Metastable patterning of plasma nanocomposite films by incorporating cellulose nanowhiskers.

A new method is presented for developing patterned, thin nanocomposite films by introducing cellulose nanowhiskers during the pulsed plasma polymerization of maleic anhydride. Metastable film structures develop as a combination of dewetting and buckling phenomena. By controlling the maleic anhydride monomer to cellulose nanowhisker weight ratio, the whiskers can be incorporated into a homogeneously covering patterned polymer film. Excess nanowhiskers are required to prevent complete dewetting and deposit dimensionally stable films. The formation of anchoring points is assumed to stabilize the film through a "pinning" effect to the substrate. The latter control the in-plane film stresses, similar to the effects of surface inhomogeneities such as artificial scratches. The different morphologies are evaluated by optical microscopy, AFM, contact angle measurements, and ellipsometry. Further analysis by infrared spectroscopy and XPS suggests esterification between the maleic anhydride and cellulose moieties.

Opposite responses of cells and bacteria to micro/nanopatterned surfaces prepared by pulsed plasma polymerization and UV-irradiation.

Chemically and topographically patterned surfaces have high potential as model surfaces for studying cell and bacteria responses to surface chemistry and surface topography at a nanoscale level. In this work, we demonstrated the possibility to combine pulsed plasma polymerization and UV-irradiation to obtain topographical patterns and chemical patterns perfectly controlled at microlateral resolution and sub-micrometer depth level. Biological experiments were conducted using human osteoprogenitor cells and Escherichia coli K12. Proliferation and orientation of cells and bacteria were analyzed and discussed according to the size and the chemistry of the features. This work showed interesting opposite behavior of bacteria compared to eukaryotic cells, in response to the surface chemistry and to the surface topography. This result may be particularly useful on medical implants. From a methodological point of view, it highlighted the importance of working with versatile and well-characterized surfaces before and after sterilization. It also points out the relevance and the necessity of analyzing eukaryotic cell and bacteria adhesion in parallel way.

Changes in silicon elastomeric surface properties under stretching induced by three surface treatments.

Poly(dimethylsiloxane) (PDMS) substrates are used in many applications where the substrates need to be elongated and various treatments are used to regulate their surface properties. In this article, we compare the effect of three of such treatments, namely, UV irradiation, water plasma, and plasma polymerization, both from a molecular and from a macroscopic point of view. We focus our attention in particular on the behavior of the treated surfaces under mechanical stretching. UV irradiation induces the substitution of methyl groups by hydroxyl and acid groups, water plasma leads to a silicate-like layer, and plasma polymerization causes the formation of an organic thin film with a major content of anhydride and acid groups. Stretching induces cracks on the surface both for silicate-like layers and for plasma polymer thin coatings. This is not the case for the UV irradiated PDMS substrates. We then analyzed the chemical composition of these cracks. In the case of water plasma, the cracks reveal native PDMS. In the case of plasma polymerization, the cracks reveal modified PDMS. The contact angles of plasma polymer and UV treated surfaces vary only very slightly under stretching, whereas large variations are observed for water plasma treatments. The small variation in the contact angle values observed on the plasma polymer thin film under stretching even when cracks appear on the surface are explained by the specific chemistry of the PDMS in the cracks. We find that it is very different from native PDMS and that its structure is somewhere between Si(O2) and Si(O3). This is, to our knowledge, the first study where different surface treatments of PDMS are compared for films under stretching.

Mechanically responsive films of variable hydrophobicity made of polyelectrolyte multilayers.

Mechanically responsive surfaces that allow to switch reversibly from a hydrophobic to a hydrophilic substrate are reported. The surfaces are constituted of polyelectrolyte multilayers deposited on modified charged silicone sheets. n bilayers of poly(allylamine)-Nafion (PAH-Naf) and m bilayers of poly(allylamine)-poly(acrylic acid) (PAH-PAA) composed the multilayers. A (PAH-Naf)(n) film possesses a water contact angle of around 105 degrees, whereas the contact angle of a (PAH-Naf)(4)-(PAH-PAA)(m) multilayer is around 50 degrees. When such a film with m < 5 and terminated by PAA is stretched out, its water contact angle increases up to around 100 degrees. Successive elongation/retraction cycles allow the water contact angle to alternate reversibly between 100 and 57 degrees indicating the reversible mechanical responsive nature of the film.

Hydrophobic mechanochemical treatment of metallic surfaces wettability measurements as a means of assessing homogeneity.

Hydrophobicity, lubrication and anticorrosion properties of steel substrates have been obtained by a deposition of thin film (i.e. by mechanochemical treatment) at room conditions. Stearic acid and paraffin were chosen as reactive molecules. Different abrasive powders were selected to generate active sites on the treated surfaces for adsorption of the reactive molecules and then, the results were compared. The surfaces were analyzed by reflection-absorption infrared spectroscopy (RAIRS). The results emphasize that, a thick layer of mixed stearic acid/paraffin was deposited onto the metallic surface after the treatment. After hexane rinsing we could only detect a very thin layer of oriented stearic acid molecules chemically adsorbed onto the metallic surface and which engages strong interactions with it. Whereas, RAIRS only provides molecular analysis, the XPS technique was complementary for discriminating the different surfaces. It was possible to show differences in thickness as well as in coverage according to the size and shape of abrasive particles. Furthermore, we could conclude that deposit layer is not uniform. Defects were always present and were dependent on abrasive powders used. Then wettability was assessed as a way to test the homogeneity of thin films generated by the mechanochemical treatment. In agreement with theoretical data, receding contact angle was very dependent on the defects in the deposited film. If holes or aggregates were increased in the deposit layer, the receding contact angle was decreased while advancing contact angles and equilibrium contact angles remained constant. A very important point for technological applications was that the homogeneity of the deposited film was governed by abrasive powder involved in mechanochemical treatment and contact angle values were a direct measurement of the homogeneity of surfaces generated by mechanochemical treatment.