Super-resolution Fluorescence Imaging of Recycled Polymer Blends via Hydrogen Bond-Assisted Adsorption of a Nile Red Derivative.

A key challenge in the recycling of multilayer plastic films of polyethylene and polyamide, as typically used for food packaging, is to assess and control the phase separation of the two types of polymers in the recycled material, the specifics of which determine the mechanical strength of the recycled material. However, visualizing the polyamide-in-polyethylene domains with conventional fluorescence methods or electron microscopy is challenging. We present a new approach that combines the point accumulation in nanoscale topography (PAINT) super-resolution method with a newly synthesized Nile Red probe (diOHNR) as the fluorescent label. The molecule was modified to undergo a hydrogen bond-assisted interaction with the polyamide phase in the blend due to its two additional hydroxyl groups but preserves the spectral properties of Nile Red. As a result, the localization density of the probe in the PAINT image is 13 times larger at the polyamide phase than at the polyethylene phase, enabling quantitative evaluation of the spatial polyamide/polyethylene distribution down to the nanoscale. The method achieved a spatial resolution of 18.8 nm, and we found that over half of the polyamide particles in a recycled sample were smaller than the optical diffraction limit. Being able to image the blends with nanoscopic resolution can help to optimize the composition and mechanical properties of recycled materials and thus contribute to an increased reuse of plastics.

Effect of Polymer Properties on the Biodegradation of Polyurethane Microplastics.

The release of fragments from plastic products, that is, secondary microplastics, is a major concern in the context of the global plastic pollution. Currently available (thermoplastic) polyurethanes [(T)PU] are not biodegradable and therefore should be recycled. However, the ester bond in (T)PUs might be sufficiently hydrolysable to enable at least partial biodegradation of polyurethane particles. Here, we investigated biodegradation in compost of different types of (T)PU to gain insights into their fragmentation and biodegradation mechanisms. The studied (T)PUs varied regarding the chemistry of their polymer backbone (aromatic/aliphatic), hard phase content, cross-linking degree, and presence of a hydrolysis-stabilizing additive. We developed and validated an efficient and non-destructive polymer particle extraction process for partially biodegraded (T)PUs based on ultrasonication and density separation. Our results showed that biodegradation rates and extents decreased with increasing cross-linking density and hard-segment content. We found that the presence of a hydrolysis stabilizer reduced (T)PU fragmentation while not affecting the conversion of (T)PU carbon into CO2. We propose a biodegradation mechanism for (T)PUs that includes both mother particle shrinkage by surface erosion and fragmentation. The presented results help to understand structure-degradation relationships of (T)PUs and support recycling strategies.

Probing the effects of polymers on the early stages of calcium carbonate formation by stoichiometric co-titration.

Potentiometric titrations are a powerful tool to study the early stages of the precipitation of minerals such as calcium carbonate and were used among others for the discovery and characterisation of key precursors like prenucleation clusters. Here we present a modified procedure for conducting such titration experiments, in which the reactants (i.e. calcium and (bi)carbonate ions) are added simultaneously in stoichiometric amounts, while both the amount of free calcium and the optical transmission of the solution are monitored online. Complementarily, the species occurring at distinct stages of the crystallisation process were studied using cryogenic transmission electron microscopy. This novel routine was applied to investigate CaCO3 nucleation in the absence and presence of polymeric additives with different chemical functionalities. The obtained results provide new insights into the critical steps underlying nucleation and subsequent ripening, such as the role of liquid mineral-rich phases and their transformation into solid particles. The studied polymers proved to interfere at multiple stages along the complex mineralisation pathway of calcium carbonate, with both the degree and mode of interaction depending on the chosen polymer chemistry. In this way, the methodology developed in this work allows the mechanisms of antiscalants - or crystallisation modifiers in general - to be elucidated at an advanced level of detail.

Phage Display Screening as a Rational Approach to Design Additives for Selective Crystallization Control in Construction Systems.

The design of additives showing strong and selective interactions with certain target surfaces is key to crystallization control in applied reactive multicomponent systems. While suitable chemical motifs can be found through semi-empirical trial-and-error procedures, bioinspired selection techniques offer a more rationally driven approach and explore a much larger space of possible combinations in a single assay. Here, phage display screening is used to characterize the surfaces of crystalline gypsum, a mineral of broad relevance for construction applications. Based on next-generation sequencing of phages enriched during the screening process, a triplet of amino acids, DYH, is identified as the main driver for adsorption on the mineral substrate. Furthermore, oligopeptides containing this motif prove to exert their influence in a strictly selective manner during the hydration of cement, where the sulfate reaction (initial setting) is strongly retarded while the silicate reaction (final hardening) remains unaffected. In the final step, these desired additive characteristics are successfully translated from the level of peptides to that of scalable synthetic copolymers. The approach described in this work demonstrates how modern biotechnological methods can be leveraged for the systematic development of efficient crystallization additives for materials science.

Quick Curing Mechanisms for All-Season Paints and Renders.

Paints and coatings are required to quickly cure under a broad variety of environmental conditions and deliver solid long-term performance. Achieving a balance during all seasons between quick curing of a coating film, i.e., early rain resistance, while maintaining sufficient workability and open time for an optimized aesthetic appearance is a challenge for the architectural coatings industry. This article describes how the colloidal physics differs between the current standard mechanism to achieve early rain resistance by inhibited coagulants in winter paints and a new mechanism that provides all-season paints. A combination of advanced physical characterization methods, such as electrophoretic mobility, dynamic light scattering and confocal laser scanning microscopy, in combination with application tests, is used to provide a comprehensive mechanism of the early rain resistance achieved by such paints. In addition, it is shown that this new system can be transferred to wood coatings and organic renders. The key finding of this article is that all-season paints combining early rain resistance at cold and damp conditions with open time at high temperatures and dry conditions rely on fast paint film formation with high early integrity rather than coagulants triggered by base evaporation.

Hydrophobin can prevent secondary protein adsorption on hydrophobic substrates without exchange.

By combining several surface analytical tools, we show that an adsorbed layer of the protein H*Protein B prevents the adsorption of secondary proteins bovine serum albumin, casein, or collagen at low-salinity conditions and at pH 8. H*Protein B is an industrially producible fusion protein of the hydrophobin family, known for its high interfacial activity. While applications of hydrophobin have been reported to facilitate adhesion of proteins under different pH conditions, careful analysis by quartz-crystal microbalance and ellipsometry prove that no additional adsorption can be found on top of the H*Protein B layer in this study. Surface analysis by X-ray photoelectron spectroscopy and secondary ion mass spectrometry proves that the hydrophobin layer stays intact even after hours of exposure to solutions of the secondary proteins and that no exchange of proteins can be detected.

Protein adsorption dynamics to polymer surfaces revisited-A multisystems approach.

Performance and safety of materials in contact with living matter are determined by sequential and competitive protein adsorption. However, cause and consequences of these processes remain hard to be generalized and predicted. In a new attempt to address that challenge, the authors compared and analyzed the protein adsorption and displacement on various thoroughly characterized polymer substrates using a combination of surface-sensitive techniques. A multiple linear regression approach was applied to model the dependence of protein adsorption, desorption, and exchange dynamics on protein and surface characteristics. While the analysis confirmed that protein properties primarily govern the observed adsorption and retention phenomena and hydrophobicity as well as surface charge are the most relevant polymer surface properties, the authors have identified several protein-surface combinations that deviate from these patterns and deserve further investigation.

Light-efficient, quantum-limited interferometric wavefront estimation by virtual mode sensing.

We describe and analyze an interferometer-based virtual modal wavefront sensor (VMWS) that can be configured to measure, for example, Zernike coefficients directly. This sensor is particularly light efficient because the determination of each modal coefficient benefits from all the available photons. Numerical simulations show that the VMWS outperforms state-of-the-art phase unwrapping at low light levels. Including up to Zernike mode 21, aberrations can be determined with a precision of about 0.17 rad (lambda/37) using low resolution (65 x 65 pixels) images and only about 400 photons total.

Coherence-gated wave-front sensing in strongly scattering samples.

We show that, by coherence-gate rejection of out-of-focus light, wave-front distortions can be measured in the presence of a scattering background that is dominant by several orders of magnitude. Applications are expected for multiphoton and confocal laser-scanning microscopy.