. Similarly, the alignment quality displays a smooth variation with the conc...

We report the successful synthesis of previously inaccessible poly(3-hydroxystyrene)-block-poly(dimethylsiloxane) (P3HS-b-PDMS) block copolymers (BCPs) with varying volume fractions, molecular weights, and narrow dispersities by sequential living anionic polymerization. The chemical structure and molecular weight were fully characterized by 1H NMR and gel permeation chromatography. The BCP phase behavior was investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy. Temperature-resolved SAXS measurements from symmetric disordered sample were used to determine the interaction parameter (ﾏ�) using mean-field theory. The results provide an estimate for interaction parameter, ﾏ⑨S/DMS(T) = 33.491/T + 0.3126, with an upper bound value of 0.39 at 150 ﾂｰC. The calculated ﾏ� for P3HS-b-PDMS is approximately 4 times higher than that observed in a commonly studied high-ﾏ� system, PS-b-PDMS. The ultrahigh interaction parameter observed here affords the formation of well-ordered materials at remarkably low molecular weight. The presence of both PDMS and P3HS provides significant versatility in terms of etch selectivity, while the hydroxystyrene domain offers additional functionality as it can be exploited for immobilizing functional organic moieties.

We explore the morphology and phase behavior of branched diblock macromonomers and their polymers. A series of macromonomers was synthesized based on a disubstituted norbornene. The first branch consists of polydimethylsiloxane (PDMS) while the second branch is a quasi-mesogenic structure incorporating one or more cyanobiphenyl (CB) moieties. Bottlebrush polymers with varying degrees of polymerization were prepared by “graft-through” ring-opening metathesis of the macromonomers. The molecules in the resulting library of macromonomers and bottlebrush polymers self-assemble to form classically observed microphase-separated structures, including spheres, hexagonally packed cylinders, bicontinuous gyroid, and lamellae. The systematic variation of molecular structure, molecular weight of each branch, and degree of polymerization of the polymers results in a diverse set of structures and properties. We report the observation of well-ordered lamellae and cylinders with d-spacings as low as 6.1 and 8.0 nm, respec...

A high level of the permanent asymmetry was built into the poly(N-methyl-N′-(2-isopropyl-6-methylphenyl)carbodiimide) system by introducing a bulky, substituted phenyl group which revealed a very interesting phenomenological behavior upon heating. This polymer undergoes P/M racemization upon thermal annealing, thus leading to the formation of a stereocomplexed structure. Predominantly P and M helices have been obtained through helix sense selective polymerization by using chiral BINOL-Ti(IV) diisopropoxide initiator with achiral N-methyl-N′-(2-isopropyl-6-methylphenyl)carbodiimide monomer. Upon thermal annealing, the specific optical rotation (SOR) of the single-handed polymer begins to decrease but never reaches zero. The SOR plateaus at a large value (−286° for M helices or +283° for P helices), and shortly thereafter the polymer forms a precipitate. The process that polymer undergoes is attributed to stereocomplexation between two complementary strands via racemization. Inspired by the phenomena analog...

Combining monodisperse building blocks that have distinct folding properties serves as a modular strategy for controlling structural complexity in hierarchically organized materials. We combine an α-helical bundle-forming peptide with self-assembling dendrons to better control the arrangement of functional groups within cylindrical nanostructures. Site-specific grafting of dendrons to amino acid residues on the exterior of the α-helical bundle yields monodisperse macromolecules with programmable folding and self-assembly properties. The resulting hybrid biomaterials form thermotropic columnar hexagonal mesophases in which the peptides adopt an α-helical conformation. Bundling of the α-helical peptides accompanies self-assembly of the peptide-dendron hybrids into cylindrical nanostructures. The bundle stoichiometry in the mesophase agrees well with the size found in solution for α-helical bundles of peptides with a similar amino acid sequence.

Microcapsules with high mechanical stability and elasticity are desirable in a variety of contexts. We report a single-step method to fabricate such microcapsules by microfluidic interfacial complexation between high stiffness cellulose nanofibrils (CNF) and an oil-soluble cationic random copolymer. Single-capsule compression measurements reveal an elastic modulus of 53 MPa for the CNF-based capsule shell with complete recovery of deformation from strains as large as 19%. We demonstrate the ability to manipulate the shell modulus by the use of polyacrylic acid (PAA) as a binder material, and observe a direct relationship between the shell modulus and the PAA concentration, with moduli as large as 0.5 GPa attained. These results demonstrate that CNF incorporation provides a facile route for producing strong yet flexible microcapsule shells.

Magnetic fields are useful for directing block copolymer (BCP) self-assembly, but to date such a field alignment has required large fields (>5 T) necessitating the use of superconducting magnets. We report an approach that circumvents this limitation by introducing labile reactive mesogens into a liquid crystalline (LC) BCP based on a norbornene backbone with a poly(lactide) minority block that forms hexagonally packed cylinders. The free mesogens co-assemble with the smectic A mesophase of the BCP and enable alignment at fields as low as 0.5 T. The remarkable field response originates from the combined effects of enhanced mobility and decreased segregation strength, and the presence of large micron-scale grains in the system. We demonstrate a robust alignment of mesogen-blended samples using simple permanent magnets. The etching of poly(lactide) yields nanoporous films, while the spatially selective microdomain immobilization by UV-induced crosslinking through a photomask provides a versatile mechanism for creating alignment patterns. We anticipate that the nanoporous materials as generated here may find application in membrane fabrication or BCP lithography, while the ability to spatially pattern alignment is promising for the design of mechanical metamaterials exploiting the shape memory effect of LC elastomers.

The interaction of fields with condensed matter during phase transitions produces a rich variety of physical phenomena. Self-assembly of liquid crystalline block copolymers (LC BCPs) in the presence of a magnetic field, for example, can result in highly oriented microstructures due to the LC BCP's anisotropic magnetic susceptibility. We show that such oriented mesophases can be produced using low-intensity fields (4 T) and superconducting magnets required to date. Low-intensity field alignment is enabled by the addition of labile mesogens that coassemble with the system's nematic and smectic A mesophases. The alignment saturation field strength and alignment kinetics have pronounced dependences on the free mesogen concentration. Highly aligned states with orientation distribution coefficients close to unity were obtained at fields as small as 0.2 T. This remarkable field response originates in an enhancement of alignment kinetics due to a reduction in viscosity, and increased magnetostatic energy due to increases in grain size, in the presence of labile mesogens. These developments provide routes for controlling structural order in BCPs, including the possibility of producing nontrivial textures and patterns of alignment by locally screening fields using magnetic nanoparticles.