The organometallic-inorganic diblock copolymer poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFDMS-b-PDMS) with a 1:6 block ratio unexpectedly forms long rodlike micelles rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared at or near ambient temperature. The cylindrical structures represent the thermodynamically preferred morphology and consist of an iron-rich PFDMS core and a corona of PDMS. The length of the micelles can be varied from 70 nm to 10 µm by altering the method of sample preparation. In addition, the dimensions of the micellar core can be controlled through variations in the length of the PFDMS block, which is achieved by altering the molecular weight of the diblock copolymer while maintaining a constant block ratio. In contrast, when micelles are formed above the T m of PFDMS (ca. 120-145°C), spherical aggregates are formed, which suggests that crystallization of the core polymer is the driving force for the formation of wormlike micelles below T m . Furthermore, the analogues with amorphous polyferrocene blocks, poly(ferrocenylmethylphenylsilane-bdimethylsiloxane) (PFMPS-b-PDMS) and poly(ferrocenylmethylethylsilane-b-dimethylsiloxane) (PFMES-b-PDMS), form spherical micelles in hexane at room temperature. This lends further support to the proposition that the crystalline nature of the PFDMS block plays a pivotal role in the unexpected formation of cylindrical micelles. To provide an application of this concept, an analogous PFDMS block copolymer with polyisoprene, PI-b-PFDMS, was prepared and, as predicted, was found to form cylindrical micelles in hexane.

This paper describes micelle exchange kinetics as a function of temperature for a pyrene derivative 1, a triglyceride containing a pyrenebutyrate ester, solubilized in aqueous micelles of Triton X-100. The kinetics were followed by stopped-flow fluorescence time-scan measurements in which the disappearance of excimer over time was monitored. Two components of the exchange process could be separated: a first-order process with an activation energy of 110 kJ/mol, and a second process with an activation energy of 160 kJ/mol. Because the second-order process had a rate (k 2 ≈ 1 × 10 6 M -1 s -1 ) at 24.6 °C that was nearly independent of the pyrene probe (1, 1-octylpyrene, 1-dodecylpyrene), the second-order process was assigned to a fusionfragmentation mechanism, rather than a "sticky-collision" mechanism. The rates of the first-order process (k 1 ≈ 12 s -1 for 1) at 24.6 °C increased with decreasing size of the probe. This step was attributed to a fragmentationgrowth mechanism in which the fragmentation rate is rate limiting. Exchange by this mechanism must involve fragmentation of a micelle containing two probe molecules to form two sub-micelles large enough to bear one of the probes.

Nanocomposites have been made by mixing soft particles (polymer latex) with hard particles (silica) in aqueous dispersions and extracting water to produce a dense film. Segregation between the two kinds of particles can be controlled, and even suppressed. The elongational modulus is strongly increased by such fillers at low deformations, and remains important at large deformations, which the samples can stand without breaking. Since the silica particles are small (200 Å), we can follow their relative displacements under stretching, by Small-Angle Neutron Scattering, through analysis and simulation of the anisotropic patterns. The latter show a crossover from affine displacements to a set of shear displacements that let the particles avoid each other at large deformations. The shear could release the localized stresses (due to polymer confinement) and dissipate more energy. In this way it may contribute to the toughness of the composite against crack propagation.Introduction. -Soft polymeric materials can be reinforced by hard inclusions called "fillers" [1,2]. Common examples are rubber reinforced by carbon black particles, and "silicone" elastomers (PDMS) reinforced by silica. The properties of interest are, at small deformations, the mechanical modulus, and, at large deformations, the resistance to tear and wear. These properties are determined by the mechanical properties of each component, by the interfacial energy [3], and by geometrical factors such as the sizes, shapes and distances of fillers [4]. However, the mechanism of reinforcement is, at present, not understood. The roles proposed for fillers include i) temporary junctions of the polymer chains [5], ii) steric restriction described by modified Einstein laws [1, 2] or more elaborated "concentrated dispersion" models [6], ramified nature of aggregates of particles [3] leading to iii) connection in a "filler network" [7], but also iv) to overlap resistance of the bushy aggregates [8].Remarkable reinforcements can be achieved with fillers that are extremely fine, e.g., nanometric: on the one hand, large increases of the modulus may be achieved, and on the other hand, the composites can still take large deformations before they rupture [1][2][3][4]9]. The origin of this toughness of nanometric composites is still in question. In this letter, we present experimental evidence for relative displacements of nanometric particles in composites that undergo large deformations. These displacements may make it possible for the material to dissipate the energy that is stored at the tip of a fracture, and thereby accommodate large deformations without rupture.