Growth-Induced Wrinkles and Dotlike Patterns of a Swollen Fluoroalkylated Thin Film by the Reaction of Surface-Attached Polymethylhydrosiloxane.

The design of hydrophobic surfaces requires a material which has a low solid surface tension and a simple fabrication process for anchoring and controlling the surface morphology. A generic method for the spontaneous formation of robust instability patterns is proposed through the hydrosilylation of a fluoroalkene bearing dangling chains, Rf = C6F13(CH2)3-, with a soft polymethylhydrosiloxane (PMHS) spin-coated gel polymer (0.8 µm thick) using Karstedt catalyst. These patterns were easily formed by an irreversible swelling reaction due to the attachment of a layer to various substrates. The buckling instability was created by two different approaches for a gel layer bound to a rigid silicon wafer substrate (A) and to a soft nonswelling silicone elastomer foundation (B). The observations of grafted Rf-PMHS films in the swollen state by microscopy revealed two distinct permanent patterns on various substrates: dotlike of wavelength λ = 0.4-0.7 µm (A) or wrinkle of wavelength λ = 4-7 µm (B). The elastic moduli ratios of film/substrate were determined using PeakForce quantitative nanomechanical mapping. The characteristic wavelengths (λ) of the patterns for systems A and B were quantitatively estimated in relation to the thickness of the top layer. A diversity of wrinkle morphologies can be achieved by grafting different side chains on pristine PMHS films. The water contact angle (WCA) hysteresis of fluorinated chain (Rf) was enhanced upon roughening the surfaces, giving highly hydrophobic surface properties for water with static/hysteresis WCAs of 136°/74° in the resulting wrinkle (B) and 119°/41° in the dotlike of lower roughness (A). The hydrophobic properties of grafted films on A with various mixtures of hexyl/fluoroalkyl chains were characterized by static CA: WCA 104-119°, ethylene glycol CA 80-96°, and n-hexadecane CA 17-61°. A very low surface energy of 15 mN/m for Rf-PMHS was found on the smoother dotlike pattern.

Effect of glucose-induced Maillard reaction on physical, structural and antioxidant properties of chitosan derivatives-based films.

This work focused on studying the physicochemical and antioxidant properties changes of varying molecular weight (Mw) chitosan-depolymerization products (CDP)-based films occurring after crosslinking by heat-treatment and Maillard reaction (MR). Based on color properties and browning index, an enhancement of films properties was observed after treatment at 90 °C with a reduction in their water content, solubility and contact angle. Brown MR products were developed in heated films containing glucose thus improving their barrier properties. This effect was more pronounced in lower Mw-CDP based films. In addition, according to TGA, EAB and TS analyses an improvement in heat-treated films thermal stability and mechanical properties was detected and further confirmed through FTIR, X-ray and SEM analyses. The evaluation of the antioxidant potential through four different assays allowed to conclude that glucose addition, thermal treatment and the use of low Mw-CDP highly enhanced the MR-modified films antioxidant capacity. Consequently, MR crosslinked chitosan-based films could be potentially used as an alternative for bioactive and functional packaging effective in food oxidation inhibition, especially using low Mw chitosan derivatives.

Thin phosphatidylcholine films as background surfaces with further possibilities of functionalization for biomedical applications.

Non-specific adsorption is a crucial problem in the biomedical field. To produce surfaces avoiding this phenomenon, we functionalized thin (7-180 nm) poly(methylhydrosiloxane) (PMHS) network films at room temperature (≈20°C) with phospholipids (PL) bearing a phosphorylcholine head. Regardless of their mode of preparation (casting or immersion), all surfaces appeared to be very hydrophilic with a captive air-bubble contact angle stabilized around 40°. The thin films were protein-repellent in phosphate saline buffer pH 7.4 according to analysis by normal scanning confocal fluorescence. Neither was any adsorption or spreading of l-α-phosphatidylcholine liposomes on such films observed. In addition, amino functional groups could be easily attached to the surface remaining available for further functionalization.

Interface of covalently bonded phospholipids with a phosphorylcholine head: characterization, protein nonadsorption, and further functionalization.

Surface anchored poly(methylhydrosiloxane) (PMHS) thin films on oxidized silicon wafers or glass substrates were functionalized via the SiH hydrosilylation reaction with the internal double bonds of 1,2-dilinoleoyl-sn-glycero-3-phosphorylcholine (18:2 Cis). The surface was characterized by X-ray photoelectron spectroscopy, contact angle measurements, atomic force microscopy, and scanning electron microscopy. These studies showed that the PMHS top layer could be efficiently modified resulting in an interfacial high density of phospholipids. Grafted phospholipids made the initially hydrophobic surface (θ = 106°) very hydrophilic and repellent toward avidin, bovine serum albumin, bovine fibrinogen, lysozyme, and α-chymotrypsin adsorption in phosphate saline buffer pH 7.4. The surface may constitute a new background-stable support with increased biocompatibility. Further possibilities of functionalization on the surface remain available owing to the formation of interfacial SiOH groups by Karstedt-catalyzed side reactions of SiH groups with water. The presence of interfacial SiOH groups was shown by zeta potential measurements. The reactivity and surface density of SiOH groups were checked by fluorescence after reaction of a monoethoxy silane coupling agent bearing Alexa as fluorescent probe.

Adsorption of alexa-labeled Bt toxin on mica, glass, and hydrophobized glass: study by normal scanning confocal fluorescence.

We studied the kinetics of adsorption of alexa-labeled Bt toxin Cry1Aa, in monomer and oligomer states, on muscovite mica, acid-treated hydrophilic glass, and hydrophobized glass, in the configuration of laminar flow of solution in a slit. Normal confocal fluorescence through the liquid volume allows the visualization of the concentration in solution over the time of adsorption, in addition to the signal due to the adsorbed molecules at the interface. The solution signal is used as calibration for estimation of interfacial concentration. We found low adsorption of the monomer compared to oligomers on the three types of surface. The kinetic adsorption barrier for oligomers increases in the order hydrophobized glass, muscovite mica, acid-treated hydrophilic glass. This suggests enhanced immobilization in soil if toxin is under oligomer state.