Block Copolymer Films Research Articles

Metal Oxide Heterostructure Array via Spatially Controlled-Growth within Block Copolymer Templates.

Nanofabrication is continuously searching for new methodologies to fabricate 3D nanostructures with 3D control over their chemical composition. A new approach for heterostructure nanorod array fabrication through spatially controlled-growth of multiple metal oxides within block copolymer (BCP) templates is presented. Selective growth of metal oxides within the cylindrical polymer domains of polystyrene-block-poly methyl methacrylate is performed using sequential infiltration synthesis (SIS). Tuning the diffusion of trimethyl aluminum and diethyl zinc organometallic precursors in the BCP film directs the growth of AlOx and ZnO to different locations within the cylindrical BCP domains, in a single SIS process. BCP removal yields an AlOx -ZnO heterostructure nanorods array, as corroborated by 3D characterization with scanning transmission electron microscopy (STEM) tomography and a combination of STEM and energy-dispersive X-ray spectroscopy tomography. The strategy presented here will open up new routes for complex 3D nanostructure fabrication.

Hierarchically Porous Copolymer Film as Immobilization Matrix for Phenol Biosensor with High Sensitivity

A hierarchically porous structure of the matrix for immobilization of bioactive molecules is of crucial importance in improving the performance of electrochemical biosensors. In the present work, a block copolymer film was prepared via spinodal-decomposition-induced macro- and mesophase separation plus extraction by rinsing (SIM2PLE). The film exhibited an interconnected porous structure including macropores and mesopores. Thus, the specific surface area of the film was greatly enhanced, which was a benefit to the subsequent immobilization of enzyme. Then the resultant porous block copolymer film was adopted to construct a high-performance electrochemical biosensor to detect phenolic compounds. The as-developed phenolic biosensor exhibited a high sensitivity (3.0 × 103 mA·M–1·cm–2), quick response (<5 s), and extremely low detection limit (7 nM at an S/N ratio of 3). Moreover,a decent linear range (0.02–35 μM) was also observed. This work demonstrates that the hierarchically porous film based on copolymer...

Defect Annihilation in the Directed Self-Assembly of Block Copolymers in Films with Increasing Thickness

We investigate directed self-assembly (DSA), with 3× density multiplication, of symmetric polystyrene-block-poly(methyl methacrylate) (L0 = 28 nm) with increasing film thicknesses and reveal a thickness limit above which the defect annihilation mechanism is different than in thinner films. Block copolymer films of increasing thickness underwent DSA on a macroscopic chemical pattern under optimum geometrical and chemical conditions. Scanning electron microscopy and grazing-incidence small-angle X-ray scattering (GISAXS) were used to characterize the long-range ordering and buried structures as a function of film thickness and thermal annealing time. Rotational GISAXS measurements revealed a critical thickness of ∼3L0, below which defect annihilation is cooperative across the film depth and above which it is faster at the free surface than in the film’s interior. In the latter case, defects can persist in the film’s interior despite perfect assembly and registration at the free surface of the film.

Conformal 3D Nanopatterning by Block Copolymer Lithography with Vapor-Phase Deposited Neutral Adlayer.

Block copolymer (BCP) lithography is an effective nanopatterning methodology exploiting nanoscale self-assembled periodic patterns in BCP thin films. This approach has a critical limitation for nonplanar substrate geometry arising from the reflow and modification of BCP films upon the thermal or solvent annealing process, which is inevitable to induce the mobility of BCP chains for the self-assembly process. Herein, reflow-free, 3D BCP nanopatterning is demonstrated by introducing a conformally grown adlayer by the initiated chemical vapor deposition (iCVD) process. A highly cross-linked poly(divinylbenzene) layer was deposited directly onto the BCP thin film surface by iCVD, which effectively prevented the reflow of BCP thin film during an annealing process. BCP nanopatterns could be stabilized on various substrate geometry, including a nonplanar deformed polymer substrate, a pyramid shape substrate, and a graphene fiber surface. A fiber-type hydrogen evolution reaction (HER) catalyst is suggested by stabilizing lamellar Pt nanopatterns on severely rough graphene fiber surfaces.

Review—Recent Advances in Block-Copolymer Nanostructured Subwavelength Antireflective Surfaces

Nanostructured Anti-Reflective (AR) surfaces have attracted a focused attention during the last few years and offer an alternative to AR coatings. Recent nanopatterning approaches have allowed fabrication of bioinspired nanostructured surfaces with unprecedented broadband and omnidirectional AR properties. However, nanofabrication methods face major challenges for reaching industrial maturity including high capital expenditure cost, scalability, reliability and adaptability of the technologies. Block copolymer (BCP) films provide one way to overcome some of these limitations by offering scalable and versatile masks to fabricate well-defined, uniform and tunable nanostructures on a variety of substrates at a modest price. This article aims at highlighting recent efforts for assembling such AR nanostructured surfaces with BCP films and the challenges yet to tackle prior to commercialization of the technology.

Tin oxide nanostructure fabrication via sequential infiltration synthesis in block copolymer thin films

Tin oxide (SnO2) nanostructures are attractive for sensing, catalysis, and optoelectronic applications. Here we investigate the fabrication of SnOx nanostructures through sequential infiltration synthesis (SIS) in block copolymer (BCP) film templates. While the growth of metal and metal oxides within polymers and BCP films via SIS has been demonstrated until now using small precursors such as trimethyl aluminum and diethyl zinc, we hypothesize that SIS can be performed using larger precursors and demonstrate SnOx SIS with tetrakis(dimethylamino)tin (TDMASn) and hydrogen peroxide. Tuning the SIS reaction and BCP chemistry resulted in highly ordered, polystyrene-block-poly(2-vinyl pyridine) (P2VP)-templated porous SnOx - AlOx and SnOx nanostructures. Detailed investigation using in-situ microbalance, high resolution electron microscopy, elemental analysis and infra-red spectroscopy shows that SnOx can directly grow within P2VP homopolymer and BCP films. Simultaneously with the growth, SnOx SIS process also contributes to the polymer etch. Performing SnOx SIS with pretreatment of a single AlOx SIS cycle increases the SnOx growth and protects the BCP template from etching. This is the first report of SnOx SIS opening a pathway for additional tetrakis-based organometallic precursors to be utilized in growth processes within polymers.

Controlled Spacing between Nanopatterned Regions in Block Copolymer Films Obtained by Utilizing Substrate Topography for Local Film Thickness Differentiation.

Various types of devices require hierarchically nanopatterned substrates, where the spacing between patterned domains is controlled. Ultraconfined films exhibit extreme morphological sensitivity to slight variations in film thickness when the substrate is highly selective toward one of the blocks. Here, it is shown that using the substrate's topography as a thickness differentiating tool enables the creation of domains with different surface patterns in a fully controlled fashion from a single, unblended block copolymer. This approach is applicable to block copolymers of different compositions and to different topographical patterns and thus opens numerous possibilities for the hierarchical construction of multifunctional devices.

Temperature-Controlled Solvent Vapor Annealing of Thin Block Copolymer Films.

Solvent vapor annealing is as an effective and versatile alternative to thermal annealing to equilibrate and control the assembly of polymer chains in thin films. Here, we present scientific and practical aspects of the solvent vapor annealing method, including the discussion of such factors as non-equilibrium conformational states and chain dynamics in thin films in the presence of solvent. Homopolymer and block copolymer films have been used in model studies to evaluate the robustness and the reproducibility of the solvent vapor processing, as well as to assess polymer-solvent interactions under confinement. Advantages of utilizing a well-controlled solvent vapor environment, including practically interesting regimes of weakly saturated vapor leading to poorly swollen states, are discussed. Special focus is given to dual temperature control over the set-up instrumentation and to the potential of solvo-thermal annealing. The evaluated insights into annealing dynamics derived from the studies on block copolymer films can be applied to improve the processing of thin films of crystalline and conjugated polymers as well as polymer composite in confined geometries.

In Situ Visualization of Solvent Swelling Dynamics in Block Copolymer Films with Atomic Force Microscopy

Atomic force microscopy (AFM) imaging was used to study the in situ swelling of terraced poly(styrene-block-methyl methacrylate) (PS-b-PMMA) thin films under cyclohexane, a selective solvent for PS...

Pre-nucleation induced fast ordering in block-copolymer films with dynamic zone annealing

Pre-nucleation induced fast ordering in block-copolymer films with dynamic zone annealing

Universal perpendicular orientation of block copolymer microdomains using a filtered plasma

Sub-10 nm patterns prepared by directed self-assembly (DSA) of block copolymer (BCP) thin films offer a breakthrough method to overcome the limitations of photolithography. Perpendicular orientation of the BCP nanostructures is essential for lithographic applications, but dissimilar surface/interfacial energies of two blocks generally favour parallel orientations, so that the perpendicular orientation could only be obtained under very limited conditions. Here, we introduce a generalized method for creating perpendicular orientations by filtered plasma treatment of the BCP films. By cross-linking the surface of disordered BCP films using only physical collisions of neutral species without ion bombardment or UV irradiation, neutral layers consistent with the BCP volume fraction are produced that promote the perpendicular orientations. This method works with BCPs of various types, volume fractions, and molecular weights individually at the top and bottom interfaces, so it was applied to orientation-controlled 3D multilayer structures and DSA processes for sub-10 nm line-spacing patterns.

Liquid Metal Covered with Thermoplastic Conductive Composites for High Electrical Stability and Negligible Electromechanical Coupling at Large Strains.

Stretchable electrode is an essential part of soft electronic devices. Practical stretchable electrodes must meet the following requirements: metallic conductivity and no resistance change in various situations such as repeated large deformation, toxic environment, and large temperature change. This study suggests a simple electrode design that meets all of these requirements simultaneously. The electrode consists of a liquid metal (LM) mesh pattern that is sandwiched between a thermoplastic block copolymer (BCP) film and a BCP/Ag flake composite film with a microfibril network structure on its surface. The electrode has a high conductivity (1.2 × 104 S/cm) and is stretchable up to 600% uniaxial strain (ε). Its resistance remains unchanged during repeated stretching cycles at ε = 300% (ΔR < 0.04 Ω) as well as under simultaneous situation of large deformation (ε = 400%) and large temperature change (20-70 °C). The electrode is anticorrosive in an acidic solution owing to the hydrophobic BCP layer that protects the LM from being etched. This study shows the connection of two separate electrodes and complete healing of scratched electrodes by finger pressing. In addition, it demonstrates the fabrication of superstretchable electroluminescence display as an example of potential uses of the electrode.

Well‐defined structures and nanoscale morphology for all‐conjugated BCPs

A series of conjugated donor–acceptor (D–A) block copolymers (BCPs) were synthesised using a one-pot Stille coupling polycondensation reaction. This involved reaction between a series of mono-bromo-functionalised Poly3-hexylthiophene (P3HT) polymers (P3HT-Br, Mn: 17, 21 and 43 kg/mol) and [N, N ′-bis (2-decyl-tetradecyl)-1,7-dibromo-3,4,9,10-perylene diimide (PBI) and [2,5-bis(trimethylstannyl)-thiophene] (T) monomers. Purification using preparative gel permeation chromatography (GPC) removed any excess P3HT and resulted in BCPs with low polydispersity index values. The P3HT-b-PBIT BCPs were characterised using 1 H-NMR and Fourier-transform infrared spectroscopy. When compared to a P3HT/PBIT polymer blend, the D–A BCP films exhibited a remarkably fine structure with a nanoscale morphology. These results indicated that these D–A BCPs have the potential for use as nanostructured active layers in polymer solar cells.

Facile synthesis of three-dimensional Au/C networks by directly carbonizing nanoporous block copolymers

Porous carbonaceous networks decorated with functional nanoparticles are highly demanded in diverse applications as their good conductivity nature as well as cheap source offers a cost-affordable alternative among numerous options. In this work, we report a new and facile strategy to prepare three-dimensional (3D) Au/C networks comprised of carbonaceous skeletons and tiny gold nanoparticles by directly carbonizing the nanoporous block copolymer films complexed with the gold salts. The robust complexation makes it ease of generating numerous dispersed gold nanoparticles with an average diameter as small as ≈15 nm confined in the carbonaceous frameworks after carbonization. Thus-developed Au/C networks are highly expected to find widespread applications such as catalysis, sensing, etc.

Path to Move Beyond the Resolution Limit with Directed Self-Assembly.

Directed self-assembly (DSA) of block copolymers (BCPs) has long been viewed as a powerful alternative to extend the resolution of optical lithography. For full-area patterning applications, despite significant progress, the two most prominent DSA methods (chemoepitaxy and graphoepitaxy) are facing a scalability challenge: the critical dimension (CD) of the guiding patterns will need to be continuously scaled down to closely match the dimension of the BCP microdomain, a task that not only contravenes some of the resolution gains achieved by density multiplication but that will also become particularly difficult below 10 nm. To avoid this conundrum, we propose here a synergistic integration of graphoepitaxy and chemoepitaxy through self-registered self-assembly (SRSA) to enable the simultaneous realization of feature density multiplication and CD shrinkage resolution gains. We report nearly perfect DSA on prepatterns with highdensity multiplication factors and CD of several multiples of the BCP microdomain size. A prepattern consisting of alternating stripes of a relatively thicker neutral mat and a thinner neutral brush with preferential wetting sidewalls serves as a topographic pattern to guide an ultrathin BCP blend film inside the trenches. As the oriented BCP pattern assembles, the blend film deploys a layer of chemical markers on the bottom surface through SRSA generating 1:1 chemical contrast patterns inside the trenches. After thorough removal of the blend film, the newly formed self-registered chemical patterns interpolated by the remaining neutral mat strips serve as the guiding patterns for a second chemoepitaxial DSA step to achieve full-area, defect-free DSA of thick BCP films.

Influence of the molecular weight in P3HT block on fully conjugated block copolymers

All-conjugated donor-acceptor block copolymers (BCP) were synthesized in a one-pot reaction by a Stille coupling polycondensation through a terminal functional polymer copolymerization process. Mono bromo end-functionalized P3HT samples with various molecular weights (P3HT-Br, Mn: 5, 9, and 26 kg/mol) were copolymerized with AA (N,Nʹ-Bis(2-decyl-1-tetradecyl)-2,6-dibromonaphthalene-1,4,5,8-tetracarboxylic acid bisimide, NDI) and BB (5,5′-bis(trimethylstannyl)-2,2′-bithiophene) type monomers. Further purification by preparative GPC removed excess P3HT to yield block copolymers of low polydispersities with different donor and acceptor block chain lengths. The block copolymers were characterized by 1H-NMR and UV–vis absorption and FTIR spectroscopy. The optical properties, film morphologies, and optoelectronic properties of the block copolymer were strongly influenced by the donor and acceptor block chain lengths. Furthermore, the fully conjugated D-A block copolymer films exhibited fine structures, smooth film morphologies, and better OPV performance than those features of P3HT/PNDIT2 polymer blends. In polymer solar cells based on the various block copolymer as active layers, the device power convention efficiency was improved by maintaining the acceptor block content at 40–50 kg/mol and increasing the P3HT chain from 5 to 26 kg/mol.

Enzymatic degradation of fluorinated Poly(ε-caprolactone) (PCL) block copolymer films with improved hydrophobicity

Fluorinated Poly(ε-caprolactone) (PCL) block copolymers PCL-PTFOA(2 h), PCL-PTFOA(4 h), PCL-PTFOA(6 h), PCL-PTFOA(8 h) were prepared via esterification by using poly(1H,1H,2H,2H-perfluorooctylacrylate) (PTFOA) with different molecular weights as reactants. It was found that PCL-PTFOA(6 h) and PCL-PTFOA(8 h) possessed the similar molecular weight via GPC analysis. PCL and fluorinated PCL block copolymers films were prepared by solution casting method. The structure and properties of film surface of the fluorinated PCL block copolymers were analyzed by energy dispersive X-ray spectrometer (EDS), scanning electron microscope (SEM), Differential scanning calorimetry (DSC), water contact angles (WCAs) and the surface free energy. The results showed that the fluorinated PCL films possessed improved hydrophobicity because of the microphase separation between fluoropolymer chain and PCL chain. The enzymatic degradation of PCL, PCL-PTFOA(2 h), PCL-PTFOA(4 h) and PCL-PTFOA(6 h) films were performed at 37 °C in a phosphate buffer solution (PBS, 0.1 M, with a pH of 7.2–7.4) with lipase and analyzed by weight loss, SEM and EDS. It was found that the introduction of fluorine-containing segment reduced the rate of enzymatic degradation of the copolymer film in the early period, while increased the finally weight loss rate with a prolonged time. In addition, the enzymatic degradation rate of PCL-PTFOA(2 h) film and PCL-PTFOA(4 h) film was faster than that of PCL-PTFOA(6 h) film.

Cyclodextrin-functionalized asymmetric block copolymer films as high-capacity reservoir for drug delivery

Asymmetric block copolymer membranes can be facilely prepared via non-solvent induced phase separation combined with self-assembly. The membrane is characterized by a thin layer of highly ordered and uniform cylindrical nano-channels on top of a non-ordered macroporous sponge-like layer. Up to date, most studies concerning block copolymer membranes are focused on separation applications. In this work, highly adsorptive and adhesive isoporous block copolymer membranes have been fabricated. Because of the functionalization with cyclodextrin, the membrane shows excellent affinity to guest molecules. Moreover, the membrane is biocompatible and is adhesive to various substrates (e.g. glass, silicon, gold and stainless steel). Triclosan as a model drug was utilized to demonstrate the applicability of the membranes as a drug reservoir. A high loading capacity (305.5 μg cm−2) was achieved. The release behavior was investigated under various pH values in vitro. A long-time extended drug release was achieved without showing an initial burst effect. Furthermore, pH-responsive release behavior was observed. The triclosan-loaded membrane exhibited a significant antibacterial effect due to the triclosan release; the diffusion out of the membrane was evaluated using a disc diffusion assay. This study provides great potential for isoporous block copolymer membranes as a delivery platform for a wide variety of biomedical applications.

Polyimide‐PEG Segmented Block Copolymer Membranes with High Proton Conductivity by Improving Bicontinuous Nanostructure of Ionic Liquid‐Doped Films

AbstractThe structure and properties of segmented block copolymer films of aromatic polyimide (PI) and poly(ethylene glycol) (PEG) doped with an ionic liquid are studied for potential polymer electrolyte membrane applications for fuel cells. Poly(amic acid) precursors of PI‐PEG copolymers of 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride, 4,4′‐(1,3‐phenylenedioxy) dianiline, and bis(3‐aminopropyl) terminated PEG (Mn≈ 1500) are synthesized and then thermally imidized in membrane films, followed by swelling in ethylammonium nitrate (EAN) ionic liquid. The small‐angle X‐ray scattering results from the EAN‐doped PI‐PEG copolymer films show disordered bicontinuous phase‐separated nanostructures described by Teubner–Strey theory, with the interface fractal dimension determined from the Porod equation. Thermal annealing of the EAN‐doped membranes at 100–140 °C results in increased correlation lengths and smoother interfaces of the bicontinuous nanostructures. Such improved nanostructures lead to the increased ionic conductivity by two to five times with the maximum conductivity of 210 mS cm−1at 60 °C and 70% RH, much greater (nearly fivefold) than that of Nafion films, while maintaining the mechanical stability possibly up to 140 °C. Moreover, the investigation of the disordered bicontinuous phase‐separated nanostructure of EAN‐doped PI‐PEG copolymer membranes is highly relevant to understanding the nanostructures of hydrated Nafion membranes and segmented block copolymers in general.

Mechanical and Thermal Properties of Styrene-diene Block Copolymers Films Obtained by Spin Casting from Different Solvents

This paper presents the solvents effect on the mechanical and thermal properties of films of styrene-butadiene and styrene-isoprene block copolymers with the majority diene phase, obtained by spin casting.