Effect of the Degree of Hydrogen Bonding on Asymmetric Lamellar Microdomains in Binary Block Copolymer Blends

Tetragonally Packed Inverted Cylindrical Microdomains from Binary Block Copolymer Blends with Enhanced Hydrogen Bonding

Hexagonally packed (HEX) cylindrical microdomains can be obtained through the self-assembly of block copolymers (BCPs) with a moderately asymmetric volume fraction of one block (f), resulting in the formation of minor cylinders. However, for next-generation lithography and high-density memory devices, it is desirable to obtain densely and tetragonally packed inverted cylindrical microdomains, which are composed of the major block in the minor matrix. The inverted cylinders differ from conventional HEX cylinders, which consist of the minor block in the matrix of the major block. In this study, we achieved this objective by utilizing a binary blend of a polystyrene-b-poly(4-vinylpyridine) copolymer (S4VP) and polystyrene-b-poly(4-hydroxystyrene) copolymer (SHS), where the P4VP block exhibited a strong hydrogen bonding interaction with the PHS block. By carefully controlling the molecular weight ratio of S4VP and SHS as well as the blend composition, we successfully observed tetragonally packed inverted PS cylinders with a square cross-section at a volume fraction of PS of 0.69.

Electrostatic crosslinking-enabled highly asymmetric lamellar nanostructures of polyzwitterionic block copolymers for lithography

For the bulk self-assembly of traditional diblock copolymers (di-BCPs), lamellar structures only occur when two constituents have similar volume fractions (f) and two alternating layers tend to have similar thicknesses. Highly asymmetric lamellar (A-LAM) structures, in which the thickness of one layer is several times higher than the other, are hardly formed in di-BCPs, while they have potential applications in nanolithography. In this work, A-LAM structures with different dimensions were constructed using a type of simple linear di-BCP, polystyrene-b-poly(4-vinylpyridine)propane-1-sulfonate (PS-b-PVPS) with the polyzwitterionic block PVPS in minority. The origin of the A-LAM structure was ascribed to the electrostatic crosslinking and confirmed by doping PS-b-PVPS block copolymers (BCPs) with N-butyl pyridinium methane sulfonate (BPMS). The morphology of compositionally asymmetric PS-b-PVPS BCPs changed from A-LAM to cylindrical structures upon salt-doping, i.e. the phase behavior of common BCPs was recovered. In addition, the morphologies of PS-b-PVPS BCPs with similar molecular weights but varied compositions were also studied, and only two kinds of structures (lamellar or ill-defined spherical structure) were observed when the volume fraction of PVPS (f_PVPS) was less than 0.5, and the composition range for the formation of the lamellar structure was found to be f_PVPS ≥ 0.188.

High-Molecular-Weight PLA-b-PEO-b-PLA Triblock Copolymer Templated Large Mesoporous Carbons for Supercapacitors and CO2 Capture

High-molecular-weight PLA₄₄₀-b-PEO₄₅₄-b-PLA₄₄₀ (LEL) triblock copolymer was synthesized through simple ring-opening polymerization (ROP) by using the commercial homopolymer HO-PEO₄₅₄-OH as the macro-initiator. The material acted as a single template to prepare the large mesoporous carbons by using resol-type phenolic resin as a carbon source. Self-assembled structures of phenolic/LEL blends mediated by hydrogen bonding interaction were determined by FTIR and SAXS analyses. Through thermal curing and carbonization procedures, large mesoporous carbons (>50 nm) with a cylindrical structure and high surface area (>600 m²/g) were obtained because the OH units of phenolics prefer to interact with PEO block rather than PLA block, as determined by FTIR spectroscopy. Furthermore, higher CO₂ capture and good energy storage performance were observed for this large mesoporous carbon, confirming that the proposed approach provides an easy method for the preparation of large mesoporous materials.

Highly Asymmetric Phase Behaviors of Polyhedral Oligomeric Silsesquioxane-Based Multiheaded Giant Surfactants

This work reports the molecular design, synthesis, and systematic study on the bulk self-assembly behaviors of three series of polyhedral oligomeric silsesquioxane (POSS)-based multiheaded giant surfactants XDPOSS-PS_n (X = 2, 3, and 4), which are composed of two, three, or four hydrophilic hydroxyl-group-functionalized DPOSS cages attached via one junction point to a hydrophobic polystyrene (PS) chain. These series of hybrid polymeric amphiphiles with precisely defined chemical structure and controllable molecular architecture are synthesized by the sequential usage of "click" reactions. By tuning molecular weights of the PS tail, we established full phase diagrams of XDPOSS-PS_n as a function of the volume fractions of PS chains (V_f^PS). We found that the self-assembled structures were greatly influenced by the molecular architecture. Strikingly, our results showed that the lamellar morphology, which usually existed at relatively symmetric compositions in common diblock copolymers, became the thermodynamically stable phase in the 3DPOSS-PS_n and 4DPOSS-PS_n samples even at an asymmetric composition up to V_f^PS = 0.842, with the ratio between the thicknesses of PS and DPOSS lamellae up to 5.32. This unusual phenomenon induced by molecular architectural variation could be explained by the large cross-sectional area of DPOSS cages at the nanophase-separated domain interface and high elastic deformation energy of clustered DPOSS cages which have relatively rigid conformation. The unique bulk self-assembly behaviors in our POSS-based multiheaded giant surfactants provide insights in developing hybrid nanomaterials toward unconventional nanostructures.

Tetragonal phase of cylinders self-assembled from binary blends of AB diblock and (A'B)n star copolymers

The phase behavior of binary blends composed of AB diblock and (A'B)_n star copolymers is studied using the polymeric self-consistent field theory, focusing on the formation and stability of the stable tetragonal phase of cylinders. In general, cylindrical domains self-assembled from AB-type block copolymers are packed into a hexagonal array, although a tetragonal array of cylinders could be more favourable for lithography applications in microelectronics. The polymer blends are designed such that there is an attractive interaction between the A and A' blocks, which increases the compatibility between the two copolymers and thus suppresses the macroscopic phase separation of the blends. With an appropriate choice of system parameters, a considerable stability window for the targeted tetragonal phase is identified in the blends. Importantly, the transition mechanism between the hexagonal and tetragonal phases is elucidated by examining the distribution of the two types of copolymers in the unit cell of the structure. The results reveal that the short (A'B)_n star copolymers are preferentially located in the bonding area connecting two neighboring domains in order to reduce extra stretching, whereas the long AB diblock copolymers are extended to further space of the unit cell.

Hydrogen bonding strength effect on self-assembly supramolecular structures of diblock copolymer/homopolymer blends

The steric hindrance effect on the hydrogen bonding strength and self-assembly supramolecular structures of the PS-b-PVPh diblock copolymer when blended with P4VP and P2VP homopolymers was investigated.