Nanoporous thin films from ionically connected diblock copolymers

in European Polymer Journal (2012), 48(5), 940-944

An ionically connected polystyrene-block-poly(ethylene oxide) diblock copolymer (PS−+PEO) has been prepared by blending a PEO block functionalized by a dimethylamino group at one extremity with a sulfonic ... [more ▼]

An ionically connected polystyrene-block-poly(ethylene oxide) diblock copolymer (PS−+PEO) has been prepared by blending a PEO block functionalized by a dimethylamino group at one extremity with a sulfonic acid terminated PS block. Proton transfer occurs from the sulfonic acid to the dimethylamino group, resulting in the formation of an ion pair acting as a junction between the two polymer blocks. This copolymer was further used to prepare thin films with a cylindrical morphology consisting of PEO cylinders embedded in a PS matrix and oriented perpendicularly to the film surface. Nanoporous thin films with sulfonate groups on the pore walls have been finally obtained after solvent extraction of the PEO microphases. The presence of those sulfonate groups was evidenced by grafting a positively charged fluorescent dye on the pore walls. [less ▲]

Using small-angle neutron scattering to characterize the structure of liposomial and micellar samples: stimuli-responsive and drug effects

Poster (2011, June 22)

Novel graft copolymers by organometallic-mediated radical polymerization of a conjugated with a non-conjugated monomer

Scientific conference (2011, February 24)

A single synthetic small molecule that generates force against a load

in Nature Nanotechnology (2011), 6

Some biomolecules are able to generate directional forces by rectifying random thermal motions. This allows these molecular machines to perform mechanical tasks such as intracellular cargo transport or ... [more ▼]

Some biomolecules are able to generate directional forces by rectifying random thermal motions. This allows these molecular machines to perform mechanical tasks such as intracellular cargo transport or muscle contraction in plants and animals. Although some artificial molecular machines have been synthesized and used collectively to perform mechanical tasks, so far there have been no direct measurements of mechanical processes at the single-molecule level. Here we report measurements of the mechanical work performed by a synthetic molecule less than 5 nm long. We show that biased Brownian motion of the sub-molecular components in a hydro- gen-bonded [2]rotaxane—a molecular ring threaded onto a molecular axle—can be harnessed to generate significant directional forces. We used the cantilever of an atomic force microscope to apply a mechanical load to the ring during single-molecule pulling–relaxing cycles. The ring was pulled along the axle, away from the thermodynamically favoured binding site, and was then found to travel back to this site against an external load of 30 pN. Using fluctuation theorems, we were able to relate measurements of the work done at the level of individual rotaxane molecules to the free-energy change as previously determined from ensemble measurements. The results show that individual rotaxanes can generate directional forces of similar magnitude to those generated by natural molecular machines. [less ▲]

A robust antibacterial coating for stainless steel

Conference (2010, March 23)

Because of corrosion, chemical resistance, relevant mechanical and esthetical properties, stainless steel is widely used in the daily life, not only in the building industry but also in the food industry ... [more ▼]

Because of corrosion, chemical resistance, relevant mechanical and esthetical properties, stainless steel is widely used in the daily life, not only in the building industry but also in the food industry, the appliances or in the medical field, including implants in orthopedic surgery. However, stainless steel is unable to prevent bacteria from adhering, proliferating and forming a resistant biofilm. Therefore, surface modification is needed for providing the metal surface with antibacterial properties. The scientific literature is very rich in describing various methods for imparting antibacterial properties to different inorganic supports. However, the activity of the coating is generally time limited by the diffusion of the biocide in the environment. Novel robust and stable antibacterial coatings on stainless steel are thus highly desirable for the durability of the functionality. In this communication, we report on an all-in-one approach to prepare robust antimicrobial films on stainless steel using the layer-by-layer deposition of polyelectrolytes. Novel biocidal multilayered polyelectrolyte films in which the polycationic layer is silver loaded and bears 3,4-dihydroxyphenylalanine (DOPA), known as a promoter of adhesion to inorganic surfaces, were deposited onto stainless steel. DOPA was incorporated in the polycationic chains by radical copolymerisation of N-methacrylated DOPA with the commercially available quaternary ammonium salt of 2-(dimethylamino)ethyl methacrylate (DMAEMA+). Polystyrene sulfonate (PSS) was the polyanionic constituent of the films. In order to boost the antibacterial activity of the polycationic layer, AgNO3 was added to the aqueous solution of P(DOPA)-co-P(DMAEMA+), which resulted in the in-situ formation of silver based nanoparticles (Ag° and AgCl) that are sources of biocial Ag+. The layer-by-layer deposition of aqueous P(DOPA)-co-P(DMAEMA+)/AgCl/Ag0 suspension and aqueous solution of PSS provides stainless steel with high antibacterial activity against Gram-negative E. Coli bacteria. Moreover, after silver depletion, films retain some antimicrobial activity, thanks to the ammonium groups of the copolymer. We will also show how the antibacterial activity of the films can then be easily re-boosted. The multi-functionality of the P(DOPA)-co-P(DMAEMA+) is a key issue in this process (i) the DOPA co-units are anchored to stainless steel, (ii) these co-units reduce partly AgNO3 into Ag0 nanoparticles and stabilize them by chelation, (iii) the chloride counter-anions react with AgNO3 by ionic exchange, leading to the in situ formation of AgCl particles, and (iv) the ammonium groups are responsible for permanent antibacterial activity. Besides the advantage of the all-in-one process, another major advantage of the approach proposed here is the implementation of the whole process of film formation, including the synthesis of P(DOPA)-co-P(DMAEMA+), in aqueous media under very mild conditions. It makes the strategy very attractive for industrial scaling-up and sustainability applications. [less ▲]

Synthesis and pH-dependent micellization of diblock copolymer mixtures

in Journal of Colloid & Interface Science (2009), 329(2), 235-243

This work focused on the preparation and the aqueous solution properties of hybrid polymeric micelles consisting of a hydrophobic poly(ε-caprolactone) (PCL) core and a mixed shell of hydrophilic poly ... [more ▼]

This work focused on the preparation and the aqueous solution properties of hybrid polymeric micelles consisting of a hydrophobic poly(ε-caprolactone) (PCL) core and a mixed shell of hydrophilic poly(ethylene oxide) (PEO) and pH-sensitive poly(2-vinylpyridine) (P2VP). The hybrid micelles were successfully prepared by the rapid addition of acidic water to a binary solution of PCL34-b-PEO114 and PCL32-b-P2VP52 diblock copolymers in N,N-dimethylformamide. These micelles were pH-responsive as result of the pH-dependent ionization of the P2VP block. The impact of pH on the self-assembly of the binary mixture of diblocks—thus on the composition, shape, size and surface properties of the micelles—was studied by a variety of experimental techniques, i.e., dynamic and static light scattering, transmission electron microscopy, Zeta potential, fluorescence spectroscopy and complement hemolytic 50 test. [less ▲]

Dithioesters and Trithiocarbonates Monolayers on Gold

in Journal of Electron Spectroscopy & Related Phenomena (2009), 172

We show that dithioester and trithiocarbonate compounds, used as chain transfer agents in reversible addition fragmentation chain transfer polymerization, form monolayers on gold. We evidence that the ... [more ▼]

We show that dithioester and trithiocarbonate compounds, used as chain transfer agents in reversible addition fragmentation chain transfer polymerization, form monolayers on gold. We evidence that the monolayers are slightly less dense than those formed by long alkanethiols on gold, but show a surface coverage that is close to the one obtained for short alkanethiols. Since the grafting density of polymer brushes is limited by the steric hindrance which inhibits the diffusion of large free polymer chains to opensurface reactive sites, the relatively high grafting density of dithioesters and trithiocarbonates anchoring groups is not expected to limit the density of the brushes [less ▲]

First insights into electrografted polymers by AFM-based force spectroscopy

in Macromolecules (2006), 39(24), 8428-8433

The very first characterization of the structural properties of polymer films obtained by electrografting is reported. AFM-based force spectroscopy was used to investigate poly-N-succinimidyl acrylate ... [more ▼]

The very first characterization of the structural properties of polymer films obtained by electrografting is reported. AFM-based force spectroscopy was used to investigate poly-N-succinimidyl acrylate (PNSA) layers electrografted directly from a silicon substrate. Quantitative analysis of compression profiles obtained in a good solvent and single molecule bridging interaction, in light of the Alexander-de Gennes model, gave access to the grafting density and degree of polymerization. A high swelling capacity has been evidenced. This report is the first evidence that polymers obtained by cathodic electrografting are in fact brush systems, and consequently the first evidence that a polymer brush can be obtained from a direct "grafting from" method, without any intermediate layer. [less ▲]

Tuning the Hydrophilicity of Gold Nanoparticles Templated in Star-Block Copolymers

in Langmuir (2006), 22

We report on a simple procedure to tune the hydrophilicity of hybrid gold nanoparticles. The nanoparticles have been prepared in the core of a poly(ethylene glycol)-block-poly( -caprolactone) (PEG-b-PCL ... [more ▼]

We report on a simple procedure to tune the hydrophilicity of hybrid gold nanoparticles. The nanoparticles have been prepared in the core of a poly(ethylene glycol)-block-poly( -caprolactone) (PEG-b-PCL) five-arm star block copolymer. A hydrophilic corona was then added to these hybrid gold nanoparticles by direct chemisorption of trithiocarbonate-containing poly(acrylic acid) chains. These polymers were synthesized by RAFT polymerization with a trithiocarbonate as the chain-transfer agent. The efficiency of the grafting was evidenced by TEM, AFM, and DLS and by the successful transfer of these nanoparticles from organic solvent to water. [less ▲]

Nanoporous Thin Films from Self-Assembled Metallo-supramolecular Block Copolymers

in Advanced Materials (2005), 17