J.P. Boilot

Bio: J.P. Boilot is an academic researcher from École Polytechnique. The author has contributed to research in topics: Nanoparticle & Sol-gel. The author has an hindex of 29, co-authored 130 publications receiving 2916 citations.

Sol-gel condensation of rapidly hydrolyzed silicon alkoxides: A joint 29Si NMR and small-angle x-ray scattering study.

Abstract: We have studied by $^{29}\mathrm{Si}$ NMR the complete condensation kinetics in the conditions of rapid hydrolysis (acidic medium, water in excess) of three silicon alkoxides. The gelation of the tetravalent tetraethoxysilane (TEOS) takes several weeks, whereas the trivalent methyltriethoxysilane (MTEOS) and vinyltriethoxysilane (VTEOS) do not form gels. From a quantitative analysis of the data, we deduce that the first steps of the condensation proceed by progressive assembling of small organized units. This accounts for the very slow kinetics (logarithmic function of time), the occurrence of highly condensed agglomerates, and the absence of gelation in trivalent systems. For the tetravalent TEOS, this is followed by an aggregation phase, which has been studied both by NMR and small-angle x-ray scattering. The fractal dimension D=1.9 and the growing kinetics (cluster size increasing as a linear function of time) are consistent with reaction-limited cluster-cluster aggregation with preferential reactivity at the external cluster sites. Finally, we suggest that the progressive transformation of the sol phase into the gel phase after the gel time can be observed by comparing static and magic-angle-spinning NMR spectra.

Synthesis and Photoluminescence of Cd1-xMnxS (x ≤ 5) Nanocrystals

Abstract: We report the synthesis of Cd1-xMnxS nanocrystals with x ≤ 5%. Special care is taken to determine the final manganese concentration in the nanoparticles. The variation of the photoluminescence spectrum of Cd1-xMnxS colloidal solutions as a function of manganese concentration is studied. Characteristic luminescence features such as emission maximum wavelength and lifetime are analyzed. We find that it is possible to isolate contributions from particles containing no, one, or more Mn2+ ions. Dopant distribution among the crystallites is random and obeys to a binomial law. The agreement with this simple statistical model allows to use simple photoluminescence experiments to determine Mn2+ mean concentration and dispersion in Cd1-xMnxS nanocrystals.

Nonmonotonic field dependence of the zero-field cooled magnetization peak in some systems of magnetic nanoparticles

Abstract: We have performed magnetic measurements on a diluted system of $\ensuremath{\gamma}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ nanoparticles $(d\ensuremath{\sim}7 \mathrm{nm})$, and on a ferritin sample. In both cases, the zero-field cooled (ZFC) peak presents a nonmonotonic field dependence, as has already been reported in some experiments, and discussed as possible evidence of resonant tunneling. Within simple assumptions, we derive expressions for the magnetization obtained in the usual ZFC, field cooled (FC) and thermoremanent magnetization (TRM) procedures. We point out that the ZFC-peak position is extremely sensitive to the width of the particle-size distribution, and give some numerical estimates of this effect. We propose to combine the FC magnetization with a modified TRM measurement, a procedure which allows a more direct access to the barrier distribution in a field. The typical barrier values that are obtained in this procedure show a monotonic decrease for increasing fields, as expected from the simple effect of anisotropy barrier lowering, in contrast with the ZFC results. From our measurements on $\ensuremath{\gamma}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ particles, we show that the width of the effective barrier distribution is slightly increasing with the field, an effect that is sufficient for causing the observed initial increase of the ZFC-peak temperatures.

Applications of hybrid organic–inorganic nanocomposites

Abstract: Organic–inorganic hybrid materials do not represent only a creative alternative to design new materials and compounds for academic research, but their improved or unusual features allow the development of innovative industrial applications. Nowadays, most of the hybrid materials that have already entered the market are synthesised and processed by using conventional soft chemistry based routes developed in the eighties. These processes are based on: a) the copolymerisation of functional organosilanes, macromonomers, and metal alkoxides, b) the encapsulation of organic components within sol–gel derived silica or metallic oxides, c) the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures, etc. The chemical strategies (self-assembly, nanobuilding block approaches, hybrid MOF (Metal Organic Frameworks), integrative synthesis, coupled processes, bio-inspired strategies, etc.) offered nowadays by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, able to direct the assembling of a large variety of structurally well defined nano-objects into complex hybrid architectures hierarchically organised in terms of structure and functions. Looking to the future, there is no doubt that these new generations of hybrid materials, born from the very fruitful activities in this research field, will open a land of promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology, medicine for example as membranes and separation devices, functional smart coatings, fuel and solar cells, catalysts, sensors, etc.

Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators

Abstract: Switches, and Actuators Masahiro Irie,*,† Tuyoshi Fukaminato,‡ Kenji Matsuda, and Seiya Kobatake †Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan ‡Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020, Japan Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan