Modulating Polymer Ultrathin Film Crystalline Fraction and Orientation with Nanoscale Curvature.

We investigated the effect of nanoscale curvature on the structure of thermally equilibrated poly-3-hexylthiophene (P3HT) ultrathin films. The curvature-induced effects were investigated with synchrotron grazing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). Our results demonstrate that nanoscale curvature reduces the polymer crystalline fraction and the crystal length. The first effect is strongest for the lowest curvature and results in a decrease in the out-of-plane thickness of the polymer crystals. On the other hand, the crystal in-plane length decreases with the increase in substrate curvature. Finally, the semi-quantitative analysis of crystal anisotropy shows a marked dependence on the substrate curvature characterized by a minimum at curvatures between 0.00851 nm-1 and 0.0140 nm-1. The results are discussed in terms of a curvature-dependent polymer fraction, which fills the interstices between neighboring particles and cannot crystallize due to extreme space confinement. This fraction, whose thickness is highest at the lowest curvatures, inhibits the crystal nucleation and the out-of-plane crystal growth. Moreover, because of the adhesion to the curved portion of the substrates, crystals adopt a random orientation. By increasing the substrate curvature, the amorphous fraction is reduced, leading to polymer films with higher crystallinity. Finally, when the thickness of the film exceeds the particle diameter, the curvature no longer affects the crystal orientation, which, similarly to the flat case, is predominantly edge on.

Direct Measurement of Surfactant-Mediated Picoforces among Nanoparticles in a Quasi-Two-Dimensional Environment.

The lack of methodologies which enable us to measure forces acting between nanomaterials is one of the factors limiting the full comprehension of their behavior and their more effective exploitation in new devices. Here we exploit the irreversible adsorption of surfactant-decorated nanoparticles at the air/water interface to investigate interparticle forces and the effect of the surfactant structure on them. We measured the interparticle repulsive forces as a function of the modulation of the interparticle distance by simultaneously performing compression isotherms and the grazing incidence small-angle X-ray scattering (GISAXS) structural characterization of the monolayers at water-vapor interfaces. Our results demonstrate that the short-range interparticle forces are strongly affected by the presence of the organic ligands, which are shown to be able to influence the interparticle repulsions even when added in micromolar amounts. In particular, we demonstrate the predominant steric nature of short-range forces, which are accounted for in terms of the compression-induced stretched-to-coiled conformational transition of the ligand hydrophobic tail.

In situ structure and force characterization of 2D nano-colloids at the air/water interface.

The control of self-assembly and the related interactions among nanoparticles (NPs) at liquid surfaces and interfaces represents a stimulating experimental challenge to fully understand the behaviour of nano-colloids confined in a 2D asymmetric environment, in turn prompting the building of novel NP-based functional monolayers. Here, we first investigate the structural evolution of a model mixed surfactant/NP monolayer as a function of the surfactant/NP bulk ratio finding that, at ratios lower than 20, the adsorption at the air/water interface of surfactant-decorated NPs is dominant. We then employed these 2D nano-colloidal monolayers as model systems for grazing incidence small angle X-ray scattering measurements, performed using synchrotron radiation, while compressing the monolayers in a Langmuir trough. The simultaneous determination of the compression work and the related reduction of the inter-particle distance at the interface enabled, for the first time, the quantitative characterization of the forces acting between adsorbed NPs, as well as their dispersion law with the inter-particle distance. Distinct surfactant reorganization processes are proposed to interpret the measured forces and the characteristic inter-particle distances.

Reactive nanomessengers for artificial chemical communication.

Artificial chemical communication is an emerging field of study driven by the need of exchanging information in delicate environments where standard procedures based on electromagnetic waves cannot be used. A non-synchronized artificial chemical communication system, based on a new modulation technique, namely reaction shift keying (RSK), is presented. The RSK implies that the quenchers are injected into the transmitter, the chemical messenger reacts and a chemically modified messenger travels towards the receiver. Encoding of "0" is obtained by means of the emission of a messenger that reaches the receiver once chemically modified. To encode the value "1", the messenger is not subjected to chemical reaction. Fluorescent carbon nanoparticle molecular messengers that exploit the reaction with Cu(ii) ions for signal modulation were synthesized. A prototypal RSK modulated chemical communication system is developed, from simulations of the communication platform to an operating prototypal system.