Abstract: Conjugated polyelectrolytes comprise an electronically delocalized backbone with pendant groups bearing ionic functionalities. Important new developments regarding their use to improve charge injection from metallic electrodes into organic semiconductors, a key requirement in emissive devices, have recently appeared. This article provides an overview of recent studies concerning the basic properties of conjugated polyelectrolytes as a function of molecular structure, and of optoelectronic devices with conjugated polyelectrolytes as essential functional components. Processes where more insightful mechanistic understanding is needed and areas of opportunity are discussed.

Abstract: An anticorrosion layer of a smart polymer coating is developed. The nature and properties of the coating simultaneously provide three mechanisms of corrosion protection: passivation of the metal degradation by controlled release of an inhibitor, buffering of pH changes at the corrosive area by polyelectrolyte layers, and self-curing of the film defects due to the mobility of the polyelectrolyte constituents in the layer-by-layer assembly.

Abstract: Three imidazolium-based ionic liquid (IL) monomers, namely, 3-(1-ethyl imidazolium-3-yl)propylmethacrylamido bromide (IL-1), 2-(1-methylimidazolium-3-yl)ethyl methacrylate bromide (IL-2), and 2-(1-ethylimidazolium-3-yl)ethyl methacrylate bromide (IL-3), and methacrylic acid (MAA) were polymerized by the reversible addition fragmentation chain transfer (RAFT) process in methanolic solutions at 70 °C, using either 2-cyanopropyl dithiobenzoate (CTA-1) or (4-cyanopentanoic acid)-4-dithiobenzoate (CTA-2) as chain transfer agents (CTAs). Under these conditions, polymers exhibited molar masses predetermined by the initial molar ratio of the monomers to the dithioester precursor, as evidenced by 1H NMR spectroscopy from chain ends analysis. These hydrophilic polymers were subsequently used as macro-CTAs in chain extension experiments in aqueous or in alcoholic solutions, affording IL-based double hydrophilic block copolymers (DHBCs) of the type PIL-1-b-PAm, PMAA-b-PIL-2 and PMAA-b-PIL-3, where PAm and PIL stand f...

Abstract: Thin films of polyelectrolyte complex were assembled using the multilayering method with direct, in situ observation of all multilayer components using attenuated total internal reflectance FTIR (ATR-FTIR). Buildup and ion doping of two representative combinations of positive and negative polyelectrolytes are controlled by salt type. The internal hydration of multilayers, measured precisely by ATR-FTIR, depends on the chemical identities of the polymers and the salt ions. The efficiency of doping inversely tracks the degree of hydration: less hydrated (“hydrophobic”) ions are more efficient dopants, and less hydrated polyelectrolye complexes are harder to dope. Given that polyelectrolyte complexation is essentially entropy-driven, driving forces for doping, or association (the inverse of doping), are rationalized by counting all species in the condensed polyelectrolyte phase, including water molecules. For any combination of uni-univalent salt ions and polyelectrolyte, the strength of polyelectrolyte asso...

Abstract: In this study, the electrospinning performance and solution properties of Nafion and its blend with another polyelectrolyte, poly(acrylic acid) (PAA), were investigated. Attempts to electrospin pure Nafion at various polymer concentrations (5−35 wt %), solvents, neutralization, and electrospinning conditions resulted in electrospraying rather than electrospinning. However, a polymer solution blend (5 wt %) of Nafion and PAA resulted in beaded fibers at 8 wt % PAA and smooth electrospinning above 12% PAA. Fiber sizes of the blend increased from 90 to 600 nm with increasing PAA content. Dynamic light scattering on pure Nafion solutions in various solvents reveals large aggregates (i.e., dispersion) of various sizes due to polymer backbone and ionic interactions. The lack of sufficient polymer chain entanglement evidenced by low viscosity and aggregate formation in Nafion solutions prohibits fiber formation during electrospinning. The addition of PAA to Nafion modifies the ionic strength of the solvent resul...

Abstract: Uptake of colloidal polyelectrolyte-coated particles and polyelectrolyte multilayer capsules has been demonstrated by living cells. The capsules for this study were prepared by poly(diallyldimethylammoniumchloride) (PDMAC) and poly(styrene sulfonate) (PSS) on SiO2. SiO2 template cores were used because of their negative charge. It was observed during the study that SiO2 templates dissolved in hydrofluoric acid after the formation of capsule-shell. The study also found that heat treatment can be used for stable encapsulation of materials inside the microcapsuels made on SiO 2. It was also found that calcium carbonate microparticles can provide a loading capacity for biological materials. The study used a confocal laser scanning microscopy (CLSM) to examine the capsule incorporation by the cells.

Abstract: A novel approach to the emulsion encapsulation was developed by combining the advantages of direct encapsulation of a liquid colloidal core with the accuracy and multifunctionality of layer-by-layer polyelectrolyte deposition. Experimental data obtained for the model oil-in-water emulsion confirm unambiguously the alternating PE assembly in the capsule shell as well as the maintenance of the liquid colloidal core. Two different mechanisms of capsule destruction upon interaction with the solid substrate were observed and qualitatively explained. The proposed method can be easily generalized to the preparation of oil-filled capsules in various oil/water/polyelectrolyte systems important in the field of pharmacy, medicine, and food industry.

Abstract: A highly effective polyelectrolyte functionalization of multi-walled carbon nanotubes (MWCNTs) by poly(diallyldimethylammonium chloride) (PDDA-MWCNTs) was employed for low temperature fuel cell applications. PDDA-MWCNTs were employed as support materials for the in situ deposition and formation of platinum nanoparticles, via the self-assembly between the negative Pt precursor and positively charged functional groups of PDDA-functionalized MWCNTs. The effect of the functionalization on the deposition and distribution of Pt nanoparticles was investigated in detail. Compared with MWCNTs functionalized by conventional acid-oxidation treatment (AO-MWCNTs), the PDDA-functionalized MWCNTs cause no structural damage on MWCNTs and provide high density and homogeneous surface functional groups for the anchoring Pt nanoparticles. Pt nanoparticles with an average particle size of 1.8 ± 0.4 nm and loading as high as 60 wt% were realized on PDDA-MWCNTs supports. The Pt/PDDA-MWCNTs electrocatalysts show significantly higher electrochemically active surface area and higher electro-catalytic activity for methanol oxidation than that of Pt/AO-MWCNTs and E-TEK Pt/C electrocatalysts.

Abstract: A new sulfonated side-chain grafting unit containing two or four sulfonic acid groups was synthesized using sulfonated 4-fluorobenzophenone (FBP) and 1,1-bis(4-hydroxyphenyl)-1,4-((4-fluorophenyl)thio)phenyl-2,2,2-trifluoroethane (3FBPT). A conventional aromatic nucleophilic substitution (SNAr) was used for copolymerization of poly(arylene ether sulfone) containing a methoxy group. After converting the methoxy group to the reactive hydroxyl group, this functionalized copolymer was reacted to graft the sulfonated side chains to make the comb-shaped sulfonated poly(arylene ether sulfone) copolymers. All the polymers were characterized by 1H NMR, thermogravimetric analysis (TGA), the water uptake, and proton and methanol transport for fuel cell applications. These comb-shaped sulfonated polymers had good properties as polyelectrolyte membrane materials. The comb-shaped copolymers with two or four sulfonic acid groups show high proton conductivity in the range of 34−147 and 63−125 mS/cm, respectively. The met...

Abstract: Maltose-modified poly(propylene imine) (PPI) dendrimers were synthesized by reductive amination of unmodified second- to fifth-generation PPI dendrimers in the presence of excess maltose. The dendrimers were characterized by using (1)H NMR, (13)C NMR, and IR spectroscopies; laser-induced liquid beam ionization/desorption mass spectrometry; dynamic light scattering analyses; and polyelectrolyte titration. Their scaffolds have enhanced molecular rigidity and their outer spheres, at which two maltose units are bonded to the former primary amino groups on the surface, have hydrogen-bond-forming properties. Furthermore, the structural features reveal the presence of a dense shell. Experiments involving encapsulation (1-anilinonaphthalene-8-sulfonic acid) and biological properties (hemolysis and interactions with human serum albumin (HSA) and prion peptide 185-208) were performed to compare the modified with the unmodified dendrimers. These experiments gave the following results: 1) The modified dendrimers entrapped a low-molecular-weight fluorescent dye by means of a dendritic box effect, in contrast to the interfacial uptake characteristic of the unmodified PPI dendrimers. 2) Both low- and high-generation dendrimers containing maltose units showed markedly reduced toxicity. 3) The desirable features of bio-interactions depended on the generation of the dendrimer; they were retained after maltose substitution, but were now mainly governed by nonspecific hydrogen-bonding interactions involving the maltose units. The modified dendrimers interacted with HSA as strongly as the parent compounds and appeared to have potential use as antiprion agents. These improvements will initiate the development of the next platform of glycodendrimers in which apparently contrary properties can be combined, and this will enable, for example, therapeutic products such as more efficient and less toxic antiamyloid agents to be synthesized.

Abstract: In the present paper, thermosensitive coatings are prepared by deposition of P(NIPAM-co-AAc) microgel particles on precoated silicon wafers. The effect of pH, substrate precoating, and preparation technique is studied. The pH value is found to significantly influence the adsorption density, while the substrate surface charge is less important. Hence, the electrostatic contribution of the particle-particle interaction seems to play a more pronounced role for the adsorption density than at least the electrostatic part of the particle-surface interaction. For the latter, also nonelectrostatic contributions like hydrogen bonding and surface roughness play an important role. Immersion of the prepared polyelectrolyte/microgel layers in buffers leads to a reorganization of the adsorbed particles at the surface.

Abstract: We report the synthesis of a new polythiophene (PT)-based molecular brush (PT-g-PDMA) by growing poly(N,N-dimethylaminoethyl methacrylate) (PDMA) chains from the PT backbone by ATRP The polymer shows a reversible pH response in aqueous solution A combination of AFM, light scattering, and 1H NMR measurements indicated that the polymer brush forms a more extended conformation with a decrease in pH from 8 to 2 due to the protonation of the Me2N− groups and increased repulsive interactions among the PDMA side chains, which drives the red shift of the absorption and PL spectra of the PT backbone The good solubility of this polythiophene-based brush in a wide range of solvents is attractive for the fabrication of functional polymer composites

Abstract: The worldwide need for clean and sustainable energy is ever-increasing, and electrochemical devices such as batteries, fuel cells, and dye-sensitized photovoltaic cells offer the most promising solutions. At the core of these devices is an electrolyte that facilitates charge transport between electrodes. Commonly used liquid or gel electrolytes prohibit widespread use of these devices owing to processing difficulties and safety concerns; however, polymer ionic conductors offer high mechanical strength and more fabrication flexibility compared to traditional electrolytes as well as better physical separation of electrodes. Polymer electrolytes are generally thin films that facilitate the transport of a given ion or ions at predetermined operating conditions. Although the desired properties of solid polymer electrolytes depend on the device application, fast ion conduction is essential to reduce electrical resistance. Layer-by-layer (LBL) assembly is a versatile thin-film fabrication technique that consists of the repeated, sequential immersion of a substrate into aqueous solutions of complementary functionalized materials. By utilizing electrostatic forces or secondary interactions such as hydrogen bonding, LBL processing provides nanometer-scale blending of polymers and other organic/inorganic materials that are otherwise impossible to construct. The composition, morphology, and bulk properties are controlled by adjusting assembly parameters such as pH and ionic strength. This technique has been adapted to many other platforms such as spraying, spin-assisted assembly, and roll-to-roll processing. The high versatility, tunability, and ease of processing from the ability to use aqueous solutions make this system a great competitor to traditionally assembled solid-state conductors. Previously, our group has focused on LBL-assembled systems that show promise as thinfilm conductors for photovoltaics, electrochromic devices, and fuel cells, but they were limited in scope of application because of low ionic conductivity values. To illustrate, the highest conductivity values achieved in an LBL film to date have been on the order of 10 5 S cm , while typical values for fully hydrated LBL films are in the 10 –10 9 S cm 1 range. Here we report the highest ionic conductivity ever obtained from an LBL assembled thin film, 3.5 10 2 S cm 1 at 98%

Abstract: Adsorption of polyelectrolytes to surfaces of opposite charge typically leads to charge neutralization and subsequent charge reversal. As can be shown by direct force measurements and stability studies, the interaction forces are dominated by repulsive forces originating from diffuse layer overlap and attractive van der Waals forces, in line with the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). Recently, the existence of an additional attractive non-DLVO force was demonstrated, and its likely origin is the attraction between patch-charge heterogeneities. With novel single molecule pulling experiments with the atomic force microscope (AFM) polymer bridging forces could be shown to represent the most important contribution to the adhesion of surfaces coated by polyelectrolytes.

Abstract: A series of water soluble, cationic conjugated polyelectrolytes (CPEs) with backbones based on a poly(phenylene ethynylene) repeat unit structure and tetraakylammonium side groups exhibit a profound light-induced biocidal effect. The present study examines the biocidal activity of the CPEs, correlating this activity with the photophysical properties of the polymers. The photophysical properties of the CPEs are studied in solution, and the results demonstrate that direct excitation produces a triplet excited-state in moderate yield, and the triplet is shown to be effective at sensitizing the production of singlet oxygen. Using the polymers in a format where they are physisorbed or covalently grafted to the surface of colloidal silica particles (5 and 30 microm diameter), we demonstrate that they exhibit light-activated biocidal activity, effectively killing Cobetia marina and Pseudomonas aeruginosa. The light-induced biocidal activity is also correlated with a requirement for oxygen suggesting that interfacial generation of singlet oxygen is the crucial step in the light-induced biocidal activity.

Abstract: We describe the synthesis, characterisation and surface-modification of magnetic nanoparticles and a poly(N-isopropylacrylamide) microgel, followed by the assembly and characterisation of magnetic nanoparticles on the microgel. To facilitate this deposition, the surface of the microgel is first modified via the layer-by-layer assembly of polyelectrolytes. One advantage of this concept is that it allows an independent optimization and fine tuning of the magnetic and thermoresponsive properties of individual components (nanoparticles and microgels) before assembling them so that the hybrid core-shell structure retains all the individual properties. The decisive parameter when exploiting the thermoresponsive and magnetic properties in such hybrid core-shell structures is the amount of heat transfer from the magnetic core onto the thermosensitive (loaded) microgel (for the subsequent heat-triggered release of drugs). Inductive heat study reveals that the heat generated by the magnetic nanoparticles is sufficient to cause the collapse of the microgel above its volume phase transition temperature. Successful confinement of positively and negatively charged magnetic nanoparticles between polyelectrolyte layers is achieved using the layer-by-layer deposition onto the microgel. Dynamic light scattering measurements show (i) the presence of each layer successfully deposited, (ii) the preservation of thermoresponsivity in the coated microgel, and (iii) that the magnetic nanoparticles do not get detached during the phase transition of the microgel. Electrophoresis measurements confirm charge reversal at every stage of layering of polycations, polyanions and magnetic nanoparticles. This unique combination of thermoresponsivity and magnetism opens up novel perspectives towards remotely controlled drug carriers.