Structures of Cationic and Anionic Polyelectrolytes in Aqueous Solutions: The Sign Effect

In this study, we use molecular dynamics simulation to explore the structures of anionic and cationic polyelectrolytes in aqueous solutions. We first confirm the significantly stronger solvation effects of single...

Revisiting the Cytotoxicity of Cationic Polyelectrolytes as a Principal Component in Layer-by-Layer Assembly Fabrication

Polycations are an essential part of layer-by-layer (LbL)-assembled drug delivery systems, especially for gene delivery. In addition, they are used for other related applications, such as cell surface engineering. As a result, an assessment of the cytotoxicity of polycations and elucidation of the mechanisms of polycation toxicity is of paramount importance. In this study, we examined in detail the effects of a variety of water-soluble, positively charged synthetic polyelectrolytes on in vitro cytotoxicity, cell and nucleus morphology, and monolayer expansion changes. We have ranked the most popular cationic polyelectrolytes from the safest to the most toxic in relation to cell cultures. 3D cellular cluster formation was disturbed by addition of polyelectrolytes in most cases in a dose-dependent manner. Atomic force microscopy allowed us to visualize in detail the structures of the polyelectrolyte–DNA complexes formed due to electrostatic interactions. Our results indicate a relationship between the structure of the polyelectrolytes and their toxicity, which is necessary for optimization of drug and gene delivery systems.

Investigating the Adsorption of Anisotropic Diblock Copolymer Worms onto Planar Silica and Nanocellulose Surfaces using a Quartz Crystal Microbalance

Electrostatic adsorption of cationic polyelectrolytes onto anionic cellulosic substrates is an attractive route for facile surface modification of biorenewable materials. Recently, attention has focused on adsorbing cationic spherical diblock copolymer...

THE USE OF REAGENTS BASED ON CATIONIC POLYELECTROLYTES FOR ACTIVATED SLUDGE DEHYDRATION

The processes of activated sludge dewatering using cationic flocculants and their binary mixtures have been investigated, recommendations have been developed for improving the technology of sludge dewatering. The results of tests to identify the optimal ratios of flocculants in the mixture during compaction and dehydration of activated sludge sludge are given, the concentration range is determined. It is shown that the use of binary mixtures of cationic flocculants makes it possible to reduce the moisture content of the sediment and reduce the content of suspended solids in the filtrate while simultaneously reducing the dose of polyelectrolytes.

Flocculation of Clay Suspensions by Anionic and Cationic Polyelectrolytes: A Systematic Analysis

The characteristics of clayey suspensions, majorly composed of quartz microparticles, in the presence of anionic and cationic polyelectrolytes were investigated using different techniques. A wide range of clay concentrations was used, i.e., from 0.07 to 1000 g/L for different experimental techniques, based on the fact that the clay concentration possible to analyze with selected experimental methods was significantly different. The optimum flocculant to clay ratio was defined as the ratio that gives the fastest initial floc growth by static light scattering or fastest initial settling velocity by settling column experiments. In case of anionic polyelectrolyte, it was observed that the optimum flocculant dose depends on the amount of cations present in the system. For suspensions made with demi-water, a lower optimum flocculant dose (<1 mg/g) than for suspensions prepared in tap water (2.28 mg/g) was observed. At these lower salinities, the supernatant remained turbid in all the experiments and was, therefore, not a good measure for optimal anionic based flocculation. The equilibrium floc size at a given shear rate was found to be independent on the shear history of the floc and only dependent on the current applied shear. This was confirmed by both light scattering and rheological analysis. In case of cationic polyelectrolyte, the optimum flocculant ratio (5–6 mg/g) corresponded to the ratio that gives the lowest electrophoretic mobility for each clay concentration and to the ratio that gives the fastest settling velocity for the highest clay concentrations (12–15 g/L), where static light scattering measurements were not possible. All investigation techniques, therefore, proved to be good indicators for predicting the optimum flocculant to clay ratio. For the lowest concentrations (1.75–8.7 g/L) studied by settling column measurements, the optimum flocculant ratio was observed to increase with decreasing clay concentration, for fixed mixing conditions. The optimum flocculant to clay ratio was not always corresponding to the clearest supernatant and the size of flocs at optimum dosage was dependent on the mixing efficiency. The equilibrium floc size at a given shear rate was found to be dependent on the shear history of the floc and the current applied shear. This was confirmed by both light scattering and rheological analysis.

Application of Nanoscale Zwitterionic Polyelectrolytes Brush with High Stability and Quantum Yield in Aqueous Solution for Cell Imaging

Cationic and zwitterionic polyelectrolytes are synthesized through atom transfer radical polymerization (ATRP), comprising a polyfluorene backbone with a small fraction of 2,1,3-benzothiadiazole and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) side chains. Due to higher charge density generated from grafted side chains, two polymers show higher water solubility and higher quantum yield. In comparison with cationic polyelectrolytes, zwitterionic polyelectrolytes are stable over a broad pH range from 1 to 13, even in 1 M NaCl solution. The absence of FRET between zwitterionic polymers and dye-labeled ssDNA indicates their ultralow nonspecific adsorption, while cationic polymer shows much stronger nonspecific interactions. The MTT assay of zwitterionic polymers exhibits their minimal cytotoxicity and potential in long-term clinical application. Most importantly, zwitterionic polymer could be efficiently taken up by cells, whereas cationic polymer stains the surface of cell due to membrane disruption generated from positive charges. The results illustrate that conjugated zwitterionic polymer could serve as a novel type of highly efficient ultralow fouling material with low cytotoxicity for labelling cell or potential biomedical applications.

Thermal Conductivity of Polyelectrolytes with Different Counterions

<div> <div> <div> <p>Polyelectrolytes are important to many applications, such as electronics and batteries. In this work, we study the thermal conductivity of polyelectrolytes with different counterions using molecular dynamics (MD) simulations. Both anionic and cationic polyelectrolytes, including poly(acrylic acid) and poly(allylamine hydrogen halide), are investigated. We have simulated a total number of 17 polyelectrolytes with different counterions and we find that all of them have thermal conductivity values between 0.2 and 0.7 W/(m.K). By analyzing thermal conductivity against different counterion descriptors (atomic mass, atomic radius, van der Waals radius and ionic radius), we find a strong negative relationship between thermal conductivity and the ionic radii of counterions. We rationalize such a discovery through analyzing the heat flux at molecular level and find that thermal conductivity shows a general increasing trend with respect to the interatomic non-bonding forces and atomic velocities. We have also found a positive correlation between the MD-calculated thermal conductivity and that from the minimum thermal conductivity model, and this correlation can also be traced back to the same molecular level origin. Our study provides new insights to the heat transfer physics in polymers and may help scientists develop polyelectrolytes with desirable thermal conductivity. </p> </div> </div> </div>