Self-assembly Of Diblock Copolymers Research Articles

Fabrication of Stable Liquid-like Wetting Buckled Surfaces as Bioinspired Antibiofouling Coatings by Using Silicon-Containing Block Copolymers.

Inspired by animals with a slippery epidermis, durable slippery antibiofouling coatings with liquid-like wetting buckled surfaces are successfully constructed in this study by combining dynamic-interfacial-release-induced buckling with self-assembled silicon-containing diblock copolymer (diBCP). The core diBCP material is polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS). Because silicon-containing polymers with intrinsic characters of low surface energy, they easily flow over and cover a surface after it has undergone controlled thermal treatment, generating a slippery wetting layer on which can eliminate polar interactions with biomolecules. Additionally, microbuckled patterns result in curved surfaces, which offer fewer points at which organisms can attach to the surface. Different from traditional slippery liquid-infused porous surfaces, the proposed liquid-like PDMS wetting layer, chemically bonded with PS, is stable and slippery but does not flow away. PS-b-PDMS diBCPs with various PDMS volume fractions are studied to compare the influence of PDMS segment length on antibiofouling performance. The surface characteristics of the diBCPs─ease of processing, transparency, and antibiofouling, anti-icing, and self-cleaning abilities─are examined under various conditions. Being able to fabricate ecofriendly silicon-based lubricant layers without needing to use fluorinated compounds and costly material precursors is an advantage in industrial practice.

Shell with Striped, Helical, and Bipolar Lamellae Structures from Soft Confinement-Induced Self-Assembly of AB Diblock Copolymers on a Nanocylinder.

The soft confinement-induced self-assembly of AB diblock copolymers on a nanocylinder is studied via a simulated annealing method. The formation of multiple copolymer shells was predicted by varying the interfacial interaction, the size of confinement, and the height and diameter of the nanocylinder. The competition between solvent repulsion and nanocylinder attraction determined the degree of encapsulation of the copolymer shell. The formation of a helical copolymer shell was induced by the maximization of conformational entropy. The preferential distribution position of copolymers on anisotropic nanocylinder surfaces was induced by interfacial energy minimization. Our study contributes to the understanding of the formation mechanism of the helical structure in block copolymer aggregates and the fabrication of copolymer shells with predesigned morphologies.

Block Copolymer Self-assembly: Exploitation of Hydrogen Bonding for Nanoparticle Morphology Control via Incorporation of Triazine Based Comonomers by RAFT Polymerization.

Synthesis of polymeric nanoparticles of controlled non-spherical morphology is of profound interest for a wide variety of potential applications. Self-assembly of amphiphilic diblock copolymers is an attractive bottom-up approach to prepare such nanoparticles. In the present work, RAFT polymerization is employed to synthesize a variety of poly(N,N-dimethylacrylamide)-b-poly[butyl acrylate-stat-GCB] copolymers, where GCB represents vinyl monomer containing triazine based Janus guanine-cytosine nucleobase motifs featuring multiple hydrogen bonding arrays. Hydrogen bonding between the hydrophobic blocks exert significant influence on the morphology of the resulting nanoparticles self-assembled in water. The Janus feature of the GCB moieties makes it possible to use a single polymer type in self-assembly, unlike previous work exploiting, e.g., thymine-containing polymer and adenine-containing polymer. Moreover, the strength of the hydrogen bonding interactions enables use of a low molar fraction of GCB units, thereby rendering it possible to use the present approach for copolymers based on common vinyl monomers for the development of advanced nanomaterials.

Easy Synthetic Access to High-Melting Sulfurated Copolymers and their Self-Assembling Diblock Copolymers from Phenylisothiocyanate and Oxetane.

Although sulfurated polymers promise unique properties, their controlled synthesis, particularly when it comes to complex and functional architectures, remains challenging. Here, we show that the copolymerization of oxetane and phenyl isothiocyanate selectively yields polythioimidocarbonates as a new class of sulfur containing polymers, with narrow molecular weight distributions (Mn=5-80 kg/mol with Đ≤1.2; Mn,max=124 kg/mol) and high melting points of up to 181 °C. The method tolerates different substituent patterns on both the oxetane and the isothiocyanate. Self-nucleation experiments reveal that π-stacking of phenyl substituents, the presence of unsubstituted polymer backbones, and the kinetically controlled linkage selectivity are key factors in maximising melting points. The increased tolerance to macro-chain transfer agents and the controlled propagation allows the synthesis of double crystalline and amphiphilic diblock copolymers, which can be assembled into micellar- and worm-like structures with amorphous cores in water. In contrast, crystallization driven self-assembly in ethanol gives cylindrical micelles or platelets.

Controlled node growth on the surface of polymersomes.

Incorporating nucleobases into synthetic polymers has proven to be a versatile method for controlling self-assembly. The formation of strong directional hydrogen bonds between complementary nucleobases provides a driving force that permits access to complex particle morphologies. Here, nucleobase pairing was used to direct the formation and lengthening of nodes on the outer surface of vesicles formed from polymers (polymersomes) functionalised with adenine in their membrane-forming domains. Insertion of a self-assembling short diblock copolymer containing thymine into the polymersome membranes caused an increase in steric crowding at the hydrophilic/hydrophobic interface, which was relieved by initial node formation and subsequent growth. Nano-objects were imaged by (cryo-)TEM, which permitted quantification of node coverage and length. The ability to control node growth on the surface of polymersomes provides a new platform to develop higher-order nanomaterials with tailorable properties.

PVA free-radical diblock copolymer for nanoencapsulation with enhanced biodegradability in the environment

The synthesis of readily biodegradable amphiphilic polyvinyl alcohol diblock copolymers (poly(VA-b-MDO)) was achieved through the combination of radical ring-opening polymerization (rROP) and reversible addition-fragmentation chain-transfer (RAFT)-living radical polymerization using 2-methylene-1,3-dioxepane (MDO) and vinyl acetate (VAc) monomers in three steps. The chemistry features solvent-free conditions (bulk polymerization) and subsequent deprotection of the acetyl group under mild conditions. With this optimized method, various lengths of poly(VA) and poly(MDO) in poly(VA-b-MDO) were synthesized by controlling the molecular weight distribution of both blocks. The self-assembly of diblock copolymers to nanoparticles with narrow size distribution and subsequent encapsulation of personal care and pharma active ingredients (e.g., curcumin and fenofibrate) and their controlled release were investigated. In vitro release experiments demonstrated that encapsulated nanoparticles release the actives at a slow and consistent rate compared to free actives. Stability experiments showed that the particle size distribution and purity of curcumin and fenofibrate remained unchanged after being exposed to light for ten months. More importantly, our environmental biodegradability studies revealed that the degradable poly(VA-b-MDO) (6b), consisting of 35 mol% poly(VA) and 65 mol% poly (MDO) blocks, achieves a biodegradability of 78% in 28 days. This is owing to the higher mole ratio of degradable polyester units in the polymer backbone as compared to poly(VA-b-MDO) (6c), which contains 64 mol% poly(VA) and 36 mol% poly(MDO) blocks (33% in 28 days). Our results provide insights into the potential applicability of these polymers in personal care and pharmaceutical products where biodegradability is a crucial factor. By developing a sustainable methodology from synthesis to application, our work helps to harness the potential of biodegradable diblock copolymers in the consumer care and medical fields.

Liquid-Like States in Micelle-Forming Diblock Copolymer Melts.

Large cell self-consistent field theory (SCFT) solutions for a neat, micelle-forming diblock copolymer melt, initialized using the structure of a Lennard-Jones fluid, reveal the existence of a vast number of liquid-like states, with free energies of order 10-3 kBT per chain higher than the body-centered cubic (bcc) state near the order-disorder transition (ODT). Computation of the structure factor for these liquids at temperatures below the ODT indicates that their intermicellar distance is slightly swollen compared to bcc. In addition to providing a mean-field picture of the disordered micellar state, the number of liquid-like states and their near-degeneracy with the equilibrium bcc morphology suggest that self-assembly of micelle-forming diblock copolymers navigates a rugged free energy landscape with many local minima. This picture provides a basis for the anomalously slow ordering kinetics of particle-forming diblock copolymer melts observed in experiments.

Controlling self-assembling co-polymer coatings of hydrophilic polysaccharide substrates via co-polymer block length ratio

HypothesisThe degree of polymerization of amphiphilic di-block co-polymers, which can be varied with ease in computer simulations, provides a means to control self-assembling di-block co-polymer coatings on hydrophilic substrates. SimulationsWe examine self-assembly of linear amphiphilic di-block co-polymers on hydrophilic surface via dissipative particle dynamics simulations. The system models a glucose based polysaccharide surface on which random co-polymers of styrene and n-butyl acrylate, as the hydrophobic block, and starch, as the hydrophilic block, forms a film. Such setups are common in e.g. hygiene, pharmaceutical, and paper product applications. FindingsVariation of the block length ratio (35 monomers in total) reveals that all examined compositions readily coat the substrate. However, strongly asymmetric block co-polymers with short hydrophobic segments are best in wetting the surface, whereas approximately symmetric composition leads to most stable films with highest internal order and well-defined internal stratification. At intermediate asymmetries, isolated hydrophobic domains form. We map the sensitivity and stability of the assembly response for a large variety of interaction parameters. The reported response persists for a wide polymer mixing interactions range, providing general means to tune surface coating films and their internal structure, including compartmentalization.

Self-Assembly of Charged Diblock Copolymers with Reduced Backbone Polarity

Charged block copolymers that can self-assemble into a host of nanostructures offer a great opportunity as next-generation battery electrolytes with outstanding ionic conductivity and mechanical robustness. The impact of ions on the self-assembly of charged block copolymers, however, remains to be fully understood. In this article, we report the phase behavior of charged-neutral block copolymers where a relatively nonpolar matrix was employed in the charged block to boost the strength of electrostatic interaction. The phase behavior was established using small-angle X-ray scattering (SAXS). We found that the overall shape of the phase boundary between ordered and disordered states is asymmetric, tilting toward the charged block-lean side of the phase portrait. However, the composition windows of the ordered phases, such as lamellae and hexagonally packed cylinders observed in this study, are comparable to those of neutral diblock copolymers and are not obviously affected by the incorporation of charges. The results obtained in this work provide insight into the impact of ions on the self-assembly of charged block copolymers as well as the design of nanostructured polymer electrolytes.

Chain Flexibility Effects on the Self-Assembly of Diblock Copolymer in Thin Films

Chain Flexibility Effects on the Self-Assembly of Diblock Copolymer in Thin Films

Self-Assembly of Gyroid-Forming Diblock Copolymers under Spherical Confinement

The self-assembly of gyroid-forming diblock copolymers (diBCPs) confined in spherical cavities was systematically investigated by simulations and experiments. The Monte Carlo simulations were carried out on the single-site bond fluctuation model of two gyroid-forming diBCPs of different volume fractions using the simulated annealing method. The experimental study was performed on gyroid-forming poly(styrene)-b-poly(lactic acid) diBCPs confined in spherical cavities. The cavities were fabricated through the assembly of polystyrene colloids to form opal structures, followed by replacement to form inverse opal structures. The surface of the cavities was composed of hydrophobic polyurethane acrylate and hydrophilic SiO2, providing confining surfaces with a different preference for specific polymeric blocks. It was observed from both the experiments and simulation that, depending on the conditions of spherical confinement, a rich array of nanostructures was self-assembled from the gyroid-forming diBCPs. The morphological predictions of simulations are qualitatively consistent with the experimental observations. The self-assembled structures depend sensitively on the surface selectivity and the degree of confinement quantified by the ratio D/L0, where D and L0 are the spherical diameter and period of the equilibrium gyroid phase, respectively. The formed nanostructured self-supporting spheres have considerable potential for applications in drug release, catalysts, optoelectronic devices, filters, and other applications.

Diblock copolymer pattern protection by silver cluster reinforcement.

Pattern fabrication by self-assembly of diblock copolymers is of significant interest due to the simplicity in fabricating complex structures. In particular, polystyrene-block-poly-4-vinylpyridine (PS-b-P4VP) is a fascinating base material as it forms an ordered micellar structure on silicon surfaces. In this work, silver (Ag) is applied using direct current magnetron sputter deposition and high-power impulse magnetron sputter deposition on an ordered micellar PS-b-P4VP layer. The fabricated hybrid materials are structurally analyzed by field emission scanning electron microscopy, atomic force microscopy, and grazing incidence small angle X-ray scattering. When applying simple aqueous posttreatment, the pattern is stable and reinforced by Ag clusters, making micellar PS-b-P4VP ordered layers ideal candidates for lithography.

Morphological evolution of poly(glycerol monomethacrylate)-stat-glycine–phenylalanine–phenylalanine–methacrylamide-b-poly(2-hydroxypropylmethacrylate) (P(GMA-stat-(MAm-GFF))-b-PHPMA) block copolymer nano-objects via polymerization-induced self-assembly

Here we report a study on the reversible addition–fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA) of self-assembling peptide-containing diblock copolymers.

Catalytic assembly of symmetric diblock copolymers in a thin film: a dissipative particle dynamics simulation study.

Obtaining a thin block copolymer film with a perfect structure by self-assembly is difficult because the system is, in general, trapped in a metastable state. We used dissipative particle dynamics (DPD) to investigate the self-assembly of AB symmetric diblock copolymers in a thin film. We discovered that addition of a small molecule (molecule C) as the third composition could help the system evade the metastable state. Therefore, imperfect structures could be corrected, and ordered structures formed. Analogous to the performance of a catalyst in catalytic chemistry, molecule C could promote assembly into an ordered structure, but was less involved within the polymer phase. Moreover, simulation results showed that the content of molecule C and its repulsive interactions with blocks A and B were quite important for promoting assembly into ordered structures effectively.

Nanospheres with Patches Arranged in Polyhedrons from Self-Assembly of Solution-State Diblock Copolymers under Spherical Confinement

Self-assembly of sphere-forming solution-state amphiphilic diblock copolymers under spherical nanopore confinement is investigated using a simulated annealing technique. For two types of cases of different pore–surface/copolymer interactions, sequences of self-assembled patchy nanospheres are obtained, and phase diagrams are constructed. Self-assembled patchy nanospheres with 1–21 solvophobic domains are observed. The outermost solvophobic domains (patches) are packed into various polyhedrons when their number is larger than 3, where three Platonic solids of a regular tetrahedron, an octahedron, and an icosahedron and seven Johnson solids of J12, J13, J17, J50, J51, J86, and J87 are identified. In addition, another Johnson solid of J84 is identified in a structure with two categories of B-domains. These polyhedrons have all or most of their faces in a triangular shape, and hence, they are closer to spherical in shape, which may relieve the chain stretching. Nanospheres with 1, 4, 6, 9, and 12 numbers of patches occur in relatively large windows in the phase diagrams of both types of cases. In one of the two types of cases, all nanospheres with any number of 1–14 patches occur in the phase diagram, whereas in the other type of cases, nanospheres with 2, 3, 5, 11, and 13 numbers of patches are absent in the phase diagram. Furthermore, at a given pore size, the number of patches changes nonmonotonically or is unchanged with an increase in the strength of the pore–surface/copolymer interactions for one type or the other type of case, respectively. Quantitative calculations are performed to elucidate mechanisms of the window size in the phase diagrams of nanospheres with different numbers of patches and structure details. All the observed phase behaviors can be well-explained based on the structure frustration, the conclusion being that the systems tend to avoid forming polyhedral structures with uneven distribution of solvophobic domains, and the differences between the two types of cases. Our results may provide a fundamental understanding of the relationship among confinement conditions, solvent conditions, and self-assembled structures.

Phase Diagrams of Polymerization-Induced Self-Assembly Are Largely Determined by Polymer Recombination.

In the current work, atom transfer radical polymerization-induced self-assembly (ATRP PISA) phase diagrams were obtained by the means of dissipative particle dynamics simulations. A fast algorithm for determining the equilibrium morphology of block copolymer aggregates was developed. Our goal was to assess how the chemical nature of ATRP affects the self-assembly of diblock copolymers in the course of PISA. We discovered that the chain growth termination via recombination played a key role in determining the ATRP PISA phase diagrams. In particular, ATRP with turned off recombination yielded a PISA phase diagram very similar to that obtained for a simple ideal living polymerization process. However, an increase in the recombination probability led to a significant change of the phase diagram: the transition between cylindrical micelles and vesicles was strongly shifted, and a dependence of the aggregate morphology on the concentration was observed. We speculate that this effect occurred due to the simultaneous action of two factors: the triblock copolymer architecture of the terminated chains and the dispersity of the solvophobic blocks. We showed that these two factors affected the phase diagram weakly if they acted separately; however, their combination, which naturally occurs during ATRP, affected the ATRP PISA phase diagram strongly. We suggest that the recombination reaction is a key factor leading to the complexity of experimental PISA phase diagrams.

Highly Conductive Solid Polymer Electrolytes by para-Fluoro/Thiol Clicked Diblock Copolymer Self-Assembly: Paving the Way for Nanostructured Materials for Lithium-Ion Conductivity

Highly Conductive Solid Polymer Electrolytes by <i>para</i>-Fluoro/Thiol Clicked Diblock Copolymer Self-Assembly: Paving the Way for Nanostructured Materials for Lithium-Ion Conductivity

Thermally and Chemically Stable Isoporous Block Copolymer Membranes.

Ultrafiltration (UF) membranes, particularly membranes fabricated from self-assembled diblock copolymers, hold promise in wastewater treatment, dairy, and food industries. Membrane development goals involve combining a highly porous selective layer with a narrow pore size distribution with a mechanically stable supporting layer to achieve constant flux. To date, isoporous integral asymmetric membranes have been formed either as flat sheets or hollow fibers, and a surface-selective layer determines membrane separation performance. A unique isoporous membrane of the poly(4-vinylbenzocyclobutene)-b-poly(4-vinylpyridine) (PVBCB-b-P4VP) diblock copolymer with a substructure of almost homogeneous porosity throughout the body of the material (three-dimensional porosity) has been developed. Moreover, the matrix of the membrane (PVCB) enables it to undergo cross-linking, allowing the membrane to be thermally sterilized and applied in high-temperature UF applications.

Simulation of Solvent Evaporation from a Diblock Copolymer Film: Orientation of the Cylindrical Mesophase

Using particle-based Monte Carlo simulations and continuum modeling, we study the self-assembly of asymmetric diblock copolymers in the course of solvent evaporation. We examine the effects of evaporation rate and solvent selectivity on the structure formation, especially the alignment of the cylindrical domains of the minority block. The comparison of the two simulation techniques facilitates identifying general trends upon parameter variation, while their inherent differences help us to understand the role of single-chain dynamics, fluctuations, and additional model details. In both cases, the simulation models feature a liquid and a gas phase with an explicit surface, across which solvent evaporates. We propose a “layer evolution model” that links processing parameters to the final morphology via the time dependence of layers, in which characteristic microphases, for example, spherical or cylindrical, can form. The evolution of these layers varies with the processing conditions and determines the morphology. This allows us to discuss the interplay of various experimentally accessible parameters, which we support by respective simulations. Our results single out two main factors to ensure the formation of minority-block cylinders, perpendicular to the film surface: (i) Fast evaporation rates induce a steep gradient in the polymer-density profile; that is, the polymer density immediately beneath the gas–liquid surface rapidly exceeds the critical value for cylinder formation. This confines cylinder formation into a layer that is thinner than the actual cylinder diameter, forcing a perpendicular alignment. (ii) A certain selectivity of the gas phase for the matrix-forming, majority block is necessary to disrupt an otherwise entropically favored surface layer of the minority block that would lead to parallel cylinder alignment.

Formation of ultrathin scarf-like micelles, ultrathin disk-like micelles and spherical micelles by self-assembly of polyurethane diblock copolymers

Ultrathin scarf-like micelles, ultrathin disk-like micelles and spherical micelles were prepared by tailoring the pH values and the length of the core-forming blocks. • The pH-responsive group was located in the core-forming blocks. • Scarf-like micelles, disk-like micelles and spherical micelles are prepared. • Ultrathin scarf-like micelles, ultrathin disk-like micelles are proved to be composed of lamellar bilayer structures. • The synergistic effect of the core-forming block length and the pH variation was well discussed. Controlling the shape and size of the nanomicelles attracts great interest and is still challenging. Herein, we synthesized a kind of diblock copolymers with the hydrophilic block (poly (ethylene glycol) methyl ether, PEG) and the core-forming block composed alternately by hydrophobic segments, hydrogen-bonding carbamates and pH-responsive groups. The synergy effect of the pH variation and the core-forming block length on the morphologies of the assemblies was well studied. Ultrathin scarf-like micelles, ultrathin disk-like micelles and spherical micelles were obtained by tailoring the pH values and the lengths of the core-forming blocks. The ultrathin scarf-like micelles and ultrathin disk-like micelles were proved to be composed of a lamellar bimolecular layer of the block copolymers. This study will supply an effective method to fabricate well-defined nanostructures.