Supramolecular Assembly of Poly(styrene)-b-poly(4-vinylpyridine) and 1-Pyrenebutyric Acid in Thin Film and Their Use for Nanofabrication

Isoporous Membranes by the Symmetric Triblock Copolymer: A Strategy to Improve the Mechanical Strength without Sharply Changing the Pore Size and Permselectivity

Isoporous membranes produced from diblock copolymers commonly display a poor mechanical property that shows many negative impacts on their separation application. It is theoretically predicted that dense films produced from symmetric triblock copolymers show much stronger mechanical properties than those of homologous diblock copolymers. However, to the best of our knowledge, symmetric triblock copolymers have rarely been fabricated into isoporous membranes before, and a full understanding of separation as well as mechanical properties of membranes prepared from triblock copolymers and homologous diblock copolymers has not been conducted, either. In this work, a cleavable symmetric triblock copolymer with polystyrene as the side block and poly(4-vinylpyridine) (P4VP) as the middle block was synthesized and designed by the RAFT polymerization using the symmetric chain transfer agent, which located at the center of polymer chains and could be removed to produce homologous diblock copolymers with half-length while having the same composition as that found in triblock copolymers. The self-assembly of these two copolymers in thin films and casting solutions was first investigated, observing that they displayed similar self-organized structures under these two conditions. When fabricated into isoporous membranes, they showed similar pore sizes (5-7% difference) and comparable rejection performance (∼10% difference). However, isoporous membranes produced from triblock copolymers showed significantly improved mechanical strength and higher toughness (2-10 times larger) as evidenced by the compacting resistance, strain-stress determination, and nanoindentation testing, suggesting the unique and novel structure-performance relationship in the isoporous membranes produced from symmetric triblock copolymers. The above finding will guide the way to fabricate mechanically robust isoporous membranes without notably changing the separation performance from rarely used symmetric triblock copolymers, which can be synthesized by the controlled polymerization as facilely as that found for diblock copolymers.

Enhanced Ordering of Block Copolymer Thin Films upon Addition of Magnetic Nanoparticles

The influence of magnetite nanoparticles coated with poly(acrylic acid) (Fe₃O₄@PAA NPs) on the organization of block copolymer thin films via a self-assembly process was investigated. Polystyrene-b-poly(4-vinylpyridine) films were obtained by the dip-coating method and thoroughly examined by X-ray reflectivity, transmission electron microscopy, atomic force microscopy, and grazing incidence small-angle scattering. Magnetic properties of the films were probed via superconducting quantum interference device (SQUID) magnetometry. It was demonstrated that due to the hydrogen bonding between P4VP and PAA, the Fe₃O₄@PAA NPs segregate selectively inside P4VP domains, enhancing the microphase separation process. This in turn, together with employing carefully optimized dip-coating parameters, results in the formation of hybrid thin films with highly ordered nanostructures. The addition of Fe₃O₄@PAA nanoparticles does not change the average interdomain spacing in the film lateral nanostructure. Moreover, it was shown that the nanoparticles can easily be removed to obtain well-ordered nanoporous templates.

Conductive Thin Films over Large Areas by Supramolecular Self-Assembly

We report a "one-step" method for preparing conductive thin films with cylindrical microdomains oriented normal to the surface over large areas using the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS₁₉-b-P4VP₅) and 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphine (HOTPP). HOTPP interacts with the P4VP block by hydrogen bonding between the hydroxyl group of HOTPP and pyridine ring of PS₁₉-b-P4VP₅, forming cylindrical P4VP(HOTPP) domains having an average diameter of ∼17 nm in a PS matrix. Dynamic light scattering, contact angle, and in situ grazing incidence small-angle X-ray scattering measurements show a morphological transition from spherical micelles in solution to cylindrical microdomains oriented normal to the substrate surface during the drying process. From the dependence of current on voltage, an average current of ∼4.0 nA is found to pass through a single microdomain, pointing to a promising route for organic semiconductor device applications.

Co-assembly of functionalized donor-acceptor molecules within block copolymer microdomains via the supramolecular assembly approach with an improved charge carrier mobility

Here, we demonstrate the three-component self-assembly of functionalized small molecules (donor and acceptor) and a polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer using the supramolecular approach. The introduction of functional groups on both the donor (1-pyrenebutyric acid, PBA) and acceptor (functionalized naphthalene diimide, FNDI) molecules can form stable charge-transfer (CT) complexes within the block copolymer domains and these supramolecules exhibited a charge carrier mobility of around 1.01 × 10^-4 cm² (V s)^-1. In this case, both the molecules can form H-bonding with P4VP chains, and as well as π-π stacking between the PBA and FNDI molecules is also possible within the block copolymer domains. These noncovalent interactions lead to the formation of stable hierarchical structures and CT complexes between PBA and FNDI, where bilayer donor-acceptor (D-A) stacks formed within the block copolymer microdomains. Overall, the organization of both functionalized donor and acceptor molecules within the block copolymer domain exhibits an enhanced charge carrier mobility, which is potentially useful in the fabrication of organic photovoltaic cells and organic light-emitting diodes.

Topochemical polymerization of hierarchically ordered diacetylene monomers within the block copolymer domains

Effect of annealing conditions on the hierarchical ordering of PCDA monomers within the block copolymer supramolecules and their subsequent topochemical polymerization.

Electrochemical and Electronic Properties of Transparent Coating from Highly Solution Processable Graphene Using Block Copolymer Supramolecular Assembly: Application toward Metal Ion Sensing and Resistive Switching Memory

Here, we have discussed the preparation of a highly solution processable graphene from a novel supramolecular assembly consisting of block copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and pyrenebutyric acid (PBA)-modified reduced graphene oxide (RGO). The PBA molecules anchored on the graphene surface form supramolecules with PS-b-P4VP through H-bonding between the carboxylic acid group of 1-pyrenebutyric acid and the pyridine ring of P4VP. The formation of a supramolecular assembly results in a highly stable solution of reduced graphene oxide in common organic solvents, such as 1,4-dioxane and chloroform. Highly transparent and mechanically stable thin films can be deposited from these supramolecular assemblies on a relatively smooth surface of different substrates such as silicon wafer, glass, indium tin oxide, and flexible polymer substrates like poly(ethylene terephthalate). The graphene surface modifier (PBA) can be selectively removed from the thin film of the hybrid material by simple dissolution, resulting in a porous structure. Hybrid thin films of around 50 nm thickness exhibit interesting electrochemical properties with an areal capacitance value of 17.73 μF/cm2 at a current density of 2.66 μA/cm2 and good electrochemical stability. The pendent P4VP chains present in the composite thin film were further exploited for electrochemical detection of metal ions. The electrical measurement of the thin film sandwich structure of the composite shows a bipolar resistive switching memory with hysteresis-like current-voltage characteristics and electrical bistability. The OFF state shows ohmic conduction at a lower voltage and trap-free space-charge-limited current (SCLC) conduction at high voltage, whereas the ON state conduction is controlled by ohmic at low bias voltage, trap-free SCLC at moderate voltage, and tarp-assisted SCLC at high voltage.

Self-assembly of an interacting binary blend of diblock copolymers in thin films: a potential route to porous materials with reactive nanochannel chemistry

Self-assembly of a binary mixture of poly(styrene)336-block-poly(4-vinyl pyridine)25 (PS336-b-P4VP25) and poly(ethylene glycol)113-block-poly(4-hydroxy styrene)25 (PEG113-b-P4HS25) is shown to give rise to a cylindrical morphology in thin films through pyridine/phenol-based hetero-complementary hydrogen bonding interactions between the P4VP and P4HS copolymer segments. Removal of the cylindrical phase (PEG-b-P4HS) allowed access to porous materials having a pore surface decorated with P4VP polymer blocks. These segments could be transformed into cationic polyelectrolytes through quaternization of the pyridine nitrogen atom. The resulting positively charged nanopore surface could recognize negatively charged gold nanoparticles through electrostatic interactions. This work, therefore, outlines the utility of the supramolecular AB/CD type of block copolymer towards preparation of ordered porous thin films carrying a chemically defined channel surface with a large number of reactive sites.

Complexation-tailored morphology of asymmetric block copolymer membranes

Hydrogen-bond formation between polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) and -OH/-COOH functionalized organic molecules was used to tune morphology of asymmetric nanoporous membranes prepared by simultaneous self-assembly and nonsolvent induced phase separation. The morphologies were characterized by field emmision scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Hydrogen bonds were confirmed by infrared (IR), and the results were correlated to rheology characterization. The OH-functionalized organic molecules direct the morphology into hexagonal order. COOH-functionalized molecules led to both lamellar and hexagonal structures. Micelle formation in solutions and their sizes were determined using dynamic light scattering (DLS) measurements and water fluxes of 600-3200 L/m(2)·h·bar were obtained. The pore size of the plain BCP membrane was smaller than with additives. The following series of additives led to pores with hexagonal order with increasing pore size: terephthalic acid (COOH-bifunctionalized) < rutin (OH-multifunctionalized) < 9-anthracenemethanol (OH-monofunctionalized) < 3,5-dihydroxybenzyl alcohol (OH-trifunctionalized).

Mesoporous block-copolymer nanospheres prepared by selective swelling

Block-copolymer (BCP) nanospheres with hierarchical inner structure are of great interest and importance due to their possible applications in nanotechnology and biomedical engineering. Mesoporous BCP nanospheres with multilayered inner channels are considered as potential drug-delivery systems and templates for multifunctional nanomaterials. Selective swelling is a facile pore-making strategy for BCP materials. Herein, the selective swelling-induced reconstruction of BCP nanospheres is reported. Two poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) samples with different compositions (PS(23600)-b-P2VP(10400) and PS(27700)-b-P2VP(4300)) are used as model systems. The swelling reconstruction of PS-b-P2VP in ethanol, 1-pyrenebutyric acid (PBA)/ethanol, or HCl/ethanol (pH = 2.61) is characterized by scanning electron microscopy and transmission electron microscopy. It is observed that the length of the swellable block in BCP is a critical factor in determining the behavior and nanostructures of mesoporous BCP nanospheres in selective swelling. Moreover, it is demonstrated that the addition of PBA modifies the swelling structure of PS(23600)-b-P2VP(10400) through the interaction between PBA and P2VP blocks, which results in BCP nanospheres with patterned pores of controllable size. The patterned pores can be reversibly closed by annealing the mesoporous BCP nanospheres in different selective solvents. The controllable and reversible open/closed reconstruction of BCP nanospheres can be used to enclose functional nanoparticles or drugs inside the nanospheres. These mesoporous BCP nanospheres are further decorated with gold nanoparticles by UV photoreduction. The enlarged decoration area in mesoporous BCP nanospheres will enhance their activity and sensitivity as a catalyst and electrochemical sensor.

Morphology, Thickness, and Composition Evolution in Supramolecular Block Copolymer Films over a Wide Range of Dip-Coating Rates

Dip-coating, an important industrial technique, has been underexploited for preparing block copolymer (BC) thin films, such that the knowledge regarding their general characteristics is limited. Here, we present an overview of the crucial factors that determine how BC film morphology evolves as a function of dip-coating rate (withdrawal speed) over a wide range, illustrated using THF solutions of a polystyrene-b-poly(4-vinyl pyridine) (PS-P4VP) diblock copolymer mixed with two small molecules, naphthol and naphthoic acid, which are hydrogen-bonders with P4VP. Key factors in determining the film morphology are the systematic variation in film thickness and, for supramolecular BCs, in film composition with dip-coating rate. The former shows a general V-shaped dependence, related to the so-called capillarity and draining regimes identified previously for dip-coated sol-gel films. The relative small molecule content in the films studied is shown to increase in the capillarity regime from low to that of the dip-coating solution and thereafter to remain constant. Together, these changes, in addition to solvent and other effects, determine the film morphology and its evolution with dip-coating rate.

Intelligent reversible nanoporous antireflection film by solvent-stimuli-responsive phase transformation of amphiphilic block copolymer

An erasure-reconstruction porous structure with reversible antireflection (AR) property at near-infrared region (NIR) was prepared for the first time based on solvent-stimuli-responsive phase transformation of polystyrene-block-poly(4-vinypyridine) (PS-b-P4VP). The inhomogeneous porous structure with a dense skin and porous underneath, which was obtained by the nonsolvent-induced phase separation of PS-b-P4VP film from micelle solution with mixed solvents (tetrahydrofuran and dimethylformamide), was used as starting porous film. Then, the film was annealed by PS-selective solvent to erase the nanopores because the PS block was swollen effectively by its selective solvent. Afterward, the nonporous film was immersed in linear aliphatic acid to reconstruct the nanoporous structure (loosely packed micelles) by the combination of the hydrogen bond interaction and the positively charge-induced repulsion between each chain. Thus, an intelligent reversible AR property in the NIR region between a high-transmittance porous state (∼99.0%) and a low-transmittance nonporous state (∼90.0%) was realized by alternate treatments of PS-selective solvent and linear aliphatic acids. This reversible erasure-reconstruction porous structure for switching between AR (98.0%) and non-AR (90.0%) properties could be recycled by at least four times.