Proton transport over nanoparticle surface in insulating nanoparticle film-based humidity sensor

We study a proton transport on the surface of insulating nanoparticles for humidity sensors. We use the approach to reveal proton transfer mechanisms in humidity sensitive materials. Hydrophilic and hydrophobic ligand-terminated silica nanoparticle films are adopted for evaluating temperature dependence of the ion conductivity. According to the activation energy of the conductivity, we explain the Grotthuss (H+ transfer) and vehicular (H3O+ transfer) mechanisms are mainly dominant on hydrophilic (-OH terminated) and hydrophobic (acrylate terminated) surface of nanoparticles, respectively. This investigation gives us a clue to understand a proton transfer mechanism in solution-processed humidity-sensitive materials such as oxide nanomaterials.

Liquid-dependent impedance induced by vapor condensation and percolation in nanoparticle film

A liquid-dependent impedance is observed by vapor condensation and percolation in the void space between nanoparticles. Under the Laplace pressure, vapor is effectively condensed into liquid to fill the nanoscale voids in an as-deposited nanoparticle film. Specifically, the transient impedance of the nanoparticle film in organic vapor is dependent on the vapor pressure and the conductivity of the condensed liquid. The response follows a power law that can be explained by the classical percolation theory. The condensed vapor gradually percolates into the void space among nanoparticles. A schematic is proposed to describe the vapor condensation and percolation dynamics among the nanoparticles. These findings offer insights into the behavior of vapor adsorbates in nanomaterial assemblies that contain void space.

Optical Gain in Semiconducting Polymer Nano and Mesoparticles

The presence of excited-states and charge-separated species was identified through UV and visible laser pump and visible/near-infrared probe femtosecond transient absorption spectroscopy in spin coated films of poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) nanoparticles and mesoparticles. Optical gain in the mesoparticle films is observed after excitation at both 400 and 610 nm. In the mesoparticle film, charge generation after UV excitation appears after around 50 ps, but little is observed after visible pump excitation. In the nanoparticle film, as for a uniform film of the pure polymer, charge formation was efficiently induced by UV excitation pump, while excitation of the low energetic absorption states (at 610 nm) induces in the nanoparticle film a large optical gain region reducing the charge formation efficiency. It is proposed that the different intermolecular interactions and molecular order within the nanoparticles and mesoparticles are responsible for their markedly different photophysical behavior. These results therefore demonstrate the possibility of a hitherto unexplored route to stimulated emission in a conjugated polymer that has relatively undemanding film preparation requirements.