Surfactant-free oil-in-water emulsions prepared with temperature and pH sensitive poly(N-isopropylacrylamide)(PNIPAM) microgel particles offer unprecedented control of emulsion stability.

Using stimulus-sensitive microgel particles as an emulsifier, we have prepared a new type of emulsion responsive to pH, ionic strength, and temperature changes. Each of these environmental changes can trigger a volume phase transition in poly(N-isopropylacrylamide) (PNIPAM) microgel particles containing some carboxylic groups. Depending on their hydrophobicity and charging state, such PNIPAM microgel particles can adsorb to the droplets of an octanol-in-water emulsion and provide excellent stability against coalescence and ripening. We have studied in detail the correlation between the particles' response to changes in the solution conditions and the corresponding response of particle-decorated emulsion droplets. In their swollen, hydrophilic state, the microgel particles consistently stabilize the octanol droplets, but inducing a microgel collapse usually results in a destabilization of the emulsion and eventually in phase separation. A notable exception was found at high pH where particles are highly charged: in this regime emulsions remain stable even upon a temperatureinduced collapse of the microgel particles and prove sensitive only to high levels of screening ions. Microscopy studies of toluene-in-water emulsions stabilized by compact polystyrene particles of variable surface charge further suggest an intimate connection between the charge and packing density of interfacial particles and hint at a charge-induced interparticle attraction.

The adsorption of poly(vinylamine) (PVA) on poly(styrene sulfate) latex particles is studied, and its consequences on the charging behavior and suspension stability are investigated. The adsorption process is assessed by batch depletion experiments and time-resolved electrophoretic mobility measurements. The adsorption of PVA appears to be basically irreversible. The rate of adsorption decreases with decreasing polymer dose. At low polymer dose, the polymer coverage corresponds to the amount of the polyelectrolyte added, while at high polymer dose, the polymer coverage saturates the surface. Stability ratios are determined by dynamic light scattering, and strongly depend on the polymer dose and salt level. The aggregation is rapid near the isoelectric point (IEP), and it slows down when moving away from it. The charge neutralization is highly nonstoichiometric with charging ratios (CR) larger than unity, meaning that several charges on an adsorbed polyelectrolyte chain are necessary to neutralize a single charge on the particle surface. By comparing the IEP for particles and polyelectrolytes of different charge densities, we find a strong dependence of the CR on the mismatch between the average distances between individual charges on the surface and on the polyelectrolyte. A simple model is proposed to explain this trend.

A combination of analytical methods and molecular modeling calculations has provided a detailed picture of the supramolecular and microscopic structure of precipitated lipophilic carotenoids. The nanoparticles have a core/shell structure (see schematic representation) in which the particle core (120 nm) consists of a variety of molecular aggregates of different sizes, and the shell (40 nm) consists of an adsorbed gelatin layer.

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Thin films of cellulose are advantageous for analytical studies in aqueous environments to investigate various factors determining the performance of cellulose-based products. However, the weak fixation of cellulose layers on common carrier materials often limits this approach. To address this problem, we suggest a novel maleic anhydride copolymer precoating technique which allows for the covalent attachment of cellulose thin films through esterification. Maleic anhydride copolymers were deposited and covalently bound onto planar, aminosilane-modified glass or silicon oxide surfaces. Cellulose was subsequently immobilized on top of the copolymer precoatings by spin coating from N-methylmorpholine-N-oxide/dimethyl sulfoxide solutions. The resulting cellulose films were thoroughly characterized with respect to layer thickness, morphology, chemical constitution, and electrical charging. The stability of the layers against shear stress was demonstrated in aqueous solutions and the covalent attachment of the cellulose to the copolymer films was proven by means of dissolution experiments followed by ellipsometry and high-resolution X-ray photoelectron spectroscopy.

The first account of inhomogeneous broadening of vibrational linewidths in non-hydrogen-bonded liquids is presented based on the combined results of isotropic spontaneous Raman studies and picosecond coherent probing experiments. The symmetric CH3-stretching vibrational linewidths studied were found to be inhomogeneously broadened to various degrees. A correlation between the inhomogeneous broadening and the liquid’s local number density distribution width is demonstrated, upon which a theoretical model for inhomogeneous broadening is developed. A stochastic line shape theory is constructed in which homogeneous and inhomogeneous broadening are treated simultaneously in terms of one vibrational correlation function. This treatment unifies the fast and slow modulation approaches to vibrational dephasing and demonstrates how isotropic spontaneous Raman scattering studies and picosecond coherent probing experiments can be used in conjunction to study the inhomogeneous broadening of vibrational linewidths.

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