Molecular transport through nanoporous silicon nitride membranes produced from self-assembling block copolymers.

To achieve fast and selective molecular filtration, membrane materials must ideally exhibit a thin porous skin and a high density of pores with a narrow size distribution. Here, we report the fabrication of nanoporous silicon nitride membranes (NSiMs) at the full wafer scale using a versatile process combining block copolymer (BCP) self-assembly and conventional photolithography/etching techniques. In our method, self-assembled BCP micelles are used as templates for creating sub-100 nm nanopores in a thin low-stress silicon nitride layer, which is then released from the underlying silicon wafer by etching. The process yields 100 nm thick free-standing NSiMs of various lateral dimensions (up to a few mm(2)). We show that the membranes exhibit a high pore density, while still retaining excellent mechanical strength. Permeation experiments reveal that the molecular transport rate across NSiMs is up to 16-fold faster than that of commercial polymeric membranes. Moreover, using dextran molecules of various molecular weights, we also demonstrate that size-based separation can be achieved with a very good selectivity. These new silicon nanosieves offer a relevant technological alternative to commercially available ultra- and microfiltration membranes for conducting high resolution biomolecular separations at small scales.

Hierarchical positioning of gold nanoparticles into periodic arrays using block copolymer nanoring templates.

We report a simple and versatile self-assembly method for controlling the placement of functional gold nanoparticles on silicon substrates using micellar templates. The hierarchical positioning of gold nanoparticles is achieved in one-step during the spontaneous phase inversion of spherical poly(styrene)-block-poly(2-vinylpyridine) copolymer micelles into nanoring structures. The placement is mainly driven by the establishment of electrostatic interactions between the nanoparticle ligands and the pyridine groups exposed at the interface. In particular, we show the formation of ordered arrangements of single gold nanoparticles or nanoparticle clusters and demonstrate that their morphologies, densities and periodicities can be tuned by simply varying the initial block copolymer molecular weight or the deposition conditions. Besides gold nanoparticles, the method can be used for controlling the assembly of a large variety of nanoscale building blocks, thus opening an attractive pathway for generating functional hybrid surfaces with periodic nanopatterns.

Gold nanoring arrays from responsive block copolymer templates.

We report a pH-mediated synthetic route for the production of ordered and size-tuneable arrays of gold nanorings using responsive block copolymer micelles as templates.

Poly(N-isopropylacrylamide) thin films densely grafted onto gold surface: preparation, characterization, and dynamic AFM study of temperature-induced chain conformational changes.

Thermally responsive poly(N-isopropylacrylamide) (PNIPAM) films are attracting considerable attention since they offer the possibility to achieve reversible control over surface wettability and biocompatibility. In this paper, we first report a new and simple method for the grafting under melt of amine-terminated PNIPAM chains onto gold surfaces modified with a self-assembled monolayer (SAM) of reactive thiols. The formation of homogeneous tethered PNIPAM films, whose thickness can be tuned by adjusting polymer molecular weight or SAM reactivity, is evidenced by using the combination of ellipsometry, X-ray photon spectroscopy, infrared spectroscopy (PM-IRRAS), and atomic force microscopy. The calculation of grafting parameters from experimental measurements indicated the synthesis of densely grafted PNIPAM films and allowed us to predict a "brushlike" regime for the chains in good solvent. In a second part, the temperature-induced responsive properties are studied in situ by conducting dynamic AFM measurements using the amplitude modulation technique. Imaging in water environment first revealed the reversible modification of surface morphology below and above the theoretical lower critical solution temperature (LCST) of PNIPAM. Then, the determination of amplitude and phase approach curves at various temperatures provided direct measurement of the evolution of the damping factor, or similarly the dissipated energy, as a function of the probe indentation into the PNIPAM film. Most interestingly, we clearly showed the subtle and progressive thermally induced chain conformational change occurring at the scale of several nanometers around the expected LCST.