Highlight Publications 2019

Polyhedral Liquid Marbles
Florian Geyer, Yuta Asaumi, Doris Vollmer, Hans-Jürgen Butt, Yoshinobu Nakamura, and Syuji Fujii
Polyhedral Liquid Marbles
A new type of armored droplet, a so-called polyhedral liquid marble, is introduced. These liquid marbles consist of liquid droplets stabilized by hydrophobic hexagonal plates made of poly(ethylene terephthalate), which adsorb to the liquid–air interface. Depending on the specific combination of plate size and droplet diameter, the plates self-assemble into highly ordered hexagonally arranged domains. Even tetrahedral-, pentahedral-, and cube-shaped liquid marbles composed of only 4 to 6 plates are demonstrated. During evaporation of the internal liquid, due to the high adsorption energy of the plates at the liquid–air interface, the overall surface area stays constant, resulting in strongly deformed polyhedral liquid marbles. In line with this, highly asymmetric polyhedral liquid marbles and letters are obtained due to the strong interfacial jamming exerted by the rigid hexagonal plates. This is particularly pronounced for larger plate sizes, leading to liquid marbles with unusually sharp edges (for example, rectangular edges). The polyhedral liquid marbles exhibit various stimuli-responsive behaviors simultaneously being exposed to water, ammonia, or tetrahydrofuran vapors. Air-driven polyhedral liquid marbles floating on water can reach velocities of several centimeters per second.
© MPI-P / Wiley-VCH (2019)
Polyhedral liquid marbles prepared using 2.48 mm sized hexagonal plates and 15 µL dyed water droplets (left) and solidified polyhedral liquid marble using cyanoacrylate (right).
Chemisorption of Atomically Precise 42-Carbon Graphene Quantum Dots on Metal Oxide Films Greatly Accelerates Interfacial Electron Transfer
Peng Han, Ian Cheng-Yi Hou, Hao Lu, Xiao-Ye Wang, Klaus Müllen, Mischa Bonn, Akimitsu Narita, Enrique Cánovas
Chemisorption of Atomically Precise 42-Carbon Graphene Quantum Dots on Metal Oxide Films Greatly Accelerates Interfacial Electron Transfer
Atomically precise graphene quantum dots (GQDs) are graphene nanostructures which have size-dependent band-gaps; furthermore, they are metal-free and hence low-cost and environmentally friendly. These features make GQDs promising building blocks in novel solar energy conversion schemes, e.g. constituting a promising alternative to organometallic dyes employed in sensitized solar cells. However, current GQD-based sensitized solar cells are characterized by modest efficiencies; which were correlated with the low affinity towards the oxide electrode of the employed physisorbed GQDs sensitizers. Here we demonstrate that chemisorption of atomically precise GQDs onto mesoporous metal oxides, enabled by their functionalization with a carboxylate group, substantially enhances electron collection in the metal oxide electrode. Chemisorption boost electron transfer rates by almost 2 orders of magnitude when compared with physisorbed sensitizers. The accelerated interfacial electron transfer can be traced to stronger donor−acceptor coupling strength enabled by chemisorption.
© ACS / MPI-P (2019)
How to Coat the Inside of Narrow and Long Tubes with a Super-Liquid-Repellent Layer — A Promising Candidate for Antibacterial Catheters
Florian Geyer, Maria D’Acunzi, Ching-Yu Yang, Michael Müller, Philipp Baumli, Anke Kaltbeitzel, Volker Mailänder, Noemí Encinas, Doris Vollmer, and Hans-Jürgen Butt
How to Coat the Inside of Narrow and Long Tubes with a Super-Liquid-Repellent Layer — A Promising Candidate for Antibacterial Catheters
Fouling of thin tubes is a major problem, leading to various infections and associated morbidities, while cleaning is difficult or even impossible. Here, a generic method is introduced to activate and coat the inside of meter-long and at the same time thin (down to 1 mm) tubes with a super-liquid-repellent layer of nanofilaments, exhibiting even antibacterial properties. Activation is facilitated by pumping an oxidative Fenton solution through the tubes. Subsequent pumping of a silane solution renders the surface of the tubes super-liquid-repellent. The wide applicability of the method is demonstrated by coating stiff and flexible tubes made of polymers, inorganic/organic hybrids, metals, and ceramics. Coated medical catheters show excellent antibacterial properties. Notably, the nanofilaments retain their antibacterial properties even in the superhydrophilic state. These findings open new avenues toward the design of biocide-free, antibacterial tubings and catheters.
© MPI-P / Wiley-VCH (2019) (2019)
SEM images of a coated LDPE tube with a total length of 2 m and an inner diameter of 1 mm at both endings and the middle of the tube (top). Formation of nanofilaments was observed at all positions. A 2 μL blood plasma drop showed very low adhesion to a coated tube and was easily removed from it (bottom).
Direct observation of gas meniscus formation on a superhydrophobic surface
Mimmi Eriksson, Mikko Tuominen, Mikael Järn, Per Martin Claesson, Viveca Wallqvist, Hans-Jürgen Butt, Doris Vollmer, Michael Kappl, Joachim Schoelkopf, Patrick A. C. Gane, Hannu Teisala, and Agne Swerin
Direct observation of gas meniscus formation on a superhydrophobic surface
Handling of fine powders in industry is often strongly affected by interparticle forces. While van der Waals interaction is always present, capillary forces become dominating in the presence of humidity due to the formation of a water meniscus. The long range interactions between hydrophobic surfaces have been attributed to the existence of nanobubbles. Formation of a bridging meniscus between these nanobubbles leads to an interaction range in the order of tens to hundreds of nanometers. However, on superhydrophobic coatings attractive interactions of more than 10 µm have been observed. By combining laser scanning confocal microscopy and colloidal probe force microscopy, we image and quantify the formation and growth of a gas meniscus during force measurements between a superhydrophobic surface and a hydrophobic microsphere immersed in water. Our data show that the super long-range attractive interactions acting on separation are due to meniscus formation and volume growth as air is transported from the surface layer.
© Mimmi Eriksson (2019)
Surface Chemistry Enhancements for the Tunable Super-Liquid Repellency of Low-Surface-Tension Liquids
William S. Y. Wong
Surface Chemistry Enhancements for the Tunable Super-Liquid Repellency of Low-Surface-Tension Liquids
The recent advent of superamphi(omni)phobicity has paradoxically demonstrated immense promise but equally severe challenges. Here, to achieve these high-performing superlyophobic states, a paradigm-shift from the traditional use of specific re-entrant geometry is demonstrated through stepwise, tunable enhancements in surface functionalization. Network fluoro-functionalized nanoparticles realized super liquid repelling properties with various low surface tension liquids, tested to a performance limit with n-decane at 23.8 mN/m.
© MPI-P / ANU (2019)
Autonomous Ultrafast Self‐Healing Hydrogels by pH‐Responsive Functional Nanofiber Gelators as Cell Matrices
Jasmina Gačanin, Jana Hedrich, Stefanie Sieste, Gunnar Glaßer, Ingo Lieberwirth, Corinna Schilling, Stephan Fischer, Holger Barth, Bernd Knöll, Christopher V. Synatschke, Tanja Weil
Autonomous Ultrafast Self‐Healing Hydrogels by pH‐Responsive Functional Nanofiber Gelators as Cell Matrices
The extracellular matrix (ECM) is a supportive environment for cells that provides mechanical and biochemical cues necessary for survival, growth, and differentiation. Artificial materials that mimic essential functions of the natural ECM can help to replace tissue that was lost due to disease or injury. These scaffolds provide support for endogenous or exogenous cells as they regenerate the lost tissue. Two major requirements for such materials are their biocompatibility, acting as a suitable 3D matrix for a number of different cells, and deposition of the material without creating additional injury. Here, we describe a new biomaterial that supports different cell types, including endothelial and neuronal cells, and can be delivered minimally invasively due to significant shear thinning behavior. The material consists of a biocompatible polypeptide backbone that was grafted with nanofiber-forming peptide sequences. We have observed active migration of cells into the material after topological seeding. Due to the non-covalent nature of the nanofiber gelators, the material readily flows upon exposure to shear force, while it immediately reforms into a hydrogel after removal of the shear stress. We anticipate that this material will find use as an injectable ECM mimic for regenerating damaged or lost tissues.
© MPI-P (2018)
Injectable Cell Matrices from Peptide Nanofiber Gelators
Molecular Hydrophobicity at a Marcoscopically Hydrophilic Surface
Jenée D. Cyran, Michael A. Donovan, Doris Vollmer, Flavio Siro Brigiano, Simone Pezzotti, Daria R. Galimberti, Marie-Pierre Gaigeot, Mischa Bonn and Ellen H.G. Backus
Molecular Hydrophobicity at a Marcoscopically Hydrophilic Surface
Chemical and physical interactions between water and silicates are ubiquitous and relevant for geochemistry and industrial processes, including chromatography, oil extraction and coatings. Characterizing the silica/water interface is important to not only understand the fundamental properties for natural occurring processes but also to improve existing technologies, such as silica coatings, which rely on wettability and thermal-resistant properties to remain effective. At the silica/water interface, we compare the microscopic water organization, from both surface sensitive vibrational sum frequency generation experiments and molecular dynamics simulations, to macroscopic information about the hydrophobicity obtained from contact angle measurements. At the microscopic level, weakly hydrogen-bonded OH groups, typical for hydrophobic interfaces, are observed that originate from water molecules interacting with hydrophobic sites of the silica surface. An increased density of these molecular hydrophobic sites, evident from an increase in weakly hydrogen bonded water OH groups, correlates with an increased macroscopic contact angle.
© MPI-P (2019)
Utilizing macroscopic and microscopic techniques to unveil hydrophobic water at a hydrophilic interface
Non-covalent interactions across organic and biological subsets of chemical space: Physics-based potentials parametrized from machine learning
Tristan Bereau, Robert A. DiStasio Jr., Alexandre Tkatchenko, and O. Anatole von Lilienfeld
Non-covalent interactions across organic and biological subsets of chemical space: Physics-based potentials parametrized from machine learning
Classical intermolecular potentials typically require an extensive parametrization procedure for any new compound considered. To do away with prior parametrization, we propose a combination of physics-based potentials with machine learning (ML), coined IPML, which is transferable across small neutral organic and biologically relevant molecules. ML models provide on-the-fly predictions for environment-dependent local atomic properties: electrostatic multipole coefficients (significant error reduction compared to previously reported), the population and decay rate of valence atomic densities, and polarizabilities across conformations and chemical compositions of H, C, N, and O atoms. These parameters enable accurate calculations of intermolecular contributions—electrostatics, charge penetration, repulsion, induction/polarization, and many-body dispersion. Unlike other potentials, this model is transferable in its ability to handle new molecules and conformations without explicit prior parametrization: All local atomic properties are predicted from ML, leaving only eight global parameters—optimized once and for all across compounds. We validate IPML on various gas-phase dimers at and away from equilibrium separation, where we obtain mean absolute errors between 0.4 and 0.7 kcal/mol for several chemically and conformationally diverse datasets representative of non-covalent interactions in biologically relevant molecules. We further focus on hydrogen-bonded complexes—essential but challenging due to their directional nature—where datasets of DNA base pairs and amino acids yield an extremely encouraging 1.4 kcal/mol error. Finally, and as a first look, we consider IPML for denser systems: water clusters, supramolecular host-guest complexes, and the benzene crystal.
© MPI-P / AIP (2019)
Correlation plots for the total intermolecular energy between reference and present calculations
Monitoring drug nanocarriers in human blood by near-infrared fluorescence correlation spectroscopy
Inka Negwer, Andreas Best, Meike Schinnerer, Olga Schäfer, Leon Capeloa, Manfred Wagner, Manfred Schmidt, Volker Mailänder, Mark Helm, Matthias Barz, Hans-Jürgen Butt & Kaloian Koynov
Monitoring drug nanocarriers in human blood by near-infrared fluorescence correlation spectroscopy
Nanocarrier-based drug delivery is a promising therapeutic approach that offers unique possibilities for the treatment of various diseases. However, inside the blood stream, nanocarriers’ properties may change significantly due to interactions with proteins, aggregation, decomposition or premature loss of cargo. Thus, a method for precise, in situ characterization of drug nanocarriers in blood is needed. Here we show how the fluorescence correlation spectroscopy that is a well-established method for measuring the size, loading efficiency and stability of drug nanocarriers in aqueous solutions can be used to directly characterize drug nanocarriers in flowing blood. As the blood is not transparent for visible light and densely crowded with cells, we label the nanocarriers or their cargo with near-infrared fluorescent dyes and fit the experimental autocorrelation functions with an analytical model accounting for the presence of blood cells. The developed methodology contributes towards quantitative understanding of the in vivo behavior of nanocarrier-based therapeutics.
© MPI-P / Springer Nature (2019)
Schematic of the NIR-FCS experiments in flowing blood.
Comparative Adsorption of Acetone on Water and Ice Surfaces
J.D. Cyran, E.H.G. Backus, M.J. van Zadel, and M. Bonn
Comparative Adsorption of Acetone on Water and Ice Surfaces
Interactions of trace gases with ice and water surfaces play a major role in atmospheric chemistry. The chemical and photochemical processes of trace gases absorbed on ice surfaces are relevant for ozone depletion and alter the chemical composition of the atmosphere. Specifically, small-oxygenated organic molecules, such as acetone, are a critical contributor to the formation of HOx radicals. Here, we combine surface-specific vibrational spectroscopy and a controllable flow cell apparatus to investigate the molecular adsorption of acetone onto the basal plane of single crystalline Ih ice with large surface area. By comparing the adsorption of acetone on the ice/air with the water/air interface, we find two different types of acetone adsorption, as apparent from the different responses of both the free O-H and the hydrogen-bonded network vibrations for ice and liquid water. Adsorption on ice occurs preferentially through interactions with the free OH group, while the interaction of acetone with the surface of liquid water appears less specific.
© MPI-P (2019)
Acetone adsorption on water and ice surfaces unraveled by interfacial spectroscopy
Well-defined metal-polymer nanocomposites: The interplay of structure, thermoplasmonics, and elastic mechanical properties
David Saleta Reig, Patrick Hummel, Zuyuan Wang, Sabine Rosenfeldt, Bartlomiej Graczykowski, Markus Retsch, and George Fytas
Well-defined metal-polymer nanocomposites: The interplay of structure, thermoplasmonics, and elastic mechanical properties
Brillouin light spectroscopy (BLS) is a reliable technique for probing sound velocities in materials. The sound velocity and its temperature and power dependencies further allow determination of thermomechanical properties like elastic moduli and the glass transition temperature. Whereas non-metallic particle-brush systems (e.g., SiO2-PS) typically show linearly dependent sound velocity on temperature and power, thus giving a segmental linear relation between the laser spot temperature and the laser power, their metallic counterparts could display strong non-linearity, as demonstrated here by using Ag-PS nanocomposite films. This non-linearity is due to the plasmonic heating in the Ag nanoparticles induced by the incident laser, and it increases as the PS chain length decreases due to the increasing Ag volume fraction. Additional annealing of the nanocomposite films also increases the non-linearity through the annealing-time-dependent aggregation of Ag nanoparticles. This work reveals the combined effects of composition and (reversible) aggregation on the mechanical and thermoplasmonic properties of metal-polymer nanocomposites. It not only deepens our understanding of the interplay of structure, thermoplasmonics, and elastic properties in metal-polymer nanocomposites but also provides a guide for customizing Ag-PS nanocomposites for potential applications.
© MPI-P (2019)
Schematic laser heating in a Ag-PS (particle-brush) film and the dependence of the laser spot temperature on the laser power.
 
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