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The adsorption of two positively charged hydroxyethylcellulose derivatives with 7 and 60 mol % positively charged groups and a cationic, hydrophobically modified hydroxyethylcellulose containing 1 mol % hydrophobic groups and 7 mol % charged groups onto flat and spherical citrate-coated gold surfaces of different sizes has been investigated. The planar surfaces were studied by means of the quartz crystal microbalance with dissipation monitoring, whereas nanoparticle suspensions were examined using dynamic light scattering and UV-vis spectroscopy. Two different driving forces for adsorption have been evaluated: the electrostatic interaction between the positive charges on the polymers and the negatively charged gold surfaces and the affinity of the polymers for gold due to hydrophobic interactions. The comparison between the data obtained from curved and planar surfaces suggests a strong correlation between surface curvature and adlayer conformation in the formation of the hybrid polymer-gold nanoparticles. The influence of particle size on the amount of adsorbed polymer has been evaluated for the different polymers. The impact of the ionic strength on polymer adsorption has been explored, and the adsorbed polymer layer has been found to protect the gold nanoparticles from aggregation when salt is added to the solution. The addition of salt to a mixture of gold particles and a charged polymer can induce a thicker adsorbed layer at low salinity, and desorption was found at high levels of salt addition.

Temperature-induced intermicellar structures in aqueous solutions of the thermoresponsive methoxypoly(ethylene glycol)-block-poly(N-isopropylacrylamide) (MPEGn-b-NIPAAM71) copolymer that exhibit a lower critical solution temperature were studied by means of turbidimetry, dynamic light scattering (DLS), shear viscosity, and rheo small-angle light scattering (rheo-SALS) methods. The length of the hydrophilic chains (MPEG) of the copolymer varies from n=0 to n=114. It is shown that this change has a major impact on the temperature-induced association behavior of the polymer in solution. The turbidity results at quiescent conditions revealed a transition peak in the turbidity curve at intermediate temperatures, and this peak as well as the cloud point is shifted toward higher temperatures with increasing length of the hydrophilic chains of the copolymer. The DLS measurements disclosed a fast and a slow relaxation mode, which both are diffusive. From the fast and slow relaxation times the sizes of unimers/micelles and intermicellar clusters, respectively, can be determined. The temperature-induced aggregation is less pronounced in solutions of copolymers with long hydrophilic chains, and the intermicellar structures exhibit an interesting transition at intermediate temperatures. In the shear viscosity measurements large association complexes are formed at high temperatures and at low shear flow for the polymers with short hydrophilic chains, whereas at high shear rates breakup of interaggregate chains was observed. For the copolymer with the highest number of hydrophilic chains (n=114), a novel transition peak was found in the viscosity data. The rheo-SALS results divulged shear-induced structural changes of the association complexes at elevated temperatures. For copolymers with short hydrophilic chains, shear-induced disruption of association complexes was found at higher temperatures, whereas for hairy micelles augmented shear flow promoted the growth of complexes.