The contamination of aquatic ecosystems with microplastics has recently been reported through many studies, and negative impacts on the aquatic biota have been described. For the chemical identification of microplastics, mainly Fourier transform infrared (FTIR) and Raman spectroscopy are used. But up to now, a critical comparison and validation of both spectroscopic methods with respect to microplastics analysis is missing. To close this knowledge gap, we investigated environmental samples by both Raman and FTIR spectroscopy. Firstly, particles and fibres >500 μm extracted from beach sediment samples were analysed by Raman and FTIR microspectroscopic single measurements. Our results illustrate that both methods are in principle suitable to identify microplastics from the environment. However, in some cases, especially for coloured particles, a combination of both spectroscopic methods is necessary for a complete and reliable characterisation of the chemical composition. Secondly, a marine sample containing particles <400 μm was investigated by Raman imaging and FTIR transmission imaging. The results were compared regarding number, size and type of detectable microplastics as well as spectra quality, measurement time and handling. We show that FTIR imaging leads to significant underestimation (about 35 %) of microplastics compared to Raman imaging, especially in the size range <20 μm. However, the measurement time of Raman imaging is considerably higher compared to FTIR imaging. In summary, we propose a further size division within the smaller microplastics fraction into 500-50 μm (rapid and reliable analysis by FTIR imaging) and into 50-1 μm (detailed and more time-consuming analysis by Raman imaging). Graphical Abstract Marine microplastic sample (fraction <400 μm) on a silicon filter (middle) with the corresponding Raman and IR images.

We report a simple method to synthesize binary polymer brushes from two incompatible polymers of different polarity. The synthetic route is based on a subsequent step-by-step grafting of carboxyl-terminated polystyrene and poly(2-vinylpyridine) to the surface of a Si wafer functionalized with 3-glycidoxypropyltrimethoxysilane. The end-functional polymers were spin-coated on the substrate, and grafting was carried out at a temperature higher than the glass transition temperature of the polymers. The composition of the binary brushes can be regulated based on grafting kinetics of the first polymer by the change of time or/and temperature of grafting. This method reveals a smooth and homogeneous polymer film on the macroscopic scale, while at the nanoscopic scale the system undergoes phase segregation effecting switching/ adaptive properties of the film. Upon exposure to different solvents, the film morphology reversibly switches from "ripple" to "dimple" structures as well as the surface energetic state switches from hydrophobic to hydrophilic. The same switching of hydrophilic/hydrophobic properties was obtained for the different ratios between two grafted polymers in the binary brush.

We report preparation of stimuli-responsive bicomponent polymeric Janus particles and investigation of their switching behavior. The first polymer was immobilized on one side of silica particles using the surface-initiated atom transfer radical polymerization, “grafting from” approach. The second polymer was immobilized using the “grafting to” method by reaction between reactive terminating groups of polymer chains and functional groups on the particle surface. On the example of mixed oppositely charged polyelectrolyte Janus particles decorated with poly(acrylic acid) and poly(2-vinylpyridine) chains, we demonstrate stimuli-responsive aggregation/disaggregation behavior upon pH changes.

Broadband dielectric spectroscopy (BDS), spectroscopic vis-ellipsometry (SE), X-ray reflectometry (XRR), and alternating current (ACC) as well as differential scanning calorimetry (DSC) are combined to study glassy dynamics and the glass transition in nanometric thin (≥5 nm) layers of polystyrene (PS) having widely varying molecular weights (27 500−8 090 000 g/mol). For the dielectric measurements two sample geometries are employed, the common technique using evaporated electrodes and a recently developed approach taking advantage of nanostructures as spacers. All applied methods deliver the concurring result that deviations from glassy dynamics and from the glass transition of the bulk do not exceed margins of ±3 K independent of the layer thickness and the molecular weight of the polymer under study. Our findings are discussed in the context of the highly controversial literature and prove that an appropriate sample preparation is of paramount importance.

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) brushes with different molecular weights M(n) and grafting densities σ were prepared by the "grafting-to" method. Changes in their physicochemical properties according to temperature were investigated with the help of in situ spectroscopic ellipsometry and in situ attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. Brush criteria indicate a transition between a brush conformation below the lower critical solution temperature (LCST) and an intermediate to mushroom conformation above the LCST. By in situ ellipsometry distinct changes in the brush layer parameters (wet thickness, refractive index, buffer content) were observed. A broadening of the temperature region with maximum deswelling occurred with decreasing grafting density. The brush layer properties were independent of the grafting density below the LCST, but showed a virtually monotonic behavior above the LCST. The midtemperature ϑ(half) of the deswelling process increased with increasing grafting density. Thus grafting density-dependent design parameters for such functional films were presented. For the first time, ATR-FTIR spectroscopy was used to monitor segment density and hydrogen bonding changes of these very thin PNIPAAm brushes as a function of temperature based on significant variations of the methyl stretching, Amide I, as well as Amide II bands with respect to intensity and wavenumber position. No dependence on M(n) and σ in the wavenumber shift of these bands above the LCST was found. The temperature profile of these band intensities and thus segment density was found to be rather step-like, exceeding temperatures around the LCST, while the respective profile of their wavenumber positions suggested continuous structural and hydration processes. Remaining buffer amounts and residual intermolecular segment/water interaction in the collapsed brushes above the LCST could be confirmed by both in situ methods.

The presence of microplastics in aquatic ecosystems is a topical problem and leads to the need of appropriate and reliable analytical methods to distinctly identify and to quantify these particles in environmental samples. As an example transmission, Fourier transform infrared (FTIR) imaging can be used to analyze samples directly on filters without any visual presorting, when the environmental sample was afore extracted, purified, and filtered. However, this analytical approach is strongly restricted by the limited IR transparency of conventional filter materials. Within this study, we describe a novel silicon (Si) filter substrate produced by photolithographic microstructuring, which guarantees sufficient transparency for the broad mid-infrared region of 4000-600 cm(-1). This filter type features holes with a diameter of 10 μm and exhibits adequate mechanical stability. Furthermore, it will be shown that our Si filter substrate allows a distinct identification of the most common microplastics, polyethylene (PE), and polypropylene (PP), in the characteristic fingerprint region (1400-600 cm(-1)). Moreover, using the Si filter substrate, a differentiation of microparticles of polyesters having quite similar chemical structure, like polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), is now possible, which facilitates a visualization of their distribution within a microplastic sample by FTIR imaging. Finally, this Si filter can also be used as substrate for Raman microscopy-a second complementary spectroscopic technique-to identify microplastic samples.

We develop the route to fabricate mixed brushlike layers on polyamide substrates (PA-6, PA-6I, PA-66) by the "grafting from" approach. The PA substrates were functionalized by NH3 plasma. The azo initiator of radical polymerization was covalently bound to the functionalized PA surface. A two-step grafting procedure was applied to graft polystyrene in the first step and poly(2-vinylpyridine) in the second step. We found remarkable differences between grafting on Si wafers and on the PA substrates. "Grafting from" the PA surface results in a dramatic increase of the surface roughness of the film which can be explained by grafting in a swollen surface layer of PA. Because of this effect, we found a substantial amount of grafted polymers even on not functionalized PA substrates, which was explained by grafting via chain transfer reaction. The synthesized mixed polymer brushes form responsive coatings which switch their morphology due to the interplay between lateral and vertical phase segregation upon exposure to selective solvent. The switching of morphology affects the change of the surface composition of the brushes and their surface energetic state. We performed the same grafting procedure on the surface of PA fabric. In this case the switching behavior was amplified by the texture of the material: wettability of the fabric with the mixed brush was switched from complete wetting to highly hydrophobic state (150°water contact angle).

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