Self-assembled structures having a regular hollow icosahedral form (such as those observed for proteins of virus capsids) can occur as a result of biomineralization processes, but are extremely rare in mineral crystallites. Compact icosahedra made from a boron oxide have been reported, but equivalent structures made of synthetic organic components such as surfactants have not hitherto been observed. It is, however, well known that lipids, as well as mixtures of anionic and cationic single chain surfactants, can readily form bilayers that can adopt a variety of distinct geometric forms: they can fold into soft vesicles or random bilayers (the so-called sponge phase) or form ordered stacks of flat or undulating membranes. Here we show that in salt-free mixtures of anionic and cationic surfactants, such bilayers can self-assemble into hollow aggregates with a regular icosahedral shape. These aggregates are stabilized by the presence of pores located at the vertices of the icosahedra. The resulting structures have a size of about one micrometre and mass of about 1010 daltons, making them larger than any known icosahedral protein assembly or virus capsid. We expect the combination of wall rigidity and holes at vertices of these icosahedral aggregates to be of practical value for controlled drug or DNA release.

Discs of finite size are a very rare form of stable surfactant self-assembly. It is shown that mixing of two oppositely charged single-chain surfactants can produce rigid nanodiscs as well as swollen lamellar liquid crystals with frozen bilayers. The crucial requirement for obtaining nanodisc self-assembly is the use of H+ and OH- as counterions. These counterions then form water and lower the conductivity to 10 microsiemens per centimeter. In the case of cationic component excess, a dilute solution of nanodiscs is in thermodynamic equilibrium with a lamellar phase. The diameter of the cationic nanodiscs is continuously adjustable from a few micrometers to 30 nanometers, with the positive charge located mainly around the edges.

The structure of asphaltene solutions in toluene was studied by small-angle neutron scattering (SANS) as a function of temperature and concentration. Temperature alters solvent quality, flocculation being expected at low temperature. SANS measurements were carried out at four different temperatures (from 73 down to 8 °C) for solute (asphaltene) volume fractions Φ ranging from =0.3 to ∼10%. Asphaltenes were found to form nanometric aggregates, whose average masses (Mw) and radii of gyration (RGZ) increased as temperature decreased. These parameters hardly varied with concentration in the dilute regime Φ e 3-4%, in which no evidence of dissociation was found. At higher Φ, apparent values of the same parameters (Mw and RGZ) decreased as repulsive interactions or aggregate interpenetration reduced the normalized intensity, I/Φ, a phenomenon reminiscent of the semidilute regime of polymers and fractal aggregates. At the two lowest temperatures studied, 8 and 20 °C, a strong scattering at low q signaled flocculation, as some of the asphaltenes formed dense domains of micronic size. This phenomenon occurred throughout the studied concentration range and entailed some limited hysteresis for time scales of the order of a few hours.

The structure of a bis-urea based reversible polymer is investigated using capillary viscosimetry, infrared spectroscopy, small-angle neutron scattering, and rheology. The highly viscoelastic solutions obtained in toluene are due to the formation of long and rigid fibrillar species. The cross section of these wires is measured and is shown to likely contain two or three molecules per axial repetition unit.