Abstract: The surface wettabilities of polymer brushes with hydrophobic and hydrophilic functional groups were discussed on the basis of conventional static and dynamic contact angle measurements of water and hexadecane in air and captive bubble measurements in water. Various types of high-density polymer brushes with nonionic and ionic functional groups were prepared on a silicon wafer by surface-initiated atom-transfer radical polymerization. The surface free energies of the brushes were estimated by Owens-Wendt equation using the contact angles of various probe liquids with different polarities. The decrease in the water contact angle corresponded to the polarity of fluoroalkyl, hydroxy, ethylene oxide, amino, carboxylic acid, ammonium salt, sulfonate, carboxybetaine, sulfobetaine, and phosphobetaine functional groups. The poly(2-perfluorooctylethyl acrylate) brush had a low surface free energy of approximately 8.7 mN/m, but the polyelectrolyte brushes revealed much higher surface free energies of 70-74 mN/m, close to the value for water. Polyelectrolyte brushes repelled both air bubbles and hexadecane in water. Even when the silicone oil was spread on the polyelectrolyte brush surfaces in air, once they were immersed in water, the oil quickly rolled up and detached from the brush surface. The oil detachment behavior observed on the superhydrophilic polyelectrolyte brush in water was explained by the low adhesion force between the brush and the oil, which could contribute to its excellent antifouling and self-cleaning properties.

Abstract: Mixing of oppositely charged polyelectrolytes in aqueous solutions may result in the formation of polyelectrolyte complexes (PEC). Phase separation and complex coacervation of polypeptides are investigated in this study. Polypeptides have identical backbones and differ only in their charged side groups, making them attractive model systems for this work. All experiments are conducted using equal chain lengths of polycation and polyanion in order to isolate and highlight effects of the interactions of the charged groups during complexation. Complex coacervation is strongly affected by the polypeptide mixing ratio (stoichiometry), ionic strength (salt concentration), total polymer concentration, pH, and temperature. To examine the effect of these parameters on complex formation we use sample turbidity as an indicator, and optical microscopy to discriminate between coacervate and precipitate. We establish phase diagrams as a function of polybase content and salt concentration using the critical salt concentrations required to reach the coacervate to solution boundary. Additionally, we examine the effect of molecular weight on the complex formation for the P(L-Lysine) (PLys)/P(L-Glutamic acid) (PGlu) system and establish a phase diagram. By determining the water content of the coacervate phase under various conditions we find that the salt content and stoichiometry of the mixed polyelectrolytes have a significant effect on the coacervate composition.

Abstract: The interactions between a series of oppositely charged polypeptide pairs are probed using isothermal titration calorimetry (ITC) in combination with turbidity measurements and optical microscopy. Polypeptide complex coacervation is described as a sequence of two distinct binding steps using an empirical extension of a simple ITC binding model. The first step consists of the formation of soluble complexes from oppositely charged polypeptides (ion pairing), which in turn aggregate into insoluble interpolymer complexes in the second step (complex coacervation). Polypeptides have identical backbones and differ only in their charged side groups, making them attractive model systems for this work. The poly(l-ornithine hydrobromide) (PO)/poly(l-glutamic acid sodium salt) (PGlu) system is used to examine the effects of parameters such as the salt concentration, pH, temperature, degree of polymerization, and total polymer concentration on the thermodynamic characteristics of complexation. Complex coacervation in all probed systems is found to be endothermic, essentially an entropy-driven processes. Increasing the screening effect of the salt on the polyelectrolyte charges diminishes their propensity to interact, leading to a decrease in the observed energy change and coacervate quantity. The pH plays an important role in complex formation through its effect on the degree of ionization of the functional groups. Plotting the change in enthalpy with temperature allows the calculation of the heat capacity change (ΔC(p)) for the PO/PGlu interactions. Finally, ITC revealed that complex coacervation is promoted when higher total polymer concentrations or polypeptide chain lengths are used.

Abstract: Healable, electrically conductive films are fabricated by depositing Ag nanowires on water-enabled healable polyelectrolyte multilayers. The easily achieved healability of the polyelectrolyte multilayers is successfully imparted to the Ag nanowire layer. These films conveniently restore electrical conductivity lost as a result of damage by cuts several tens of micrometers wide when water is dropped on the cuts.

Abstract: Interpolyelectrolyte complexes (IPECs) are typically formed when two polyelectrolytes of opposite charge are mixed together in solution. We present an overview of different strategies for the preparation of micellar IPECs, i.e., structures where such IPEC domains form the core or the shell of micelles. In addition, vesicular architectures are considered, where the IPEC domain forms a membrane layer. One intriguing feature of IPECs is that their formation can be directed, their stability towards changes in pH or ionic strength can (to a certain extent) be predicted, and their size can be controlled. Especially the use of ionic/non-ionic block copolymers offers unique potential for the preparation of well-defined and sophisticated nanostructured materials. We also discuss possible applications, especially in the field of life sciences, including biocompatibility, the controlled uptake/release of guest substances, the immobilization of enzymes, or the controlled formation of inorganic/organic hybrid materials.

Abstract: Living cells interfaced with a range of polyelectrolyte coatings, magnetic and noble metal nanoparticles, hard mineral shells and other complex nanomaterials can perform functions often completely different from their original specialisation. Such “cyborg cells” are already finding a range of novel applications in areas like whole cell biosensors, bioelectronics, toxicity microscreening, tissue engineering, cell implant protection and bioanalytical chemistry. In this tutorial review, we describe the development of novel methods for functionalisation of cells with polymers and nanoparticles and comment on future advances in this technology in the light of other literature approaches. We review recent studies on the cell viability and function upon direct deposition of nanoparticles, coating with polyelectrolytes, polymer assisted assembly of nanomaterials and hard shells on the cell surface. The cell toxicity issues are considered for many practical applications in terms of possible adverse effects of the deposited polymers, polyelectrolytes and nanoparticles on the cell surface.

Abstract: We report the synthesis of anionic sterically stabilized diblock copolymer nanoparticles via polymerization-induced self-assembly using a RAFT aqueous dispersion polymerization formulation. The anionic steric stabilizer is a macromolecular chain-transfer agent (macro-CTA) based on poly(potassium 3-sulfopropyl methacrylate) (PKSPMA), and the hydrophobic core-forming block is based on poly(2-hydroxypropyl methacrylate) (PHPMA). The effect of varying synthesis parameters such as the salt concentration, solids content, relative block composition, and anionic charge density has been studied. In the absence of salt, self-assembly is problematic when using a PKSPMA stabilizer because of lateral repulsion between highly charged anionic chains. However, in the presence of added salt this problem can be overcome by reducing the charge density within the coronal stabilizer layer by either (i) statistically copolymerizing the KSPMA monomer with a nonionic comonomer (2-hydroxyethyl methacrylate, HEMA) or (ii) using a ...

Abstract: Tough, dense polyelectrolyte complexes (PECs) with well-defined cross-sections are prepared using a laboratory extruder and plasticizing the complexes with salt water. Stoichiometric starting materials yield stoichiometric complexes of poly(diallyldimethylammonium) (PDADMA) and poly(styrene sulfonate) (PSS). As an example of this enabling technology, macroscopic tubes of PEC are produced. Microscopy images of cross-sections of rods, tape, and tubes show a pore volume of less than 10% in the bulk of the extruded complex and fully dense material towards the surface, where the shear is greatest. Thermal gravimetric analysis reveals the expected salt content for PECs doped with NaCl, and a lack of salt for PECs rinsed in water. The fact that doped PECs are transparent suggests they are supersaturated with salt. Residual stress following extrusion is relieved by exposure to solutions of NaCl. Stress relaxation experiments show decreasing equilibrium moduli as a function of increasing salt doping, consistent with prior results on multilayers of the same polymers.

Abstract: Membrane fouling remains one of the most problematic issues surrounding membrane use in water and wastewater treatment applications. Organic and biological fouling contribute to irreversible fouling and flux decline in these processes. The aim of this study was to reduce both organic and biological fouling by modifying the surface of commercially available poly(ether sulfone) (PES) membranes using the polyelectrolyte multilayer modification method with poly(styrenesulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDADMAC), and silver nanoparticles (nanoAg) integrated onto the surface as stable, thin (15 nm) films. PSS increases the hydrophilicity of the membrane and increases the negative surface charge, while integration of nanoAg into the top PSS layer imparts biocidal characteristics to the modified surface. Fouling was simulated by filtering aqueous solutions of humic acid (5 and 20 mg L–1), a suspension of Escherichia coli (106 colony-forming units (CFU) mL–1), and a mixture of both foulants ...

Abstract: Soluble macromolecules are essential to Nature's control over biomineral formation. Following early studies where macromolecules rich in aspartic and glutamic acid were extracted from nacre, research has focused on the use of negatively charged additives to control calcium carbonate precipitation. It is demonstrated that the positively charged additive poly(allylamine hydrochloride) (PAH) can also cause dramatic changes in calcite morphologies, yielding thin films and fibers of CaCO3 analogous to those produced with poly(aspartic acid) via a so-called PILP (polymer-induced liquid precursor) phase. The mechanism by which PAH induces these effects is investigated using a range of techniques including cryo transmission electron microscopy (TEM), Raman microscopy, and thermogravimetric analysis, and the data show that hydrated Ca2+/PAH/CO32- droplets initially form in solution, before coalescing and ultimately crystallizing to give calcite, together with small quantities of vaterite. It is suggested that it is the initial formation of hydrated Ca2+/PAH/CO32- droplets that is key to this process, rather than a specific polymer/mineral interaction. These results are discussed in terms of their relevance to biomineralization processes and highlight the opportunity for using counter-ion-induced phase separation of polyelectrolytes as a method for generating minerals with non-crystallographic morphologies.

Abstract: The alternate deposition of polyanions and polycations on a solid substrate leads to the formation of nanometer to micrometer films called Polyelectrolyte Multilayers This step-by-step construction of organic films constitutes a method of choice to functionalize surfaces with applications ranging from optical to bioactive coatings The method was originally developed by dipping the substrate in the different polyelectrolyte solutions Recent advances show that spraying the polyelectrolyte solutions onto the substrate represents an appealing alternative to dipping because it is much faster and easier to adapt at an industrial level Multilayer deposition by spraying is thus greatly gaining in interest Here we review the current literature on this deposition method After a brief history of polyelectrolyte multilayers to place the spraying method in its context, we review the fundamental issues that have been addresses so far We then give an overview the different fields where the method has been applied

Abstract: Engineered nanoparticles made from noble metals, rare-earth oxides or semiconductors are emerging as the central constituents of future nanotech developments. In this review, a survey of the complexing strategies between nanoparticles and oppositely charged polyelectrolytes developed during the last three years and based on electrostatic interactions is presented. These strategies include the one-step synthesis of stable and functionalized nanoparticles, the one- and multilayer coating of individual nano-objects, the controlled clustering of particles and the generation of capsules and thin films with superior functionalities. Among the formulation processes reported, three main classes are identified: the direct mixing route, the desalting transition pathway and the well-known layer by layer method. Finally, some latter developments, trends and applications of electrostatic assemblies in materials science and nanomedicine are highlighted.

Abstract: A systematic study of the interfacial energy (γ) of polypeptide complex coacervates in aqueous solution was performed using a surface forces apparatus (SFA). Poly(l-lysine hydrochloride) (PLys) and poly(l-glutamic acid sodium salt) (PGA) were investigated as a model pair of oppositely charged weak polyelectrolytes. These two synthetic polypeptides of natural amino acids have identical backbones and differ only in their charged side groups. All experiments were conducted using equal chain lengths of PLys and PGA in order to isolate and highlight effects of the interactions of the charged groups during complexation. Complex coacervates resulted from mixing very dilute aqueous salt solutions of PLys and PGA. Two phases in equilibrium evolved under the conditions used: a dense polymer-rich coacervate phase and a dilute polymer-deficient aqueous phase. Capillary adhesion, associated with a coacervate meniscus bridge between two mica surfaces, was measured upon the separation of the two surfaces. This adhesion ...

Abstract: Microencapsulation is an imperative technology in pharmacy, food industry and medicine. However, the current level of the development requires not only the fabrication of the emulsion systems, but also their functionalization in order to impart it multifunctional properties. One of the most perspective approaches to attain additional functionality to the emulsion particles is the use of the layer-by-layer modification of their surface. This technique permits the step-wise adsorption of various components (polyelectrolytes, nanoparticles, proteins, enzymes, etc.) as the layer growth is governed by their electrostatic, hydrogen bonding, hydrophobic, etc. forces and allows the formation of multilayer shells with nanometer (thickness) precision. The proposed review surveys the layer-by-layer approach for modification of both polymer and Pickering emulsions with polyelectrolyte or nanoparticle multilayers together with the demonstration of the application examples of the modified emulsion systems, where the emulsion particles play simultaneously the role of the template for layer-by-layer assembly as well as of the inner load.

Abstract: 150–200 nm diameter capsules containing 60–70 wt% of poorly soluble drugs, paclitaxel and camptothecin, were produced by layer-by-layer (LbL) assembly on drug nanocores in a solution containing uncharged stabilizers. Optimization of capsule shell architecture and thickness allowed for concentrated colloids (3–5 mg mL−1) that are stable in isotonic salt buffers. Nanoparticle aggregation during the washless LbL-assembly was prevented by using low molecular weight block-copolymers of poly(amino acids) (poly-L-lysine and poly-L-glutamic acid) with polyethylene glycol (PEG) in combination with heparin and bovine serum albumin at every bilayer building step. Minimal amounts of the polyelectrolytes were used to recharge the surface of nanoparticles in this non-washing LbL process. Such PEGylated shells resulted in drug nanocapsules with high colloidal stability in PBS buffer and increased protein adhesion resistance. The washless LbL polyelectrolyte nanocapsule assembly process, colloidal stability and nanoparticle morphology were monitored by dynamic light scattering and electrophoretic mobility measurements, UV-vis spectroscopy, TEM, SEM and laser confocal microscopy imaging.

Abstract: We present a theory for polyelectrolyte gels that allow the effective charge of the polymer backbone to self-regulate. Using a variational approach, we obtain an expression for the free energy of gels that accounts for the gel elasticity, free energy of mixing, counterion adsorption, local dielectric constant, electrostatic interaction among polymer segments, electrolyte ion correlations, and self-consistent charge regularization on the polymer strands. This free energy is then minimized to predict the behavior of the system as characterized by the gel volume fraction as a function of external variables such as temperature and salt concentration. We present results for the volume transition of polyelectrolyte gels in salt-free solvents, solvents with monovalent salts, and solvents with divalent salts. The results of our theoretical analysis capture the essential features of existing experimental results and also provide predictions for further experimentation. Our analysis highlights the importance of the self-regularization of the effective charge for the volume transition of gels in particular, and for charged polymer systems in general. Our analysis also enables us to identify the dominant free energy contributions for charged polymer networks and provides a framework for further investigation of specific experimental systems.

Abstract: This paper is focused on the synthesis of gold nanoparticles (AuNPs) using highly branched polyethylenimine (PEI) and acylated polyethylenimine (PEI-C12) as reducing as well as stabilizing agent and their role as catalysts. The AuNPs are characterized by XRD, TEM, HRTEM, AFM, UV–vis and FT-IR techniques. The AuNPs, in a PEI polyelectrolyte matrix, is found to be a stable and active catalyst for the selective reduction of nitro compounds using NaBH4 under mild reaction conditions. This catalytic system is stable for several months without any obvious colloidal aggregation.

Abstract: Polyelectrolytes (PEs) are widely used in applications such as water purification, wastewater treatment, and mineral recovery. Although much has been learned in past decades about the behavior of PEs in bulk aqueous solutions, their molecular behavior at a surface, and particularly an oil–water interface where many of their applications are most relevant, is largely unknown. From these surface spectroscopic and thermodynamics studies we report the unique molecular characteristics that several common polyelectrolytes, poly(acrylic acid) and poly(methylacrylic acid), exhibit when they adsorb at a fluid interface between water and a simple insoluble organic oil. These PEs are found to adsorb to the interface from aqueous solution in a multistepped process with a very thin initial layer of oriented polymer followed by multiple layers of randomly oriented polymer. This additional layering is thwarted when the PE conformation is constrained. The adsorption/desorption process is highly pH dependent and distinctly different than what might be expected from bulk aqueous phase behavior.

Abstract: We report on the correlation of polyelectrolyte chain dynamics in polyelectrolyte complexes (PECs) with the deposition mode and chain mobility of polyelectrolytes (PEs) within layer-by-layer-assemb...