Aniline was polymerized in the presence of ultrafine colloidal
silica particles (hydrodynamic
diameter 35 nm) in aqueous media and, given a sufficient silica
concentration, colloidally stable
polyaniline−silica particles were obtained. The particle size of
the resulting dispersions was determined
by both dynamic light scattering and disk centrifuge
photosedimentometry. The typical size of these
polyaniline−silica particles is in the range 300−600 nm and is
insensitive to the concentration of
components in the reaction mixture, temperature, or acidity of the
reaction mixture. Particles produced
at 0 °C are spherical and their shape becomes less defined when
polymerization proceeds at 25 °C. As
the silica size is increased, the composite particles become larger and
their raspberry morphology more
distinct. The electrical conductivity of a typical polyaniline
(37.8 wt%)−silica composite is 6.1 × 10-2
S
cm-1 at 25 °C. It grows with increasing
temperature and does not depend on the frequency in the
investigated range from 20 Hz to 1 MHz.
Turbulent humidity fluctuations in the convective boundary layer (CBL) under clear-sky conditions were investigated by deriving moments up to fourth-order. Highresolution humidity measurements were collected with a water vapour differential absorption lidar system during the HD(CP) 2 Observational Prototype Experiment (HOPE). Two cases, both representing a well-developed CBL around local noon, are discussed. While the first case (from the intensive observation period (IOP) 5 on 20 April 2013) compares well with what is considered typical CBL behaviour, the second case (from IOP 6 on 24 April 2013) shows a number of non-typical characteristics. Both cases show similar capping inversions and wind shear across the CBL top. However, a major difference between both cases is the advection of a humid layer above the CBL top during IOP 6. While the variance profile of IOP 5 shows a maximum at the interfacial layer, two variance peaks are observed near the CBL top for IOP 6. A marked difference can also be seen in the third-order moment and skewness profiles: while both are negative (positive) below (above) the CBL top for IOP 5, the structure is more complex for IOP 6. Kurtosis is about three for IOP 5, whereas for IOP 6, the distribution is slightly platykurtic. We believe that the entrainment of an elevated moist layer into the CBL is responsible for the unusual findings for IOP 6, which suggests that it is important to consider the structure of residual humidity layers entrained into the CBL.
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