Mesoporous silica aerogel particles of ca. 5 μm in diameter can be conveniently produced by grinding in an aqueous phosphate buffer at pH 7. The pores in the suspended aerogel particles are spherical and their diameter is 18–20 nm, as measured by NMR cryoporometry. NMR diffusiometry revealed that diffusion of water is hindered inside the pores of the aerogel. In spite of steric hindrance, bulk water and pore water exchange rapidly on the millisecond timescale in the suspension, indicating a highly interconnected pore network. The adsorption of methylene blue (MB), as a model compound, was studied on the silica aerogel particles. The process was followed by on-line UV-Vis spectrophotometry after injecting the dye into the aerogel suspension. Biphasic kinetics were observed with the first process complete in ca. 80 s and the second in ca. 600 s. A detailed kinetic model was developed for the interpretation of the results. It postulates a relatively fast adsorption process with Langmuir-type kinetics, and the aggregation of aerogel particles covered by the dye on a longer timescale. The aggregates are involved in a reversible sedimentation process which actually removes MB from the suspension.

Dendrimers are extensively studied for drug delivery and catalysis, most of which are pH dependent. Phosphate buffer solutions (PBSs) are often used to adjust the pH. We have found that phosphate ions become incorporated into poly(amidoamine) (PAMAM) dendrimer molecules by forming H-bonds with tertiary nitrogens. We show that this specific interaction between H₂PO₄ ⁻ and HPO₄ ²⁻ ions and generation five PAMAM dendrimers causes a decrease in hydrodynamic size, disturbing the outcome of the size exclusion chromatography analysis. We monitored this interaction by ¹H and ³¹P high resolution NMR, NMR-diffusiometry, pH-potentiometry and infrared spectroscopy. Failing to take into account this effect may lead to incorrect conclusions and misinterpreting interactions of PAMAM dendrimers with drug molecules and subsequently incorrect dosing. The phosphate salts of amino terminated generation five PAMAM dendrimers are stable for years when stored in the dark, even in dilute aqueous solutions, which has important implications for the shelf-life of dendrimer-based drug delivery systems.

Mixing weak acids and bases can produce highly complicated binary mixtures, called pseudo‐protic ionic liquids, in which a complex network of effects determines the physicochemical properties that are currently impossible to predict. In this joint computational‐experimental study, we investigated 1‐methylimidazole‐acetic acid mixtures through the whole concentration range. Effects of the varying ionization and excess of either components on the properties, such as density, diffusion coefficients, and overall hydrogen bonding structure were uncovered. A special emphasis was put on understanding the multiple factors that govern the conductivity of the system. In the presence of an excess of acetic acid, the 1‐methylimidazolium acetate ion pairs dissociate more efficiently, resulting in a higher concentration of independently moving, conducting ions. However, the conductivity measurements showed that higher concentrations of acetic acid improve the conductivity beyond this effect, suggesting in addition to standard dilution effects the occurrence of Grotthuss diffusion in high acid‐to‐base ratios. The results here will potentially help designing novel electrolytes and proton conducting systems, which can be exploited in a variety of applications.

In this study, we report the findings of a morphological analysis of a resorcinol–formaldehyde (RF)-based carbon aerogel (CA) and its graphene oxide (GO)-doped version (CA-GO), prepared for possible applications as an electrode material. Beyond some electron microscopic and N₂ sorption investigations, we mostly used NMR cryoporometry and relaxometry to characterize the gels in a wet state, as they are usually applied. The precursor RF polymer aerogel was prepared both with and without GO and was subsequently carbonized into carbon aerogel. Modifying the polymer aerogel using GO resulted in a larger variety of C-O bonds in both polymer aerogels. However, the most important changes occurred in the morphology of the carbon aerogels. NMR relaxometry revealed the highly hydrophilic nature of the pore wall of the RF polymer aerogels, as demonstrated by their uniform wetting behavior. The carbonization resulted in a mostly hydrophobic pore wall decorated by some oxygen-containing spots and a macroporous system. Doping with GO after pyrolysis resulted in spherical pores in the CA and cylindrical pores in the CA-GO, which is potentially a more promising material for electrochemical use than CA.