Emergence of a Metastable Laves C14 Phase of Block Copolymer Micelle Bearing a Glassy Core

Nouri, Babak; Chen, Chun-Yu; Huang, Yu-Shan; Mansel, Bradley W.; Chen, Hsin‐Lung

doi:10.1021/acs.macromol.1c01385

Cited by 14 publications

(21 citation statements)

References 59 publications

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“…Here, the selection of the ordered state is governed by a competition between chain stretching and interfacial tension subject to the constraint of constant density and thus exposes the geometric role of particle packing on the selection of ordered state symmetry. While bcc is the most commonly observed particle packing in block polymer melts, various Frank–Kasper phases have been observed as well, − consistent with their emergence in other forms of soft matter. − However, Laves phases are much less commonly observed in diblock copolymer melts − than other Frank–Kasper phases, and theory predicts that only the C14 and C15 Laves phases are likely to be stable . Moreover, the Laves phases seen to date appear in block polymer phase diagrams as stability windows rather than the line compounds that emerge for intermetallic compounds.…”

Section: Introductionmentioning

confidence: 84%

“…To understand the need for our approach, it is useful to recall first existing methods to produce Laves phases in diblock copolymers. Theory predicts that Laves phases are metastable in neat melts because of the entropically unfavorable chain stretching needed to accommodate the particle volume asymmetry of the structures. , However, for neat block copolymers melts, Laves phases have been formed via thermal processing routes − , that presumably leverage the intrinsic distribution of micelle volumes in the liquid-like packing state, which emerges upon deep cooling, to promote subsequent ordering into a Laves phase after reheating. These are inherently nonequilibrium processes whose molecular mechanisms are not well understood .…”

Section: Introductionmentioning

confidence: 99%

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Laves Phase Field in a Diblock Copolymer Alloy

et al. 2022

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Laves phases are a class of tetrahedrally close-packed Frank− Kasper phases with AB 2 stoichiometry. While these phases appear as intermetallic line compounds in a variety of metallic alloys, it is challenging to stabilize Laves phases in reconfigurable soft matter because of the substantial difference in preferred volume between the large A particles and small B particles. Surprisingly, perhaps the conceptually simplest approachblending two diblocks with incompatible core blockshas not been explored yet. Using self-consistent field theory, we predict that a Laves phase should emerge as a phase field in the eutectic phase diagram of an AB/B′C diblock copolymer blend if (i) the AB and B′C diblock copolymers are selected such that their neat melts produce bcc phases with the particle volume ratio of the desired Laves phase and (ii) the repulsion between A and C blocks is sufficiently strong to minimize mixing between micelles. This diblock "alloying" approach produces phase behavior that closely mimics that arising in intermetallic compound-producing metal alloys and should provide a relatively simple synthetic route to produce soft Frank−Kasper phases that are challenging to achieve by conventional polymer-based approaches. Article pubs.acs.org/Macromolecules

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Section: Introductionmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Laves Phase Field in a Diblock Copolymer Alloy

et al. 2022

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“…Annealing LLP-1 at 30 °C for 7 days led to the emergence of a well-ordered BCC phase with a lattice parameter a of 19.8 nm, as shown in Figure a. This was in parallel with the development of BCC order upon heating the LLP-1 phase to 80 °C (> T g core ) observed previously and also in Figure . Nevertheless, Figure a demonstrates that the transition from LLP-1 to BCC was able to occur at T g corona < T < T g core , so the development of the BCC phase stemmed from the intrinsic characteristics of the micelles inherited from the LLP-1 phase instead of any possible change of micelle size upon heating to 80 °C.…”

Section: Resultsmentioning

confidence: 99%

“…In a previous study, we revealed the emergence of the Laves C14 phase in a compositionally asymmetric poly(2-vinylpyridine)- block -poly(dimethylsiloxane) (P2VP- b -PDMS) . We showed that applying specific thermal processing led to the formation of particles with a specific size distribution in the micellar liquid phase that was subsequently trapped in the nonequilibrium LLP phase in the time scale of the cooling process.…”

Section: Introductionmentioning

confidence: 99%

Phase Control of Colloid-like Block Copolymer Micelles by Tuning Size Distribution via Thermal Processing

et al. 2022

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The formation of a Frank–Kasper (FK) phase in a one-component block copolymer (bcp) has been attributed to the sufficiently large conformational asymmetry parameter that leads to the deformation of the micellar core into the polyhedral shape templated by the Voronoi cells for relieving the packing frustration of the coronal blocks. Here we present the insight into the evolution of body-centered cubic (BCC) and Laves C14 phases from the corresponding metastable liquidlike packing (LLP) phases in a conformationally symmetric poly(2-vinylpyridine)-block-poly(dimethylsiloxane) (P2VP-b-PDMS) forming the colloid-like micelle with a hard P2VP core and a soft PDMS corona at the temperature of micelle ordering (T g corona < T a < T g core). Different thermal processing conditions were applied to produce four distinct types LLP phase characterized by different average micelle size and size dispersity. The LLP phase was found to transform to BCC, C14 and a reorganized LLP phase with increasing polydispersity of particle size, showing the existence of a proper range of size dispersity for the formation of the Laves phase. The real-space analysis of the local environments of the particles revealed that the C14 phase can accommodate the particles with a broader range of interparticle distance and a less uniform local environment, such that the PDMS coronal blocks of the micelles with greater size dispersity suffered a lower degree of packing frustration when they organized into a C14 lattice. In view of the colloid-like nature of the micelle, a size fractionation process found in the crystallization of polydisperse colloidal particles was proposed as the mechanism for directing the effective development of C14 phase from the LLP phase. Due to the metastable nature of the ordered phases, their order–disorder transition temperatures were found to depend strongly on the structures of the LLP phases from which they developed and a strong memory effect underlying the phase transitions was identified.

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“…The highly ordered local and complex lattice structures of FK phases were first found in metal alloys; here, the coordination number (CN) should be greater than 12 for at least one polyhedron, while other topologically close-packed polyhedrons should have CNs of 12, 14, 15, or 16. − Slightly distorted tetrahedra are always observed because regular tetrahedra could not occupy the space completely; thus, these tetrahedra would be impossible to exist if all of the polyhedra were exactly highly regular. − The FK phases C14, C15, A15, σ, H, and Z (and 22 others) have been observed experimentally in soft-matter systems, including block copolymers, liquid crystals, dendrimers, and giant amphiphiles based on inorganic polyhedral oligomeric silsesquioxane (POSS) cages or other inorganic nanoparticles. − …”

Section: Introductionmentioning

confidence: 99%

Mesoporous Phenolic/POSS Hybrids Induced by Microphase Separation Arising from Competitive Hydrogen Bonding Interactions

2022

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We used ring-opening living polymerization to synthesize various linear poly(ethylene oxide−b−caprolactone) (PEO-b-PCL, EC) diblock copolymers featuring PCL blocks of various molecular weights and prepared phenolic resins with various double-decker silsesquioxane (DDSQ) cage compositions in the form of phenolic/DDSQ (PDDSQ) hybrids. Upon forming PDDSQ/EC blends, competitive hydrogen bonding of the phenolic OH units of PDDSQ occurred with both ether units of the PEO block and C�O units of the PCL block, with the fraction of hydrogen-bonded C�O groups increasing upon increasing the PDDSQ compositions but decreasing upon increasing the molecular weight of the PCL block in EC diblock copolymers. Small-angle X-ray scattering revealed the self-assembled structures and corresponding phase diagram of these PDDSQ/EC blends after thermal polymerization at 150 °C, with the d-spacing increasing upon increasing the molecular weight of PCL block in the EC diblock copolymers. After removal of the EC diblock copolymer template, we obtained mesoporous phenolic/DDSQ hybrids possessing high surface areas and pore volumes, with the highly ordered mesoporous structures featuring double-gyroid, hexagonal-packing cylindrical, spherical, and even Frank−Kasper (FK) structures depending on the molecular weight of PCL block and the content of the PPDSQ hybrid. Overall, this study provides a general principle for obtaining mesoporous double-gyroid and FK phases mediated by diblock copolymer compositions through competitive hydrogen-bonding interactions.

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Emergence of a Metastable Laves C14 Phase of Block Copolymer Micelle Bearing a Glassy Core

Cited by 14 publications

References 59 publications

Laves Phase Field in a Diblock Copolymer Alloy

Laves Phase Field in a Diblock Copolymer Alloy

Phase Control of Colloid-like Block Copolymer Micelles by Tuning Size Distribution via Thermal Processing

Mesoporous Phenolic/POSS Hybrids Induced by Microphase Separation Arising from Competitive Hydrogen Bonding Interactions

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