This work focuses on the synthesis method of Au nanoparticles protected by a well-defined polymer monolayer. Nanosized, spherical gold clusters coated with poly(N-isopropylacrylamide) (PNIPA) grafts were prepared by controlled radical polymerization. The polymerization of N-isopropylacrylamide was initiated from the surface of a gold nanoparticle modified with 4-cyanopentanoic acid dithiobenzoate for a reversible-addition-fragmentation chain-transfer polymerization. The number mean diameter of the Au core was 3.2 nm as observed by high-resolution transmission electron microscopy. The molar mass of the PNIPA ligand was 21000 g/mol by gel permeation chromatography. The changes in the surface plasmon of gold were investigated in different media, and as functions of particle concentration, as well as of temperature in aqueous solutions. The particles were soluble at least slightly in water, forming aggregates. The area and the maximum wavelength of the plasmon band in water decreased with dilution and increasing temperature. During the collapse of PNIPA ligands the surroundings of the gold surface change from hydrophilic to hydrophobic.

An aerosol flow reactor was used for the first time for high-throughput, high yield synthesis of spherical lignin particles with given inherent hydrophilicity, depending on the precursor biomolecule. In situ fractionation via Berner type impactor afforded populations with characteristic sizes ranging from ∼30 nm to 2 μm. The as-produced, dry lignin particles displayed excellent mechanical integrity, even after redispersion under high shear in either mineral oil or water. They were effective in the stabilization of oil-in-water (O/W) Pickering emulsions with tunable droplet size, depending on the dimension of the lignin particles used for emulsification. The emulsion stability correlated with particle concentration as well as the respective lignin type. For the O/W emulsions stabilized with the more hydrophilic lignin particles, negligible changes in phase separation via Ostwald ripening and coalescence were observed over a period of time of more than two months. Together with the fact that the lignin particle concentrations used in emulsification were as low as 0.1%, our results reveal a remarkable ability to endow emulsified systems with high colloidal stability. Overall, we offer a new, high-yield, scalable nanomanufacturing approach to producing dry spherical lignin particles with size control and high production capacity. A number of emerging applications for these organic particles can be envisioned and, as a proof-of-concept, we illustrate here surfactant-free emulsification.

Flaxseed oil was emulsified in whey protein isolate (WPI) and spray-dried. Powder characteristics and oxidative stability of oil at relative humidities (RH) from RH approximately 0% to RH 91% at 37 degrees C were analyzed. Oil droplets retained their forms in drying and reconstitution, but the original droplet size of the emulsion was not restored when the powder was dispersed in water. The particles seemed to be covered by a protein-rich surface layer as analyzed by electron spectroscopy for chemical analysis (ESCA). Oxidation of flaxseed oil dispersed in the WPI matrix was retarded from that of bulk oil but followed the same pattern as bulk oil with respect to humidity. A high rate of oxidation was found for both low and high humidity conditions. The lowest rate of oxidation as followed by peroxide values was found at RH 75%, a condition that is likely to diverge significantly from the monolayer moisture value. A weak baseline transition observed for the WPI matrix in a differential scanning calorimetry (DSC) thermogram suggested a glassy state of the matrix at all storage conditions. This was not consistent with the observed caking of the powder at RH 91%. Scanning electron microscopy (SEM) images revealed a considerable structural change in the WPI matrix in these conditions, which was suggested to be linked with a higher rate of oxygen transport. Possible mechanisms for oxygen transport in the whey protein matrix under variable RHs are discussed.

The effect of poly(oxyethylene), PEO, on the thermal response rate of aqueous solutions of poly(N-isopropylacrylamide), PNIPAM, block and graft copolymers has been discussed. The PNIPAM-b-PEO/water system reveals thermoresponsive properties similar to the PNIPAM/water system. In PNIPAM-g-PEO/water solutions, however, PEO provides hydrophilic channels, facilitating the diffusion of water molecules through the collapsed polymer aggregate at temperatures above the demixing temperature of the aqueous copolymer solution. As a result, the thermal response of the aqueous PNIPAM-g-PEO system is significantly faster than in the case of either pure PNIPAM or PNIPAM-b-PEO, indicating the influence of the macromolecular architecture. An attempt has also been made to correlate the thermal response kinetics of the aqueous solutions of different copolymers with the miscibility of the polymer constituents, i.e., PEO and the thermoresponsive PNIPAM backbone, which can vitrify during phase separation.