Light-controlled directional liquid drop movement on TiO2 nanorods-based nanocomposite photopatterns.

Patterned polymeric coatings enriched with colloidal TiO(2) nanorods and prepared by photopolymerization are found to exhibit a remarkable increase in their water wettability when irradiated with UV laser light. The effect can be completely reversed using successive storage in vacuum and dark ambient environment. By exploiting the enhancement of the nanocomposites hydrophilicity upon UV irradiation, we prepare wettability gradients along the surfaces by irradiating adjacent surface areas with increasing time. The gradients are carefully designed to achieve directional movement of water drops along them, taking into account the hysteresis effect that opposes the movement as well as the change in the shape of the drop during its motion. The accomplishment of surface paths for liquid flow, along which the hydrophilicity gradually increases, opens the way to a vast number of potential applications in microfluidics

Controlled Swapping of Nanocomposite Surface Wettability by Multilayer Photopolymerization

Single-layered photopolymerized nanocomposite films of polystyrene and TiO2 nanorods change their wetting characteristics from hydrophobic to hydrophilic when deposited on substrates with decreasing hydrophilicity. Interestingly, the addition of a second photopolymerized layer causes a swapping in the wettability, so that the final samples result converted from hydrophobic to hydrophilic or vice versa. The wettability characteristics continue to be swapped as the number of photopolymerized layers increases. In fact, odd-layered samples show the same wetting behavior as single-layered ones, while even-layered samples have the same surface characteristics as double-layered ones. Analytical surface studies demonstrate that all samples, independently of the number of layers, have similar low roughness, and that the wettability swap is due to the different concentration of the nanocomposites constituents on the samples surface. Particularly, the different interactions between the hydrophilic TiO2 nanorods and the underlying layer lead to different amounts of nanorods exposed on the nanocomposites surface. Moreover, due to the unique property of TiO2 to reversibly increase its wettability upon UV irradiation and subsequent storage, the wetting characteristics of the multilayered nanocomposites can be tuned in a reversible manner. In this way, a combination of substrate, number of photopolymerized layers, and external UV light stimulus can be used in order to precisely control the surface wettability properties of nanocomposite films, opening the way to a vast number of potential applications in microfluidics, protein assays, and cell growth

Spectral Imaging of UV-Blocking Carbon Dot-Based Coatings for Food Packaging Applications

Nowadays, there is an increased demand to develop alternative non-plastic packaging to be used in the food industry. The most popular biodegradable films are cellulose and poly(lactic acid) (PLA); however, there is still the need to increase their UV absorption to protect the packaging content. In this work, we have covered those biodegradable films with thin coatings based on carbon dots (CDs) dispersed in polyvinyl alcohol (PVA) deposited by spin- or spray-coating techniques. We report a strong increase in the UV light-absorbing properties, together with a detailed morphological characterization; moreover, we show the results of a new microscopy and spectral imaging technique applied to the coated samples. The scientific and technological novelty of this approach is the possibility of characterizing large areas of the material surface by the simultaneous detection of PL spectra in all the pixels of a highly spatially-resolved two-dimensional (2D) map of the surface. We report UV-excited PL maps whose detailed information allows us to clearly identify regions with different spectral behaviors and to compare their characteristic signals for different CDs:PVA deposition techniques

Nanocomposite pattern-mediated magnetic interactions for localized deposition of nanomaterials.

We present a method to create, align, and locate magnetic wires throughout and on the surface of patterned polymer matrices, following the magnetophoretic transport and self-assembly of ferromagnetic nanoparticles under a static magnetic field during laser photopolymerization of monomer/nanoparticle casted solutions. The resulting films have the ability to attract and immobilize small quantities of magnetic nanomaterials locally on the ferromagnetic wires, as proved by a detailed topography study. Magnetic studies on the films before and after the spontaneous deposition, demonstrate that the deposited nanomaterials alter significantly the magnetic character of the system, making thus possible their macroscopic identification. This offers the possibility to realize sensing devices based on hybrid materials with magnetic properties

Special Issue: Innovations in Semiconducting Block Copolymers

The current Special Issue entitled “Innovations in Semiconducting Block Copolymers” aims to discuss cutting-edge research regarding the synthesis, characterization and application of semiconducting block copolymers, with a special focus on the realization of novel and innovative nanostructured materials for the production of advanced devices suitable in different fields, ranging from sensors applications to optic photovoltaics [...

Anti-Oxidation Agents to Prevent Dye Degradation in Organic-Based Host–Guest Systems Suitable for Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) have been extensively studied as they offer a practical solution to increase the efficiency of silicon-based photovoltaics (PVs). In this context, the use of natural and organic luminescent materials is desirable in order to obtain sustainable and environmentally friendly devices. Moreover, solution-processable organic host–guest systems based on Foerster Resonant Energy Transfer (FRET) processes offer the possibility to exploit a low-cost technique to obtain an efficient energy downshift from the UV–visible to red or deep red emissions in order to concentrate the radiation in the area of maximum efficiency of the PV device. Nevertheless, organic materials are subjected to photodegradation that reduces their optical properties when exposed to UV light and oxygen. In this work, we incorporated two different antioxidant molecules (i.e., octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Octa) and L-ascorbic acid (L-Asc)) in a three-dye host–guest system and studied the corresponding optical properties after prolonged irradiation times in air. It was found that the presence of the antioxidants, especially L-Asc, slowed the system’s photodegradation down whilst at the same time retaining high emission efficiencies and without interfering with the cascade Resonant Energy Transfer processes among the dyes inserted in the nanochannels of the host

Aggregation-Induced Förster Resonance Energy Transfer in Polybenzofulvene/Dye Nanoparticles

Polymeric nanoparticles are versatile scaffolds to develop smart multichromophoric systems whose collective optical properties can be tuned in view of a specific application. Addition of water (nonsolvent) to diluted THF solutions of a blue emitting π-stacked polymer and a yellow emitting dye induces nanoparticle polymer/dye coaggregation. At 70% water content, concomitantly to nanoparticle shrinking, the emission efficiency increases and the color switches from blue to yellow. Time-resolved fluorescence analysis demonstrates that the switch in the nanoparticle emission is governed by an aggregation-induced Förster resonance energy transfer (FRET) process from the polymer to the molecularly embedded dye activated at a local concentration of about 10–2 M within the nanoparticle