The sizes of single ENPs and the structure of agglomerated or aggregated ENPs are of great importance for the properties of the end products 1 and also after release for their behaviour in the environment. The use of identical measurement principles for particles in different media is hence preferable in order to avoid discrepancies in the measured results. Up to now, different techniques with different limitations are used with sometimes incomparable results. To control the performance of such processes, among other things the input aerosol as well as the produced dispersions have to be characterized.
During transfer from the gas phase into the liquid phase and vice versa, property changes of the ENPs may occur. This increases the importance of liquid phase ENPs. The ENPs in the gas phase are often transferred into the liquid phase shortly after synthesis to avoid agglomeration and to reduce the potential release of ENPs into the environment (air) mainly during handling. Here we consider only ENPs in the liquid and gas phases, which often occur in one process chain for producing nanostructured materials. Introduction Engineered nanoparticles (ENP) can be synthesized in gases (aerosols) 1 and liquids (dispersions) 2 and introduced into solids (solid nanostructured materials composites). We show that it is possible to use the well-established aerosol measurement technique (N + SMPS) in colloid science with all its advantages concerning size resolution and accuracy. However, while the high-resolving ADC is limited due to the dependency on a predefined density of the investigated system, the transfer of dispersed particles into an aerosol and subsequent analysis with SMPS are an adequate way to characterize binary systems, independent of the density of concerned particles, but matching the high resolution of the ADC. While DLS is, as expected, unable to resolve the binary dispersion, SEM, ADC and SMPS are able to give quantitative information on the two particle sizes. The differences, advantages and disadvantages of each method are discussed, especially with respect to the size resolution of the techniques and their ability to distinguish the particle sizes of the mixed dispersion. The results are compared to scanning electron microscopy (SEM) measurements and two frequently applied techniques for characterizing colloidal systems: Dynamic light scattering (DLS) and analytical disc centrifugation (ADC).
gold–PVP nanoparticles (∼20 nm), silver–PVP nanoparticles (∼70 nm) and their 1 : 1 ( m : m) mixture. The capabilities of this new instrument combination (N + SMPS) for the analysis of dispersions were investigated, using three different dispersions, i.e. To achieve a transfer from dispersed particles to aerosolized particles, a newly developed nebulizer (N) is used that, unlike commonly used atomizers, produces significantly smaller droplets and therefore reduces the problem of the formation of residual particles. A well-known and accepted aerosol measurement technique, the scanning mobility particle sizer (SMPS), is applied to characterize colloidally dispersed nanoparticles.