We investigate the nanostructure and the linear rheological properties of polybutylacrylate (PBA) filled with Stöber silica particles grafted with PBA chains. The silica volume fractions range from 1.8 to 4.7%. The nanostructure of these suspensions is investigated by small-angle neutron scattering (SANS), and we determine their spectromechanical behavior in the linear region. SANS measurements performed on low volume fraction composites show that the grafted silica particles are spherical, slightly polydisperse, and do not form aggregates during the synthesis process. These composites thus constitute model filled polymers. The rheological results show that introducing grafted silica particles in a polymer matrix results in the appearance of a secondary process at low frequency: for the lowest volume fractions, we observe a secondary relaxation that we attribute to the diffusion of the particles in the polymeric matrix. By increasing the silica volume fraction up to a critical value, we obtain gellike behavior at low frequency as well as the appearance of a structure factor on the scattering intensity curves obtained by SANS. Further increasing the silica particle concentration leads to composites exhibiting solidlike low-frequency behavior and to an enhanced structure peak on the SANS diagrams. This quantitative correlation between the progressive appearance of a solidlike rheological behavior, on one hand, and a structure factor, on the other hand, supports the idea that the viscoelastic behavior of filled polymers is governed by the spatial organization of the fillers in the matrix.

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The formation of amorphous carbon or graphite from C 60 under neutron irradiation is a logical expectation. Therefore we have recorded the FT-Raman spectra of both the amorphous carbon and graphite as well (Fig. 4). The two sharper graphite D and G bands are observed at 1291 and 1588 cm À1 , respectively. Similar bands were observed for amorphous carbon at 1300 and 1592 cm À1 . The very strong band at 1300 cm À1 indicates the strong disordered structure in amorphous carbon. It is clearly seen that there are no traces of these Raman features in the spectra of irradiated C 60 in Fig. 3. Probably the extent of surface decomposition is very weak, not detectable by conventional FT-Raman spectroscopy but strong enough to destroy to efficiency of Raman scattering.FT-Raman spectroscopic studies of irradiated C 60 crystals indicated a quite early decomposition of the samples already at the lowest neutron dose applied, close to 10 15 n cm [2]. Our earlier positron lifetime spectroscopic and DSC studies [3] indicated that C 60 resists up to a neutron dose of approx 10 16 n cm À2 . This difference can be explained by the fact that Raman spectroscopy is very sensitive to the slight surface decomposition which did not affect the general properties of the bulk material. It was not possible to detect the formation of amorphous carbon or graphite by FT-Raman spectroscopy but weak features of polymerised C 60 were detected. It can be concluded that FT-Raman spectroscopy is a very sensitive tool for the detection of the minor surface decomposition of polycrystalline C 60 .

Poly(lactic acid)/poly(ɛ‐caprolactone)/carbon nanotube (PLA/PCL/CNT) nanocomposites (NCs) were melt‐processed in a conventional industrial‐like twin‐screw extruder maintaining a constant PLA/PCL 80/20 wt. ratio. CNTs located in the thermodynamically favored PCL phase and, as a result, the “sea–island” morphology of the unfilled blend was replaced by a more continuous PCL dispersed phase in the ternary NCs. Rheological and electrical percolation took place at the same CNT contents (over 1.2 wt %) that TEM images suggest continuity of the PCL phase. The electrical and the low‐strain mechanical behaviors upon CNT addition were similar in the reference binary PLA/CNT and ternary PLA/PCL/CNT NCs. In the percolated NCs, the conductivity became 106–107 times higher than in the insulating compositions, while the Young modulus increased linearly upon the addition of CNT (12% increase at 4.9 wt % loading). Moreover, all the PLA/PCL/CNT NCs showed a ductile behavior (elongation at break >130%) similar to that of the unfilled PLA/PCL blend (140%), in contrast to the brittle behavior of binary PLA/CNT NCs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45265.

We investigate the influence of hydrodynamic and particle-particle interactions on the microstructure and rheological properties of semidilute colloidal suspensions of structureless particles. The time evolution is described in a mesoscopic setting in which the correlation tensor (second moment of the pair correlation function) is used as the microstructural state variable. Numerical solutions of the governing equations are then presented as linear and nonlinear responses of the suspensions to simple viscometric flows.

We report in this paper an original and simple method for the grafting of polymer chains on colloidal silica particles. We first synthesize an alkoxyamine bi-functional initiator, by coupling 2-methyl-2-[N-tert-butyl-N-(dimethoxyphosphoryl-2,2-dimethylpropyl)aminoxy]propionic acid (MAMA) and an acrylate coupling agent, 3-(trimethoxysilyl)propyl acrylate (TPMA). Based on the fact that MAMA dissociates at 25 uC, but activates polymerization of acrylates at only 110 uC, it is possible to stop the reaction after the insertion of only one CLC acrylate double bond, in the temperature range 25-80 uC. This synthetic methodology is called ''in situ thermo-dependant trapping of carbon radicals''. The ''new'' initiator obtained at that stage is then grafted on Sto ¨ber silica particles, by simple condensation of its alkoxysilane functions. We show that the initiatorgrafting density is twice as high as the value obtained by our first approach of ''trapping of carbon radicals''. The last step of the synthesis process is the grafting from polymerization of polybutylacrylate (PBA). Transmission electron microscopy (TEM) images and small-angle neutron scattering (SANS) spectra show that the PBA-grafted silica particles are spherical, with a narrow size distribution, and do not form aggregates. Moreover, by this versatile route, the grafted polymer density, the molecular weight and therefore the polymer-layer morphology, can be easily controlled and tuned. It can also be extended to other monomers that work well with SG1 nitroxide.

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