Superlattice Structure from Self-Assembly of High‑χ Block Copolymers via Chain Interdigitation

Flexible and shape-tunable features of block copolymers (BCPs) with high Flory–Huggins interaction parameters (high χ value) have drawn intensive attention due to their rich phase behaviors. Herein, this work aims to examine a fascinating superlattice structure obtained from the self-assembly of high-χ BCP, polystyrene-block-polydimethyl­siloxane (PS-b-PDMS), as evidenced by reciprocal-space imaging from small-angle X-ray scattering (SAXS) and by real-space imaging from transmission electron microscopy (TEM). Surprisingly, an interesting reversible order–order transition from superlattice structure with chain interdigitation to typical lamellae with bilayer texture can be identified by in situ temperature-resolved SAXS. In contrast to the diblock (PS-b-PDMS)n (n = 1), the forming superlattice structure will be greatly impeded in star-block (PS-b-PDMS)n (n = 3 and 4) with equivalent arm length, suggesting a topological effect on self-assembly due to their star-shaped architecture. Accordingly, a lamellae-forming PS-b-PDMS with chain interdigitation (wet-brush-like chain packing) was proposed to be the origin of the forming superlattice structure. This finding provides an insight for the possible model with ladder-like structure and corresponding transformation mechanisms of high-χ BCPs. Also, the topological effect from star-block architecture may play an important role to justify the formation of such a unique self-assembled texture. These results implicitly explore the feasibility to acquire a superlattice structure from a simple coil–coil diblock copolymer

Controlled Orientation of Plasma-Treated Diblock Copolymer Films from the Responsive Functionalized Substrate through Solvent Annealing

This study demonstrates a new technique for controlled orientation of nanostructured block copolymer (BCP) thin films through solvent annealing using polystyrene-block-polydimethyl­siloxane (PS-b-PDMS) as a representative BCP system. A two-step substrate functionalization of an intrinsic oxide layer (SiO2) wafer is performed by using hydroxyl-terminated PS (PS-OH) followed by hydroxyl-terminated PDMS (PDMS-OH). By varying the grafting percentage of the PS and PDMS brushes on the substrate, it is possible to give different degrees of stretching and recoiling of grafted PS and PDMS, respectively, using PS-selective solvent for solvent annealing, resulting in roughness variation; that is termed a responsive functionalized substrate. With the appropriate roughness of the functionalized substrate under solvent annealing, the development of perpendicularly oriented cylinders of PDMS in the nanostructured PS-b-PDMS thin films can be driven from the bottom of the film. Moreover, by taking advantage of air plasma treatment, it is possible to generate a top-capped neutral layer on the film surface, giving induced perpendicular cylinders from the top surface of the thin film after solvent annealing. Consequently, it is possible to attain the formation of film-spanning perpendicular cylinders of PDMS in the PS-b-PDMS thin film under solvent annealing through the self-alignment process of the perpendicularly oriented cylinders from the top and the bottom surface of the thin film

Controlled Orientation of Silicon-Containing Diblock Copolymer Thin Films by Substrate Functionalization Under Vacuum

This work demonstrates a simple approach to control the orientation of the self-assembled nanostructured block copolymer thin films of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) by functionalization of the oxide layer (SiO2) on the Si substrate followed by thermal annealing under low-pressure environmental conditions. The substrate can be functionalized through two-step grafting of hydroxy-terminated polystyrene brush (PS–OH brush) followed by hydroxy-terminated polydimethylsiloxane brush (PDMS–OH brush) onto the wafer substrate. By controlling the grafting ratio of PS–OH and PDMS–OH brushes, the affinities of the PS and PDMS blocks with the substrates can be fine-tuned to provide a neutral substrate in order to form perpendicular cylinders from the bottom after thermal annealing. Owing to the vacuum-driven orientation [i.e., thermal annealing under low-pressure environment conditions (∼10–4 Pa)], the orientation of the cylinders can be controlled at the air/polymer interface. Interestingly, by combining the vacuum-driven approach with substrate functionalization, perpendicular cylinders from the air/polymer interface and substrate/polymer interface can be generated, respectively. Consequently, well-aligned perpendicular cylinders with long-range ordering can be fabricated by the self-alignment process

Layered Thin Film Deposition via Extreme Inter-Brush Slip in a Lamellar Block Copolymer

Creating ultrathin films via ballistic impact-induced frictional material transfer could be a new approach for additive manufacturing compared with current solvent-assisted polymer coatings. The covalently bonded A block brushes and B block brushes are robust mechanical units in A/B lamellar diblock copolymers (BCPs). The parallel brush–brush interfaces with low entanglement density present a unique set of slip planes that can undergo extreme deformation by shearing and delamination by tensile forces. Impact of microspheres comprised of concentric glassy–rubbery brush layers against a rigid substrate at ballistic strain rates causes adiabatic shock heating that permits compressional thinning of the bottommost layers via slip over both types of BCP brushes. In cooler regions, the mechanical contrast between the glassy A blocks and rubbery B blocks induces extensive slip across the rubbery block brushes. For angled impacts, the increased shear stress enhances brush slip and the particle slides across the substrate accompanied by delamination across the slip planes and unique frictional transfer of discrete B-block-A A-block B layers

Synthesis, Molecular Characterization, and Phase Behavior of Miktoarm Star Copolymers of the AB_<i>n</i> and A_<i>n</i>B (<i>n</i> = 2 or 3) Sequences, Where A Is Polystyrene and B Is Poly(dimethylsiloxane)

Novel miktoarm star copolymers of polystyrene­[poly­(dimethylsiloxane)n] or PS­(PDMS)n (n = 2 or 3) type as well as of the inversed sequence, namely, (polystyrene)n[poly­(dimethylsiloxane)] or (PS)nPDMS (n = 2 or 3), were synthesized by combining living anionic polymerization with chlorosilane chemistry. The miktoarm star copolymers were extensively characterized through size exclusion chromatography, vapor pressure/membrane osmometry, proton nuclear magnetic resonance, and differential scanning calorimetry, in order to verify the successful synthesis. All samples with varying volume fractions and narrow dispersity indices (D̵ < 1.1) were morphologically characterized by transmission electron microscopy and small-angle X-ray scattering, in order to study their self-assembly behavior as well as to examine the effect of the complex architecture on the final adopted morphologies. For specific PS­(PDMS)n (n = 2 or 3), morphologies different from those expected from theoretical predictions (self-consistent field theory or Gaussian statistics) were obtained, while for the inversed sequences, namely, (PS)nPDMS (n = 2 or 3), no discrepancies were evident. This fact further confirmed the impact of the number of arms as well as the flexibility of the segments (PS being stiffer than PDMS) on the structure/property relationship

Vacuum-Driven Orientation of Nanostructured Diblock Copolymer Thin Films

This work aims to demonstrate a facile method for the controlled orientation of nanostructures of block copolymer (BCP) thin films. A simple diblock copolymer system, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), is chosen to demonstrate vacuum-driven orientation for solving the notorious low-surface-energy problem of silicon-based BCP nanopatterning. By taking advantage of the pressure dependence of the surface tension of polymeric materials, a neutral air surface for the PS-b-PDMS thin film can be formed under a high vacuum degree (∼10–4 Pa), allowing the formation of the film-spanning perpendicular cylinders and lamellae upon thermal annealing. In contrast to perpendicular lamellae, a long-range lateral order for forming perpendicular cylinders can be efficiently achieved through the self-alignment mechanism for induced ordering from the top and bottom of the free-standing thin film

Defining Morphological Transformations of “Soft Nature” Diblock Viscoelastic Structured Polymers

Structured diblock copolymer liquids consisting exclusively of “soft” segments with glass-transition temperatures well below room temperature have not been studied extensively in the literature in terms of self-assembly properties to date. Despite their “soft nature”, these types of diblock copolymers are capable of forming well-ordered topologies at low temperatures. This ability is attributed to their low dispersity indices (Đ) and relatively high Flory–Huggins interaction parameter, χ, between the chemically different involved blocks. Herein, we report a comprehensive study of the synthesized copolymers on molecular and thermal characterization, along with the structure–property relationship of two types of polydiene-b-polysiloxane copolymers by manipulating the monomer’s ratio during synthesis. Emphasis was given to the self-assembly behavior when the molecular characteristics (volume fraction and degree of polymerization) of the involved blocks varied to assess the limits of the phase stability. Specially, poly(butadiene) (PB1,2) or poly(isoprene) (PI1,4) was utilized as the first segment, while poly(dimethylsiloxane) (PDMS) was used as the second block in all cases. The molecular characteristics’ diversity combined with the ability to design/synthesize block copolymers with well-ordered phases ranging from spheres, cylinders, lamellar, and finally network structures is quite promising for nanotechnology applications in soft electronics. Also, the inherent properties of the copolymers, such as thermal stability, hydrophobicity, and flexibility, render them potential candidates for stretchable and/or wearable applications

Vacuum-Driven Orientation of Nanostructured Diblock Copolymer Thin Films

This work aims to demonstrate a facile method for the controlled orientation of nanostructures of block copolymer (BCP) thin films. A simple diblock copolymer system, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), is chosen to demonstrate vacuum-driven orientation for solving the notorious low-surface-energy problem of silicon-based BCP nanopatterning. By taking advantage of the pressure dependence of the surface tension of polymeric materials, a neutral air surface for the PS-b-PDMS thin film can be formed under a high vacuum degree (∼10–4 Pa), allowing the formation of the film-spanning perpendicular cylinders and lamellae upon thermal annealing. In contrast to perpendicular lamellae, a long-range lateral order for forming perpendicular cylinders can be efficiently achieved through the self-alignment mechanism for induced ordering from the top and bottom of the free-standing thin film