Spherical Polyelectrolyte Microgels in Salt-Free Solution. 2. Combined Analysis of Static Structure and Viscosity and Quantitative Testing of the Mode−Mode Coupling Approximation

Functional Nano-Objects by Electrostatic Self-Assembly: Structure, Switching, and Photocatalysis

The design of functional nano-objects by electrostatic self-assembly in solution signifies an emerging field with great potential. More specifically, the targeted combination of electrostatic interaction with other effects and interactions, such as the positioning of charges on stiff building blocks, the use of additional amphiphilic, π-π stacking building blocks, or polyelectrolytes with certain architectures, have recently promulgated electrostatic self-assembly to a principle for versatile defined structure formation. A large variety of architectures from spheres over rods and hollow spheres to networks in the size range of a few tenths to a few hundred nanometers can be formed. This review discusses the state-of-the-art of different approaches of nano-object formation by electrostatic self-assembly against the backdrop of corresponding solid materials and assemblies formed by other non-covalent interactions. In this regard, particularly promising is the facile formation of triggerable structures, i.e. size and shape switching through light, as well as the use of electrostatically assembled nano-objects for improved photocatalysis and the possible solar energy conversion in the future. Lately, this new field is eliciting an increasing amount of understanding; insights and limitations thereof are addressed in this article. Special emphasis is placed on the interconnection of molecular building block structures and the resulting nanoscale architecture via the key of thermodynamics.

Preliminary results on the influence of engineered artificial mucus layer on phonation

PURPOSE Previous studies have confirmed the influence of dehydration and an altered mucus (e.g., due to pathologies) on phonation. However, the underlying reasons for these influences are not fully understood. This study was a preliminary inquiry into the influences of mucus architecture and concentration on vocal fold oscillation. METHOD Two excised human larynges were investigated in an in vitro setup. The oscillations of the vocal folds at various airflow volume rates were recorded through the use of high-speed imaging. Engineered mucus containing polymers (interconnected polymers and linear polymers) was applied to the vocal folds. From the high-speed footage, glottal parameters were extracted through the use of objective methods and were compared to a gold standard (physiological saline solution). RESULTS Variations were found for all applications of mucus. Fundamental frequency dropped and the oscillatory behavior (speed quotient [SQ], closing quotient [CQ]) changed for both larynges. The 2 applied mucus architectures displayed different effects on the larynges. The interconnected polymer displayed clear low-pass filter characteristics not found for the linear polymer. Increase of polymer concentration affected parameters to a certain point. CONCLUSION The data confirm results found in previous studies. Furthermore, the different effects-comparing architecture and concentration-suggest that, in the future, synthetic mucus can be designed to improve phonation.

Molecular structure encodes nanoscale assemblies: understanding driving forces in electrostatic self-assembly

Supramolecular nanoparticles represent a key field in recent research as their synthesis through self-assembly is straightforward and they often can respond to external triggers. A fundamental understanding of structure-directing factors is highly desirable for a targeted structure design. This contribution demonstrates a quantitative relation between the size of supramolecular self-assembled nanoparticles and the free energy of association. Nanoparticles are prepared by electrostatic self-assembly of cationic polyelectrolyte dendrimers as model macroions and oppositely charged di- and trivalent organic dye molecules relying on the combination of electrostatic and π-π-interactions. A systematic set of sulfonate-group carrying azo-dyes was synthesized. Light scattering and ζ-potential measurements on the resulting nanoparticles yield hydrodynamic radii between 20 nm < R(H) < 50 nm and positive ζ-potential values indicating a positive particle charge. Studies on dye self-aggregation and dendrimer-dye association by isothermal titration calorimetry (ITC) and UV-vis spectroscopy allow for the correlation of the thermodynamic parameters of dendrimer-dye association with the size of the particles, showing that at least a free energy gain of ΔG ≈ - 32 kJ mol(-1) is necessary to induce dendrimer interconnection. Structural features of the azo dyes causing these to favor or prevent nanoparticle formation have been identified. The dye-dye-interaction was found to be the key factor in particle size control. A simple model yields a quantitative relation between the free energy and the particle sizes, allowing for predicting the latter based on thermodynamic measurements. Hence, a set of different molecular "building bricks" can be defined where the choice of building block determines the resulting assembly size.

Assemblies of double hydrophilic block copolymers and oppositely charged dendrimers

The association of poly(ethylene oxide-b-methacrylic acid) and poly(amidoamine) dendrimers was examined by dynamic light scattering and small angle neutron scattering. With increasing amounts of the G4 dendrimer as the counterion, the size of the assemblies increases until it reaches a hydrodynamic radius of about 70 nm. The structure is consistent with poly(methyl methacrylate) (PMAA) chains closely aggregating with the dendrimers at low dendrimer amounts and volume-filling PMAA blocks at higher dendrimer contents. Similar behavior was observed for G4 and G2 dendrimers, while smaller G0 molecules showed an opposite dependence. The results represent an example of finite size assemblies formed by "electrostatic self-assembly" that are stable in aqueous solution and represent equilibrium structures, the structure and size of which can be tuned through the building units, loading ratio, and pH.

Adsorption of charged macromolecules on oppositely charged porous column materials

A family of cationic polyelectrolytes possessing defined chain lengths, narrow chain length distributions, uniform charge density, but substituents of different hydrophilicity at the quaternary ammonium group served as model compounds for adsorption studies. These studies quantitatively revealed that polymer characteristics and electrostatic parameters affect the adsorption behavior on oppositely charged porous column materials. The presence of electrostatic exclusion, in addition to size exclusion, was proved comparing molecular, electrostatic and geometrical parameters. The dominance of electrostatic effects could be concluded evaluating the relation between molecular and electrostatic dimensions. The results provide a contribution how to estimate the threshold for electrostatic exclusion from pores as a function of dimensions and experimental conditions.

Self-consistent mode-coupling theory for the viscosity of rodlike polyelectrolyte solutions

A self-consistent mode-coupling theory is presented for the viscosity of solutions of charged rodlike polymers. The static structure factor used in the theory is obtained from polymer integral equation theory; the Debye-Huckel approximation is inadequate even at low concentrations. The theory predicts a nonmonotonic dependence of the reduced excess viscosity eta(R) on concentration from the behavior of the static structure factor in polyelectrolyte solutions. The theory predicts that the peak in eta(R) occurs at concentrations slightly lower than the overlap threshold concentration, c*. The peak height increases dramatically with increasing molecular weight and decreases with increased concentrations of added salt. The position of the peak, as a function of concentration divided by c*, is independent of salt concentration or molecular weight. The predictions can be tested experimentally.

Nanoparticles of a polyelectrolyte-fatty acid complex: carriers for Q10 and triiodothyronine

Poly(ethylene imine) (PEI) was used for the complexation of dodecanoic acid (C12) resulting in a poly(ethylene imine) dodecanoate complex (PEI-C12) with a lamellar nanostructure and a repeat unit of 2.9 nm. PEI-C12 was doped with coenzyme Q10 and the hormone triiodothyronine as typical hydrophobic and pharmacological active compounds, respectively. The PEI-C12 acts as a guest matrix that dissolves both molecules up to weight uptakes of about 20% (w/w) and 15% (w/w), respectively, both without crystallization. Agglomerate-free dispersions of core-shell type nanoparticles were developed. Ratios of PEI to C12 of 2:1 or higher were found to be suitable for this purpose. The particles exhibit hydrodynamic diameters in the range of 80-150 nm, which depend on the preparation conditions. Each particle consists of a relatively compact core surrounded by a diffuse corona. PEI-C12 forms the core, while non-complexed PEI acts as a cationic-active dispersing agent. It was found that the nanoparticles show high zeta potentials (approximately +40 mV) and are stable in NaCl solutions at concentrations of up to 0.3 mol x l(-1). The stabilization of the nanoparticles results from a combination of ionic and steric contributions. A variation of the pH value was used to activate the dissolution of the particles. The PEI-C12 nanoparticles may have potential as carriers for hydrophobic drugs.