title: Hydrophobic Silica Nanoparticles Induce Gel Phases in Phospholipid Monolayers.
abstract: Silica nanoparticles (SiNP) can be incorporated in phospholipid layers to form hybrid organic-inorganic bidimensional mesostructures. Controlling the dynamics in these mesostructures paves the way to high-performance drug-delivery systems. Depending on the different hydrophobicity/hydrophilicity of SiNP, recent X-ray reflectivity experiments have demonstrated opposite structural effects. While these are reasonably well understood, less is known about the effects on the dynamics, which in turn determine molecular diffusivity and the possibility of drug release. In this work we characterize the dynamics of a mixed Langmuir layer made of phospholipid and hydrophobic SiNP. We combine X-ray photon correlation spectroscopy and epifluorescence discrete Fourier microscopy to cover more than 2 decades of Q-range (0.3-80 μm(-1)). We obtain evidence for the onset of an arrested state characterized by intermittent stress-relaxation rearrangement events, corresponding to a gel dominated by attractive interactions. We compare this with our previous results from phospholipid/hydrophilic SiNP films, which show an arrested glassy phase of repulsive disks.
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma , Parma, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Orsi
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma , Parma, Italy.
authors.forename: Tiziano
authors.initials: T
authors.lastname: Rimoldi
authors.affiliation: Consiglio Nazionale delle Ricerche - Istituto per l'Energetica e le Interfasi, U.O.S. Genova (CNR IENI) , Genova, Italy.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Guzmán
authors.affiliation: Consiglio Nazionale delle Ricerche - Istituto per l'Energetica e le Interfasi, U.O.S. Genova (CNR IENI) , Genova, Italy.
authors.forename: Libero
authors.initials: L
authors.lastname: Liggieri
authors.affiliation: Consiglio Nazionale delle Ricerche - Istituto per l'Energetica e le Interfasi, U.O.S. Genova (CNR IENI) , Genova, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Ravera
authors.affiliation: ESRF-The European Synchrotron, CS 40220, 38043 Grenoble, Cedex 9, France.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Ruta
authors.affiliation: Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma , Parma, Italy.|Consiglio Nazionale delle Ricerche - Istituto per l'Energetica e le Interfasi, U.O.S. Genova (CNR IENI) , Genova, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Cristofolini