Omar Azzaroni

Ionic Transport Through Single Solid-State Nanopores Controlled with Thermally Nanoactuated Macromolecular Gates

Single solid-state nanopores modified with poly-N-isopropylacrylamide (NIPAM) brushes display thermally controlled gating properties. Below the lower critical solubility temperature (LCST) NIPAM brushes are swollen and, consequently, dramatically reduce the effective cross section of the nanopores (see image). Conversely, above the LCST the brushes dehydrate and suffer a transition into a collapsed state, which promotes the widening of the nanopore and enables a substantial flow of ions.

Responsive Polymers End-Tethered in Solid-State Nanochannels: When Nanoconfinement Really Matters

Solid state nanochannels modified with supramolecular architectures are a new and interesting class of stimuli-responsive nanofluidic element. Their fundamental understanding requires describing the behavior of soft-materials in confined geometries and its responses to changes in solution conditions. Here, a nanochannel modified with a polyelectrolyte brush is studied with a molecular theory that incorporates the conformational behavior of the polymers, electrostatic, van der Waals, and repulsive interactions coupled with the ability of the polymer segments to regulate their charge through acid-base equilibrium. The theory predicts pH-dependent ionic conductivity in excellent agreement with experimental observations. The polymer chains undergo large conformational changes triggered by variations in the outer solution environment and the conductivity of the device is shown to be controlled by the charge state of the polymer. The degree of polymer charge is largely affected by charge regulation and nanoconfinement effects. The molecular calculations show that the apparent pK(a) inside the pore departs from that in solution when increasing the curvature of the nanochannel.

Proton-regulated rectified ionic transport through solid-state conical nanopores modified with phosphate-bearing polymer brushes

We describe the use of polyprotic polymer brushes to construct robust signal-responsive chemical devices mimicking the transport properties of proton regulated biological channels.

Synthesis of gold nanoparticles inside polyelectrolyte brushes

In this work we report on the synthesis and characterization of Au nanoparticles grown in the inner environment of cationic polyelectrolyte brushes. The nanocomposite synthesis relies on loading the macromolecular film with AuCl4− precursor ions followed by their in situ reduction to Au nanoparticles. We observed that the nanoparticles are uniform in size and are fully stabilized by the surrounding polyelectrolyte chains. Moreover, XRR analysis revealed that the Au NPs are formed within the polymer-brush layer. AFM experiments confirmed that the swelling behaviour of the brush layer is not perturbed by the presence of the loaded NPs. The Au NP-poly-METAC nanocomposite is remarkably stable to aqueous environments, suggesting the feasibility of using this kind of nanocomposite systems as robust and reliable stimuli-responsive platforms.

Polydopamine Meets Solid-State Nanopores: A Bioinspired Integrative Surface Chemistry Approach To Tailor the Functional Properties of Nanofluidic Diodes

The ability to modulate the surface chemical characteristics of solid-state nanopores is of great interest as it provides the means to control the macroscopic response of nanofluidic devices. For instance, controlling surface charge and polarity of the pore walls is one of the most important applications of surface modification that is very relevant to attain accurate control over the transport of ions through the nanofluidic architecture. In this work, we describe a new integrative chemical approach to fabricate nanofluidic diodes based on the self-polymerization of dopamine (PDOPA) on asymmetric track-etched nanopores. Our results demonstrate that PDOPA coating is not only a simple and effective method to modify the inner surface of polymer nanopores fully compatible with the fabrication of nanofluidic devices but also a versatile platform for further integration of more complex molecules through different covalent chemistries and self-assembly processes. We adjusted the chemical modification strategy to obtain various configurations of the pore surface: (i) PDOPA layer was used as primer, precursor, or even responsive functional coating; (ii) PDOPA layer was used as a platform for anchoring chemical functions via the Michael addition reaction; and (iii) PDOPA was used as a reactive layer inducing the metallization of the pore walls through the in situ reduction of metallic precursors present in solution. We believe that the transversal concept of integrative surface chemistry offered by polydopamine in combination with the remarkable physical characteristics of asymmetric nanopores constitutes a new framework to design multifunctional nanofluidic devices employing soft chemistry-based nanofunctionalization techniques.

Photoresponsive polymer brushes for hydrophilic patterning.

The use of photolabile protecting groups (PGs) as a means to create latent hydrophilic surfaces is presented. Naturally hydrophobic PGs, based on o-nitrobenzyl chemistry, are used on polymer side chains, poised for cleavage upon exposure to UV light. Removal of the PGs liberates the hydrophilic polymer, thereby switching the surface wettability from hydrophobic to hydrophilic. This switch can be augmented by increasing the surface roughness. Additionally, this system is also shown to be spatially addressable, a highly desirable property for applications which require specific regions of a surface to switch their wettability.

Facile Large-Scale Fabrication of Proton Conducting Channels

A new approach to the facile large-scale fabrication of robust silicon membranes with artificial proton conducting channels is presented. Ordered two-dimensional macroporous silicon was rendered proton conducting by growing a thick uniform polyelectrolyte brush using surface-initiated atom transfer radical polymerization throughout the porous matrix. The fabricated silicon-poly(sulfopropyl methacrylate) hybrid membranes were evaluated for their proton conductivity, ion exchange capacity, and water uptake. With proton conductivities in the range of 10(-2) S/cm, these proof-of-concept experiments highlight a promising alternative for producing tailorable proton conducting membranes. This approach constitutes a benchmark for the preparation and study of model systems and, in addition, for the large-scale fabrication of membranes suitable for a wide range of technological applications.

Highly Proton‐Conducting Self‐Humidifying Microchannels Generated by Copolymer Brushes on a Scaffold

Filling in the gaps: Macroporous silicon membranes modified with sulfonated polymer brushes have been synthesized by pore-filling surface polymerization (see picture) to give proton-conducting channels with tailor-made, finely tuned physicochemical characteristics. These membranes display high conductivity values (ca. 10(-2) S cm(-1)) regardless of the humidity, thus surpassing the performance of nafion.

Metal electrodeposition on self-assembled monolayers: a versatile tool for pattern transfer on metal thin films

Self-assembled monolayers (SAMs) of thiols on metals have attracted considerable scientific interest because their wide range of applications including their potential use for serial fabrication of nano/microstructures. Different methods have been proposed involving SAM patterning by different techniques. The patterned SAM is then used as a resist for etching, deposition on the uncovered regions or for self-assembly on the patterned SAM surface. In this work new applications of SAM-covered metals based on their excellent anti-adherent properties and their ability to allow pattern transfer from a metallic substrate to metal or alloy electrodeposits are presented. We have used electrodeposition on SAM-covered electrodes to prepare thin standing-free metal or alloy films, for patterning metal and alloy surfaces in the micro- and meso- scale, and to fabricate metallic molds and replicas of metallic masters. The SAM-covered molds produced by this technique can also be used for patterning soft and rigid polymeric films. The method is fast, inexpensive and requires only basic instrumentation available at any chemical laboratory.

A facile route for the preparation of azide-terminated polymers. "Clicking" polyelectrolyte brushes on planar surfaces and nanochannels

In this work we describe the facile preparation of azide-terminated polymers by conventional radical polymerization (cRP) using azo initiators bearing azide groups. We show that cRP provides a convenient avenue for the preparation of azide end-functional polymers in a one-step process. The versatility of this chemical methodology was demonstrated by the synthesis of unprecedented azide end group-functionalized sodium polystyrene sulfonate (PSSNa) and poly(2-methacryloyloxyethyl-trimethylammonium chloride) (PMETAC) which were then “clicked” onto alkyne-terminated silicon surfaces and polyethylene terephthalate nanochannels to form polyelectrolyte brush layers. The facile synthesis of the end-functionalized macromolecular building blocks will enable the creation of a wide variety of “clickable” architectures using very simple synthetic tools. We are confident that these results will constitute a key element in the “click” chemistry toolbox and, as such, will have strong implications for the molecular design of interfaces using macromolecular architectures.