Synthesis of Janus polyaniline–polyelectrolyte complex membrane via in situ confined polymerization

Polyelectrolyte complex (PEC) membranes prepared from poly(styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) were modified by crossflow polymerization of aniline (ANI). The PEC membranes were used as separators in a two-compartment setup where ANI monomer and ammonium persulfate (APS) oxidant diffused through the membranes to form polyaniline (PANI). APS and ANI having different distributions throughout the membranes, the reaction led to the asymmetric polymerization of PANI on one face of each PEC membrane thus producing Janus membranes. Due to the excess PANI content, the membrane displayed distinct asymmetric electrical conductivities on each face. Interestingly, very different ANI polymerizations were obtained when nonstoichiometric PEC membranes having different molar ratio of cationic and anionic polyelectrolytes (P⁺:P^? represents PDADMAC:PSS) were used and transport of APS was fastest through the 2:1 PEC when compared to the 1:2 PEC. In all experiments, the polymerization was most intense on the ANI side of the membranes. Also, the influence of NaCl both during PEC fabrication and during polymerization was studied and found to have some effect on the solute permeability. Results showed that a higher content of PANI was formed on PEC membranes having excess P⁺ and with no NaCl added during PEC fabrication. Although X-ray diffraction confirmed the presence of PANI on both sides of each membrane, scanning electron microscopy images demonstrated that both sides of each membrane had different PANI content deposited. Electrical conductivity measurements using a four-point probe setup also showed that the PEC–PANI exhibits asymmetric electrical property on different sides. © 2021 Society of Industrial Chemistry.     

Improved rheological properties and stability of multiwalled carbon nanotubes/polymer in harsh environment

This work aims to improve the rheological properties and stability of multiwalled carbon nanotubes (MWCNTs)/acrylamide (AA) base skeleton polymer blends at harsh environment of high salinity-high temperature (HS-HT) or various pH. Different co/terpolymers have been accomplished to modify the structure of AA polymer by free-radical copolymerization of AA-based monomers. Anionic, cationic, and hydrophobic functional groups were used for the synthesis of polyelectrolyte, polyampholytic, and partially hydrophobic AA polymer types. The conversion, molecular weight, and poly dispersity of co/terpolymers have been evaluated by nuclear magnetic resonance (¹H-NMR), gel permeation chromatography, and differential scanning calorimetry analysis. The effects of sonication power, concentration of polymer, and concentration of MWCNTs were also investigated on rheological behavior of co/terpolymers. The results show that negative polyelectrolyte and polyampholytic polymers are the best candidates for the improvement of MWCNTs/polymer stability and viscosity at HS-HT and alkali environment, respectively. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47205.     

Enhanced hollow fiber membrane performance via semi-dynamic layer-by-layer polyelectrolyte inner surface deposition for nanofiltration and forward osmosis applications

The layer-by-layer (LBL) polyelectrolyte deposited membranes have drawn increasing attention in various applications due to the ease of selective layer formation and their stability and versatility. In this study, the LBL deposition was performed at the inner surface of the polyethersulfone (PES) hollow fiber substrate to form composite nanofiltration (NF) membrane. The semi-dynamic deposition procedure was adopted with the aid of syringes. The newly developed inner deposited (id-LBL) membranes were then tested in NF and forward osmosis (FO) applications and the performance were compared with outer surface deposition as well as some literature data. The id-LBL membranes could not only withstand higher operating pressure but also possess superior hardness rejection especially in high concentration mixed salt solutions (more than 95% rejection to Mg²⁺ and Ca²⁺ in a 5000 ppm total dissolved salt (TDS) mixture under 4.8 bar). As for the FO process, with only two layer deposition, the id-LBL membranes also demonstrated significant performance improvement with increased water flux (up to 70 L/m² h using 0.5 M MgCl₂ as draw solution in active layer facing draw solution configuration) and reduced salt leakage (around 0.5 g/m² h using 1 M MgCl₂ draw solution in active layer facing feed water configuration). This study suggests that for hollow fiber substrate, the inner surface is more suitable for the formation of the selective layer via LBL deposition than the outer surface.     

TiO2-incorporated polyelectrolyte composite membrane with transformable hydrophilicity/hydrophobicity for nanofiltration separation

The wettability of the membrane surface has shown obvious influent on the separation performance of the membrane. In this work, a hydrophilic PDA-[PDDA/TiO₂]⁺ Cl⁻ membrane was prepared by a one-step codeposition of poly(diallyldimethylammonium chloride) (PDDA) polyelectrolyte solution containing positively charged TiO₂@PDDA nanoparticles with the assistance of dopamine (DA). Such positively charged membrane can be transformed into a hydrophobic membrane PDA-[PDDA/TiO₂]⁺ PFO⁻ via the counterion exchange between Cl⁻ and PFO⁻ (perfluorooctanoate). The transformation between hydrophilicity and hydrophobicity is reversible. For both hydrophilic and hydrophobic membranes, the nanofiltration performances were respectively investigated by the aqueous solution and ethanol solution of dyes including methyl blue (MB), Congo red (CR) and Evans blue (EB), and as well metal salt aqueous solution. The consecutive running stability and anti-fouling performance of both hydrophilic and hydrophobic membranes were explored. The results revealed that both membranes showed high nanofiltration performances for retention of dyes in (non)aqueous solution. For the hydrophilic membrane, the rejection of salts in a sequence is MgSO₄ > Na₂SO₄ > MgCl₂ > NaCl. Moreover, both of the hydrophilic and hydrophobic membranes showed high stability and antifouling property.     

Porous ceramics with tailored pore size and morphology as substrates for coral larval settlement

The growing demand for stony corals as ornamental aquarium animals requires defined aquacultural breeding strategies. For the sexual propagation of corals, material substrates are needed, that attract larvae and support their settlement and development. In this study, five types of highly porous ceramic materials were developed following the example of coral skeleton. The applicability of these settlement substrates was tested using larvae of the stony coral Pocillopora damicornis. Partial sintering of pressed clay pellets, freeze casting of clay and alumina-mullite based slurries and direct foaming of high alkane phase emulsified suspensions (HAPES) using alumina were employed. By the addition of mm-sized spherical polystyrene beads as sacrificial templates during freeze casting (alumina-mullite), superficial pores in the size of the larvae were created. The inorganic substrates featured open porosities between 35% (pressed clay) and 83% (foamed alumina), pore sizes ranging from nm to mm-scale and pore morphologies dominated by interparticle porosity (pressed), lamellar pores (freeze casting) and cellular pore types (direct foaming). The ceramic substrates were incubated in artificial sea water for 3 months to induce necessary biofilm formation and algae growth. Afterwards, individual substrates were exposed to 5 coral larvae, and their settlement behavior was monitored over 14 days. At the end of this period, all ceramic materials were successfully accepted as settlement substrates, with a mean settlement rate of 46.2%, and no significant differences between the substrate types. On samples with large surface superficial pores, a significantly reduced survival of settled larvae (79%) compared to the other porous materials (93–98%) was determined, suggesting a non-ideal surface topography. While alumina foam samples (HAPES) exhibit the most promising results in terms of settlement and survival of larvae, clay-based substrates provide a more economic solution for the sexual propagation of corals in aquaculture.     

Protein Encapsulation Using Complex Coacervates: What Nature Has to Teach Us

Protein encapsulation is a growing area of interest, particularly in the fields of food science and medicine. The sequestration of protein cargoes is achieved using a variety of methods, each with benefits and drawbacks. One of the most significant challenges associated with protein encapsulation is achieving high loading while maintaining protein viability. This difficulty is exacerbated because many encapsulant systems require the use of organic solvents. By contrast, nature has optimized strategies to compartmentalize and protect proteins inside the cell—a purely aqueous environment. Although the mechanisms whereby aspects of the cytosol is able to stabilize proteins are unknown, the crowded nature of many newly discovered, liquid phase separated “membraneless organelles” that achieve protein compartmentalization suggests that the material environment surrounding the protein may be critical in determining stability. Here, encapsulation strategies based on liquid–liquid phase separation, and complex coacervation in particular, which has many of the key features of the cytoplasm as a material, are reviewed. The literature on protein encapsulation via coacervation is also reviewed and the parameters relevant to creating protein‐containing coacervate formulations are discussed. Additionally, potential opportunities associated with the creation of tailored materials to better facilitate protein encapsulation and stabilization are highlighted.     

Patterning a π-conjugated polyelectrolyte through sequential polymerization of a bifunctional ionic liquid monomer

An electronically conductive polyelectrolyte is prepared by the sequential polymerization of a bifunctional imidazolium-based ionic liquid (IL) monomer, composed of a thienyl and vinyl containing cation paired with a tetrafluoroborate anion. In the first step, potentiodynamic electropolymerization of the thienyl moiety forms a cationic polyalkylthiophene that is soluble in select organic solvents. Cyclic voltammetry (CV) was used to determine the polymer p-doping potential (0.31 V) and the bipolaronic state (1.49 V). The polymer exhibits electrochromism, converting from red in the neutral state (λ_max = 443 nm) to dark blue in the polaronic state (λ_max = 819 nm). The solution-processable polymer can be cast into a film, masked and patterned by UV-initiated free radical polymerization of the vinyl moiety. Small-angle X-ray scattering (SAXS) revealed that the insoluble crosslinked polyalkylthiophene–polyvinylimidazolium adopts a lamellar structure with a lattice spacing of 3.3 nm. Four-probe d.c. conductivity measurements determined the de-doped electrical conductivity was 1.0 × 10⁻² S/cm. The results underscore the importance of the anion in controlling the polymerization of IL monomers.     

Electrostatic Control of Structure in Self‐Assembled Membranes

Self‐assembling peptide amphiphiles (PAs) can form hierarchically ordered membranes when brought in contact with aqueous polyelectrolytes of the opposite charge by rapidly creating a diffusion barrier composed of filamentous nanostructures parallel to the plane of the incipient membrane. Following this event, osmotic forces and charge complexation template nanofiber growth perpendicular to the plane of the membrane in a dynamic self‐assembly process. In this work, we show that this hierarchical structure requires massive interfacial aggregation of PA molecules, suggesting the importance of rapid diffusion barrier formation. Strong PA aggregation is induced here through the use of heparin‐binding PAs with heparin and also with polyelectrolytes of varying charge density. Small angle X‐ray scattering shows that in the case of weak PA‐polyelectrolyte interaction, membranes formed display a cubic phase ordering on the nanoscale that likely results from clusters of PA nanostructures surrounded by polyelectrolyte chains.     

Chitosan—A versatile semi-synthetic polymer in biomedical applications

This review outlines the new developments on chitosan-based bioapplications. Over the last decade, functional biomaterials research has developed new drug delivery systems and improved scaffolds for regenerative medicine that is currently one of the most rapidly growing fields in the life sciences. The aim is to restore or replace damaged body parts or lost organs by transplanting supportive scaffolds with appropriate cells that in combination with biomolecules generate new tissue. This is a highly interdisciplinary field that encompasses polymer synthesis and modification, cell culturing, gene therapy, stem cell research, therapeutic cloning and tissue engineering. In this regard, chitosan, as a biopolymer derived macromolecular compound, has a major involvement. Chitosan is a polyelectrolyte with reactive functional groups, gel-forming capability, high adsorption capacity and biodegradability. In addition, it is innately biocompatible and non-toxic to living tissues as well as having antibacterial, antifungal and antitumor activity. These features highlight the suitability and extensive applications that chitosan has in medicine. Micro/nanoparticles and hydrogels are widely used in the design of chitosan-based therapeuticsystems. The chemical structure and relevant biological properties of chitosan for regenerative medicine have been summarized as well as the methods for the preparation of controlled drug release devices and their applications.     

Electrochemically Stimulated Release from Liposomes Embedded in a Polyelectrolyte Multilayer

Triggered release of an entrapped dye from vesicles embedded in a polyelectrolyte multilayer (PEM), as a consequence of the electrochemically induced local pH change in the vicinity of the electrode, is reported. The PEM was deposited on an indium tin oxide (ITO) electrode wherein lipid vesicles filled with a fluorescent dye were embedded. The use of vesicles with a strong negative charge and the polyelectrolyte species of the PEM matrix with a polycation as topmost layer enabled the generation of a stable layer of liposomes in the PEM.