The concentrations of rare earth elements (REEs) in seawater display systematic variations related to weathering inputs, particle scavenging and water mass histories.Here we investigate the REE concentrations of water column profiles in the Atlantic sector of the Southern Ocean, a key region of the global circulation and primary production. The data reveal a pronounced contrast between the vertical profiles in the
The topography of a surface consists of structures of different length scales. The surface roughness caused by these structures plays a decisive role in interfacial properties. Atomic Force Microscopy (AFM) can be applied to measure the surface topography with great accuracy and thus facilitates roughness quantification. Here, however, the data reduction poses a challenge. In a conventional approach, surface roughness parameters are evaluated based on averaging height differences, which leads to values dominated by the largest height differences of the surface topography. To quantify contributions of smaller structures to the roughness, a previous study presented a tunable local background correction, which eliminates structures on a larger than selected scale. Therefore, this method only considers surface structures smaller than the chosen scale. A different approach to quantify surface roughness on all length scales covered by AFM measurements uses Fourier transformation of the surface topography to calculate the power spectral density, which describes the amplitudes of different contributing spatial frequencies.In the current study, a new approach based on power spectral density is used to quantify surface roughness parameters as a function of the length scale of contributions to the surface topography. This procedure allows a comprehensive characterization of surface roughness and an intuitive comparison of different surfaces.The usefulness of this method and its compatibility to local background correction is demonstrated by analyzing several commercially available carbon fibers with and without different fiber surface treatments.
To investigate the wetting behavior of unsized carbon fibers with a sizing dispersion and the wettability of sized fibers with the liquid polymeric resin, contact angle measurements by capillary rise experiments are performed by tensiometry. First, the sizing behavior of fibers with different degrees of surface activation is analyzed. Increasing activation levels result in increasing oxygen surface concentrations and accordingly increasing polar components of the surface energies. These conditions result in a better wettability of the higher activated fibers. Secondly, the influence of the type of sizing dispersion is addressed by using two water-based epoxy sizing dispersions, i.e. a standard epoxy sizing and an advanced functional epoxy sizing with high reactivity. Using the functional sizing the wettability is further improved. Finally, the influence of the sizing on the wettability of the carbon fibers by the matrix polymer during resin infiltration is investigated using the differently sized fibers and a liquid epoxy resin. Carbon fibers with functional sizing show improved wettability by the resin compared to fibers with standard sizing. The results show that the wetting behavior of carbon fibers with respect to sizing and polymer matrix can be controlled by a suitable choice of surface activation of the fibers and reactivity of the polymeric sizing dispersion.
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