Silane surface modification is an important tool applied to improve and/or change the properties of various substrates which find applications in various industries including medicine, transportation, construction, energy, biotechnology etc. Maintaining the integrity of the treated surface is very important to ensure the longevity and performance of the coating; however this is affected strongly by the wetting interactions at the interface.
Dipodal silanes possess two silicon atoms that can covalently bond to a surface (whereas conventional silane coupling agents only offer one such silicon atom for surface attachment). Dipodal silanes offer a distinctive advantage over conventional silanes in terms of maintaining the integrity of surface coatings, adhesive primers and composites in aqueous environments through improved ‘wet&’ durability. Such improved durability is associated with an increased crosslink density of the interphase formed across the surface, and its resistance to hydrolysis. Calculations based on the equilibrium constant for dissociation of the Si-O-Si bonds to silanols suggest that dipodal silanes may have 100,000 times greater resistance to hydrolysis than conventional silanes. Hydrolytic stability data for dipodal silanes with both hydrophobic alkyl functionality and hydrophilic PEG functionality will be compared to that obtained for conventional silanes, titanates and phosphonates with similar functionality. New dipodal silanes with “pendant” rather than “bridged” functionality will be introduced together with their stability data in aqueous environments. Significantly, in neutral and mildly acidic environments, dipodal silanes clearly demonstrate improved resistance to hydrolysis compared to conventional silanes, titanates and phosphonates, with several hydrophobic “pendant” dipodal silanes providing the best performance.

Electrochemical oxidation lithography is a scanning force lithography mode which demonstrated to be a useful tool to fabricate nanostructures with nanometer resolution. Applications of this technique include the fabrication of split-ring resonator arrays for plasmonic applications, as well as the fabrication of nanoelectronic device features, i.e., nanometric gap structures,[1] carbon nanotube assemblies,[2] single particle placement among others. The functionalization steps involved in the fabrication of such structures strongly depend on the wetting properties of the templates as well as on the utilization of tailor-made chemical interactions. In particular for optical applications there is a strong desire to utilize substrates others than silicon wafers for the fabrication of nanostructures. Up to now these possibilities were not at hand. Here we report on the extension of the range of suitable substrates for the electrochemical oxidation and functionalization process. Electrochemical oxidation lithography is based on the local electrochemical oxidation of a self-assembled monolayer consisting of n-octadecyltrichlorosilane (OTS) by means of a negatively biased conductive SFM tip. The self-assembly of OTS is however not limited only to the functionalization of silicon but can be applied also to a number of other technologically relevant materials, i.e., indium tin oxide, titanium dioxide and metal oxides like aluminum oxide. We investigated the peculiarities of the self-assembly of OTS on these substrates and studied in detail the characteristics of the electro-oxidation process. Essential parameters for the self-assembly as well as for the oxidation process are presented in a comparative study. In depth Scanning Kelvin Probe investigations were performed with the aim to elucidate the chemical nature of the formed species in the oxidation process. As a main result the strong shielding performance of the OTS monolayer could be demonstrated which effectively screens the surface potential of the underlying substrates; a result which has significant impact in the design and manipulation of electronic properties of nanostructured surfaces.[3]
These results open on the one hand the spectrum of applicable substrates for the fabrication of functional nanostructures and pave on the other hand also the way towards new applications since for the first time also transparent substrates could be used to combine the advantages of electro-oxidative SFM lithography with applications which essentially require transparent substrate materials.
[1] T.S. Druzhinina, S. Hoeppener, U.S. Schubert, Small 2012, 8, 852-857.
[2] T.S. Druzinina, C. Höppener, S. Hoeppener, U.S. Schubert, Langmuir 2013, doi.org/10.1021/la4000878.
[3] D. Meroni, S. Ardizzone, U.S. Schubert, S. Hoeppener, Adv. Funct. Mater. 2012, 20, 4376-4382.

The iCVD method is a powerful technology for engineering surfaces which utilizes the richness organic chemistry. In many cases, covalent bonding (grafting), can be achieved at the interface between the substrate and the film. The resultant conformal polymeric coatings, deposited without solvents, and at low substrate temperature (~room temperature), represent an enabling technology in many different fields of application.
For iCVD, one or more monomers species are feed simultaneously with an initiator into a vacuum chamber (~0.1 to 1 torr). The initiator, typically tert-butyl peroxide, thermally cracks over resistively heated filament wires (~250 to 300°C). The radicals produced initiated chain growth polymerization of the monomers on cooled surface (~25°C).
Surface Energy Control:
For poly(perfluorodecyl acrylate), p(PFDA), the degree of crystallinity and the orientation of the crystallites, parallel or perpendicular to the substrate, and the surface morphology, can be tuned using the iCVD process parameters (initiator to monomer flow rate ratio, filament temperature, and substrate temperature). Grafting is achieved by covalently bond of trichlorovinylsilane vapor to a silicon wafer. Polymerization through the surface vinyl groups creates anchoring point for synthesizing grafted polymer chains, resulting in durable superhydrophobic and oleophobic surfaces.
Surface Texturing Control:
Trichlorovinylsilane has been used as an adhesion promoter between polydimethyldisiloxane (PDMS) and heavily crosslinked, hard, poly(ethylene glycol diacrylate) p(EGDA) films deposited by iCVD. This system is buckled to construct highly ordered herringbone patterns through a new sequential wrinkling strategy.
Prevention of Biofouling on Reverse Osmosis Membranes:
The amine groups present in RO membranes with maleic anhydride (MA) at the interface between a zwitterionic polymer and substrate to form covalent bonds. Without MA grafting, zwitterionic films delaminated from the membrane when placed in water. The ultrathin (~20 nm) iCVD films showed anti-fouling properties against proteins and microbes without significantly impairing water flux or salt rejection performance.
Responsive iCVD films for biotechnology:
Longitudinal tissue constructs were formed inside the microgrooves of PDMS conformally coated with iCVD poly(N-isopropylacrylamide), p(NIPAAm). Its temperature response produces both swelling and a hydrophilicity change, allowing retrieval of the tissue construct from the microgroove, useful for 3D cell culture applications in tissue engineering and drug discovery

In nature, an electrical potential generated by an ionic gradient across the cell membrane plays a vital role in regulating the behaviors of membrane proteins for functioning. Examples of such proteins include certain G-protein-coupled receptors that undergo a conformational change upon electrical perturbation in the cell membrane and alter their binding affinities towards agonist ligands. Inspired by this notion, we designed a smart surface featuring a voltage-sensing molecular monolayer of an ionic headgroup-appended oligoether. By a conformational change in response to an applied electric field, this monolayer can capture and release a dendritic ionic guest molecule. When the conformational transition is restricted by a congested molecular design, the monolayer is not operable electrically in guest release. This finding not only paves the way for new electroactive materials affording high responsiveness and broad control scopes, but also provides implications for understanding the essential role of membrane potential in the function of membrane proteins.

Superhydrophobic surfaces, such as lotus leaves [1], exhibit extraordinary water repellent and self-cleaning properties. Recently, superhydrophobic surfaces were combined with photocatalytic materials to produce multifunctional surfaces. Reports on the preparation of superhydrophobic photocatalytic surfaces are limited and the techniques are problematic. Either they were created under extreme experimental conditions or the catalyst particles were embedded in the polymer matrix with reduced surface contact area, leading to lower photocatalytic activity. Scaling these techniques to produce large areas would be difficult. In addition, some films were not robust and lost their superhydrophobicity upon light irradiation.

Here we present a novel method for preparing superhydrophobic surfaces composed of photocatalytic particles. No chemical modification of the particle surfaces was required to achieve superhydrophobicity. Superhydrophobic surfaces were fabricated by printing polydimethylsiloxane (PDMS) into arrays of cylindrical cones that measure 400 µm base diameter, 25 µm tip diameter and 1000 µm tall on 500 µm pitch[2]. Catalyst particles of silicon phthalocyanine dispersed in a glass matrix, which we have shown to generate singlet oxygen (1O2) under 669nm light irradiation[3], were adhered onto the printed PDMS posts. Superhydrophobicity can be maintained, even with hydrophilic catalytic particles, due to this significant hierarchical structure. The surface has a water contact angle of 160° and maintains superhydrophobicity in contact with water under visible irradiation from a diode laser.
Another important feature of the high aspect ratio primary roughness is that it enables easy access to the plastron, i.e. the stable layer of air under the solid-liquid interface. Printing the PDMS posts on a porous membrane, and supporting the membrane over a plenum, provides a means to control the gas composition of the plastron and thus study catalysis at the solid-liquid-gas interface. The generation of 1O2 in the plastron region and the trapping of this short-lived reactive species after it travels across gas-liquid interface and is solvated in the supported solution were demonstrated. Because 1O2 generates no waste or byproducts, the fabricated superhydrophobic and photocatalytic composite surface can be used in water purification and disinfection, such as oxidizing toxic organic molecules and deactivating bacteria[4], as well as the synthesis important intermediates. Quantification of 1O2 as a function of plastron gas composition and flow rate was achieved using 9, 10-anthracene dipropionic acid as the trapping agent.
References
1. W. Barthlott, C. Neinhuis. Planta 1997, 202, 1-8.
2. M. Barahman, A. M. Lyons, Langmuir, 2011, 27, pp 9902-9909.
3. D. Bartusik, D. Aebisher, B. Ghafari, A. M. Lyons, A. Greer, Langmuir 2012, 28, 3053.
4. D. Bartusik, D. Aebisher, A. M. Lyons, A. Greer, Environ. Sci. Technol. 2012, 46, 12098.

Hydrophilicity is desirable for membranes in the water sector. Hydrophilic surfaces are less susceptible to fouling. They also improve water flux by facilitating more complete wetting of membrane structures to increase their effective porosity. However, most membranes are made from relatively hydrophobic polymers selected for their superior stability, mechanical integrity, and compatibility with traditional phase inversion fabrication techniques. Methods to hydrophilize hydrophobic membrane surfaces (e.g., plasma treatment, polymer chain grafting, or nanoparticle attachment) often suffer from lack of effectiveness, stability, or scalability. Additionally, they may compromise membrane performance by obstructing membrane pores or damaging structures that provide membrane selectivity.
In light of these challenges, a facile method for fabricating hydrophilic electrospun mats was developed. Stable nanofibers were electrospun from a solution of polysulfone (PSf) and polysulfone-block-poly(ethylene glycol) (PSf-b-PEG) in N,N-dimethylformamide. The ratio of PSf-b-PEG to PSf homopolymer in the electrospinning solution was varied, along with the total polymer concentration, to obtain nanofiber mats of differing composition and comparable structure. The nanofiber mats were then annealed in warm deionized water to drive the hydrophilic poly(ethylene glycol) (PEG) blocks toward the nanofiber surfaces. The water-insoluble PSf block and PSf homopolymer anchor the hydrophilic PEG block to the rest of the fiber, preventing its dissolution into aqueous environments.
As-spun and annealed fibers and fiber mats were characterized for morphological and material properties. Scanning electron microscopy shows that the fibers are cylindrical and mostly smooth with mean fiber diameters of 200 to 300 nm. Water contact angle decreased as annealing time increased, with drops from over 140° to less than 10° occurring with high PSf-b-PEG content and long annealing times. X-ray photoelectron spectroscopy revealed an increase of C-O bonds relative to C-C bonds as contact angle decreased, indicating that the reduction in contact angle was due to enrichment of PEG blocks at the fiber surface. Transmission electron micrographs and elemental mapping of the low contact angle fibers show that the fiber surface retains some PSf; the PEG enrichment that occurs does not form an exclusive PEG layer. Organic carbon concentration in the water used to anneal the fibers was low but increased with annealing time. When tested as a microfiltration membrane under gravity-driven flow, nanofiber mats rejected latex particles while allowing high water flux.
The use of PSf and PSf-b-PEG in this work demonstrates the potential this fabrication method has as a platform for producing high performance membranes. The bulk and surface properties of nanofibers can be tailored through custom pairing of other homopolymers and block copolymers to achieve application-specific membrane design requirements.

Osmosis describes the flow of water across semipermeable membranes powered by the chemical free energy contained in salinity gradients. It is a fundamental transport process for water in all living systems, and its applications are countless. While osmosis can fundamentally be expressed in simple terms via the van&’t Hoff ideal gas formula for the osmotic pressure, it is a complex phenomenon taking its roots in the subtle interactions occurring at the scale of the membrane nanopores.
I will first discuss some molecular views of osmosis, allowing to rationalize the osmotic pressure across nanochannels. I will then show that specific designs of nanofluidic devices allow to build an osmotic diode, leading to water flow rectification. This osmotic diode functionality opens new opportunities for water purification and complex flow control in nanochannels.
I will then report experiments on fluid transport at the nanoscales, in particular across nanopores, nanochannels and nanotubes. I will first demonstrate osmotically driven flow in nanochannels, as well as flow rectification in asymmetric nanochannels in line with the theoretical predictions for the osmotic diode.
Finally I will focus on the study of osmotic transport inside a single Boron-Nitribe nanotube. This trans-membrane nanofluidic device was developped using nanomanipulation tools using nanoscale building blocks. Experiments show unprecedented energy conversion from salt concentration gradients. Applications in the field of osmotic energy harvesting will be discussed.
References: see http://www-lpmcn.univ-lyon1.fr/~lbocquet
laquo; Giant osmotic energy conversion measured in a single transmembrane boron-nitride nanotube raquo;, A. Siria, P. Poncharal, A.-L. Biance, R. Fulcrand, X. Blase, S. Purcell, and L. Bocquet, Nature 494 455-458 (2013)
laquo; Nanofluidic osmotic dio