Structure and Mechanical Properties of an O70 (Fddd) Network-Forming Pentablock Terpolymer

Effect of Film Thickness on the Self-Assembly of CBABC Symmetric Pentablock Terpolymer Melts under 1D Confinement: A Dissipative Particle Dynamic Study

The study investigates the impact of film thickness on the phase behavior of pentablock terpolymers, denoted as C3B3A6B3C3, when subjected to wall confinement by utilizing the dissipative particle dynamics method. Phase diagrams were constructed to elucidate how factors such as block-block interaction strength, film thickness, and wall properties affect the self-assembly structures. In cases where the wall exhibits no preference for any of the blocks, lamellae phases with orientations perpendicular to the wall are observed. The order-disorder transition (ODT) temperature is found to be influenced by the interaction between the polymer and the wall in thin confinement scenarios. When the wall displays a preference for specific blocks, the orientation of lamellae structures undergoes variations. Lamellae tend to align parallel to the wall when the wall favors A or C blocks, and they orient perpendicularly when B blocks are favored. Furthermore, the mechanical properties of the lamellae structures are related to the conformations of the polymer chains. Structures where chains predominantly adopt a loop conformation exhibit enhanced elastic properties. The ratio of looping to bridging conformations can be adjusted by altering the film thickness and wall selectivity.

Dissipative Particle Dynamics Simulation for the Self-Assembly of Symmetric Pentablock Terpolymers Melts under 1D Confinements

The phase behavior of CBABC pentablock terpolymers confined in thin films is investigated using the Dissipative Particle Dynamic method. Phase diagrams are constructed and used to reveal how chain length (i-block length), block composition and wall selectivity influence the self-assembly structures. Under neutral walls, four categories of morphologies, i.e., perpendicular lamellae, core-shell types of microstructures, complex networks, and half-domain morphologies, are identified with the change in i-block length. Ordered structures are more common at weak polymer-polymer interaction strengths. For polymers of a consistent chain length, when one of the three components has a relatively smaller length, the morphologies transition is sensitive to block composition. With selective walls, parallel lamellae structures are prevalent. Wall selectivity also impacts chain conformations. While a large portion of chains form loop conformations under A-selective walls, more chains adopt bridge conformation when the wall prefers C-blocks. These findings offer insights for designing nanopatterns using symmetric pentablock terpolymers.

Effect of Block Sequence on the Solution Self-Assembly of Symmetric ABCBA Pentablock Polymers in a Selective Solvent

Solution self-assembly of multiblock polymers offers a platform to create complex functional self-assembled nanostructures. However, a complete understanding of the effect of the different single-molecule-level parameters and solution conditions on the self-assembled morphology is still lacking. In this work, we have used dissipative particle dynamics to investigate the solution self-assembly of symmetric ABCBA linear pentablock polymers in a selective solvent and examined the effect of the block sequence, composition, and polymer concentration on the final morphology and polymer conformations. We confirmed that block sequence has an effect on the self-assembled morphologies, and it has a strong influence on polymer conformations that give place to physical gels for the sequence where the solvophilic block is located in the middle of the macromolecule. Our results are summarized in terms of morphology diagrams in the composition-concentration parameter space.

Formation of Perpendicular Three-Dimensional Network Nanostructures in ABC-Star Copolymers

Perpendicular arrangements in hierarchical nanostructures show superior mechanical properties and provide great opportunities for the development of advanced membranes because different channels are connected by the perpendicular blocks. To obtain these perpendicular hierarchical nanostructures, we use a simple ABC-star terpolymer because of the existence of a conjunction point by using the A block as a polymer network template, which guides the BC phase separation accordingly. When χ_BC is 10, the formed phase and the corresponding phase diagram of ABC-star are similar to those of the AB₂ triblock because of the mixture between the B and C blocks. Interestingly, at increased χ_BC, the B and C blocks phase separate, leading to the formation of a series of perpendicular nanostructures, including perpendicular lamellae-in-lamellae (L_⊥), perpendicular lamellae-in-cylinder (C_⊥), and even perpendicular three-dimensional polymer networks (G_⊥). The corresponding stability regime of each phase is identified through the dedicated comparison of free energy, which can well explain the missing phases in Monte Carlo simulations. Our proposed design route according to the target structures and the calculated phase diagram can provide useful guidance for the experimental observation of these perpendicular nanostructures.

Formation of Multicontinuous 3D Network Nanostructures with Increased Complexity in ABC-Type Block Copolymers

The multicontinuous network nature of polymer nanostructures provides them with many opportunities to fabricate multifunctional materials with specific mechanical, transport, optical, and other novel properties. In this paper, we generate an effective design principle to craft a series of multicontinuous network structures with controllable channels, including multicontinuous gyroid and O⁷⁰ network morphologies via the self-assembly of ABC-type block copolymers. Importantly, we achieve a much wider (∼25%) compositional range than that of AB diblock copolymers (∼3%), which would increase the widespread application of these multicontinuous polymer networks. Even for the simplest ABC linear system, this method is valid for generating multicontinuous network structures, where gyroids and O⁷⁰ are found to possess large phase regions. This finding can theoretically explain the experimental observation of gyroid and O⁷⁰ phases. We believe that our proposed design principle along with the calculated phase diagram provides a compelling panacea for the fabrication of multicontinuous 3D network nanostructures.

Periodic and Aperiodic Tiling Patterns from a Tetrablock Terpolymer System of the A1BA2C Type

Two tetrablock terpolymers of the S₁IS₂P type, where S, I, and P denote polystyrene, polyisoprene, and poly(2-vinylpyridine), respectively, were prepared anionically. S₁IS₂P-1 (S₁/I/S₂/P = 0.35/0.16/0.34/0.15, four numbers being volume fractions of S₁, I, S₂, and P block chains) has a structure with double hexagonal cylinders, while S₁IS₂P-2 (S₁/I/S₂/P = 0.47/0.15/0.22/0.16) has an unusual double tetragonal structure. Moreover, 13 binary blends were prepared from these two parent polymers. Among them, five blends with α(= φ_S1/φ_S2) covering the range 1.50 ≤ α ≤ 1.86 were confirmed to have a 3.3.4.3.4 Archimedean tiling structure, in which their P domains adopt five satellite I domains, while four blends with α covering the range 1.37 ≤ α ≤ 1.48 were revealed to be a quasicrystalline tiling structure with dodecagonal symmetry.

3D-TEM study on the novel bicontinuous microdomain structure

An ordered bicontinuous double-diamond (OBDD) morphology was found in polystyrene-block-(poly-4-vinylphenyldimethylvinylsilane-graft-polyisoprene), PS-b-(PVS-g-PI), block-graft copolymer. We obtained a 3D image of the microdomain structure formed in PS-b-(PVS-g-PI) using 3D-TEM. The 3D image shows that the polystyrene (PS) phase consists of two independent and interwoven networks. The structures of the two networks are identical and include tetrapod units that form planar six-membered rings. The features of the networks agree with those in the OBDD morphology, indicating that PS-b-(PVS-g-PI) exhibits ordered three-dimensional OBDD networks with the PS phase in the polyisoprene (PI) matrix phase. The grafted PI chains induce the frustration of the PS chains; thus, the effects of the specific interface are more dominant than those of packing frustration in the formation of the morphology, and the OBDD phase is stabilized.

Theoretical simulations of nanostructures self-assembled from copolymer systems

This article provides an overview of recent simulation investigations of the nanostructures and structure–property relationships in copolymer systems.

Real-space evidence of the equilibrium ordered bicontinuous double diamond structure of a diblock copolymer

The ordered bicontinuous double diamond (OBDD) structure has long been believed to be an unstable ordered network nanostructure, which is relative to the ordered bicontinuous double gyroid (OBDG) structure for diblock copolymers. Using electron tomography, we present the first real-space observation of the thermodynamically stable OBDD structure in a diblock copolymer composed of a stereoregular block, syndiotactic polypropylene-block-polystyrene (sPP-b-PS), in which the sPP tetrapods are interconnected via a bicontinuous network with Pn3̄m symmetry. The OBDD structure underwent a thermally reversible order-order transition (OOT) to OBDG upon heating, and the transition was accompanied with a slight reduction of domain spacing, as demonstrated both experimentally and theoretically. The thermodynamic stability of the OBDD structure was attributed to the ability of the configurationally regular sPP block to form helical segments, even above its melting point, as the reduction of internal energy associated with the helix formation may effectively compensate the greater packing frustration in OBDD relative to that in the tripods of OBDG.

Direct measurement of interface anisotropy of bicontinuous structures via 3D image analysis

A very important morphological parameter in two-phase fluids is the interface anisotropy, which can be quantified using the interface tensor, q(ij). However, the computation of this tensor for complex interfaces is not straightforward. A novel method (the local cross product method, LCPM) to compute the interface tensor of two-phase fluids using 3D imaging coupled with differential geometry is presented here. The method was used to evaluate the degree of anisotropy of phase separated systems with bicontinuous morphologies subjected to uniaxial and shear deformation fields. A model bicontinuous structure (i.e., the gyroid surface) was used to assess the accuracy and precision of the method. The method was then used to track the anisotropy changes of an immiscible polymer blend with cocontinuous morphology, during uniaxial deformation and subsequent retraction. It was found that the dependence of the anisotropy on the Hencky strain of both the gyroid surface and the cocontinuous blend follow the same trend. The retraction of the blend after uniaxial extension is accompanied by an exponential decay of the second invariant of q(ij), which obeys the relation: |II(q)|/Q(2) approximately e(-0.129t).

Direct small-angle-neutron-scattering observation of stretched chain conformation in nanocomposites: more insight on polymer contributions in mechanical reinforcement

In this paper we present a direct measurement of stretched chain conformation in polymer nanocomposites in a large range of deformation using a specific contrast-matched small angle neutron scatttering (SANS) method. Whatever are the filler structure and the chain length the results show a clear identity of chain deformation in pure and reinforced polymer and offer more insight on the polymer chain contribution in the mechanical reinforcement. It suggests that glassy layer or glassy paths, recently proposed, should involve only a small fraction of chains. As a result, the remaining filler contribution appears strikingly constant with deformation as explained by continuous locking-unlocking rearrangement process of the particles.