Characterization by fluorescence energy transfer of the core of polyisoprene-poly(methyl methacrylate) diblock copolymer micelles

Fluorescence decay measurements of the rate of non-radiative direct energy transfer have been employed to characterize the core and the core-corona interface of polyisoprene-poly(methyl methacrylate) (PI-PMMA) diblock copolymer micelles in acetonitrile. These micelles consist of a core of the insoluble PI blocks and a corona of the soluble PMMA blocks. The block copolymers are labeled, at the block junction, with a single fluorescent dye, either a donor chromophore (phenanthrene) or an acceptor chromophore (anthracene). Because the polymers are junction-labeled, the chromophores are naturally confined to the interface of each micelle. Analysis of fluorescence decay data indicate that energy transfer takes place on a flat spherical surface, which implies a strong segregation between PI and PMMA in the micelle. From the data analysis, a micellar core radius of (7.6 ± 0.8) nm is calculated from which a number-average aggregation number of 98 ± 22 is obtained. Static light scattering measurements give a weight-average aggregation number of 127 ± 6. The PI-PMMA micelles are star-like with stretched PMMA corona blocks. The corona thickness of the micelles varies from 15.8 to 17.7 nm, using the hydrodynamic radius and core radius obtained from dynamic light scattering and fluorescence decay measurements, respectively

On the stability of lithocholate derivative supramolecular tubules

The self-assembly of a mannose-labelled bile salt derivative gives rise to a metastable nematic phase of monodisperse nanotubes in aqueous solutions that are characterized by a crystalline order. This work is addressed to study the relative stability of these tubular aggregates in order to have full control of such a system for possible applications. By using a static light scattering method we evaluate both the solubilities of the metastable nanotubes and of stable nanocrystals, demonstrating that these are remarkably lower than the critical micellar concentration of typical bile salts and other ionic conventional surfactants. A partial stability map is developed by combining solubility and calorimetry data, where a nematic nanotube phase region is highlighted below 60-65 °C

Supracolloidal Atomium

Nature suggests that complex materials result from a hierarchical organization of matter at different length scales. At the nano- and micrometer scale, macromolecules and supramolecular aggregates spontaneously assemble into supracolloidal structures whose complexity is given by the coexistence of various colloidal entities and the specific interactions between them. Here, we demonstrate how such control can be implemented by engineering specially customized bile salt derivative-based supramolecular tubules that exhibit a highly specific interaction with polymeric microgel spheres at their extremities thanks to their scroll-like structure. This design allows for hierarchical supracolloidal self-assembly of microgels and supramolecular scrolls into a regular framework of “nodes” and “linkers”. The supramolecular assembly into scrolls can be triggered by pH and temperature, thereby providing the whole supracolloidal system with interesting stimuli-responsive properties. A colloidal smart assembly is embodied with features of center-linker frameworks as those found in molecular metal–organic frameworks and in structures engineered at human scale, masterfully represented by the Atomium in Bruxelles

Association of a Hydrophobically Modified Polyelectrolyte and a Block Copolymer Followed by Fluorescence Techniques

By using absorption and fluorescence (steady-state and time-resolved) techniques, the interaction between a poly(acrylic acid) (PAA), randomly grafted with pyrene (Py) units (PAAMePy55), and a triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) (EO20PO68EO20, P123) was investigated. From the fluorescence data, it is shown that upon addition of P123 a decrease of the (pyrene−pyrene, Py−Py) intramolecular association, i.e., a decrease of dynamic and static excimer formation, is observed. Time-resolved fluorescence data reveal the existence of two types of monomers (monomers that are able to form excimer, MAGRE, and isolated monomers) and two excimers. Addition of P123 causes also an increase of the amount of isolated Py monomers. The overall fluorescence data suggest that the PAAMePy55 and the P123 block copolymer associate strongly at low pH, leading to the formation of P123 micelles surrounded by one PAAMePy55 chain, where the pyrene groups are located at the PPO/PEO interface of the P123 micelles. Steady-state fluorescence results also showed that an excess of P123 micelles in solution is required for the association to occur. At high pH (pH 9 and above) the situation is less clear. The steady-state (particularly in the I1/I3 ratio) and time-resolved fluorescence results indicate a contact between the pyrene groups and PEO, which then would imply that there may be an interaction, but much weaker than at low pH