Structural Analysis of Colloidal Titania-Based Ribbons and Their Self-Assembly upon Drying

Our paper has been published in Small Structures!

 

 

 

Synchrotron-based small- and wide-angle X-ray scattering is used to elucidate the structure of low-dimensional lepidocrocite–titanate-based nanofilaments. In the colloidal state, they consist of quantum-confined 1D NFs, loosely associated into nanoribbons, one lepidocrocite sheet thick (about 4 Å), 30–40 Å wide (5–8 NFs), and more than 300 Å long. In the dry state, they reach a final state of extended sheets, stacked three to about twenty high, whose crystallinity increases with stack height, in parallel with a decrease in photocatalytic activity. These findings suggest a kinetic pathway for the self-assembly of initially 1D titanate nanoribbons into 2D and ultimately 3D structures, providing context for a recent body of work on these low-dimensional materials.

Two-Step Reshaping of Acicular Gold Nanoparticles

 Our paper has been published in Nano Letters!

Anisometric plasmonic nanoparticles find applications in various fields, from photocatalysis to biosensing. However, exposure to heat or to specific chemical environments can induce their reshaping, leading to loss of function. Understanding this process is therefore relevant both for the fundamental understanding of such nano-objects and for their practical applications. We followed in real time the spontaneous reshaping of gold nanotetrapods in solution via optical absorbance spectroscopy, revealing a two-step kinetics (fast tip flattening into {110} facets, followed by slow arm shortening) with characteristic times a factor of 6 apart but sharing an activation energy around 1 eV. Synchrotron-based X-ray scattering confirms this time evolution, which is much faster in solution than in the dry state, highlighting the importance of the aqueous medium and supporting a dissolution–redeposition mechanism or facilitated surface diffusion. High-temperature transmission electron microscopy of the dry particles validates the solution kinetics.

Shedding Light on the Birth of Hybrid Perovskites

Our paper has been published in Chemistry of Materials! 

 

We combined synchrotron SAXS and environmental TEM to reveal the pathway leding from precursors to MAPI perovskites. This result was also featured on the cover.

 

Confinement Effects on the Structure of Entropy-Induced Supercrystals

Our paper has just been published in Small. Using LCTEM we were able to follow the desorption kinetics of gold nanoparticles from a 2D supercrystal deposited on a solid substrate.

The time and dose dependence of the process reveals that the desorption is due to loss of adhesion between the particles and the substrate, presumably due to charge buildup under the electron beam.

Polymorphous Packing of Pentagonal Nanoprisms

 Our paper has just been published in Nano Letters.

Pentagonal packing is a long-standing and rich mathematical topic: in two dimensions, the optimal (highest packing fraction η=0.921) packing of regular pentagons is a double-lattice arrangement, called the "pentagonal ice ray".

We pack pentagonal nanoprism into long-range mesocrystals by evaporation induced self-assembly and find the ice-ray structure, but also an arrangement devised by Albrecht Dürer in the 16^th century, with a slightly lower packing fraction (η=0.854), as well as intermediate polymorphs that can be obtained by a continuous sliding transformation between these two configurations.

We discuss the subtle relation between the orientational and positional order, as well as the presence of defects in the lattices.

Extracting the morphology of gold bipyramids from SAXS experiments

Our paper has just been published in Journal of Applied Crystallography.

 

We validate the use of the bicone model for extracting the form factor of gold bipyramids in solution from SAXS data.

Real-Time In Situ Observations Reveal a Double Role for Ascorbic Acid in the Anisotropic Growth of Silver on Gold

Our paper has just been published in J. Phys. Chem. Letters!

 

The preprint is available here. 

What we have found is that ascorbic acid, widely used as a mild reducing agent, also plays a shape-directing role. These two actions are difficult to decouple, since a reductant is always needed to perform reduction reactions. The workaround we found was employing the reactive species generated by the electron beam in the observation cell. 

The result is well captured by the following movies, recorded with and without ascorbic acid (all other things being equal.)

With ascorbic acid 

Without ascorbic acid

From Chains to Monolayers: Nanoparticle Assembly Driven by Smectic Topological Defects

Our paper has just been published in Nano Letters!

Insights into the Formation Mechanism of CdSe Nanoplatelets Using in Situ X-ray Scattering

Our paper has been published in Nano Letters!

What rank for Paris-Saclay?

[UPDATED on 21/05/2024 with the 2021-2023 positions (Figures 1 and 2)]
The Paris-Saclay University was officially created on December 29, 2014, but in some shape or another the project had started as early as 2010 or even in 2008, depending on the point of view. Among the declared goals of this endeavour was improving (by the year 2020) the position of the new university in the Shanghai (ARWU) ranking with respect to the Paris-Sud University, which is the main partner to the project.
In 2020, Paris-Saclay was finally ranked in the ARWU, and it jumps to 14th place overall (and to first place in mathematics!) Congratulations to my (former) colleagues for this tremendous progress!

It is interesting to compare the current and predicted ranking of Paris-Saclay (letters and red error bars).

A) The first prediction was made in 2012 by Dominique Vernay, chair of the Foundation for Scientific Cooperation (FSC) Paris-Saclay Campus (top official of the project at the time), who was confident that the new institution would reach the top 10 "of the most attractive universities in the world" [1,2]. This declaration was generally understood at the time as referring to the ARWU ranking, where the size increase of the institution would have the largest effect.

B) The 2017 objectives of Paris-Saclay were more modest, only aiming for the top 20 of the ARWU ranking. This estimation is supported by 2015 projections that predict a rank between 18 and 26 [1,2]. For reference, the same calculation for the COMUE Sorbonne Universités (resulting from the merger of Université Pierre et Marie Curie (UPMC) and Université Paris-Sorbonne) predicted the 40th place in 2016. Sorbonne Universités was finally ranked in the ARWU in 2018, at the 36th place, dropped to 44 in 2019 and oscillates around 40 since (see the Figure below.) As expected, there is no improvement with respect to the UPMC position.

 

Paris-Saclay and the Sorbonne are joined in the top 50 by the PSL University (ranked 41st) and followed by the University of Paris (ranked 69th). In France the Paris region really dominates this ranking: fifth on the list is Grenoble Alpes Universit, in the 101-150 pack.

Nanoparticle-Templated Self-Assembly of Viral Capsids Probed by Time-Resolved Absorbance Spectroscopy and X-Ray Scattering

Our paper has just been published in Phys. Rev. Applied!

Controlling the symmetry of supercrystals formed by plasmonic core-shell nanorods with tunable cross-section

Our paper has just been published in Nanoscale!

Nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging genome or polyelectrolyte

Our paper has just been published in Nature Comm.!

Direct Liquid to Crystal Transition in a Quasi-Two-Dimensional Colloidal Membrane

Our paper has just been published in J Phys Chem Lett !

Isotropic, nematic, and lamellar phases in colloidal suspensions of nanosheets

Our paper has just been published in PNAS!

The effect of gramicidin inclusions on the local order of membrane components

Our paper has just been published in The European Physical Journal E!

Coupling between Inclusions and Membranes at the Nanoscale

Our paper has just been published in Physical Review Letters!

Reversible strain alignment and reshuffling of nanoplatelet stacks confined in a lamellar block copolymer matrix

Our paper has just been published in Nanoscale!

We show that the orientation and stacking state of nanoplatelets confined within a polymer matrix can be reversibly controlled simply by pulling on the material.

Impressions from ECIS 2017 - day 2

Highlights from the morning session of the second day. I managed to miss Jacob Klein's plenary talk (on Interfacial water).

Parallel session on topics 5 and 6 (roughly, inorganic colloids)

• Andrés Guerrero-Martínez (Madrid University) on the reshaping, fragmetation and welding of gold nanoparticles using femtosecond lasers.
• Two more talks on responsive Au@polymer systems: Jonas Schubert (Dresden University) and Rafael Contreras-Cáceres (Málaga University)
• Pavel Yazhgur (postdoc at the ESPCI, Paris after a remarkable PhD at the LPS, Orsay!) on hyperuniform binary mixtures. I should write a post on hyperuniformity at some point...

Parallel session on topic 3 (polymers, liquid crystals and gels)

• Hans Juergen Butt on the crystallization of polymers or water in alumina pores.

Impressions from ECIS 2017

I'm in Madrid for the 31st conference of the European Colloid and Interface Society. Here are some highlights from the morning session:

Michael Cates on active colloids (plenary session)

I arrived late and missed some of this talk, plus I'm not a specialist in the area of active colloids. What I found interesting is the search for the minimal modification of the various Hohenberg-Halperin models (B and H) that yield interesting behaviour; I still haven't understood how breaking the time-reversal symmetry comes into play. Here is a reference I promised myself I would read on the flight back home.

Parallel session on topics 5 and 6 (roughly, inorganic colloids)

Two talks on secondary structures in gold nanoparticle systems with potential applications to SERS:

• Christian Kuttner (Dresden University) discussed the protein-mediated formation of raspberry-shaped gold clusters consisting of small particles adsorbed onto larger ones. Nice SAXS measurements reveal the presence of both particle populations.
• Joachim Koetz (Potsdam University) presented the growth of small (hemi)spherical gold clusters on triangular gold nanosheets. Several notable publications, on the synthesis of the platelets (followed by time-resolved SAXS), on their surface deposition for catalysis and detection applications and on the study of their vibrational modes using ultrafast X-ray diffraction (in collaboration with the group of Matias Bargheer.)

Two other talks focused on magnetic nanoparticles:

• Laura Rossi (Utrecht University) on the self-assembly of hematite cubes (paper not yet published).
• Golnaz Isapour (Fribourg University, in the group of Marco Lattuada) on color-changing materials based on responsive polymers (pNIPAM for temperature and PVP for pH).

Aside from the nice work, the last talk also references a paper on Color change in chameleons, from which I learned that structures that generate structural colors are called iridophores (great name!), in contrast with the pigment-bearing chromatophores. I have already written about structural colors on this blog.