Copolymer Thin Films Research Articles

Synthesis of carboxylic acid-functionalized polymethacrylate-b-polystyrene as an Ag ion-loadable block copolymer thin film template

We report the synthesis of thiopropionic acid-functionalized polymethacrylate-b-polystyrene (PMATA-b-PS) as a template for patterning Ag nanoarrays. Reversible addition-fragmentation chain transfer (RAFT) polymerization of silyl-protected propagyl methacrylate followed by chain extension with styrene produced a block copolymer precursor. Deprotection of the trimethylsilyl group and subsequent thiol-yne reaction afforded the target, PMATA-b-PS. While the entire series of the precursor was in the disordered phase, microphase separated morphologies were identified from PMATA-b-PS, indicating an increased interaction parameter (χ) as a result of introducing the acid groups. As a preliminary result, we show that an Ag nanoparticle array can be fabricated by selectively associating Ag+ ions to the PMATA cylinders in the thin film of PMATA-b-PS and removing the organic polymer layer by oxygen plasma treatment.

Block copolymers as efficient cathode interlayer materials for organic solar cells

Emerging needs for the large-scale industrialization of organic solar cells require high performance cathode interlayers to facilitate the charge extraction from organic semiconductors. In addition to improving the efficiency, stability and processability issues are major challenges. Herein, we design block copolymers with well controlled chemical composition and molecular weight for cathode interlayer applications. The block copolymer coated cathodes display high optical transmittance and low work function. Conductivity studies reveal that the block copolymer thin film has abundant conductive channels and excellent longitudinal electron conductivity due to the interpenetrating networks formed by the polymer blocks. Applications of the cathode interlayers in organic solar cells provide higher power conversion efficiency and better stability compared to the most widely-applied ZnO counterparts. Furthermore, no post-treatment is needed which enables excellent processability of the block copolymer based cathode interlayer.

Nanoscratch-Directed Self-Assembly of Block Copolymer Thin Films

Directed self-assembly (DSA) of block copolymer (BCP) thin films is of particular interest in nanoscience and nanotechnology due to its superior ability to form various well-aligned nanopatterns. Herein, nanoscratch-DSA is introduced as a simple and scalable DSA strategy allowing highly aligned BCP nanopatterns over a large area. A gentle scratching on the target substrate with a commercial diamond lapping film can form uniaxially aligned nanoscratches. As applied in BCP thin films, the nanoscratch effectively guides the self-assembly of overlying BCPs and provides highly aligned nanopatterns along the direction of the nanoscratch. The nanoscratch-DSA is not material-specific, allowing more versatile nanofabrication for various functional nanomaterials. In addition, we demonstrate that the nanoscratch-DSA can be utilized as a direction-controllable and area-selective nanofabrication method.

Ultra-Fast Vertical Ordering of Lamellar Block Copolymer Films on Unmodified Substrates

To utilize the full potential of block copolymer (BCP) thin films for use in technological devices ranging from ion conduction membranes and transistors to nanowire array antennas, rapid self-assembly of lamellar block copolymers (l-BCPs) with vertically oriented lamellar domains on a variety of unmodified substrates is needed. l-BCPs have an inherently larger interfacial area for transport compared to their cylindrical counterpart. Our observations demonstrate that the as-cast weakly ordered vertically oriented state of l-BCP films of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) from the directional evaporation of select solvents act as “seed templates” for their ultra-fast evolution (≈30 s) into well-ordered vertically oriented nanostructures, using a thermal gradient-based cold zone annealing (CZA) technique. Vertical lamellae are obtained on unmodified substrates, Quartz and Kapton, and the kinetics of l-BCP ordering is much faster by CZA as compared to the isotropic oven annealing. The rapid ordering kinetics of vertical l-BCPs is tested and found applicable to different molecular masses and film thicknesses ranging from 20 nm to 480 nm, which ultimately flip over to their equilibrium parallel morphology at the upper limits of annealing times. This rapid ordering strategy for the vertical orientation of l-BCPs using roll-to-roll compatible CZA would be highly relevant for fundamental studies of interfacial transport as well as for industrial applications from membranes to nanowires.

Chain Conformation Control of Fluorene-Benzothiadiazole Copolymer Light-Emitting Diode Efficiency and Lifetime.

The β-phase, in which the intermonomer torsion angle of a fraction of chain segments approaches ∼180°, is an intriguing conformational microstructure of the widely studied light-emitting polymer poly(9,9-dioctylfluorene) (PFO). Its generation can in turn be used to significantly improve the performance of PFO emission-layer-based light-emitting diodes (LEDs). Here, we report the generation of β-phase chain segments in a copolymer, 90F8:10BT, containing 90% 9,9-dioctylfluorene (F8) and 10% 2,1,3-benzothiadiazole (BT) units and show that significant improvements in performance also ensue for LEDs with β-phase 90F8:10BT emission layers, generalizing the earlier PFO results. The β-phase was induced by both solvent vapor annealing and dipping copolymer thin films into a solvent/nonsolvent mixture. Subsequent absorption spectra show the characteristic fluorene β-phase peak at ∼435 nm, but luminescence spectra (∼530 nm peak) and quantum yields barely change, with the emission arising following efficient energy transfer to the lowest-lying excited states localized in the vicinity of the BT units. For ∼5% β-phase chain segment fraction relative to 0% β-phase, the LED luminance at 10 V increased by ∼25% to 5940 cd m-2, the maximum external quantum efficiency by ∼61 to 1.91%, and the operational stability from 64% luminance retention after 20 h of operation to 90%. Detailed studies addressing the underlying device physics identify a reduced hole injection barrier, higher hole mobility, correspondingly more balanced electron and hole charge transport, and decreased carrier trapping as the dominant factors. These results confirm the effectiveness of chain conformation control for fluorene-based homo- and copolymer device optimization.

Dispersity-Driven Stabilization of Coexisting Morphologies in Asymmetric Diblock Copolymer Thin Films

Despite decades of research, characterization of the effects of polymer chain dispersity on the structural properties of block copolymer thin films remains challenging. We present an integrated exp...

Combined experimental and theoretical study, characterization, and nonlinear optical properties of doped-poly (p-nitroaniline -co- o-aminophenol) thin films

Hydrochloric acid doped poly (p-nitroaniline -co- o-aminophenol) [PpNAoAP] is synthesized via oxidative polymerization method using ferric chloride as an initiator and PEG200 as a soft template. By using PVD technique, the resulting doped [PpNAoAP]TF thin film was fabricated by evaporation of a thin layer (thickness ≈ 200 ± 5 nm) on a freshly cleaved mica substrate at a low deposition rate. Different techniques including FT-IR, 1HNMR, XRD, and SEM were used to characterize the resulting copolymer thin film. CATSTEP and DMol3 techniques were used to optimize the samples using DFT program. The optical constant values for the resulted [PpNAoAP]TF films are measured and comparable with experimental and CATSTEP processes. The computed structure and optical properties resulted from CATSTEP method are in good agreement with the obtained experimental data. The combined experimental of thin films and computed theoretical data of isolated molecules of [PpNAoAP]TF produce a promising outcome to be a good candidate for optoelectronic devices and polymer-solar cell applications.

Vapor deposition of stable copolymer thin films in a batchiCVDreactor

AbstractThis study demonstrates the deposition of poly(ethylhexyl acrylate‐co‐ethylene glycol dimethacrylate) (P(EHA‐co‐EGDMA)) copolymer thin films in a batch type initiated chemical vapor deposition (iCVD) reactor. Crosslinked copolymers are desired for many applications because of their high stable properties. iCVD polymers derived by monomers bearing only one vinyl bond are usually linearly structured polymers and hence they are not durable, which is unfavorable for many real‐world applications. Robust crosslinked iCVD films can be produced with the help of crosslinkers. In a typical iCVD process, copolymer thin film is produced by constantly feeding monomer vapor and crosslinker into the reactor. The monomer/crosslinker ratio should be precisely controlled for fabrication of reproducible thin films. In order to eliminate problems caused by adjusting the flowrates of precursors, a closed‐batch type iCVD reactor was used for the first time in this study to produce copolymer thin films. The variation of precursors' partial pressures allowed control over the copolymer thin film structures. As compared with homopolymer, copolymers showed the better chemical and thermal stable properties. Almost 40% of the copolymer thin film remained on the substrate surface at an annealing temperature of 300°C, whereas the homopolymer film was completely removed at an annealing temperature of 280°C.

Formation, Stability, and Annihilation of the Stitched Morphology in Block Copolymer Thin Films

The directed self-assembly of block copolymer thin films offers promise for next-generation lithography, providing access to small feature dimensions for electronic devices. Defective assembly, whe...

Cyclic Water Storage Behavior of Doubly Thermoresponsive Poly(sulfobetaine)-Based Diblock Copolymer Thin Films

The cyclic swelling and collapse behavior of a doubly thermoresponsive diblock copolymer thin film, consisting of a zwitterionic poly(sulfobetaine), poly(N,N-dimethyl-N-(3-methacrylamidopropyl)-amm...

Electrodeposited Copolymer Films with Tunable Conductivity

Conducting copolymer films were prepared from pyrrole (Py) and 1,12-di-(1-pyrrolyl) dodecane (DiPy) in an attempt to prepare conducting films that can be used as sensitive material of chemiresistor gas sensors. Copolymer thin films were obtained by electrochemical oxidation in a lithium perchlorate/acetonitrile electrolyte with different feed ratios of comonomers. Increasing the portion of DiPy in the comonomer mixture resulted in the formation of thinner and less rough copolymer films and to a modification of their morphology from a granular structure to a clover-like structure. In addition, copolymer films with very different conductivities were obtained by varying the comonomers ratio. Indeed, the conductivity of the copolymer containing 91% of Py was 2 × 105 times higher than the conductivity of the polymer containing 91% of DiPy, indicating that it is possible to tune the conductivity of the film by varying the composition of the initial comonomer mixture.

Polystyrene-block-poly(ethylene oxide) Thin Films Fabricated from a Solvent Mixture for the Co-Assembly of Polymers and Proteins.

The co-assembly of peptides and proteins in poly(styrene-block-ethylene oxide) (PS-b-PEO) thin films has proven to be a promising method to fabricate polymer–biomolecule functional materials. Contrary to the covalent immobilization of biomolecules on surfaces, co-assembly presents the opportunity to arrange cargo within thin films, which can be released upon exposure to an aqueous environment. The use of a mixed solvent system ensures the solubilization of hydrophobic polymer as well as the solubilization and protection of the biomolecule cargo. However, to produce largely defect-free films of PS-b-PEO from a solvent mixture containing water is challenging due to the narrow range of solvent miscibility and polymer/protein solubility. This work explores the limits of using a benzene/methanol/water solvent mixture for the production of thin PS-b-PEO films and provides a template for the fabrication optimization of block copolymer thin films in different complex solvent systems. The film quality is analyzed using optical microscopy and atomic force microscopy and correlated to the solvent composition. By adjusting the solvent composition to 80/18.8/1.2 vol % benzene/methanol/water, it was possible to reliably fabricate thin films with less than 1% macroscopic defect surface coverage. Using the optimized solvent composition, we also demonstrate the fabrication of ordered PS-b-PEO films containing lysozyme. Furthermore, we show the release of lysozyme into aqueous media, which highlights the potential use of such films for drug delivery applications.

Synthesis of 3D Dendritic Gold Nanostructures Assisted by a Templated Growth Process: Application to the Detection of Traces of Molecules.

Complex architectures like 3D gold dendritic nanostructures were synthesized by an in situ templated growth method using a thin film of a block copolymer [polystyrene-b-poly(4-vinylpyridine)] deposited onto silicon substrates. The overall study has demonstrated the strong link between the morphology, size, and distribution of the structures and the synthetic physicochemical parameters, such as pH, reaction temperature, concentration, and nature of reactants. A nonequilibirum state of the medium has been required to create a fractal growth of the gold structures onto a prepatterned gold-seeded surface and has led to a better control of the structures' surface coverage rate. Those as-prepared nanodendrites have also exhibited high electrocatalytic activity toward a significant enhancement factor, as well as important sensitivity, thanks to tip effects. The electrochemical experiment results have demonstrated efficient adsorption and quantification of very low traces of specific molecules like glutathione or hexadecanethiol.

Synthesis and characterization of Poly (ortho-aminophenol-co-para-toluidine) and its application as semiconductor thin film

Hydrochloric acid doped poly (ortho-aminophenol–co-para-toluidine) as a conjugated semiconducting copolymer is synthesized in acidic medium via the oxidative polymerization method. The spin coating technique is applied to deposit with appropriate adhesion of doped copolymer thin film. The resulting doped poly (ortho-aminophenol–co-para-toluidine) (POAPT) thin film is characterized by the various techniques to explore its structural, morphological, and optical properties. Density-functional theory (DFT) calculations were implemented utilizing Cambridge Serial Total Energy Package (CASTEP) from Accelrys based on a plane-wave pseudopotential. The optical dispersion of poly (ortho-aminophenol–co-para-toluidine) thin film is expressed in the single oscillator terms of Wemple–Didomenico (WD) model. The parameters Eg is 2.02 eV, n and k (at 2.36 eV) are 1.73 and 3.27×10-8, respectively, n∞ is 1.633, λo is 172.65 nm and So is 2.126 nm-2. Based on the resulting data of optical analysis and conductivity the doped poly (ortho-aminophenol–co-para-toluidine) thin film was found to have promising applications in optoelectronic devices area.

Shearing with solvent vapor annealing on block copolymer thin films for templates with macroscopically aligned nanodomains

A template with macroscopically aligned nanopatterns can be an effective vehicle for arranging nanoscale particles or rods in a particular orientation to achieve their anisotropic properties. A room-temperature process is also desirable for nanoscale patterning of heat-sensitive functional molecules such as organic fluorophores. Here, large-area orientation of nanodomains of block copolymers is demonstrated by simultaneous shearing and solvent vapor annealing at room temperature. The shear-aligned nanodomains are applied to a chemical template for nanoscale patterning of green fluorescent molecules. In addition, the grooved nanochannels obtained from the macroscopically aligned nanodomains work as a physical template for guiding Au nanorods to end-to-end assemblies which exhibit the polarization-dependent plasmonic extinction.

Fabrication of Dual Nanopatterns by Spatial Control of Nanodomain Orientation of Block Copolymer Thin Films

Block copolymers (BCPs) with various types of nanodomains have potential application to next-generation nanolithography and storage media because of relatively low cost and time-saving process. To ...

Enabling future nanomanufacturing through block copolymer self-assembly: A review

• Introduction covers criteria of nanomanufacturing and concepts of block copolymers in thin film and solution state. • Next, state-of-the-art in block copolymer thin film and solution processing is described. • Overview of key contribution of block copolymers in energy, environmental, photonic, and biological applications. • Outlook for impact and influence of block copolymers in nanomanufacturing including areas such as catalysis, membranes, metasurfaces and drug delivery nanodevices. Self-assembly approaches, e.g. colloidal, emulsion and polymer phase separation, provide scientists with an exotic yet direct platform to access technologically desired nanostructures at competitive costs. In particular, soft nanomaterial systems such as block copolymer (BCP) materials present a powerful means to tailor templates and spatially controlled systems that are amenable to large scale manufacturing practices. BCP nanoarchitectures in bulk, solution and thin film form can act as structural motifs to template foreign materials and pave the way towards important applications across industry and society. While extensive literature and research efforts exist on electronic device uses using BCPs, we look at nascent applications outside the integrated circuit realm. Recent reports are discussed including for example; light-harvesting (energy – section 2), metasurfaces (photonics – section 3), nanofiltration membranes (environmental – section 4) and antibacterial activity (biological – section 5). We endeavour to illustrate the window of opportunity presented through BCP self-assembly for nanomanufacturing. We believe the highlights discussed will aid in directing new research initiatives and facilitate the large-scale integration of BCP materials with broad societal impact.

Bicyclic Topology Transforms Self-Assembled Nanostructures in Block Copolymer Thin Films.

Ongoing efforts in materials science have resulted in linear block copolymer systems that generate nanostructures via the phase separation of immiscible blocks; however, such systems are limited with regard to their domain miniaturization and lack of orientation control. We overcome these limitations through the bicyclic topological alteration of a block copolymer system. Grazing incidence X-ray scattering analysis of nanoscale polymer films revealed that bicyclic topologies achieve 51.3-72.8% reductions in domain spacing when compared against their linear analogue, which is more effective than the theoretical predictions for conventional cyclic topologies. Moreover, bicyclic topologies achieve unidirectional orientation and a morphological transformation between lamellar and cylindrical domains with high structural integrity. When the near-equivalent volume fraction between the blocks is considered, the formation of hexagonally packed cylindrical domains is particularly noteworthy. Bicyclic topological alteration is therefore a powerful strategy for developing advanced nanostructured materials for microelectronics, displays, and membranes.

Poly(2-vinylpyridine)-b-poly(fluorinated methacrylate) Block Copolymers Forming 5 nm Domains Containing Metallocene

Directed self-assembly (DSA) of thin films of a block copolymer (BCP) is a promising approach for sub-10 nm lithographic patterning. In this paper, a series of poly(2-vinylpyridine)-block-poly(pent...

Evident phase separation and surface segregation of hydrophobic moieties at the copolymer surface using atomic force microscopy and SFG spectroscopy

HypothesisCopolymers are developed to enhance the overall physical and chemical properties of polymers. The surface nature of a copolymer is relevant to creating efficient materials to improve adhesion and biocompatibility. We hypothesize that the improved adhesion, as a surface property, is due to phase separation, surface segregation, and the overall molecular organization of different polymer components at the copolymer surface. ExperimentsThe surface structure of a copolymer composed of 2-hydroxyethyl methacrylate (HEMA) monomer and 2-phenoxyethyl methacrylate (PhEMA) monomer was analyzed in comparison to the polyHEMA and polyPhEMA homopolymers using atomic force microscopy (AFM) and sum frequency generation (SFG) spectroscopy. FindingsThe contrast in the phase images was due to the variance in the hydrophobic level provided by the hydroxyl and phenoxy modified monomers in the copolymer. The distribution of the adhesion values, supporting the presence of hydrophobic moieties, across the polymer surface defined the surface segregation of these two components. SFG spectra of the copolymer thin film showed combined spectral features of both polyHEMA and polyPhEMA thin films at the polymer surface. The tilt angles of the alpha-methyl group of homopolymers using the polarization intensity ratio analysis and the polarization mapping method were estimated to be in the range from 48° to 66°.