Hierarchical Structures of Hydrogen-Bonded Liquid-Crystalline Side-Chain Diblock Copolymers in Nanoparticles

Abstract

Here we show that it is possible to control the overall morphology as well as hierarchical microstructure of lamellae-forming block copolymers within nanoparticles by altering side-chain content and processing temperature. We used cholesteryl hemisuccinate (CholHS) as hydrogen-bonded side chains and poly(styrene)-block-poly(4-vinylpyridine) (PS−P4VP) as backbone to produce submicrometer particles with the aerosol method. With CholHS-to-P4VP repeat unit ratio of 0.25 and 0.50, we obtained onion-like particles with either single CholHS layers sandwiched between P4VP rich lamellae or smectic P4VP(CholHS) layers perpendicular to the polymer domain interfaces. When the fraction of CholHS was increased to 0.75, the onion-like structure broke down due to increased splay deformation energy of the liquid crystalline P4VP(CholHS) domains. The onion-like structure could be re-established, however, when the particles were produced at a higher temperature which made the CholHS molecules partially soluble into the PS phase. Because of the reversible nature of the hydrogen bonds, it was possible to selectively remove the CholHS side chains from the particles. ■ INTRODUCTIONSubmicrometer-sized particles with inner structures have promising applications for instance as templates for porous materials 1 or as microenvironments for chemical reactions. 2 Block copolymers offer a promising way to achieve inner structures in the 10−100 nm length scale thanks to the possibility to control their microphase separation. 3 The microphase-separated structures can take the form of, for example, alternating lamellae, hexagonally packed cylinders, or spheres in face-centered cubic lattice. The morphology depends on the relative volumes of the polymer blocks and the strength of their mutual interactions. The block with the lowest surface energy typically concentrates on the surface of the material. 4−6 This controls the final microphase-separated structure of block copolymer in particles whose radius is smaller than the coherence length of the structures. The surface-induced orientation results in spherically symmetric structures in spherical particles. For instance, computational studies predict that block copolymers with symmetric block volumes microphase separate into concentric shells of alternating domains. 7−12 The morphology can be described as "onion-like". However, if the size of the particles is incommensurate with the periodicity of the domains, more exotic morphologies can arise. 9,11,13 Since the early report by Thomas et al., 14 the onionlike morphology has been observed also experimentally in a number of works. 15−28 In particles prepared by the so-called good solvent-poor solvent method, the surface layer can be controlled by the choice of surfactants. 19 By further modifying the surface interactions, it is possible to turn the onion-like structures to "tulip-bulb"-like or even change the shape of the particles from spherical to prolate spheroidal with block copolymer lamellae stacked orthogonal to the long axis. 22 Stacked lamel...

P4VP and oligo(phenylenevinylene)-perylenebisimide mixed donor-acceptor supramolecular comb polymer complexes with improved charge carrier mobility

“…Noncovalent interactions like the hydrogen bonding and ionic interactions have been used to develop “bottle‐brush” polymeric structures between linear polymers and small surfactant molecules . Poly(4‐vinyl pyridine) (P4VP) is the most widely studied polymer that has been explored for the hydrogen bonding interactions of the pyridine nitrogen with aromatic hydroxyl or carboxyl units of small surfactant molecules . Most of these studies focused on the self‐organization in the bulk state .…”

“…Poly(4‐vinyl pyridine) (P4VP) is the most widely studied polymer that has been explored for the hydrogen bonding interactions of the pyridine nitrogen with aromatic hydroxyl or carboxyl units of small surfactant molecules . Most of these studies focused on the self‐organization in the bulk state . In the recent years, this self‐assembly has been used to bring together π‐conjugated molecules in a “supramolecular comb polymer” architecture with promising improvements in their charge carrier mobilities.…”

Supramolecular Modification of ABC Triblock Terpolymers in Confinement Assembly

“…As a result, the interfacial equilibrium area decreases and chains are able to pack more densely at the P4VP/PS and the P4VP/PT interface. The formation of planar interfaces is preferred in such arrangements [38]. On the mesoscale, i.e., the length scale of block copolymer microphase separation (10–100 nm), the dense chain packing leads to flattening of the previously spherical P4VP domains that now adopt a lenticular shape (Figure 4b).…”

“…For BCPs, the spherical confinement generates new structures that are otherwise not found in bulk [24,25,26,27,28,29]. The inner structure of the final colloids structure is conveniently modified by the use of additives such as metal precursors [30,31], homopolymers [32,33,34], nanoparticles [35,36], and HB donors [37,38,39]. To expand the range of the inner structures and the number of functional domains within one microparticle, the confinement assembly of ABC triblock terpolymers should be considered.…”

Confined crystallization and melting behaviors of poly(ethylene glycol) end‐functionalized by hydrogen bonding groups: Effect of contents for functional units

“…[1][2][3][4][5] Hydrogen bonding motifs are most widely used in the context of supramolecular assembly with various building polymers, and polymers containing multiple hydrogen bondings have received significant interest in applications such as surgical fixation devices, controlled drug delivery, and tissue engineering scaffolds. [6,7] The performance of hydrogen bonded polymers are crucially related to the intrinsic properties of the parent materials (e.g., the backbone flexibility or rigidity, backbone chain length) as well as compatibility, [8] bonding strength, [9] and content of hydrogen bonded unit, [10] which provides a variety of possibilities for the development of materials.…”