The layer-by-layer growth of multilayer assemblies of two polysaccharides, the polyanion hyaluronan (HA) and the polycation chitosan (CH), was investigated using atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectroscopy, with primary emphasis on the effect of the polysaccharide molecular weights on the film thickness and surface morphology. The HA/CH multilayers exhibit an exponential increase of the optical film thickness with the number of deposited bilayers. We show that the multilayer thickness at a given stage depends on the size of both CH, the diffusing polyelectrolyte, and HA, the non-diffusing species. Assemblies (12 bilayers) of high molecular weight polysaccharides (HA, 360,000; CH, 160,000) were twice as thick (approximately 900 nm vs approximately 450 nm) as those obtained with low molecular weight polymers (HA, 30,000; CH, 31,000), as assessed by AFM scratch tests. The exponential growth rate is the same for the high and low molecular weight pairs; the larger film thicknesses observed by SPR and by AFM arising from an earlier onset of the steep exponential growth phase in the case of the high molecular weight pair. In all cases, isolated islets form during the deposition of the first CH layer onto the underlying HA. Upon further film growth, individual islets coalesce into larger vermiculate features. The transition from distinct islands to vermiculate structures depends on the molecular weights of the polysaccharides and the lower molecular weight construct presents larger worm-like surface domains than the high molecular weight pair.

Phase-separated, ultrathin organic films can serve as surface templates for the selective and patterned deposition of macromolecules on the submicron scale. [1±6] Deposition is generally directed by chemical differences in the domains or domain edges generated by phase separation. We demonstrate herein that a chemically homogeneous surface exhibiting solid/fluid-phase coexistence can also be used as an COMMUNICATIONS

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The stereoselective phospholipase A2-catalyzed hydrolysis of patterned phospholipid bilayers consisting of the l- and d-isomers of alpha-dilauroylphosphatidylcholine (DLPC) and alpha-dipalmitoylphosphatidylcholine (DPPC) is reported. The stereochemically directed enzyme lithography demonstrated herein allows the parallel modification of large surface areas and constitutes a potentially useful method to structure biomimetic films, given the stereospecific action of many enzymes.

Two types of nanocomposites have been fabricated by a ball-milling technique. The first type consists of untreated titanium dioxide (TiO 2 ) incorporated into low-density polyethylene (LDPE). For the second one, TiO 2 filler chemically treated with trisilanol phenyl-polyhedral oligomeric silsesquioxane (TP-POSS) as compatibilizing agent was ball-milled with LDPE. All specimens were tested by microstructure analysis and thermal, dielectric characterization techniques. Microstructure analysis by atomic force microscopy and scanning electron microscopy show clearly an increased dispersion in presence of POSS. Scanning electron microscopy even shows the formation of a particular structure due possibly to interactions between functionalization. It was observed that the modification of the surface of TiO 2 by the POSS decreased the dielectric loss. All nanocomposites containing treated TiO 2 revealed an improvement in thermal conductivity, with the most distinct value of 19% in case of LDPE containing 5 wt % treated TiO 2 . The incorporation of TiO 2 fillers seems to reduce the dielectric breakdown strength of the nanocomposites. However, nanocomposites containing 3 and 5 wt % treated TiO 2 have exhibited a slightly enhancement in dielectric breakdown strength up to 5%. The improvement in surface resistance to partial discharge was found in all nanocomposites specimens, especially for both types of composite containing 7 wt % untreated and treated TiO 2 .

Thin layers of black phosphorus attract a growing interest in electronics and optoelectronics for their bidimensional properties (2D) giving raised to high mobility and tunable direct band gap. Thin films are however unstable in air and synthesis of high quality samples consisting of pristine few-layered materials remains challenging, as a result. We recently established that a combination of oxygen, light and moisture provides the conditions leading to a photo-oxidation of the layers. In controlled conditions, the kinetic of the reaction is well captured by a redox model, but the evolution is less clear in normal humidity conditions where water can simply accumulate at the surface and forms droplets. In the present study, we investigate the wetting properties of thin black phosphorous films and its evolution during degradation using FastScan atomic force microscopy in different humidity conditions. From a statistical analysis of the bubbles formed, the wettability is found to decrease with layer thickness. This difference in surface tension between thinner and thicker layers is ascribed to an accumulation of phosphoric acid in the bubbles, which reveals increasing degradation rates with decreasing layer thickness. From our analysis and a simple rate equation model, it is found that: i) A threshold humidity is necessary for water condensation; ii) The photo-oxidation occurs on single bubble sites; iii) Black phosphorus layers immersed in water slowly thickens and crumbles anisotropically due to water etching during degradation.

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