Standard transmission electron microscopy nanoparticle sample preparation generally requires the complete removal of the suspending liquid. Drying often introduces artifacts, which can obscure the state of the dispersion prior to drying and preclude automated image analysis typically used to obtain number-weighted particle size distribution. Here we present a straightforward protocol for prevention of the onset of drying artifacts, thereby allowing the preservation of in-situ colloidal features of nanoparticles during TEM sample preparation. This is achieved by adding a suitable macromolecular agent to the suspension. Both research- and economically-relevant particles with high polydispersity and/or shape anisotropy are easily characterized following our approach ( http://bsa.bionanomaterials.ch ), which allows for rapid and quantitative classification in terms of dimensionality and size: features that are major targets of European Union recommendations and legislation.

Data on airborne particles are critical to protecthuman health. Anthropogenic (e.g., soot, and tire and brake wear) as well as biogenic (e.g., pollen and spores) particles are usually monitored by active samplers located in urban environments; thus, very few data are available for remote, mountainous areas. In addition, bioaerosol analysis is time-consuming and skill-intensive. Hence, to avoid the obstacles of active sampling (i.e., the high cost and power consumption) and simplify data analysis, we investigated passive sampling combined with automated analysis as a method for pollen detection. We deployed two Sigma-2 passive samplers for 12 week-long periods during 2018 in San Michele all’Adige, Italy, where airborne pollen has been monitored by a volumetric Hirst-type sampler since 1990. To obtain the morpho-chemical information of single particles, we then analyzed the samples using (i) automated optical microscopy (OM) followed by image analysis based on the particle sizes and grey values, and (ii) automated scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX). The automated OM detected bright particles (i.e., from natural sources) in the size range of 20–80 µm, which accurately represented the total pollen, and the SEM/EDX filtered the particles by size, shape and chemical composition, which enabled us to identify the likely pollen candidates (the “pollen-like” fraction). Overall, automated analytical techniques can concurrently provide data on airborne anthropogenic, geogenic and biogenic particles, including pollen. Furthermore, passive sampling offers a reliable option for collecting data in aerobiological studies, especially in remote areas, where maintaining active samplers is challenging.

Chemical modification of wood mainly aims at improving dimensional stability, resistance to biodeterioration and surface degradation. In some cases, it is specifically targeted at adapting or improving mechanical performance. However, a general understanding of the effects of chemical modification on the mechanical properties of wood, which would facilitate more efficient modification strategies, is missing. Here, a combined experimental and simulation study is provided to gain a more general understanding of the mechanical behaviour of chemically modified wood. In the first part of this study, the mechanical properties of chemically modified Norway spruce are studied experimentally. In Mora Mendez et al. (Wood Sci Technol 2019), simulations of different types of chemical modifications will be presented using a multi-scale model and the outcome will be compared with the obtained experimental data. Chemical modification was based on a two-step modification process. The first step involved methacrylation of the OH-groups in the cell wall. In the second step, in situ polymerization of styrene was induced in the methacrylated samples, which resulted in a partial cell wall and lumen filling. Tensile stiffness and rolling shear stiffness were analysed for methacrylated and polymerized samples. Whereas only small changes in mechanical properties were found for methacrylated samples, the polymerization process led to pronounced increases in elastic modulus and shear stiffness because of weight percent gains of 60–95%. Yet, the specific stiffness was lowered, as the density increase was disproportionate to the stiffness increase. Moreover, a pronounced improvement in rolling shear modulus (GRT) by a factor of 4.5 was obtained for the in situ polymerized specimen.

This work reports on streaming potential measurements through natural capillaries in wood and investigates the cause of a time-dependent zeta potential measured during the equilibration of wood cell-walls with an electrolyte solution. For the biomaterial, this equilibration phase takes several hours, which is much longer than for many other materials that have been characterized by electrokinetic measurements. During this equilibration phase the zeta potential magnitude is decaying due to two parallel mechanisms: (i) the swelling of the cell-wall which causes a dimensional change reducing the charge density at the capillary interface; (ii) the transport of ions from the electrolyte solution into the permeable cell-wall which alters the electrical potential at the interface by internal charge compensation. The obtained results demonstrate the importance of equilibration kinetics for an accurate determination of the zeta potential, especially for materials that interact strongly with the measurement electrolyte. Moreover, the change in zeta potential with time can be correlated with the bulk swelling of wood if the effect of electrolyte ion diffusion is excluded. This study shows the potential of streaming potential measurements of wood, and possibly of other hygroscopic and nanoporous materials, to reveal kinetic information about their interaction with liquids, such as swelling and ion uptake.

Chitosan is a promising biocompatible polymer for regenerative engineering applications, but its processing remains challenging due to limited solubility and rigid crystalline structure. This work represents the development of electrospun chitosan/poly(ethylene oxide) blend nanofibrous membranes by means of a numerical analysis in order to identify and tailor the main influencing parameters with respect to accessible surface nitrogen functionalities which are of importance for the biological activity as well as for further functionalization. Depending on the solution composition, both gradient fibers and homogenous blended fiber structures could be obtained with surface nitrogen concentrations varying between 0 and 6.4%. Response surface methodology (RSM) revealed chitosan/poly(ethylene oxide) ratio and chitosan molecular weight as the main influencing factors with respect to accessible nitrogen surface atoms and respective concentrations. The model showed good adequacy hence providing a tool to tailor the surface properties of chitosan/poly(ethylene oxide) blends by addressing the amount of accessible chitosan.

The adhesion behavior of polyelectrolyte multilayers consisting of poly(diallyldimethylammonium chloride), PDDA, and poly(styrenesulfonate), PSS, toward a silicon AFM tip was studied during their build-up on wood, a chemically heterogeneous, micrometer rough biomaterial and compared with a nanometer rough substrate, namely quartz. The atomic force microscopy-based force mapping approach generated high-resolution topography-, and adhesion maps within the first bilayers, which point toward a homogeneous layer-by-layer build-up on the biomaterial surface, and therefore indicate an even charge distribution. By analyzing the force-distance curves in every pixel of the mapping, new insights into the specific interactions of the polyelectrolyte multilayers at the surface were achieved. The characteristic odd-even effect of polyelectrolyte multilayers cannot only be determined on quartz, but also on the biomaterial wood, however, only after an offset of two bilayers. This is potentially due to the specific roughness and charge of wood in comparison to commonly used quartz.

Advanced Materials InterfacesVolume 4, Issue 1 1600289 Communication Bio-Inspired Superhydrophobic and Omniphobic Wood Surfaces Huizhang Guo, Corresponding Author Huizhang Guo [email protected] Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandE-mail: [email protected], [email protected]Search for more papers by this authorPeter Fuchs, Peter Fuchs Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorKirstin Casdorff, Kirstin Casdorff Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorBenjamin Michen, Benjamin Michen Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorMunish Chanana, Munish Chanana Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorHarald Hagendorfer, Harald Hagendorfer Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorYaroslav E. Romanyuk, Yaroslav E. Romanyuk Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorIngo Burgert, Corresponding Author Ingo Burgert [email protected] Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandE-mail: [email protected], [email protected]Search for more papers by this author Huizhang Guo, Corresponding Author Huizhang Guo [email protected] Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandE-mail: [email protected], [email protected]Search for more papers by this authorPeter Fuchs, Peter Fuchs Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorKirstin Casdorff, Kirstin Casdorff Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorBenjamin Michen, Benjamin Michen Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorMunish Chanana, Munish Chanana Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorHarald Hagendorfer, Harald Hagendorfer Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorYaroslav E. Romanyuk, Yaroslav E. Romanyuk Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandSearch for more papers by this authorIngo Burgert, Corresponding Author Ingo Burgert [email protected] Wood Materials Science, Institut for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, SwitzerlandE-mail: [email protected], [email protected]Search for more papers by this author First published: 09 November 2016 https://doi.org/10.1002/admi.201600289Citations: 45Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract Bio-inspired superhydrophobic and omniphobic wood surfaces that exhibit extremely low wettability for both, aqueous (blue drop) and non-aqueous (red drop) liquids, were obtained by adding a nano-scaled structure to the intrinsically micro-scaled texture of the wood surface. Citing Literature Supporting Information As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Filename Description admi201600289-sup-0001-S1.pdf1.5 MB Supplementary admi201600289-sup-0002-S2.avi3.8 MB Supplementary admi201600289-sup-0003-S3.avi5.4 MB Supplementary admi201600289-sup-0004-S4.avi2.9 MB Supplementary admi201600289-sup-0005-S5.avi2.1 MB Supplementary admi201600289-sup-0006-S6.avi3.1 MB Supplementary Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Volume4, Issue1Special Issue: Max-Planck Institute of Colloids and Interfaces Perspectives in Interface Research January 9, 20171600289 RelatedInformation

Surface functionalization by means of controlled deposition of charged polymers or nanoparticles using the layer-by-layer (LbL) approach has been used to modify mostly engineered materials with well-defined surface chemistry and morphology. In this regard, natural and inhomogeneous interfaces have gained very little attention. Furthermore, natural substrates are susceptible to alterations by factors commonly used to control the growth of multilayers, such as pH, temperature and ionic strength. Here, we study the impact of sorption kinetics of a bilayer system (Poly(diallyldimethylammonium chloride) (PDDA) and Poly(sodium 4-styrenesulfonate) (PSS)) on a natural heterogeneous wood surface at neutral pH, without salt addition, on the multilayer buildup. To overcome analytical limitations we introduce a complementary approach based on UV reflectance spectroscopy, atomic force microscopy (AFM) and zeta potential measurements. Compared to immersion times used for ideal substrates, we found that a high surface coverage requires relatively long immersion, approximately 30min, into polyelectrolyte solutions, while a sufficient removal of polyelectrolyte excess during the washing step, requires even longer, about 100min. Based on these findings, we show that film growth can be controlled kinetically. Long immersion times provide well-defined and regular multilayers. The obtained data points to specific requirements to be considered when LbL treatments are applied to rough, porous and heterogeneous surfaces, and thereby sets a basis for a successful transfer of various surface functionalization approaches already shown on ideal surfaces.

Trimethyl-ammonium functionalized cellulose nanofibers (CNF) display a positively charged surface over a wide pH and ionic strength range, and constitute therefore not only an interesting biobased sorbent material, but also a positively charged model surface to investigate sorption phenomena. In the current work, CNF were totally or partially covered by humic acid (HA) at pH ∼6, and the desorption process of HA from CNF was thereafter studied in batch and continuous filtration experiments at various pH and ionic strength. It is found that the desorbed amount of HA increases and the kinetic of desorption is faster via increasing the pH and ionic strength of the solution. Moreover, the desorption is affected by the extent of CNF coverage with HA and by the presence of free HA in solution. The present work gives insights into the interaction of HA with permanently positively charged surfaces and was successfully exploited for the removal of HA from CNF filters for regeneration allowing multiple filter utilization.

Protection from liquid water and UV radiation are equally important, and a sophisticated approach is needed when developing surface coatings that preserve the natural and well-appreciated aesthetic appearance of wood. In order to prevent degradation and prolong the service life of timber, a protective coating was assembled using carnauba wax particles and zinc oxide nanoparticles via layer-by-layer deposition in water. For this purpose, a facile sonication route was developed to produce aqueous wax dispersion without any surfactants or stabilizers. The suspension was stable above pH 4 due to the electrostatic repulsion between the negatively charged wax particles. The particle size could be controlled by the initial wax concentration with average particle sizes ranging from 260 to 360 nm for 1 and 10 g/L, respectively. The deposition of wax particles onto the surface of spruce wood introduced additional roughness to the wood surface at micron level, while zinc oxide provided nano roughness and UV-absorbing properties. In addition to making wood superhydrophobic, this novel multilayer coating enhanced the natural moisture buffering capability of spruce. Moreover, wood surfaces prepared in this fashion showed a significant reduction in color change after exposure to UV light. A degradation of the wax through photo catalytic activity of the ZnO particles was measured by FTIR, indicating that further studies are required to achieve long-term stability. Nevertheless, the developed coating showed a unique combination of super hydrophobicity and excellent moisture buffering ability and some UV protection, all achieved using an environmentally friendly coating process, which is beneficial to retain the natural appearance of wood and improve indoor air quality and comfort. (C) 2016 Elsevier B.V. All rights reserved.

Despite great promises of cellulose nanofibers for water treatment, current technologies have lacked the exclusive use of cellulose nanofibers (CNF) in high-flux filters having an affinity for a desired contaminant. To tackle this, we prepared porous and functionalized filters via solvent exchange, supercritical drying, and freeze-drying of cationic CNF and compared them to conventional CNF filters obtained by the paper-making process. Porosity and pore size were evaluated in the dry state qualitatively and quantitatively via scanning electron microscopy and mercury intrusion porosimetry, respectively. The permeance of water and a solution containing a negatively charged model molecule (humic acid) through these filters was measured at various pressures and correlated to the filters' structure. As compared to the CNF filters made via paper-making, the porosity, pore size, and permeance were increased after processing via solvent exchange, supercritical drying, and freeze-drying routes. Those filters which were prepared via freeze-drying displayed the highest permeance reported so far for CNF filters, which is about an order of magnitude higher than the permeance of CNF filters made via paper-making and having the same grammage. While the permeability was clearly affected by the processing technique, the functional filters showed a comparable adsorption capacity for humic acid. The filtration of a humic acid solution provided an initial removal of nearly 100% without noticeable reduction in flow. Considering the diluted concentration of HA in natural waters, we expect that large volumes of HA solution could be treated with the present CNF filters, with the possibility to regenerate these filters for multiple utilizations. The present concept of utilizing functional cellulose nanofibers in highly permeable filters working on the adsorption principle may be extended to encompass removal of other water contaminants for a better supply of clean water.

One of the most significant limitations for a wider utilisation of the renewable and CO2-storing resource wood is its low ultraviolet (UV) light stability. The protection of the wood surface without altering its aesthetic appeal requires an optically transparent but UV protective coating which should be strongly attached to the rough and inhomogeneous substrate. For this purpose, ZnO nanostructures were deposited onto the wood surface via a chemical bath deposition process. The morphology of crystalline ZnO was controlled by aluminium nitrate or ammonium citrate in the growth step resulting in nanorod arrays or platelet structures, respectively. Detailed structural, chemical and mechanical characterisations as well as accelerated weathering exposure revealed the effective performance of the platelet structure, which formed a dense and thin ZnO coating on spruce. The total colour change (Delta E in the CIE system) was calculated to be 20.5 for unmodified wood, while it was about three for the modified samples after 4 weeks accelerated weathering test. Moreover, the ZnO coating also suppressed crack initiation and propagation indicating a substantial increase in durability.

Nanofibrillated cellulose (NFC) is a natural fibrous material that can be readily processed into membranes. NFC membranes for fluid separation work in aqueous medium, thus in their swollen state. The present study is devoted to a critical investigation of porosity, pore volume, specific surface area, and pore size distribution of dry and wet NFC nanopapers, also known as membranes, with various established techniques, such as electron microscopy, helium pycnometry, mercury intrusion, gas adsorption (N2 and Kr), and thermoporometry. Although these techniques can be successfully applied to inorganic materials (e.g., mesoporous silica), it is necessary to appraise them for organic and hydrophilic products such as NFC membranes. This is due to different phenomena occurring at the materials interfaces with the probing fluids. Mercury intrusion and gas adsorption are often used for the characterization of porosity-related properties; nevertheless, both techniques characterize materials in the dry state. In parallel, thermoporometry was employed to monitor the structure changes upon swelling, and a water permeance test was run to show the accessibility of the membranes to fluids. For the first time, the methods were systematically screened, and we highlighted the need of uniform sample treatments prior to the measurements (i.e., sample cutting and outgassing protocols) in order to harmonize results from the literature. The need for revising the applicability range of mercury intrusion and the inappropriateness of nitrogen adsorption were pointed out. We finally present a table for selecting the most appropriate method to determine a desired property and propose guidelines for results interpretation from which future users could profit.

Precise knowledge regarding cellular uptake of nanoparticles is of great importance for future biomedical applications. Four different endocytotic uptake mechanisms, that is, phagocytosis, macropinocytosis, clathrin- and caveolin-mediated endocytosis, were investigated using a mouse macrophage (J774A.1) and a human alveolar epithelial type II cell line (A549). In order to deduce the involved pathway in nanoparticle uptake, selected inhibitors specific for one of the endocytotic pathways were optimized regarding concentration and incubation time in combination with fluorescently tagged marker proteins. Qualitative immunolocalization showed that J774A.1 cells highly expressed the lipid raft-related protein flotillin-1 and clathrin heavy chain, however, no caveolin-1. A549 cells expressed clathrin heavy chain and caveolin-1, but no flotillin-1 uptake-related proteins. Our data revealed an impeded uptake of 40 nm polystyrene nanoparticles by J774A.1 macrophages when actin polymerization and clathrin-coated pit formation was blocked. From this result, it is suggested that macropinocytosis and phagocytosis, as well as clathrin-mediated endocytosis, play a crucial role. The uptake of 40 nm nanoparticles in alveolar epithelial A549 cells was inhibited after depletion of cholesterol in the plasma membrane (preventing caveolin-mediated endocytosis) and inhibition of clathrin-coated vesicles (preventing clathrin-mediated endocytosis). Our data showed that a combination of several distinguishable endocytotic uptake mechanisms are involved in the uptake of 40 nm polystyrene nanoparticles in both the macrophage and epithelial cell line.

Although small round gold nanoparticles (Au NPs) possess only a small degree of shape anisotropy, they support localized surface plasmon resonances and exhibit intrinsic optical anisotropy. These inherent features promote depolarized light scattering, whose temporal fluctuations carry information about rotational Brownian dynamics, and thus can be used to describe the size distribution of round Au NPs. We demonstrate that this allows for a much more accurate determination of particle size and polydispersity through depolarized dynamic light scattering when compared to standard particle sizing with light scattering.

Ceramic filters, working on the depth filtration principle, are known to improve drinking water quality by removing human pathogenic microorganisms from contaminated water. However, these microfilters show no sufficient barrier for viruses having diameters down to 20 nm. Recently, it was shown that the addition of positively charged materials, for example, iron oxyhydroxide, can improve virus removal by adsorption mechanisms. In this work, we modified a common ceramic filter based on diatomaceous earth by introducing a novel virus adsorbent material, magnesium oxyhydroxide, into the filter matrix. Such filters showed an improved removal of about 4-log in regard to bacteriophages MS2 and PhiX174. This is explained with the electrostatic enhanced adsorption approach that is the favorable adsorption of negatively charged viruses onto positively charged patches in an otherwise negatively charged filter matrix. Furthermore, we provide theoretical evidence applying calculations according to Derjaguin-Landau-Verwey-Overbeek theory to strengthen our experimental results. However, modified filters showed a significant variance in virus removal efficiency over the course of long-term filtration experiments with virus removal increasing with filter operation time (or filter aging). This is explained by transformational changes of MgO in the filter upon contact with water. It also demonstrates that filter history is of great concern when filters working on the adsorption principles are evaluated in regard to their retention performance as their surface characteristics may alter with use.