Structure and Dynamics of Dendronized Polymer Solutions: Gaussian Coil or Macromolecular Rod?

We investigate the conformation of well-defined dendronized polymers (denpols) based on poly­(norborene) (PNB) and poly­(<i>endo</i>-tricycle­[4.2.2.0]­deca-3,9-diene) (PTD) backbones employing static and dynamic light scattering. Their synthesis by ring-opening metathesis polymerization (ROMP) led to fully grafted and high molecular weight denpols with narrow polydispersity. In dilute solutions, the persistence lengths were estimated by static (radius of gyration) and dynamic (translational diffusion) chain conformational properties of the denpols and were compared to their homologue precursor PNB. The conformation of denpols with a third generation side dendron conforms to a semiflexible chain with a persistence length of about 6–8 nm, virtually independent of the contour length. In the semidilute regime, the thermodynamics and cooperative diffusion of denpols resemble the behavior of the precursor solutions as described by the scaling theory of flexible polymers above the crossover concentration. The assumption of extremely high chain rigidity for this class of polymers is clearly not supported, at least for the third generation dendron

Static and Dynamic Plasmon-Enhanced Light Scattering from Dispersions of Polymer-Grafted Silver Nanoprisms in the Bulk and Near Solid Surfaces

Polarized (VV) and depolarized (VH) static (SLS) and dynamic light scattering (DLS) experiments were conducted in dispersions of sterically stabilized silver nanoprisms in three different solvents where strong plasmon-enhanced scattering was observed. In the dilute regime, hydrodynamic sizes obtained from VV and VH were in good agreement with TEM data. VV correlation functions revealed two relaxation modes, reflecting the translational and rotational diffusions unambiguously. Increasing the concentration, the bimodal nature of the correlation functions was retained, and it appeared that the VH correlation function was more strongly influenced. Evanescent-wave DLS was shown to probe rotational and translational diffusion in the vicinity of a hard wall. It is suggested that DLS methodologies can be successfully applied to this type of metallic nanoparticles for characterization and exploration of their dynamics

Semifluorinated Alkanes at the Air–Water Interface: Tailoring Structure and Rheology at the Molecular Scale

Semifluorinated alkanes form monolayers with interesting properties at the air–water interface due to their pronounced amphi-solvophobic nature and the stiffness of the fluorocarbons. In the present work, using a combination of structural and dynamic probes, we investigated how small molecular changes can be used to control the properties of such an interface, in particular its organization, rheology, and reversibility during compression–expansion cycles. Starting from a reference system perfluor­(dodecyl)­dodecane, we first retained the linear structure but changed the linkage groups between the alkyl chains and the fluorocarbons, by introducing either a phenyl group or two oxygens. Next, the molecular structure was changed from linear to branched, with four side chains (two fluorocarbons and two hydrocarbons) connected to extended aromatic cores. Neutron reflectivity at the air–water interface and scanning force microscopy on deposited films show how the changes in the molecular structure affect molecular arrangement relative to the interface. Rheological and compression–expansion measurements demonstrate the significant consequences of these changes in molecular structure and interactions on the interfacial properties. Remarkably, even with these simple molecules, a wide range of surface rheological behaviors can be engineered, from viscous over viscoelastic to brittle solids, for very similar values of the surface pressure