Accueil >
Production scientifique
Structure, vibration, relaxations dans les systèmes désordonnés
(39) Production(s) de l'année 2017
|
|
Granular materials flow like complex fluids
Auteur(s): Kou Binquan, Cao Yixin, Li Jindong, Xia Chengjie, Li Zhifeng, Dong Haipeng, Zhang Ang, Zhang Jie, Kob W., Wang Yujie
(Article) Publié:
Nature, vol. 551 p.360 (2017)
Texte intégral en Openaccess :
|
|
|
Methods to locate saddle points in complex landscapes
Auteur(s): Bonfanti S., Kob W.
(Article) Publié:
The Journal Of Chemical Physics, vol. 147 p.204104 (2017)
Texte intégral en Openaccess :
Ref HAL: hal-01656760_v1
DOI: 10.1063/1.5012271
WoS: 000416842200006
Exporter : BibTex | endNote
4 Citations
Résumé: .We present a class of simple algorithms that allows to find the reaction path in systems with a complexpotential energy landscape. The approach does not need any knowledge on the product state and doesnot require the calculation of any second derivatives. The underlying idea is to use two nearby points inconfiguration space to locate the path of slowest ascent. By introducing a weak noise term, the algorithmis able to find even low-lying saddle points that are not reachable by means of a slowest ascent path. Sincethe algorithm makes only use of the value of the potential and its gradient, the computational effort to findsaddles is linear in the number of degrees of freedom, if the potential is short-ranged. We test the performanceof the algorithm for two potential energy landscapes. For the M¨uller-Brown surface we find that the algorithmalways finds the correct saddle point. For the modified M¨uller-Brown surface, which has a saddle point thatis not reachable by means of a slowest ascent path, the algorithm is still able to find this saddle point withhigh probability
|
|
|
Determination of the local density of polydisperse nanoparticle assemblies
Auteur(s): Genix A.-C., Oberdisse J.
(Article) Publié:
Soft Matter, vol. 13 p.8144-8155 (2017)
Texte intégral en Openaccess :
Ref HAL: hal-01653297_v1
DOI: 10.1039/c7sm01640a
WoS: WOS:000415352100017
Exporter : BibTex | endNote
13 Citations
Résumé: Quantitative characterization of the average structure of dense nanoparticle assemblies and aggregates is a common problem in nanoscience. Small-angle scattering is a suitable technique, but it is usually limited to not too big assemblies due to the limited experimental range, low concentrations to avoid interactions, and monodispersity to keep calculations tractable. In the present paper, a straightforward analysis of the generally available scattered intensity – even for large assemblies, at high concentrations – is detailed, providing information on the local volume fraction of polydisperse particles with hard sphere interactions. It is based on the identical local structure of infinite homogeneous nanoparticle assemblies and their subsets forming finite-sized clusters. The approach is extended to polydispersity, using Monte-Carlo simulations of hard and moderately sticky hard spheres. As a result, a simple relationship between the observed structure factor minimum – termed the correlation hole – and the average local volume fraction on the scale of neighboring particles is proposed and validated through independent aggregate simulations. The relationship shall be useful as an efficient tool for the structural analysis of arbitrary aggregated colloidal systems.
|
|
|
Temperature dependence of hypersound attenuation in silica films via picosecond acoustics
Auteur(s): Huynh A., Peronne E., Gingreau C., Lafosse X., Lemaitre A., Perrin B., Vacher R., Ruffle B., Foret M.
(Article) Publié:
Physical Review B, vol. 96 p.174206 (2017)
Texte intégral en Openaccess :
Ref HAL: hal-01653086_v1
DOI: 10.1103/PhysRevB.96.174206
WoS: WOS:000415167900001
Exporter : BibTex | endNote
3 Citations
Résumé: We report picosecond acoustic measurements of longitudinal sound dispersion and attenuation in an amorphous SiO2 layer at temperatures from 20 to 300 K over frequencies ranging from about 40 to 200 GHz. The sample is a radio frequency cathodic sputtered silica layer grown on a sapphire substrate with an aluminum filmtransducer deposited on top. Acoustic attenuation is evaluated from the simultaneous analysis of three successive echoes using transfer matrix calculation. Results are found to follow rather well a model combining coupling to thermally activated relaxations of structural defects and interactions with thermal vibrations. This leads to a nontrivial variation of the attenuation coefficient with frequency and temperature. The number density of relaxing defects in the SiO2 layer is found to be slightly higher than that in bulk v-SiO2. In contrast, similar anharmonic contribution to acoustic absorption is observed in both systems. The velocity variations are also measured and are compared to the dynamical velocity changes deduced from the sound attenuation.
|
|
|
Tuning Local Nanoparticle Arrangements in TiO2-Polymer Nanocomposites by Grafting of Phosphonic Acids
Auteur(s): Genix A.-C., Schmitt-Pauly C., Alauzun Johan G., Bizien Thomas, Mutin P. Hubert, Oberdisse J.
(Article) Publié:
Macromolecules, vol. 50 p.7721-7729 (2017)
Texte intégral en Openaccess :
Ref HAL: hal-01627751_v1
DOI: 10.1021/acs.macromol.7b01371
WoS: WOS:000412965900033
Exporter : BibTex | endNote
5 Citations
Résumé: The influence of surface-modification of TiO2-nanoparticles with phosphonic acid molecules on the structure of polymer nanocomposites has been studied by small-angle scattering and transmission electron microscopy. The grafting of phosphonic acids was done by phase transfer into chloroform, and polymer nanocomposites have been formulated by solvent casting with two polymers of slightly different hydrophobicity, PMMA and PEMA. By analyzing the shape of the scattering curves around the interparticle correlation peak, and in particular the depth of the correlation hole, information on nearest neighbor correlations between nanoparticles is obtained. While local nanoparticle arrangements are found to be independent of the global particle volume fraction, they are controlled by the degree of hydrophobicity of the alkyl phosphonic acid grafts with respect to hydrophobicity of matrix. Quantitative analysis of the correlation hole thus evidences the fine-tuning of local nanocomposite structure with phosphonic acids.
|