Sylvie Roke

2011 present: Julia Jacobi Chair in photomedicine, École Polytechnique Fédérale Lausanne (EPFL), CH. 2005 2012: Max Planck Research Group Leader (W2 /C3) of a centrally announced open theme independent research group. Host: The Max-Planck Institute for Metals Research, Stuttgart, DE. 2005 2005: Alexander von Humboldt Fellow, dept. of Applied Physical Chemistry, Heidelberg University, DE. 2004 2005: Postdoctoral Fellow, FOM-Institute for Plasma Physics, NL.

Size dependence of second-harmonic scattering from nanoparticles: Disentangling surface and electrostatic contributions

Bingxin Chu, Arianna Marchioro, Sylvie Roke

Polarimetric angle-resolved second-harmonic scattering (AR-SHS) is an all-optical tool enabling the study of unlabeled interfaces of nano-sized particles in an aqueous solution. As the second harmonic signal is modulated by interference between nonlinear contributions originating at the particle's surface and those originating in the bulk electrolyte solution due to the presence of a surface electrostatic field, the AR-SHS patterns give insight into the structure of the electrical double layer. The mathematical framework of AR-SHS has been previously established, in particular regarding changes in probing depth with ionic strength. However, other experimental factors may influence the AR-SHS patterns. Here, we calculate the size dependence of the surface and electrostatic geometric form factors for nonlinear scattering, together with their relative contribution to the AR-SHS patterns. We show that the electrostatic term is stronger in the forward scattering direction for smaller particle sizes, while the ratio of the electrostatic to surface terms decreases with increasing size. Besides this competing effect, the total AR-SHS signal intensity is also weighted by the particle's surface characteristics, given by the surface potential phi(0) and the second-order surface susceptibility chi((2))(s,2). The weighting effect is experimentally demonstrated by comparing SiO2 particles of different sizes in NaCl and NaOH solutions of varying ionic strengths. For NaOH, the larger chi((2))(s,2) values generated by deprotonation of surface silanol groups prevail over the electrostatic screening occurring at high ionic strengths; however, only for larger particle sizes. This study establishes a better connection between the AR-SHS patterns and surface properties and predicts trends for arbitrarily-sized particles.

AIP Publishing2023

Water Structure at the Hydrophobic Nanodroplet Surface Revealedby Vibrational Sum Frequency Scattering Using Isotopic Dilution br

Sergey Kulik, Saranya Pullanchery Sankara Narayanan, Sylvie Roke

The water structure at the hydrophobic/waterinterface is key toward understanding hydrophobicity at themolecular level. Herein, we characterize the hydrogen-bondingnetwork of interfacial water next to sub-micron-sized hydrophobicoil droplets dispersed in water using isotopic dilution vibrationalsum frequency scattering (SFS) spectroscopy. The relativeintensity of different modes, the frequency shift of the uncoupledO-D spectrum, and a low-frequency shoulder (2395 cm-1) revealthat water forms an overall stronger hydrogen-bonding networknext to hydrophobic droplets compared to bulk water and the air/water interface. Half of the spectral width of the oil droplet SFSspectrum is determined by inter- and intramolecular coupling of water molecules. Isotopic dilution also confirms the presence of abroad distribution (ca. 2640-2745 cm-1) of non-water-hydrogen-bonded O-D modes that are red-shifted and broadenedcompared to similar species at the air/water interface. This band corroborates the presence of charge transfer between water and oil

AMER CHEMICAL SOC2022

Size dependence of second-harmonic scattering from nanoparticles: Disentangling surface and electrostatic contributions

Bingxin Chu, Arianna Marchioro, Sylvie Roke

AIP Publishing2023

Size dependence of second-harmonic scattering from nanoparticles: Disentangling surface and electrostatic contributions

Tribute to Dor Ben-Amotz

Water Structure at the Hydrophobic Nanodroplet Surface Revealedby Vibrational Sum Frequency Scattering Using Isotopic Dilution br

Water Structure at the Hydrophobic Nanodroplet Surface Revealedby Vibrational Sum Frequency Scattering Using Isotopic Dilution br

Tribute to Dor Ben-Amotz

Size dependence of second-harmonic scattering from nanoparticles: Disentangling surface and electrostatic contributions