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The optical response of nanoplasmonic colloids in disperse phase is strictly related to their shape. However, upon self-assembly, new optical features, for example, bonding or antibonding modes, emerge as a result of the mutual orientations of nanoparticles. The geometry of the final assemblies often determines which mode is dominating in the overall optical response. These new plasmon modes, however, are mostly observed in silico, as self-assembly in the liquid phase leads to cluster formation with a broad range of particle units. Here we show that low-symmetry clustering of gold nanorods (AuNRs) in solution can also reveal antibonding modes. We found that UV-light irradiation of colloidal dispersions of AuNRs in N-methyl-2-pyrrolidone (NMP), stabilized by poly(vinylpyrrolidone) (PVP) results in the creation of AuNRs clusters with ladderlike morphology, where antibonding modes can be identified. We propose that UV irradiation induces formation of radicals in solvent molecules, which then promote cross-linking of PVP chains on the surface of adjacent particles. This picture opens up a number of relevant questions in nanoscience and is expected to find application in light induced self-assembly of particles with various compositions and morphologies.

Scaling laws concerning a solution of linear macromolecules have been investigated by means of a relativistic theory of self-diffusion in a simple liquid. A pure liquid medium has been modeled as a four-dimensional continuum characterized by a spacetime metric, where the equation for the Brownian movement, r 2 ∝ Dt, is interpreted as a covariant law provided by an invariant self-diffusion coefficient. The local diffusivity change due to the presence of a chain molecule has then been associated with a geometrical coordinate transformation that can be studied by using classical relativistic formalisms. Special and general theories of relativity (SR and GR) have been used to study the behavior of ideal and real chains, i.e., single coils and concentrated polymer solutions, respectively. Application of SR gives scaling laws for the average end-to-end distance and global relaxation time of an ideal macromolecule (i.e., with no excluded volume effects). Einstein equations of GR for a curved and empty space return the Stokes law and the Flory formula for a real coil in a fourdimensional space. In a concentrated dispersion, they predict a new scaling behavior (involving mean size, time, viscosity, and diffusion coefficients) of which the current values of universal exponents represent a solution in both low and high molecular weight regimes and for ideal and real chains. In the end, it is suggested a correspondence between Brownian motion and field theory, and the interpretation of a polymer chain-ina-tube as a geodesic path.

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Addition of tricalcium phosphate (alpha-TCP) powders as an aqueous dispersion to a polymethylmethacrylate (PMMA) bone cement is shown to produce a class of composites that due to their microstructure and mechanical properties may be suitable for application as bone substitutes. The PMMA forms a solid cellular matrix with open cells about 100 micrometer in size and incorporating TCP clusters. The TCP aggregates inside the cells form a porous network, with average mesopore diameters of about 0.1 micrometer, that is accessible from the outer surface. If TCP is added to PMMA in the form of dried powders, the composites are not applicable as bone substitutes. The dynamic elastic modulus (DEM) and compressive and tensile strengths were measured and discussed for both classes of composites. The mechanical properties of the bone-substitute composites, although lower than the other class of composites, are still competitive with those properties of a porous ceramic matrix of hydroxyapatite and with those of natural bones.