Multilayer polymer thin films for fabrication of ordered multifunctional polymer nanocomposites

Quantitative analysis of biomolecule release from polystyrene-block-polyethylene oxide thin films

Block copolymers have garnered recent attention due to their ability to contain molecular cargo within nanoscale domains and release said cargo in aqueous environments. However, the release kinetics of cargo from these thin-films has not yet been reported. Knowledge of the release quantities and release profiles of these systems is paramount for applications of these systems. Here, Polystyrene-block-poly(ethylene oxide) (PS-b-PEO) was co-assembled with fluorescein isothiocyanate isomer I-lysozyme (FITC-LZ) and fluorescein isothiocyanate isomer I-TAT (FITC-TAT), such that these molecular cargos arrange within the PEO domains of the thin films. We show that high loading ratios of cargo/PS-b-PEO do not significantly impact the nanostructure of the films; however, a loading limit appears to be present with aggregates of protein forming at the microscale with higher loading ratios. The presence of lysozyme (LZ) within the films was confirmed qualitatively after aqueous exposure through photo-induced force microscopy (PiFM) imaging at the Amide I characteristic peak (∼1650 cm^-1). Furthermore, we demonstrate that LZ maintains activity and structure after exposure to the polymer solvent (benzene/methanol/water mix). Finally, we demonstrate quantitatively 20-80 ng cm^-2 of cargo is released from these films, depending on the cargo incorporated. We show that the larger molecule lysozyme is released over a longer time than the smaller TAT peptide. Finally, we demonstrate the ability to tune the quantity of cargo released by altering the thickness of the PS-b-PEO thin-films during fabrication.

Efficient Moisture-Induced Energy Harvesting from Water-Soluble Conjugated Block Copolymer-Functionalized Reduced Graphene Oxide

This Research Article demonstrates a very simple approach of a moisture-induced power-generating phenomenon using water-soluble rod-coil conjugated block copolymer (poly(3-hexythiophene)-block-poly(4-styrenesulfonic acid) (P3HT-b-PSSA)-modified reduced graphene oxide. The block copolymer-modified reduced graphene oxide (BCP-RGO) was prepared by noncovalent surface functionalization cum in situ reduction of graphene oxide. A simple device made from BCP-RGO can generate voltage upon exposure to water vapor or under different humidity conditions. The open-circuit voltage generated from the diode-like device varies with respect to the relative humidity, and the device can act as a self-powered humidity sensor. The as-prepared BCP-RGO is able to produce a maximum power density of 1.15 μW/cm² (short-circuit current density J _SC = 6.40 μA/cm²) at a relative humidity of 94%. Meanwhile, the BCP-RGO device produces a very high power density of 0.7 mW/cm² (at a short-circuit current density of 1.06 mA/cm²) after 91% water absorption. We believe that the material presented here will be very useful for a self-biased humidity sensor and moisture-induced energy harvesting. The diode-like response of the BCP-RGO device with humidity or after water absorption will make the material applicable for self-biased humidity-controlled electronic switching.

Metal-Immobilized Micellar Aggregates of a Block Copolymer from a Mixed Solvent for a SERS-Active Sensing Substrate and Versatile Dip Catalysis

Here, we have reported micellar aggregations of an amphiphilic block copolymer in mixed solvent and their subsequent use as a template for the fabrication of a very dense, tunable metal nanoparticle-decorated surface for SERS and flexible dip catalysis applications. A silver nanoparticle-immobilized layer on silicon substrates shows excellent SERS (surface-enhanced Raman scattering)-based sensing performance for model analyte rhodamine B up to 10^-6 M concentration with a well-defined calibration curve. Furthermore, a facile approach to the preparation of metal NP-immobilized BCP membranes as efficient dip catalyst for two model reactions (the reduction of nitrophenol and the Suzuki-Miyaura reaction of iodobenzene or 2,7-diiodofluorene with phenyl boronic acid) is also demonstrated. The Ag NP-decorated film exhibits high efficiency and extensive reusability in a prototype reaction such as the reduction of nitrophenol by sodium borohydride with a very high turnover number, >126 (for a single use), whereas the Pd NP-immobilized film also has a high, ∼100%, reaction yield and extensive reusability and applicable for different aromatic systems. This work provides a new platform for the design and synthesis of a functionalizable, flexible, and highly mechanically stable dip catalyst which is highly demanded in the catalytic production of value-added chemicals and environmental applications such as wastewater treatment.

Core@Corona Functional Nanoparticle-Driven Rod-Coil Diblock Copolymer Self-Assembly

Herein, a novel strategy to overcome the influence of π-π stacking on the rod-coil copolymer organization is reported. A diblock copolymer poly(3-hexylthiophene)-block-poly(ethylene glycol methyl ether methacrylate) (P3HT-b-PEGMA) was synthesized by the Huisgen cycloaddition, so-called "click chemistry", combining the PEGMA and P3HT blocks synthesized by atom transfer radical polymerization and Kumada catalyst transfer polymerization, respectively. Using a dip-coating process, we controlled the original film organization of the diblock copolymer by the crystallization of the P3HT block via π-π stacking. The morphology of the P3HT-b-PEGMA films was influenced by the incorporation of gold nanoparticles (GNPs) coated by poly(ethylene glycol) ligands. Indeed, the crystalline structuration of the P3HT sequence was counterbalanced by the addition in the film of gold nanoparticles finely localized within the copolymer PEGMA matrix. Transmission electron microscopy and time-of-flight secondary ion mass spectrometry analysis validated the GNP homogeneous localization into the compatible PEGMA phase. Differential scanning calorimetry showed the rod block crystallization disruption. A morphological transition of the self-assembly is observed by atomic force microscopy from P3HT fibrils into out-of-plane cylinders driven by the nanophase segregation.

Luminescent films for chemo- and biosensing

Luminescent films have received great interest for chemo-/bio-sensing applications due to their distinct advantages over solution-based probes, such as good stability and portability, tunable shape and size, non-invasion, real-time detection, extensive suitability in gas/vapor sensing, and recycling. On the other hand, they can achieve selective and sensitive detection of chemical/biological species using special luminophores with a recognition moiety or the assembly of common luminophores and functional materials. Nowadays, the extensively used assembly techniques include drop-casting/spin-coating, Langmuir-Blodgett (LB), self-assembled monolayers (SAMs), layer-by-layer (LBL), and electrospinning. Therefore, this review summarizes the recent advances in luminescent films with these assembly techniques and their applications in chemo-/bio-sensing. We mainly focused on the discussion of the relationship between the sensing properties of the films and their architecture. Furthermore, we discussed some critical challenges existing in this field and possible solutions that have been or are being developed to overcome these challenges.

Micropore extrusion-induced alignment transition from perpendicular to parallel of cylindrical domains in block copolymers

The orientation transition from perpendicular to parallel alignment of PEO cylindrical domains of PEO-b-PMA(Az) films has been demonstrated by extruding the block copolymer (BCP) solutions through a micropore of a plastic gastight syringe. The parallelized orientation of PEO domains induced by this micropore extrusion can be recovered to perpendicular alignment via ultrasonication of the extruded BCP solutions and subsequent annealing. A plausible mechanism is proposed in this study. The BCP films can be used as templates to prepare nanowire arrays with controlled layers, which has enormous potential application in the field of integrated circuits.

Amphiphilic and Thermoresponsive Conjugated Block Copolymer with Its Solvent Dependent Optical and Photoluminescence Properties: Toward Sensing Applications

Herein, we present a new class of amphiphilic, thermoresponsive rod-coil conjugated block copolymer having regioregular poly(3-hexyl thiophene) and poly(N-isopropylacrylamide). Optical and luminescence properties of theses polymers significantly depend on the self-assembled nanostructures formed in different solvent and are easily tailored by chnaging the solvent composition or external stimuli like heat. Unique optical and electronic properties of this block copolymer are believed to make it promising for applications like sensor, fluorescence thermometer, optoelectronic, and bioelectronics devices.

Mixed-morphology and mixed-orientation block copolymer bilayers

Three-dimensional block copolymer structures with long-range order and mixed symmetries.