Quantifying surface properties of silica particles by combining Hansen Parameters and Reichardt's Dye indicator data

To obtain quantitative understanding of the effects of a chemisorbed organic modification on the surface of particles, the use of Reichardt's dye (RD) and Hansen solubility parameter (HSP) is discussed, whereby the S should be understood in terms of “similarity” rather than solubility as dispersibility is in focus. Silica nanoparticles modified to different extents with a medium chain silane including completely hydrophilic and hydrophobic particles are chosen. During spray‐drying such particles form fully redispersible micro‐raspberry superstructures. After qualitative estimations of the particles' polarity based on measuring both immersion time and ability of modified particles to stabilize oil–water emulsions, surface properties are quantified by HSP and RD. With increasing hydrophobicity, i.e., increasing amount of silane at the surface, all three contributions to HSP change. At the same time, RD analysis reveals that the normalized solvent polarity parameter decreases progressively. HSP and RD analysis are in good agreement, giving strong confidence on each method applied individually. This work demonstrates that after noticeable attempts for combined solubility parameters in case of molecules, carbon allotropes, and gelators, such studies can be extended toward functional (nano)particles and that a full picture of particle surface properties is possible via the combination of different, quantitative techniques

Transfer of Individual Micro- and Nanoparticles for High- Precision 3D Analysis Using 360° Electron Tomography

A versatile approach is demonstrated, providing a general routine for an extensive and advanced 3D characterization of individually selected micro- and nanoparticles, enabling the combination of complementary and scale-bridging techniques. Quintessential to the method is the transfer of individual particles onto tailored tips using a conventional scanning electron microscope equipped with a suitable micromanipulator. The method enables a damage- and contamination-free preparation of freestanding particles. This is of significant importance for applications addressing the measurement of structural, physical, and chemical properties of specifically selected particles, such as 360° electron tomography, atom probe tomography, nano X-ray tomography, or optical near-field measurements. In this context, the method is demonstrated for 360° electron tomography of micro-/macroporous zeolite particles with sizes in the micrometer range and mesoporous alpha-hematite nanoparticles exhibiting sizes of 50–100 nm, including detailed pre- and postcharacterization on the nanoscale.“Deutsche Forschungsgemeinschaft” (DFG) within the framework of the SPP 1570 (project DFG SP 648/4-3 “3D analysis of complex pore structures using ET and high-resolution TEM”) and the research training group GRK 1896 (“In situ Microscopy with Electrons, X-rays and Scanning Probes”) as well as through the Cluster of Excellence “Engineering of Advanced Materials” at the Friedrich-Alexander-Universität Erlangen-Nürnberg (Germany)FIBJulian Losche

Electrically Addressable Hybrid Architectures of Zinc Oxide Nanowires Grown on Aligned Carbon Nanotubes

The fabrication and characterization of hybrid architectures of ZnO nanowires (ZNWs) grown on organized carbon nanotubes (CNTs), by a two-step chemical vapor deposition (CVD) process involving CNT growth from a hydrocarbon source followed by ZNW growth using a Zn metal source, is reported. The ZNWs grow uniformly and radially from individual CNTs and CNT bundles, and the aligned morphology of the CNTs is not disturbed by the ZNW growth process. The nucleation and growth of ZnO crystals on CNTs are analyzed in relation to the classical vapor–solid mechanism. Importantly, the CNTs make uniform and distributed electrical contact to the ZNWs, with up to a 1000-fold yield advantage over conventional ZNW growth on a flat substrate. Hybrid ZNW/CNT sheets are fabricated by scalable CVD, rolling, and printing methods; and their electrical properties, which are governed by transport through the anisotropic CNT network, are characterized. Functional interaction between the ZNWs and CNTs is demonstrated by photoconductive behavior and photocurrent generation of the hybrid material under UV illumination. There is significant future opportunity to extend these processing methods to fabricate other functional oxides on CNTs, and to build devices that harness the attractive properties of ZNWs and CNTs with high volumetric efficiency over large areas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77980/1/2470_ftp.pd

Anisotropic nanomaterials: structure, growth, assembly, and functions

Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications

Exhibitive Nano-to-Micron Scale Sedimentation Dynamics of Colloidal Formulations Through Direct Visualization

The study of sedimentation behavior of nanoparticle dispersions is important for revealing particle size and colloidal stability characteristics. Quantitative appraisal of real-world colloidal systems in their native state, is key for replacing prevailing empiricism in formulation science by knowledge-based design. Herein, we choose fuel cell inks as one case-example amongst many other possibilities to present a new visualization technique, called Transmittogram. This technique readily depicts the time-resolved settling behavior of solid-liquid dispersions, measured by analytical centrifugation (AC). Although AC enables the causal examination of agglomeration, settling, and creaming behavior of dispersions, along with its consequent effect on structure formation and product properties, the understanding of the main transmission readout is often non-intuitive and complex. Transmittograms are, therefore, the missing link for straightforward data interpretation. First, we illustrate the utility of transmittogram analysis using model silica nanoparticle systems and further validate it against known characteristics of the system. Then, we demonstrate the application of transmittograms to characterize fuel cell inks, showing the strength of the approach in deconvoluting and distilling information to the reader. Finally, we discuss the potential of the technique for routine analysis using analytical centrifugation.<br /

From In Situ Characterization to Process Control of Quantum Dot Systems

AbstractQuantum confined semiconductor nanoparticles (quantum dots, QDs) are promising candidates for various applications in emerging fields like electronics, solar cells, sensors and diagnostics. However, a larger scale production of QDs at high product quality is still missing. One of the key requirements to address this issue in the near future was identified to be a fast and in situ applicable characterization method. Suitable characterization requires knowledge on the full shape of the particle size distributions (PSDs) under investigation. Thus, determination of a mean particle size together with the width of the PSD is not sufficient. In the following, a method will be presented that allows the derivation of arbitrary shaped PSDs for QDs with direct band gap based on their optical absorbance spectra. After validation of the technique by means of ZnO nanoparticles the transfer of the concept to other QD materials like PbS and PbSe will be proven. Therefore we will extend our methodology and show how our approach can be used to derive spectral properties like the size dependent band gap energy. This is realized by proper calibration of the calculation results against PSDs determined by an independent analysis technique like transmission electron microscopy (TEM)