Colloidal Self-Assembly of Silver Nanoparticle Clusters for Optical Metasurfaces.

Optical metasurfaces are two-dimensional assemblies of nanoscale optical resonators and could constitute the next generation of ultrathin optical components. The development of methods to manufacture these nanostructures on a large scale is still a challenge, while most performance demonstrations were obtained with lithographically fabricated metasurfaces that are restricted to small scales. Self-assembly fabrication routes are promising alternatives and have been used to produce original nanoresonators.

Impact of polyelectrolyte adsorption on the rheology of concentrated poly(-isopropylacrylamide) microgel suspensions.

We explore the impact of three water-soluble polyelectrolytes (PEs) on the flow of concentrated suspensions of poly(-isopropylacrylamide) (PNIPAm) microgels with thermoresponsive anionic charge density. By progressively adding the PEs to a jammed suspension of swollen microgels, we show that the rheology of the mixtures is remarkably influenced by the sign of the PE charge, PE concentration and hydrophobicity only when the temperature is increased above the microgel volume phase transition temperature , namely when microgels collapse, they are partially hydrophobic and form a volume-spanning colloidal gel. We find that the original gel is strengthened close to the isoelectric point, attained when microgels are mixed with cationic PEs, while PE hydrophobicity rules the gel strengthening at very high PE concentrations.