Self‐assembly of Protein Nanoarrays on Block Copolymer Templates

There is considerable interest in developing functional protein arrays on the nanoscale for high‐throughput protein‐based array technology, and for the study of biomolecular and cell interactions at the physical scale of the biomolecules. To these ends, self‐assembly based techniques may be desirable for the nanopatterning of proteins on large sample areas without the use of lithography equipment. We present a fast, general approach for patterning proteins (and potentially other biomolecules) on the nanoscale, which takes advantage of the ability of block copolymers to self‐assemble into ordered surface nanopatterns with defined chemical heterogeneity. We demonstrate nanoarrays of immunoglobulin and bovine serum albumin on polystyrene‐block‐poly(methyl methacrylate) templates, and illustrate the applicability of our technique through immunoassays and DNA sensing performed on the protein nanoarrays. Furthermore, we show that the pattern formation mechanism is a nanoscale effect originating from a combination of fluid flow forces and geometric restrictions templated by an underlying nanopattern with a difference in protein adsorption behavior on adjacent, chemically distinct surfaces. This understanding may provide a framework for extending the patterning approach to other proteins and material systems.     

Reinforcement of Shear Thinning Protein Hydrogels by Responsive Block Copolymer Self‐Assembly

Shear thinning hydrogels are promising materials that exhibit rapid self‐healing following the cessation of shear, making them attractive for applications including injectable biomaterials. Here, self‐assembly is demonstrated as a strategy to introduce a reinforcing network within shear thinning artificially engineered protein gels, enabling a responsive transition from an injectable state at low temperatures with a low yield stress to a stiffened state at physiological temperatures with resistance to shear thinning, higher toughness, and reduced erosion rates and creep compliance. Protein‐polymer triblock copolymers capable of the responsive self‐assembly of two orthogonal networks are synthesized. Midblock association forms a shear‐thinning network, while endblock aggregation at elevated temperatures introduces a second, independent physical network into the protein hydrogel. These reversible crosslinks introduce extremely long relaxation times and lead to a five‐fold increase in the elastic modulus, significantly larger than is expected from transient network theory. Thermoresponsive reinforcement reduces the high temperature creep compliance by over four orders of magnitude, decreases the erosion rate by at least a factor of five, and increases the yield stress by up to a factor of seven. Combined with the demonstrated potential of shear thinning artificial protein hydrogels for various uses, this reinforcement mechanism broadens the range of applications that can be addressed with shear‐thinning physical gels.     

Wafer‐Level Self‐Organized Copolymer Templates for Nanolithography with Sub‐50 nm Feature and Spatial Resolutions

Robust lithographic templates, with sub‐50 nm feature and spatial resolutions, that exhibit high patterning integrity across a full‐wafer are demonstrated using self‐organized copolymer reverse micelles on 100 mm Si wafers. A variation of less than 5% in the feature size and periodicity of polymeric templates across the entire wafer is achieved simply by controlling the spin‐coating process. Lithographic pattern transfer using these templates yields Si nanopillar arrays spanning the entire wafer surface and exhibiting high uniformity inherited from the original templates. The variation in geometric characteristics of the pillar arrays across the full‐wafer surface is validated to be less than 5% using reflectance spectroscopy. The physical basis of the change in reflectance with respect to sub‐10 nm variations in geometric parameters of pillar arrays is shown by theoretical modelling and simulations. Successful fabrication of highly durable TiO₂ masks for nanolithography with sub‐50 nm feature width and spatial resolutions is achieved through highly controlled vapour phase processing of reverse micelle templates. This allows lithographic pattern‐transfer of organic templates with a feature thickness and separation of less than 10 nm, which is otherwise not possible through other approaches reported in literature.     

Block Copolymer Packing Limits and Interfacial Reconfigurability in the Assembly of Periodic Mesoporous Organosilicas

Here poly(N,N‐dimethylacrylamide)‐block‐poly(styrene) block copolymer micelles (BCPs) are advanced and applied to assemble periodic mesoporous organosilicas (PMOs) with noncylindrical pores. Using these BCP micelles, it is found that pore dimensions (11–23 nm), wall thicknesses (5–9 nm), and overall porosities (26%–78%) are independently programable, depending only on relative inputs for BCP and matrix former. Notably, the degree of order in all films improves as BCP loading approaches a packing limit of 63 vol%. Beyond this limit and regardless of pore dimensions, both porogen packing in the film and pore structure after thermal processing show significant deviations away from spherical close‐packed lattices. The surprising absence of film collapse in this regime allows here to quantify the evolution of pore structure through the thermally driven interfacial reconfigurability of BCP micelles in the hybrid films when porogen loading exceeds the packing limit by using both scattering techniques and scanning transmission electron microscopy tomography. Finally, the PMOs here give dielectric constants of 1.2 and 1.5 above and below the BCP packing limit, respectively—the lowest ever reported for this matrix material.     

Hierarchical Directed Self‐Assembly of Diblock Copolymers for Modified Pattern Symmetry

Block copolymer lithography exploiting diblock copolymer thin films is promising for scalable manufacture of device‐oriented nanostructures. Nonetheless, its intrinsic limitation in the degree of freedom for pattern symmetry within hexagonal dot or parallel line array greatly diminishes the potential application fields. Here, we report multi‐level hierarchical self‐assembled nanopatterning of diblock copolymers for modified pattern symmetry. Sequential hierarchical integration of two layers of diblock copolymer films with judiciously chosen molecular weights and chemical composition creates nanopatterned morphology with modified pattern symmetry, including sparse linear cylinder or lamellar arrays. Internal structure of the hierarchically patterned morphology is characterized by grazing‐incidence small‐angle X‐ray scattering throughout the film thickness. Pattern transfer of the modified nanopattern generates linear metal nanodot array with uniform size and regular spacing as a typical example of functional nanopatterned structures.     

Site‐Specific Placement of Au Nanoparticles on Chemical Nanopatterns Prepared by Molecular Transfer Printing Using Block‐Copolymer Films

Inexpensive, large area patterning of ex‐situ synthesized metallic nanoparticles (NPs) at the nanoscale may enable many technologies including plasmonics, nanowire growth, and catalysis. Here, site‐specific localization of Au NPs onto nanoscale chemical patterns of polymer brushes is investigated. In this approach, patterns of hydroxyl‐terminated poly(styrene) brushes are transferred from poly(styrene‐block‐methyl methacrylate) (PS‐b‐PMMA) block copolymer films onto a replica substrate via molecular transfer printing, and the remaining areas are filled with hydroxyl‐terminated poly(2‐vinyl pyridine) (P2VP‐OH) brushes. Citrate‐stabilized Au NPs (13 nm) selectively bind to P2VP‐OH functionalized regions and the quality of the resulting assemblies depends on high chemical contrast in the patterned brushes. Minimization of the interpenetration of P2VP‐OH chains into PS brushes during processing is the key for achieving high chemical contrast. Large area hexagonal arrays of single Au NPs with a placement accuracy of 3.4 nm were obtained on patterns (～20 nm spots, ～40 nm pitch) derived from self‐assembled cylinder‐forming PS‐b‐PMMA films. Linear arrays of Au NPs were generated on patterns (40 nm lines, 80nm pitch) derived from lamellae‐forming PS‐b‐PMMA that had been directed to assemble on lithographically defined masters.     

Directed Self‐Assembly as a Route to Ferromagnetic and Superparamagnetic Nanoparticle Arrays

Block co‐polymer patterns are attractive candidates for nanoparticle assemblies. Directed self‐assembly of block co‐polymers in particular allows for long range ordering of the patterns, making them interesting scaffolds for the organization of magnetic particles. Here, a method to tune the channel width of polymer‐derived trenches via atomic layer deposition (ALD) of alumina is reported. The alumnia coating provides a much more thermally robust pattern that is stable up to 250 °C. Using these patterns, magnetic coupling in both ferromagnetic and superparamagnetic nanocrystal chains is achieved.     

Topological Effects on Globular Protein‐ELP Fusion Block Copolymer Self‐Assembly

Perfectly defined, monodisperse fusion protein block copolymers of a thermoresponsive coil‐like protein, ELP, and a globular protein, mCherry, are demonstrated to act as fully biosynthetic analogues to protein‐polymer conjugates that can self‐assemble into biofunctional nanostructures such as hexagonal and lamellar phases in concentrated solutions. The phase behavior of two mCherry‐ELP fusions, E₁₀‐mCherry‐E₁₀ and E₂₀‐mCherry, is investigated to compare linear and bola fusion self‐assembly both in diluted and concentrated aqueous solution. In dilute solution, the molecular topology impacts the stability of micelles formed above the thermal transition temperature of the ELP block, with the diblock forming micelles and the bola forming unstable aggregates. Despite the chemical similarity of the two protein blocks, the materials order into block copolymer‐like nanostructures across a wide range of concentrations at 30 wt% and above, with the bola fusion having a lower order‐disorder transition concentration than the diblock fusion. The topology of the molecule has a large impact on the type of nanostructure formed, with the two fusions forming phases in the opposite order as a function of temperature and concentration. This new system provides a rich landscape to explore the capabilities of fusion architecture to control supramolecular assemblies for bioactive materials.     

Hierarchical Structuring in Block Copolymer Nanocomposites through Two Phase‐Separation Processes Operating on Different Time Scales

Tailoring the size and surface chemistry of nanoparticles allows one to control their position in a block copolymer, but this is usually limited to one‐dimensional distribution across domains. Here, the hierarchical assembly of poly(ethylene oxide)‐stabilized gold nanoparticles (Au‐PEO) into hexagonally packed clusters inside mesostructured ultrathin films of polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) is described. A close examination of the structural evolution at different nanoparticle filling fractions and PEO ligand molecular weights suggests that the mechanism leading to this structure‐within‐structure is the existence of two phase separation processes operating on different time scales. The length of the PEO ligand is shown to influence not only the interparticle distances but also the phase separation processes. These conclusions are supported by novel mesoscopic simulations, which provide additional insight into the kinetic and thermodynamic factors that are responsible for this behavior.     

Nano Spray‐Dried Block Copolymer Nanoparticles and Their Transformation into Hybrid and Inorganic Nanoparticles

A novel combination of block copolymer (BCP) nano spray‐drying (NSD), solvent annealing, and selective metal oxide growth is utilized to create functional polymer nanoparticles, polymer‐metal‐oxide hybrid nanoparticles, and templated metal oxide nanoparticles with tunable composition, internal morphology, and porosity. NSD of BCPs from chloroform and toluene solutions results in porous and nonporous nanoparticles, respectively, with various degrees of phase separation. Further tuning of the nanoparticle internal morphology is performed by solvent annealing the spray‐dried particles with judicious choice of the nonsolvent dispersion medium and the surfactant, yielding assembly of both blocks at the surface of the nanoparticles. Finally, ZnO and Al₂O₃ are grown inside the polar blocks of phase‐ordered nanoparticles using a sequential infiltration synthesis method, in a post‐assembly process, resulting in hybrid BCP‐ZnO particles and BCP‐templated Al₂O₃ nanoparticles, as demonstrated by scanning transmission electron microscopy tomography. These structure engineering methods open new ways to direct and template functional nanoparticles.     

Highly Oriented Nanofibrils of Regioregular Poly(3‐hexylthiophene) Formed via Block Copolymer Self‐Assembly in Liquid Crystals

A novel method making use of block copolymer self‐assembly in nematic liquid crystals (LCs) is described for preparing macroscopically oriented nanofibrils of π‐conjugated semiconducting polymers. Upon cooling, a diblock copolymer composed of regioregular poly(3‐hexylthiophene) (P3HT) and a liquid crystalline polymer (LCP) in a block‐selective LC solvent can self‐assemble into oriented nanofibrils exhibiting highly anisotropic absorption and polarized photoluminescence emission. An unusual feature of the nanofibrils is that P3HT chains are oriented along the fibrils' long axis. This general method makes it possible to use LCs as an anisotropic medium to grow oriented nanofibrils of many semiconducting polymers insoluble in LCs.     

Spontaneous Lamellar Alignment in Thickness‐Modulated Block Copolymer Films

Here, spontaneous lamellar alignment in a thickness‐modulated block copolymer film is presented as a facile, scalable, and general approach for creating a highly aligned lamellar morphology. Thickness‐modulated block copolymer films are prepared on neutral surfaces by various methods, such as solution dropping, dewetting‐induced self‐organized patterning, and thermal imprinting. Regardless of the film preparation method, the self‐assembled lamellar domains become spontaneously aligned along the thickness gradient after sufficient thermal annealing. Real‐time AFM imaging reveals that spontaneous alignment occurs through the directional growth of well‐ordered domains along the thickness gradient, which is accompanied by defect dynamics, with vertical linear defects moving from thicker parts of the film towards the thinner ones, reducing their length and thus the associated energy. The mechanism underlying this interesting self‐aligning behavior is provided by a ‘geometric anchoring’ phenomenon, originally envisioned to account for the liquid crystal alignment under a non‐flat geometry of confinement. This novel self‐aligning principle offers a valuable opportunity to control nanoscale alignment in block copolymer films by manipulating the, much larger, microscale morphology.     

Self‐Assembly and Metallization of Resorcinarene Microtubes in Water

Amphiphilic resorcinarene‐based multiwalled microtubes, millimetres in diameter and centimetres in length, are generated in water. The thickness of the tube wall approaches 300 nm. Their self‐assembly properties are investigated using transmission electron microscopy, scanning electron microscopy, atomic‐force microscopy, dynamic light scattering, X‐ray diffraction, UV‐vis spectra, and Fourier transform IR techniques. From these studies, the structures critical for the self‐assembly of resorcinarene into microtubes in aqueous media are determined. Furthermore, the study manifests a feasible method that aims to completely change the structure from a microtube to a sheet‐like morphology by selectively eliminating key groups. Subsequently, resorcinarene‐capped water‐soluble gold nanoparticles (AuNPs) are fabricated. By utilizing the obtained microtubes as a template, a gold/organic microtubular composite is successfully prepared.     

Highly Photoluminescent and Environmentally Stable Perovskite Nanocrystals Templated in Thin Self‐Assembled Block Copolymer Films

Ordered nanostructured crystals of thin organic–inorganic metal halide perovskites (OIHPs) are of great interest to researchers because of the dimensional‐dependence of their photoelectronic properties for developing OIHPs with novel properties. Top‐down routes such as nanoimprinting and electron beam lithography are extensively used for nanopatterning OIHPs, while bottom‐up approaches are seldom used. Herein, developed is a simple and robust route, involving the controlled crystallization of the OIHPs templated with a self‐assembled block copolymer (BCP), for fabricating nanopatterned OIHP films with various shapes and nanodomain sizes. When the precursor solution consisting of methylammonium lead halide (MAPbX₃, X = Br^?, I^?) perovskite and poly(styrene)‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) is spin‐coated on the substrate, a nanostructured BCP is developed by microphase separation. Spontaneous crystallization of the precursor ions preferentially coordinated with the P2VP domains yields ordered nanocrystals with various nanostructures (cylinders, lamellae, and cylindrical mesh) with controlled domain size (≈40–72 nm). The nanopatterned OIHPs show significantly enhanced photoluminescence (PL) with high resistance to both humidity and heat due to geometrically confining OIHPs in and passivation with the P2VP chains. The self‐assembled OIHP films with high PL performance provide a facile control of color coordinates by color conversion layers in blue‐emitting devices for cool‐white emission.     

Eliminating the Trade‐Off between the Throughput and Pattern Quality of Sub‐15 nm Directed Self‐Assembly via Warm Solvent Annealing

The directed self‐assembly (DSA) of block copolymers (BCPs) has been suggested as a promising nanofabrication solution. However, further improvements of both the pattern quality and manufacturability remain as critical challenges. Although the use of BCPs with a high Flory‐Huggins interaction parameter (χ) has been suggested as a potential solution, this practical self‐assembly route has yet to be developed due to their extremely slow self‐assembly kinetics. In this study, it is reported that warm solvent annealing (WSA) in a controlled environment can markedly improve both the self‐assembly kinetics and pattern quality. A means of avoiding the undesirable trade‐off between the quality and formation throughput of the self‐assembled patterns, which is a dilemma which arises when using the conventional solvent vapor treatment, is suggested. As a demonstration, the formation of well‐defined 13‐nm‐wide self‐assembled patterns (3σ line edge roughness of ≈2.50 nm) in treatment times of 0.5 min (for 360‐nm‐wide templates) is shown. Self‐consistent field theory (SCFT) simulation results are provided to elucidate the mechanism of the pattern quality improvement realized by WSA.     

Tunable Mechanoresponsive Self‐Assembly of an Amide‐Linked Dyad with Dual Sensitivity of Photochromism and Mechanochromism

Photo‐ and mechanoluminescent materials that exhibit tunable emission properties when subjected to external stimuli have a wide variety of applications. However, most mechanoresponsive materials have a mechano‐induced structural transition from crystalline to amorphous phase, and there are only few reports on the crystalline to crystalline transformation. This study reports an amide‐linked dyad P1 containing spiropyran and naphthalimide chromophores with dual sensitivity of photochromism and mechanochromism. Under light and mechanical stimuli, P1 performs different color transition. With mechanical force, the morphologies of P1 change from microfiber to nanosphere and the amide group in P1 plays a vital role in these transition processes. Mechanical force can induce the morphology change of P1 through enhancing π–π stacking and destroying hydrogen bonds. These results demonstrate the feasibility of the design strategy for new mechanoresponsive switching materials: both π?π stacking and hydrogen bonding of the dyad contribute the mechano‐induced crystalline/crystalline transformation.     

Linking Group Influences Charge Separation and Recombination in All‐Conjugated Block Copolymer Photovoltaics

All‐conjugated block copolymers bring together hole‐ and electron‐conductive polymers and can be used as the active layer of solution‐processed photovoltaic devices, but it remains unclear how molecular structure, morphology, and electronic properties influence performance. Here, the role of the chemical linker is investigated through analysis of two donor–linker–acceptor block copolymers that differ in the chemistry of the linking group. Device studies show that power conversion efficiencies differ by a factor of 40 between the two polymers, and ultrafast transient absorption measurements reveal charge separation only in block copolymers that contain a wide bandgap monomer at the donor–acceptor interface. Optical measurements reveal the formation of a low‐energy excited state when donor and acceptor blocks are directly linked without this wide bandgap monomer. For both samples studied, it is found that the rate of charge recombination in these systems is faster than in poly­mer–polymer and polymer–fullerene blends. This work demonstrates that the linking group chemistry influences charge separation in all‐conjugated block copolymer systems, and further improvement of photovoltaic performance may be possible through optimization of the linking group. These results also suggest that all‐conjugated block copolymers can be used as model systems for the donor–acceptor interface in bulk heterojunction blends.     

Self‐Assembled SERS Substrates with Tunable Surface Plasmon Resonances

The fabrication of surface‐enhanced Raman spectroscopy (SERS) substrates that are optimized for use with specific laser wavelength–analyte combinations is addressed. In order to achieve large signal enhancement, temporal stability, and reproducibility over large substrate areas at low cost, only self‐assembly and templating processes are employed. The resulting substrates consist of arrays of gold nanospheres with controlled diameter and spacing, properties that dictate the optical response of the structure. Tunability of the extended surface plasmon resonance is observed in the range of 520–1000 nm. It is demonstrated that the enhancement factor is maximized when the surface plasmon resonance is red‐shifted with respect to the SERS instrument laser line. Despite relying on self‐organization, site‐to‐site enhancement factor variations smaller than 10% are obtained.