Low dimension polymer-based nanostructures for photovoltaics

In this thesis it is discussed the effect of the low dimensionality on several physical properties of hybrid nanostructures for new generation photovoltaics. We investigated several hybrid and organic model systems, consisting of an organic polymer playing the role of electron donor and a low-dimension nanostructure (1D or 0D) which acts as electron acceptor and transporter. Model potential molecular dynamics has been used to characterize the polymer morphology onto the nanostructured substrates. In particular, the wrapping phenomena on one-dimensional structures (ZnO nanoneedles and carbon nanotubes) have been analyzed as a function of several physical variables such as temperature, substrate crystallography, polymer chain length and density. It has been thus possible to observe that wrapped configurations are only metastable on carbon nanotubes at room temperature and in absence of solvents. Nevertheless, wrapped configurations induced by the solvent can be frozen due to the interactions among neighboring polymer chains. According to this study, it is possible to enhance the polymer-nanotube alignment (and thus improving the polymer transport properties) through a suitable tuning of the synthesis parameters. Conversely, wrapped geometries are stable on ZnO nanoneedles, due to the small polymer mobility on the ZnO surface. The results obtained on the morphology of polymer-ZnO hybrids have then been used as a starting point to evaluate the electronic structure and the optical absorption properties. Hybrid models consisting in a 120-atoms ZnO nanoparticle and a set of oligothiophenes have been studied through the density functional theory, and the energy-level alignment has been obtained by using the Δ-self-consistent-field method. 120-atoms ZnO nanoparticles have been synthesized and found to be particularly stable. They therefore not only represent a useful model for computational studies, but are also of potential technological interest. An important result thus obtained is to demonstrate that the interaction between the two organic/inorganic moieties shifts the energy levels, giving rise to a nonstaggered junction. This phenomenon is not present in planar ZnO substrates, but it is rather induced by the nanostructuration of the hybrid polymer/metal oxide system. From the methodological standpoint, a simplified model to predict the energy-level alignment at the interface has been developed, allowing to spare computational resources. Finally, since the atomic configuration of the 120-atoms ZnO nanoparticles is unknown, we calculated the optical absorption spectra in the near ultra-violet of a set of (ZnO)60 isomers: this information can be compared to experimental spectroscopic data and can thus be used to elucidate the most abundant structure of this cluster. The results of the present work suggest that the use of nanostructures, although opening interesting technological possibilities such as increasing the donor/acceptor interface, also requires a critical readdressing of our understanding of morphologies and electronic level alignment in low-dimension systems

Thermal boundary resistance from transient nanocalorimetry: a multiscale modeling approach

The Thermal Boundary Resistance at the interface between a nanosized Al film and an Al_{2}O_{3} substrate is investigated at an atomistic level. A room temperature value of 1.4 m^{2}K/GW is found. The thermal dynamics occurring in time-resolved thermo-reflectance experiments is then modelled via macro-physics equations upon insertion of the materials parameters obtained from atomistic simulations. Electrons and phonons non-equilibrium and spatio-temporal temperatures inhomo- geneities are found to persist up to the nanosecond time scale. These results question the validity of the commonly adopted lumped thermal capacitance model in interpreting transient nanocalorimetry experiments. The strategy adopted in the literature to extract the Thermal Boundary Resistance from transient reflectivity traces is revised at the light of the present findings. The results are of relevance beyond the specific system, the physical picture being general and readily extendable to other heterojunctions.Comment: 12 pages, 8 figure

Promising Perspectives on the Use of Fullerenes as Efficient Containers for Beryllium Atoms

The possibility of using fullerenes as containers for toxic beryllium atoms is studied by a multi-scale approach in which first-principles and classical molecular dynamics simulations are combined. By studying the energetics, electronic and spectroscopic properties of Be-fullerene systems and by simulating their interaction at finite temperature in vacuo and in representative biological environments it is concluded that: i) Be endohedral complexes can be obtained by implanting Be atoms at energies >2.3 eV that is consistent with laser implantation technologies; ii) it is in principle possible to distinguish stable endohedral complexes from metastable exohedral ones by optical absorption, suggesting that optical spectroscopy can be a valuable a non-destructive technique to assist the synthesis and the control of implanted films iii) the Be-endohedral complexes are long-lived and thermodynamically stable and can confine beryllium both in vacuo and in aqueous solution; iv) Be@C60 complexes are likely unable to penetrate the selectivity filters of a prototypical protein showing that fullerene prevents undesired interactions with biomolecules and toxicity effects of Be2+ related to replacement of the Ca2+. Overall, these results provide an assessment on the possibility to encapsulate Be atoms into fullerenes by ion implantation to synthesize inert and highly stable and safe molecular containers for toxic beryllium radionuclides. Great opportunities are expected for the realization and application of Be-C60 complexes to nanotechnology and nanomedicine with particularly appealing perspectives in the field of neutron capture therapy of cancer

Photoacoustic Sensing of Trapped Fluids in Nanoporous Thin Films: Device Engineering and Sensing Scheme

Accessing fluid infiltration in nanogranular coatings is an outstanding challenge, of relevance for applications ranging from nanomedicine to catalysis. A sensing platform, allowing to quantify the amount of fluid infiltrated in a nanogranular ultrathin coating, with thickness in the 10 to 40 nm range, is here proposed and theoretically investigated by multiscale modelling. The scheme relies on impulsive photoacoustic excitation of hypersonic mechanical breathing modes in engineered gas-phase synthesised nanogranular metallic ultathin films and time-resolved acousto-optical read-out of the breathing modes frequency shift upon liquid infiltration. A superior sensitivity, exceeding 26x103 cm^2/g, is predicted upon equivalent areal mass loading of a few ng/mm^2. The capability of the present scheme to discriminate among different infiltration patterns is discussed. The platform is an ideal tool to investigate nano fluidics in granular materials and naturally serves as a distributed nanogetter coating, integrating fluid sensing capabilities. The proposed scheme is readily extendable to other nanoscale and mesoscale porous materials.Comment: 14 pages, 4 figure

Preparation of gellan-cholesterol nanohydrogels embedding baicalin and evaluation of their wound healing activity

[EN] In the present work, the preparation, characterization and therapeutic potential of baicalin-loaded nanohydrogels are reported. The nanohydrogels were prepared by sonicating (S nanohydrogel) or autoclaving (A nanohydrogel) a dispersion of cholesterol-derivatized gellan in phosphate buffer. The nanohydrogel obtained by autoclave treatment showed the most promising results: smaller particles ( similar to 362 nm vs. similar to 530 nm), higher homogeneity (polydispersity index = similar to 0.24 vs. similar to 0.47), and lower viscosity than those obtained by sonication. In vitro studies demonstrated the ability of the nanohydrogels to favour the deposition of baicalin in the epidermis. A high biocompatibility was found for baicalin-loaded nanohydrogels, along with a great ability to counteract the toxic effect induced by hydrogen peroxide in cells, as the nanohydrogels re-established the normal conditions (similar to 100% viability). Further, the potential of baicalin-loaded nanohydrogels in skin wound healing was demonstrated in vivo in mice by complete skin restoration and inhibition of specific inflammatory markers (i.e., myeloperoxidase, tumor necrosis factor-alpha, and oedema.Financial support from University "Sapienza" - Progetti di Ricerca: grant RP116154C2EF9AC8 and grant RM11715C1743EE89 are acknowledged.Manconi, M.; Manca, M.; Caddeo, C.; Cencetti, C.; Di Meo, C.; Zoratto, N.; Nácher Alonso, A.... (2018). Preparation of gellan-cholesterol nanohydrogels embedding baicalin and evaluation of their wound healing activity. European Journal of Pharmaceutics and Biopharmaceutics. 127:244-249. https://doi.org/10.1016/j.ejpb.2018.02.015S24424912

Dynamic Local Structure in Caesium Lead Iodide: Spatial Correlation and Transient Domains

Metal halide perovskites are multifunctional semiconductors with tunable structures and properties. They are highly dynamic crystals with complex octahedral tilting patterns and strongly anharmonic atomic behaviour. In the higher temperature, higher symmetry phases of these materials, several complex structural features have been observed. The local structure can differ greatly from the average structure and there is evidence that dynamic two-dimensional structures of correlated octahedral motion form. An understanding of the underlying complex atomistic dynamics is, however, still lacking. In this work, the local structure of the inorganic perovskite CsPbI$_3$ is investigated using a new machine learning force field based on the atomic cluster expansion framework. Through analysis of the temporal and spatial correlation observed during large-scale simulations, we reveal that the low frequency motion of octahedral tilts implies a double-well effective potential landscape, even well into the cubic phase. Moreover, dynamic local regions of lower symmetry are present within both higher symmetry phases. These regions are planar and we report the length and timescales of the motion. Finally, we investigate and visualise the spatial arrangement of these features and their interactions, providing a comprehensive picture of local structure in the higher symmetry phases

Co-Loading of Ascorbic Acid and Tocopherol in Eudragit-Nutriosomes to Counteract Intestinal Oxidative Stress

The present study aimed at developing a new vesicular formulation capable of promoting the protective effect of ascorbic acid and tocopherol against intestinal oxidative stress damage, and their efficacy in intestinal wound healing upon oral administration. A pH-dependent copolymer (Eudragit® L100), a water-soluble prebiotic fibre (Nutriose® FM06), a phospholipid mixture (Lipoid S75), and two natural antioxidants (ascorbic acid and tocopherol) were combined to fabricate eudragit-nutriosomes by a simple, solvent-free procedure. The vesicles were spherical and oligolamellar, with some multicompartment structures in Eudragit-nutriosomes, small in size (~100 nm), with highly negative zeta potential. The effect of Eudragit® and Nutriose® on the stability on storage and in simulated gastrointestinal fluids were confirmed by the Turbiscan® technology and in vitro studies, respectively. Eudragit-nutriosomes exhibited a protective effect against H2O2-induced oxidative stress, and a proliferative effect in Caco-2 cells, as they provided the closure of the scratched area after 96 h of incubation. Keywords: Eudragit, Nutriose, phospholipid vesicles, antioxidant, intestinal wound healin

Ag/In lead‐free double perovskites

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A Summary of Methods for Fire Tests of Roof Coverings

AbstractThe testing method about the fire performance of roof covering and materials has not been put into operation in China. This article focuses on two main international testing about fire performance of roof covering and materials, comparing the difference between the two test methods

Atomistic investigation of the solubility of 3-alkylthiophene polymers in tetrahydrofuran solvent

We study the solubility properties of regioregular oligo(3-alkylthiophene)s in tetrahydrofuran solvent as a function of their alkyl chains length by an atomistic investigation based on model potential molecular dynamics. We make use of the Flory-Huggins theory that is typically used to study the miscibility of macromolecules and that is here applied for the first time to study the solubility of conjugated conducting polymers in a typical organic solvent. The properties of the isolated solvent and polymer are correctly reproduced, and the calculated solubilities of the oligo(3-alkylthiophene)s in tetrahydrofuran as a function of their side chains lengths are in agreement with available experimental data. Present investigation shows that the atomistic approach based on molecular dynamics is a powerful tool to study the solubility of alkylthiophenes in molecular solvents