Positron annihilation spectroscopy: a new frontier for understanding nanoparticle loaded polymer brushes

Nanoparticle-loaded polymer brushes are powerful tools for the development of innovative devices. However, their characterization is challenging and arrays of different techniques are typically required to gain sufficient insight. Here we demonstrate for the first time the suitability of positron annihilation spectroscopy (PAS) to investigate, with unprecedented detail and without making the least damage to samples, the physico-chemical changes experienced by pHresponsive polymer brushes after protonation and after loading of silver nanoparticles. One of the most important findings is the depth profiling of silver nanoparticles inside the brushes. These results open up a completely new way to understand the structure and behavior of such complex systems

Photocatalytic Lithography

Patterning, the controlled formation of ordered surface features with different physico-chemical properties, is a cornerstone of contemporary micro- and nanofabrication. In this context, lithographic approaches owe their wide success to their versatility and their relative ease of implementation and scalability. Conventional photolithographic methods require several steps and the use of polymeric photoresists for the development of the desired pattern, all factors which can be deleterious, especially for sensitive substrates. Efficient patterning of surfaces, with resolution down to the nanometer scale, can be achieved by means of photocatalytic lithography. This approach is based on the use of photocatalysts to achieve the selective chemical modification or degradation of self-assembled monolayers, polymers, and metals. A wide range of photoactive compounds, from semiconducting oxides to porphyrins, have been demonstrated to be suitable photocatalysts. The goal of the present review is to provide a comprehensive state-of-the-art photocatalytic lithography, ranging from approaches based on semiconducting oxides to singlet oxygen-based lithography. Special attention will be dedicated to the results obtained for the patterning of polymer brushes, the sculpturing of metal nanoparticle arrays, and the patterning of graphene-based structures

Photocatalytic Lithography

Patterning, the controlled formation of ordered surface features with different physico-chemical properties, is a cornerstone of contemporary micro- and nanofabrication. In this context, lithographic approaches owe their wide success to their versatility and their relative ease of implementation and scalability. Conventional photolithographic methods require several steps and the use of polymeric photoresists for the development of the desired pattern, all factors which can be deleterious, especially for sensitive substrates. Efficient patterning of surfaces, with resolution down to the nanometer scale, can be achieved by means of photocatalytic lithography. This approach is based on the use of photocatalysts to achieve the selective chemical modification or degradation of self-assembled monolayers, polymers, and metals. A wide range of photoactive compounds, from semiconducting oxides to porphyrins, have been demonstrated to be suitable photocatalysts. The goal of the present review is to provide a comprehensive state-of-the-art photocatalytic lithography, ranging from approaches based on semiconducting oxides to singlet oxygen-based lithography. Special attention will be dedicated to the results obtained for the patterning of polymer brushes, the sculpturing of metal nanoparticle arrays, and the patterning of graphene-based structures.ISSN:2076-341

ON/OFF switching of silicon wafer electrochemistry by pH-responsive polymer brushes

pH-Switchable electrochemical properties are demonstrated for the first time for native oxide-coated silicon wafer electrodes. Ultrathin and ultrathick pH-responsive poly(methacrylic acid) (PMAA) brushes, obtained by surface-initiated atom transfer radical polymerization, were used to achieve redox gating. PMAA brushes are reversibly switched between their protonated and deprotonated states by alternating acidic and basic pH, which corresponds to a swelling/collapsing behavior. As a result, the electrochemical properties of the PMAA brush-modified silicon electrode are switched “ON” and “OFF” simply by changing pH. The electrochemical properties of the modified electrode were examined by means of cyclic voltammetry and electrochemical impedance spectroscopy both in the absence and presence of ruthenium(III) hexamine, a well-known cationic redox probe.ISSN:2050-7526ISSN:2050-753

Superhydrophobic and photoactive films on polymer surfaces

Transparent and flexible polymeric films might represent cheap and versatile materials for applications such as low cost solar cell covers. However, their use is limited by their low mechanical hardness and UV-light sensitivity. The use of oxide coatings has been proposed to enhance the mechanical properties and UV-resistance of polymers[1]. Oxide films might also impart self-cleaning or anti-stain properties to polymer surfaces. This might represent an innovative solution to a common issue for the service life of solar cells, i.e. the loss of incident light through scattering or absorption by accumulated dust. As a matter of fact, each g/m2 of dirt on cell covers reduces their efficiency up to 33%[2]. As installed solar panels are difficult to access, self-cleaning cell covers might be a viable solution. To achieve this goal, the main challenge to overcome is the development of low temperature syntheses for the deposition of active and adhesive oxide films over polymers. In this study, adhesive, antireflective, self-cleaning or anti-stain oxide films are deposited over transparent polymers by a two-step approach. First, the polymer surface is engineered to improve the oxide adhesion by providing a homogeneous distribution of suitable functional groups. Second, a low temperature synthesis is developed to obtain transparent, photoactive or superhydrophobic TiO2/SiO2-based films starting from a colloidal oxide suspension grown under microwaves irradiation. The obtained materials are characterized for their optical (UV-vis spectroscopy), mechanical (hardness and adhesion tests), and photocatalytic properties (stain removal). Further, durability tests under environmental conditions and accelerated aging under UV-light are performed

Patterning of Stretchable Organic Electrochemical Transistors

The fabrication of stretchable electronic devices is presently rather challenging on account of both the limited number of materials showing the desired combination of mechanical and electrical properties and the lack of techniques to process and pattern them. Here we report on a fast and reliable transfer patterning process to fabricate high-resolution metal microelectrodes on polydimethylsiloxane (PDMS) by using ultrathin Parylene films (2 μm thick). By combining transfer patterning of metal electrodes with orthogonal patterning of the conducting polymer poly­(3,4-ethylenedioxythiophene) doped with polystyrenesulfonate (PEDOT:PSS) on a prestretched PDMS substrate and a biocompatible “cut and paste” hydrogel, we demonstrated a fully stretchable organic electrochemical transistor, relevant for wearable electronics, biosensors, and surface electrodes to monitor body conditions