Fluorine-free omniphobic slippery surfaces made of PDMS-like molecules: surface structure and wetting properties

International audienceSurfaces covered with omniphobic coatings are investigated for many applications from anti-icing, anti-corrosive to self-cleaning uses as they allow droplets of many liquids to easily slide without pinning. To this end, PDMS-like molecules can be grafted onto glass substrates by specific process conditions 1,2. These molecules are supposedly covalently grafted to the substrate, leading to the fabrication of omniphobic surfaces with low sliding angles and low hysteresis (< 10°) for a broad range of liquids. By studying the influence of the fabrication process on the surface structure and wetting properties (contact angles CA, hysteresis CAH and sliding angles SA) of the coated substrate, we highlight here the key features that lead to a highly slippery PDMS-based coating

A silicone-based slippery polymer coating with humidity–dependent nanoscale topography

International audienceHypothesis: Slippery Omniphobic Covalently Attached Liquids (SOCAL) have been proposed for making omnirepellent thin films of self-assembled dimethylsiloxane polymerbrushes grafted from silica surfaces. Smooth and flat at very small scale, these fluid surfaces could exhibit a more complex multiscale structure though showing very weak contact angle hysteresis (less than 5°).Experiment: In this work, coatings were deposited on glass surfaces from an acidic dimethoxydimethylsilane solution under carefully controlled relative humidity. Ellipsometry mapping was used to analyze the surface structuration with nanometric thickness sensitivity. The sliding properties were determined using a drop shape analyzer with a tilting device, and chemical analyses of the coatings were performed using on-surface techniques (XPS, ATR-FTIR spectroscopy).Findings: Coated materials possessed an unexpected surface structure with multiscale semispherical-like features, which surprisingly, did not increase the contact angle hysteresis. A careful study of some parameters of the coating process and the related evolution of the surface properties allowed us to propose a new model of the chemical organization of the polymer to support this remarkable liquid-like behavior. These structures are made of endgrafted strongly adsorbed Guiselin brushes with humidity-dependent thickness: the higher the humidity, the thinner and the more slippery the coating

Simultaneously measuring the dichroism and the dielectric response of an azobenzene-doped organic glass former

International audienceWe have designed an experimental setup allowing to simultaneously measure both the dielectric response of a supercooled liquid and the dynamics of azobenzene chromophores dispersed in it. Both the azobenzene chromophores and the organic glass former have been synthesized with similar reaction paths: they are chemically similar, apart from the azobenzene group responsible for the strong optical absorption in the [350; 450 nm] range for the chromophores, while the embedding supercooled liquid is optically transparent. This material is deposited on transparent electrodes with an inter-electrode gap as small as 4 µm—obtained thanks to optical lithographic techniques. We show that our setup is sensitive enough to measure the coupling between the dielectric macroscopic response and the isomerization dynamics of 1% of chromophores excited by a 0.5–5 mW/cm2 light beam. We demonstrate that this coupling neither comes from the heating of the sample due to the light absorption nor from changes of the sample shape with light. Finally, we discuss the few physical effects, which may give rise to this coupling, and show that our experiment could test some recent predictions done in the framework of random first order transition theory of the glassy state

Bis antennae amphiphilic cyclodextrins : the first examples.

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A Highly Efficient, Angle-Insensitive Solar Quantum Concentrator Based on Microstructured Plastic Optical Fiber

International audienceA new device made of very specific microstructured fluorescent plastic optical fibers, capable of concentrating solar radiation towards photovoltaic solar cells is studied in the QUYOS project. This device transforms a multidirectionnal and polychromatic flux of solar light to a monochromatic and monodirectionnal intense flux of light with a high conversion efficiency. The very specific behaviour of these fibers is due to the convergence of several quantum phenomena. Mainly the coincidence of the fluorescent band of the dye with the forbidden band of the photonic crystal from the microstructured fiber restricts the phase space of desexcitation only along the axis of the fiber. Moreover, a coupling of the fluorescence with the allowed modes of the central waveguide of the fiber does enhance the radiative desexcitation thanks to the Purcell effect

Amphiphilic Behavior of New Cholesteryl Cyclodextrins: A Molecular Study

International audienceAmphiphilic cyclodextrins (CDs) are good candidates to functionalize natural membranes as well as synthetic vesicles. In this paper, we describe the synthesis of the amphiphilic permethylated monocholesteryl α-CD (TASC). Its interfacial behavior is compared with that of the permethylated mono- and dicholesteryl β-CD analogues (TBSC and TBdSC). Langmuir isotherms suggest a reorganization upon compression for all compounds, which is quantified using neutron as well as X-ray reflectivity. The in-plane structure is characterized by atomic force microscopy (AFM) on monolayers deposited on solid substrates. A model involving a reorientation of the CD with respect to the interface to adjust its conformation to the available area per molecule is proposed. Although we observe for TBSC a rearrangement similar to TASC and TBdSC, it is already achieved at lower surface pressures compared with its disubstituted derivative. This specific behavior is explained by an increased structural flexibility and compressibility compared with TBdSC and TASC. The average number of water molecules per CD was determined using the neutron data and validated from X-ray data, which also allows the determination of the CD’s molecular volume. The permethylated CD molecules are strongly hydrated in the film, but the α-CD analogue is less hydrated than the β-CD derivatives, and hydration decreases with compression