Creating Aligned Nanopores by Magnetic Field Processing of Block Copolymer/Homopolymer Blends

Abstract

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 (T odt) 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 T odt decreases linearly with PEG concentration until the onset of macrophase separation, inferred by PEG crystallization. Beyond this point, T odt 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 strategy can be extended to other BCP/homopolymer blends to produce nanoporous materials with reliable control of pore alignment and effective pore dimensions.

High-throughput morphology mapping of self-assembling ternary polymer blends

“…13 For example, blending offers ways to tune domain size and spacing, 14,15 guide self-assembly towards desirable and novel morphologies, 16 direct domains to form nonregular device-oriented geometries, 17 promote vertical domain-orientation, 18,19 accelerate ordering kinetics, [20][21][22][23] enable templatedirected selection between coexisting morphologies, 24 and control pore size in BCP membranes. 25,26 The recent work by some of our authors highlights opportunities for materials synthesis via polymer self-assembly afforded using a particular category of blends: ternary blends of a diblock copolymer with very low molecular weight homopolymers (#$3 kg mol À1 ) that are chemically equivalent to each block. When the degree of polymerization of each homopolymer (N H ) is much lower the than that of the polymer block in which it resides (e.g.…”

Ordered Mesoporous Microcapsules from Double Emulsion Confined Block Copolymer Self-Assembly

“…The self-assembly of BCPs yields well-defined nanostructures whose morphology depends on the polymer composition with length scales of 5–100 nm determined by the polymer size. − To achieve membranes from BCP self-assembly with size-selective permeability, pores have to be introduced to the initially dense BCP film that connect the two surfaces through the bulk of the material. In flat BCP membranes, common methods of introducing porosity include the selective etching of one polymer block or the inclusion of a sacrificial small molecule porogen during the self-assembly and film formation, followed by its selective dissolution, as well as combinations of BCP self-assembly with spinodal decomposition leading to hierarchical structures. − A common BCP nanostructure used for membranes contains one-dimensional porous cylinders, which require alignment perpendicular to the film to ensure connected pores throughout the membrane. , Methods to achieve alignment of BCP structures in flat membranes include the application of external electrical or magnetic fields, shear, or tuning of the preferential wetting at the substrate– and air–polymer interfaces. ,− However, these methods have only been demonstrated in flat membrane systems on solid substrates. They are not applicable to the fabrication of microcapsules from double emulsion drop templates due to the presence of only liquid–liquid interfaces and the lack of a solid substrate or air–polymer interface.…”

Versatile strategies to tailor the glass transition temperatures of bottlebrush polymers

“…Artificial blends of precision polymers offer a significant promise for preparing multifunctional materials with precisely tunable properties. 22,[34][35][36][37][38][39]54 To address the gaps between unique T g,∞BB at different N SC , we hypothesized that a binary blend of PBP can be prepared to afford a chemically homogeneous mixture with its T g located between the unique T g,∞BB of each component. To test this hypothesis, we examined the T g of PBP-S2 13 (A, T g,∞BB = 35 °C), PBP-S8 12 (B, T g,∞BB = 74 °C) and their artificial blends (4 samples, w A : w B = 3 : 1, 2 : 1, 1 : 1, and 1 : 3, respectively, Fig.…”