Membranes from poly(aryl ether)‐based ionomers containing multiblock segments of randomly distributed nanoclusters of 18 sulfonic acid groups

Multiblock copolymers 1a (M_n = 31,500–47,400) of sulfonated poly(aryl ether)s were synthesized by polycondensation of 4,4′‐difluorobenzophenone (DFBP), bis(4‐hydroxyphenyl)sulfone (BHPS), and an hydroxy‐terminated sulfonated oligomer, which was synthesized from DFBP and 2,2′,3,3′,5,5′‐hexaphenyl‐4,4′‐dihydroxybiphenyl a . The copolymerization of trimeric monomer b with DFBP and BHPS gave a series of copolymers 1b (M_n = 26,200–45,900). The copolymers were then sulfonated with chlorosulfonic acid to give ionomers 3a with hydrophilic multiblock segments and ionomers 3b with segments containing clusters of 18 sulfonic acid groups. The proton exchange membranes cast from ionomers 3a and 3b were characterized with regard to thermal stability, water uptake, proton conductivity, and morphology. Transmission electron microscopy images of 3a‐1 and 3b‐1 revealed a phase separation similar to that of Nafion that may explain their higher proton conductivities compared with randomly sulfonated copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4762–4773, 2009     

Modeling the Interactions between Membranes and Inclusions: Designing Self‐Cleaning Films and Resealing Pores

The design of responsive membranes whose interactions with inclusions can be controlled through the application of an external stimulus is reviewed with the aim to establish guidelines for introducing functionality into the materials. For a photo‐reactive AB membrane, we find that a gradient in light intensity can be harnessed to clean the system of any C “impurities”, or target the delivery of C to specific locations. By modeling the interactions between a lipid bilayer and Janus nanoparticles, we design a synthetic membrane with stable pores that can be controllably opened and closed. This leads to design rules for creating nanoparticle‐bilayer assemblies where the pores open and the cargo is released only when local environmental conditions reach a critical value.

     

Synthesis and Evaluation of Novel Proton Exchange Membranes Containing the Semisquaric Acid Group

We focus our attention here on semisquaric acid, which is known to show high acidity, as a new proton dissociating group for proton exchange membranes (PEMs). The introduction of a squaric acid group into aromatic polymers was conducted by the reaction of lithiated aromatic polymers and diisopropoxy squarate, followed by treatment with hydrochloric acid. A resulting polyphenylsulfone membrane with the squaric acid group introduced (PPSf‐SQ, IEC = 4.1 meq·g⁻¹) showed proton conductivity of 1.0 × 10⁻¹ S·cm⁻¹ at 80 °C under 95% relative humidity, which indicates that the semisquaric acid has the potential to become an alternative proton‐conducting group for PEMs.

     

Nanoscopic Structure of a Metallo‐supramolecular Polyelectrolyte–Amphiphile Complex,Elucidated by X‐ray Scattering and Molecular Modeling

A combination of molecular modeling and X‐ray scattering was used to elucidate the structure of the metallosupramolecular polyelectrolyte–amphiphile complex (PAC) self‐assembled from Fe^II, 1,4‐bis(2,2′:6′,2″‐terpyridin‐4′‐yl)benzene, and dihexadecyl phosphate (DHP). An approximate structure of the semi‐ordered material was derived from the analysis of the X‐ray scattering data. The experimental data provided sufficient input for obtaining a useful starting configuration for molecular modeling. Various models of the supramolecular architecture are presented and discussed in terms of their total energies and scattering patterns. In an iterative approach each level of the structural hierarchy was refined until satisfactory agreement of calculated and experimental scattering patterns was reached. The remarkable sensitivity of the simulated scattering curves to even the smallest structural changes at all length scales restricts the arbitrariness of modeling. The final model of PAC consists of flat lamellae of alternating strata of interdigitated DHP monolayers and nematically ordered polyelectrolyte chains.     

Amphiphilic Nanoparticles Control the Growth and Stability of Lipid Bilayers with Open Edges

Molecular amphiphiles self‐assemble in polar media to form ordered structures such as micelles and vesicles essential to a broad range of industrial and biological processes. Some of these architectures such as bilayer sheets, helical ribbons, and hollow tubules are potentially useful but inherently unstable owing to the presence of open edges that expose the hydrophobic bilayer core. Here, we describe a strategy to stabilize open bilayer structures using amphiphilic nanoparticle surfactants that present mixtures of hydrophilic and hydrophobic ligands on their surface. We observe that these particles bind selectively to the open edge of bilayer membranes to stabilize otherwise transient amphiphile assemblies. We show how such particles can precisely control the size of lipid tubules, how they can inhibit the formation of undesirable assemblies such as gallstone precursors, and how they can stabilize free‐floating lipid microdiscs.     

Synthesis and properties of polyimide ionomers containing sulfoalkoxy and fluorenyl groups

A series of sulfopropylated and sulfobutylated polyimide copolymers containing fluorenyl groups, SPI‐4, were synthesized to investigate the effect of alkyl side chains on the properties (stability, mechanical strength, water uptake, and proton conductivity) of the polymimide electrolyte membranes. SPI‐4 showed much better hydrolytic stability (in 10% MeOH aq at 100 °C) than the main chain sulfonated polyimide, SPI‐1. Tough, flexible, and ductile membranes were obtained from these copolymers. At high relative humidity all the SPI‐4 membranes showed high mechanical properties (>34 MPa of the maximum stress) and proton conductivity (>0.1 Scm^?1). These properties are comparable to or even better than those of the perfluorosulfonic acid ionomer (Nafion 112). The new polyimide ionomers have proved to be a possible candidate as polymer electrolyte membrane for PEFCs and DMFCs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4439–4445, 2005     

Enhancing Gelation Ability of a Dendritic Gelator through Complexation with a Polyelectrolyte

Let's stick together : The gelation ability of a dendritic gelator has been enhanced by its complexation with a polyelectrolyte (see figure). This concept provides a route to construct novel functional or ordered materials by complexation of other low‐molecular‐mass functional species with polyelectrolytes.

     

Responsive Polyelectrolyte Multilayers Assembled at High Ionic Strength with an Unusual Collapse at Low Ionic Strength

Responsive polyelectrolyte multilayers (PEMs) of poly(diallyl dimethyl ammonium chloride) (PDADMAC) and poly(styrene sodium sulfonate) (PSS) with thicknesses between 350 and 400 nm for 11 deposited polyelectrolyte layers were fabricated assembling the polyelectrolytes at 3 M NaCl. When the 3 M NaCl bulk solution is replaced by water, the PEMs release water, approximately a 46% of the total mass, and experience a thickness reduction of more than 200 nm. Changes in thickness and water content are fully reversible. The film recovers its original thickness and water content when it is exposed again to a 3 M NaCl solution. A responsive polymer film is achieved with the capability of swelling at high ionic strength and collapsing in water with variations in thickness of hundred of nanometers.     

Role of the preparation procedure in the formation of spherical and monodisperse surfactant/polyelectrolyte complexes

Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed.     

Variable temperature 19F solid‐state NMR study of the effect of electrostatic interactions on thermally‐stimulated molecular motions in perfluorosulfonate ionomers

This study uses variable temperature ¹⁹F solid‐state nuclear magnetic resonance (SSNMR) spectroscopy to determine the influence of electrostatic interactions on the T₁, T_1ρ, and T₂ values of Nafion®. Because of a “homogenizing” of the T₁'s as a result of spin diffusion, it was not possible to resolve from the T₁ experiments the relative motions of the side‐ and main‐chain. The initial increase in T_1ρ as a function of increasing temperature has been attributed to backbone rotations that increase with increasing temperature. The maxima observed in the T_1ρ plots suggest a change in the dominant relaxation mechanism at that temperature. The similarity in relaxation behavior of the side‐ and main‐chains suggests that the motions are dynamically coupled, because of the fact that the side‐chain is directly attached to the main‐chain. Two T_1ρ values were observed for the main‐chain at high temperatures, which has been attributed to a thermally activated ion‐hopping process. The results of T₂ studies show that correlated motions of the side‐ and main‐chain exist at low temperatures. However, at elevated temperatures the T₂ values for the side‐chain increase rapidly while remaining relatively constant for the main‐chain, indicating an onset of mobility of the side‐chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2177–2186, 2007     

Two Types of Block Copolymer Micelles with Ion‐Containing Cores

We report a combined experimental and theoretical study of micellization of block copolymer with hydrophilic nonionic corona‐forming blocks and weak polyelectrolyte (wPE) core‐forming blocks with pH‐triggered solubility in aqueous solutions. We demonstrate that in addition to micelles with neutral cores, there exist two other types of micelles with PE‐ or ionomer‐like cores, in which monovalent counterions are released or condensed on core wPE block, respectively. The transition between the two types of micelles occurred upon changes in ionization of the PE core block and resulted in nonmonotonous changes of aggregation number as a function of pH. Such micelles with stimulus responsive cores represent promising nanocarriers for controlled delivery applications.

     

Compression-inhibited pore formation of polyelectrolyte multilayers containing weak polyanions: a scanning force microscopy study.

Morphological changes of poly(acrylic acid)/poly(diallyldimethylammonium chloride) multilayers induced by low pH were investigated by scanning force microscopy. The weakened interaction between the charged polymer chains in the protonation process is believed to be the reason for this variation. Kinetic studies have shown that during protonation phase separation and dissociation of the multilayers took place successively. The compression of the multilayers, however, caused a transition of the multilayers from a rubbery state to a glassy state. As a result, the closely compacted multilayers lost their sensitivity to pH change. An increase of electrostatic and hydrophobic interactions, can decrease the free energy of the multilayers, and stabilize the films. By compression of the multilayers with a rubber stamp having geometric patterns, films with spatially localized pores were produced.     

Gold Nanoparticle‐Hybridized “Nano‐Sponge” Polymer Coatings to Enhance the Reliability and Sensitivity of Biosensors

We have created a new functional biosensor coating composed of polyelectrolyte multilayers containing gold nanoparticles. This gold‐hybridized polyelectrolyte multilayer film possesses a stable nanoporous structure under physiological conditions. Antibody molecules were successfully conjugated onto the gold nanoparticles within the film. This functional coating successfully extinguished false signals from non‐specific binding of proteins and cells and also provided highly enhanced detection sensitivity. Furthermore, the drastic differences in protein and cellular adhesion properties between a chip coated with the nanoporous PEM film and a bare chip demonstrate that morphological control of biological interactions on chip surfaces is possible.

     

Dynamic interactive membranes with pressure-driven tunable porosity and self-healing ability

When pressure is applied to dynamic interactive membranes consisting of micelles composed of a triblock copolymer, their morphologies can be fine-tuned. Membranes with a range of porosities are accessible which can regulate and thereby control filtration performance and also display effective autonomous healing.     

"Janus" supermolecular liquid crystals--giant molecules with hemispherical architectures

Liquid crystals represent a unique class of self-organising systems, which although found in many day-to-day practical material applications, such as displays, are also intimately entwined with living processes. They have the potential, just like living systems, to provide us with a unique vehicle for the development of self-ordering nano- and mesoscopic-engineered materials with specific functional properties. In this article we describe a new concept for the design of self-assembling functional liquid crystals as segmented or "Janus" liquid-crystalline supermolecular materials in the form of structures that contain two different types of mesogenic units, which favour different types of mesophase structure, grafted onto the same star-shaped scaffold to create supermolecules that contain different hemispheres. The materials exhibit chiral nematic and chiral smectic C phases.     

Mimicking the cell membrane with block copolymer membranes

Cell membranes are essential barriers in Nature. To understand their properties and functions and to develop desirable applications, a simple and elegant approach is to study membranes that mimic the cell membrane. Lipid bilayers represent simple models that are physiologically representative when in the form of mixtures of various lipids, but they are not adequately stable even when covered with amphipathic proteins or when combined with polymers, thus preventing technological applications. This makes necessary the design of completely synthetic membranes. In this respect, amphiphilic copolymers that self‐assemble under dilute aqueous conditions and generate supramolecular polymer vesicles or films are ideal candidates for synthetic membranes. Their versatility in terms of chemistry and properties (permeability, mechanical stability, thickness), if appropriately designed, enable the insertion of biological molecules, such as membrane proteins and biopores, or the attachment of biomolecules at their surfaces. Here, we present the domain of synthetic membranes based on amphiphilic copolymers beginning with their generation and up to their applications in medicine, the food industry, and technology. Even though significant progress has been made in combining them with membrane proteins, open questions remain with respect to desired properties that could accommodate biological molecules and support further development of the field, from both the point of view of fundamental understanding and of applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012