major contributions, peer journals

Light–heat conversion dynamics in highly diversified water-dispersed hydrophobic nanocrystal assemblies

A.Mazzanti, Z. Yang, M. G. Silva, N. Yang, G. Rizza, P.E. Coulon, C. Manzonif, A. M. de Paula, G. Cerullo, G. Della Valle and M.P. Pileni
Proc. Natl. Acad. Sci. USA, 2019, 116,  8161-8166

We investigate, with a combination of ultrafast optical spec- troscopy and semiclassical modeling, the photothermal proper- ties of various water-soluble nanocrystal assemblies. Broadband pump–probe experiments with ∼100-fs time resolution in the vis- ible and near infrared reveal a complex scenario for their transient optical response that is dictated by their hybrid composition at the nanoscale, comprising metallic (Au) or semiconducting (Fe3 O4 ) nanostructures and a matrix of organic ligands. We track the whole chain of energy flow that starts from light absorption by the individual nanocrystals and subsequent excitation of out-of- equilibrium carriers followed by the electron–phonon equilibra- tion, occurring in a few picoseconds, and then by the heat release to the matrix on the 100-ps timescale. Two-dimensional finite- element method electromagnetic simulations of the composite nanostructure and multitemperature modeling of the energy flow dynamics enable us to identify the key mechanism presiding over the light–heat conversion in these kinds of nanomaterials. We demonstrate that hybrid (organic–inorganic) nanocrystal assem- blies can operate as efficient nanoheaters by exploiting the high absorption from the individual nanocrystals, enabled by the dilu- tion of the inorganic phase that is followed by a relatively fast heating of the embedding organic matrix, occurring on the 100-ps timescale.

major contributions, peer journals

Mechanical properties of supracrystal.

The mechanical properties of three-dimensional self-assembled nanocrystals, as so-called supracrystals, are correlated with: i) the type of terminate groups of coating agents used to stabilize the nanocrystals; ii) their interactions with the nanocrystal surface atoms; iii) the nanocrystal morphology; iv) the interparticle distance between nanocrystals; v) translational and orientational ordering of atomic lattice planes of nanocrystals. The Young moduli evolve from a few MPa to GPa by controlling the various factors mentioned above.

Source : Mechanical properties of supracrystal. M.P Pileni EPL, 2017, 119, 37002

major contributions, peer journals

3D superlattices of uniform metal nanocrystals differing by their sizes called binary supracrystals.

By mixing uniform large and small nanocrystals (NCs), three-dimensional (3D) crystalline structures referred to as supracrystals (SCs) are produced. The small NCs fill in the interstices of large NCS self-assembled in well-defined patterns. Various binary structures are produced, in specific conditions, as predicted by a hard-sphere model. It is demonstrated that the ligands used to stabilize NCs play the role of a key parameter in the final structure, as well as the crystalline structure of the NCs, called nanocrystallinity, with production of one-component SCs characterized by vicinal surfaces. Quasi-binary SCs are produced either by a ligand exchange process during the SC growth or through magnetic forces. Using magnetic NCs having two different diameters shows unexpected destructive magnetic property.

Source : 3D superlattices of uniform metal nanocrystals differing by their sizes called binary supracrystals J.Wei,  Z. Yang, and MP.Pileni, EPL, 2017,  119,  38005


major contributions

Solubilization by reverse micelles: solute localization and structure perturbation.

In the system AOT-isooctane-water, the reverse micelle radii, governed by the water content, vary upon addition of small amounts of compounds solubilized in the microemulsion. These small variations were measured by high-resolution small-angle X-ray scattering. Structural changes are related to the solubilization sites by means of simple geometrical models. Solutes situated at the interface decrease the water core radius; solutes located in the water core increase this radius.

Source : Solubilization by reverse micelles: solute localization and structure perturbation.
M.P. Pileni, T. Zemb and C. Petit Chem. Phys. Letters., 1985, 118, 414.

major contributions

Reverse micelles : a microreactors.

In this paper an extensive introduction to  reverse micellar properties is given. It  is shown that reverse micelles can be used as microreactors to produce either well-defined nanosized crystallites or chemically modified enzymes. Solubilization of macromolecules induces either the gelation of droplets or a  percolation process followed by a phase transition. In the latter case this could favor the extraction of  product reactions catalyzed by enzymes. Finally, a summary gives some prospective aspects of the use of such water-in-oil droplets.

Source : Reverse micelles : a microreactors. M.P. Pileni. J. Phys.Chem., 1993, 97, 6961-6974.

major contributions

Self assembled monolayer of nanosized particles differing by their sizes.

Reverse micelles are  used to control the size of silver sulfide particles. After these particles are  coated with dodecanethiol, they are extracted from micelles and dispersed in heptane solution. The size of the particles is determined by transmission electron microscopy and small-angle X-ray scattering. On a solid support, a self organization of the nanosized particles in a hexagonal network is observed. The self assembly is obtained for various particle sizes (from 3  to 6  nm) and solid supports. The network takes place on a  long-range domain which is usually larger than 5 x  lo5 nm2,  By leaving a solid support in the colloidal solution, multilayers of nanoparticles are  observed, indicating that the self assembly is mainly due to Van der Waals and dispersion forces.

Source : Self assembled monolayer of nanosized particles differing by their sizes.
L.Motte, F. Billoudet and M.P. Pileni J. Phys. Chem., 1995, 99, 16425-16429.

major contributions

Nanosized Particles Made in Colloidal Assemblies. M.P.Pileni Langmuir.

 In this feature article, syntheses of nanosized particles by using colloidal assemblies as a template are described. We asked ourselves the following question: What parameters play a role in the control of the size, shape, and polydispersity? We know that parameters such as the shape of colloidal assemblies, the hydration of the head polar group, the water molecules bounded to the interface, etc. play a major role. However, there are a number of exceptions preventing any generalization. It is shown that the chemical mechanism in nanoparticles production in colloidal assemblies can differ from those usually observed in homogeneous solution. This shows that the solution chemistry cannot always be transferred to colloidal systems. It is possible to select the size and markedly reduce the polydispersity by a surface treatment of the nanoparticles. This favors formation of mono- and multilayers made of nanoparticles, and it is found that these particles form crystals organized in a three-dimensional face-centered cubic superlattice.

Source : Nanosized Particles Made in Colloidal Assemblies. M.P.Pileni Langmuir, 1997, 13, 3266-3276.

major contributions

Nanocrystals self assemblies: fabrication and collective properties.

In this feature article, the methods of obtaining various mesostructures made of nanocrystals are described. With silver and silver sulfide, the nanocrystals are able to self organize in 2D and 3D super lattices to form “supra” crystals. With cobalt and ferrites nanocrystals, it has been possible to make ribbons, dots, or labyrinths. These mesostructures present new physical properties differing from those of the isolated nanocrystal and from those of the bulk phase. Collective optical, magnetic, and transport properties are demonstrated. By applying a magnetic field during the deposition process of nanocrystals, the easy axes of the particles are oriented along the direction of the applied field, inducing again the collective magnetic properties.

Source : Nanocrystals self assemblies: fabrication and collective properties.
M.P. Pileni J. Phys. Chem., 2001, 105, 3358 – 3372 .

major contributions

Mesostructured Fluids in oil rich regions: Structural and templating approaches.

In this feature article, a phase diagram of a divalent surfactant is presented and discussed. The formation of the thermodynamically stable state of self-assembled supra-aggregates is demonstrated. Two different types of mesostructured fluids are described with either formation of a lamellar phase, containing and surrounded by a bicontinuous microemulsion, or interdigitated reverse micelles. These microstructures are used as templates where the control of the shape of copper nanocrystals is related to that of the microstructure. However, the template is not the only parameter which controls the shape of nanocrystals.

Source : Mesostructured Fluids in oil rich regions: Structural and templating approaches. M.P. Pileni Langmuir, 2001, 17, 7476-7487.

major contributions

Ferrite Magnetic Fluids: A New Fabrication Method and Magnetic Properties of Nanocrystals differing by their size and composition.

In this paper we outline different ways to make magnetic fluids from colloidal selfassemblies (normal and reverse micelles) and describe the preparation of both ferrite nanocrystals with various compositions and cobalt metal nanocrystals. The general magnetic behaviors are described but it is found that these are not applicable to the whole variety of ferrites produced. Ferrite and cobalt magnetic fluids are organized in 3D superlattices to form various mesoscopic structures. Within a number of limitations, the magnetic properties of both the above nanocrystals and these fluids have been determined and described.

Source : Ferrite Magnetic Fluids: A New Fabrication Method and Magnetic Properties of Nanocrystals differing by their size and composition. M.P. Pileni Advanced Functionalized Material, 2001, 11 , 323- 336.