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2 PhDs positions opening

The 2018 doctoral award campaign of the Ministry of Higher Education, Research and Innovation (MESRI in french) is open for ED 2MIB.

It takes place in 4 phases:

1/ Student applications on the ED's website before April 27th
2/ Selection of only one candidate for each project before April 30th
3/ Audition of the candidates by the CIM Pole Jury of the ED (May 18th)
4/ Validation and publication of the results by the ED (June 15th).
 
The candidate will pass an oral examination in front of a Jury (May 18th).
If you are interested, please contact us in advance so we can prepare well the audition which is determinant in the selection process.

click here for details and application:

subject 1: Nanocomposites plasmoniques: amélioration des propriétés d'interfaces

subject 2: Matériaux structurés innovants: étude structurale par diffusion des rayons X

The surprising self-organization of nanotubes in a very dilute columnar liquid-crystal phase

Liquid crystals have found wide applications in many fields ranging from detergents to information displays. They are an important class of “soft matter” and they are increasingly being used in the “bottom-up” self-assembly approach of the nano-structuration of materials. Moreover, liquid-crystalline organizations are frequently observed by biologists. A research team of the LPS, in collaboration with researchers from CEA-Saclay (NIMBE-LIONS), has recently discovered that one of the four major lyotropic liquid-crystal phases, the columnar one, is actually much more stable (by a factor 100 in concentration!) than considered up to now.

Nanotubes (or nanorods) in colloidal suspensions form a columnar liquid-crystal when they spontaneously organize parallel to each other, on a two-dimensional lattice perpendicular to their axes, like a bunch of pencils (Figure a). This organization was so far only expected in concentrated suspensions where the nanorods are close to contact. Here, researchers at LPS and LIONS have shown that very dilute suspensions of clay imogolite nanotubes form a columnar liquid-crystal. Imogolites are aluminosilicates (or aluminogermanates) that have raised increasing interest in the last decade. In contrast with carbon nanotubes, they are easily obtained by sol-gel processes at low temperature. Moreover, the presence of hydroxyl groups on their surface makes these nanotubes quite hydrophilic, which allows producing aqueous suspensions.

Figure: a) Schematic representation of the organisation of the nanotubes in the columnar hexagonal liquid-crystalline phase (a et b are the unit vectors of the hexagonal lattice) ; b) Small angle X-ray scattering pattern of the columnar phase aligned in an electric field; c) Structure factor showing the reflections (indicated by the red lines) of the hexagonal lattice.

 

Texture observations of very dilute suspensions (volume fraction ~ 0.3%) by polarized-light microscopy revealed the existence of an unexpected liquid-crystalline phase. Small-angle X-ray scattering measurements, performed at the SOLEIL synchrotron (Swing beamline) showed that this new phase is a columnar hexagonal liquid crystal (Figure b, c).

Despite the high dilution, the nanotubes are perfectly organized on a hexagonal lattice with a spacing (~ 80 nm) fifteen times larger than the nanotube diameter. This dilute liquid-crystal is so fluid that the nanotubes are easily aligned in an electric field, which is a prerequisite for future applications. This work has important implications for the statistical physics of colloidal suspensions of charged rod-like particles, like biopolymers, and their fundamental understanding. It also opens new perspectives, for instance, in the field of nanocomposite materials where the organization of anisotropic particles is required to improve physical properties.

 

Reference

Paineau E., Krapf, M.E.M., Amara M.S., Matskova, N.V., Dozov, I., Rouzière S., Thill, A., Launois, P. et Davidson, P.. A liquid-crystalline hexagonal columnar phase in highly-dilute suspensions of imogolite nanotubes. Nat. Commun., 7, 10271 (2016)

Contacts

Erwan Paineau (erwan-nicolas.paineau@u-psud.fr)

Patrick Davidson (patrick.davidson@u-psud.fr)

Laboratoire de Physique des Solides, CNRS, Univ. Paris Sud, Université Paris Saclay, 91405 Orsay cedex, France

Review article free to download

We are pleased to share that our review article "Colloidal Design of Plasmonic Sensors Based on Surface Enhanced Raman Scattering", published in Journal of Colloid and Interface Science, is now available online and free to download until December 26, 2017. This is a joint work with Luis Liz Marzan (CIC Biomagune, Spain). You can access the article by cliking on the following link: https://authors.elsevier.com/a/1W0BD4-sDFY5b.

 

 

Abstract: This feature article focuses on the use of colloid chemistry to engineer metallic nanostructures toward application in surface enhanced Raman scattering (SERS) sensing, in particular for ‘real-life’ applications, where the analyte may be present in complex mixtures. We present a broad summary of the field, including recent advances that have been developed during the past 10 years. Real-life applications require a rational design and we aimed at identifying the key elements involved in it. The discussion is centered around colloidal plasmonic nanoparticles and therefore we start from the library of morphologies that have been reported in the literature. To complete the picture, colloidal self-assembly, surface chemistry and the combination with materials science techniques are highlighted. Considering the progress in the field, SERS may ultimately realize its full potential as an ultrasensitive tool for routine analytical applications.