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Krafft M.P.,Charles Sadron Institute | Fainerman V.B.,Donetsk Medical University | Miller R.,MPI of Colloids and Interfaces
Colloid and Polymer Science | Year: 2015

An equation of state for insoluble monolayers was applied to describe the isotherms of phospholipids measured in presence of a fluorocarbon in the gas phase. The observed co-adsorption mechanism of dipalmitoylphosphatidylcholine (DPPC) and the fluorocarbon molecules manifests itself in remarkable differences of the cohesion surface pressure Πcoh. Due to the interaction of the adsorbed fluorocarbon molecules with DPPC, the mutual interaction energy between DPPC molecules is reduced, leading to a very effective fluidization of the monolayer. Equilibrium and dynamic surface tension data taken from literature for phospholipids adsorbed from an aqueous solution or dispersion, in absence and presence of perfluorohexane (PFH) in the adjacent vapor phase, have been analyzed by the proposed theory. It was found that the adsorption equilibrium constant for dioctanoylphosphatidylcholine (di-C8PC) is increased in the presence of PFH and the intermolecular interaction between the components is strong. The dynamic surface tensions of the given systems are described by a diffusion-controlled adsorption mechanism. © 2015 Springer-Verlag Berlin Heidelberg

Kovalchuk V.I.,NASU F. D. Ovcharenko Institute of Biocolloidal Chemistry | Ravera F.,CNR Institute of Neuroscience | Liggieri L.,CNR Institute of Neuroscience | Loglio G.,University of Florence | And 6 more authors.
Advances in Colloid and Interface Science | Year: 2010

For the understanding of short-time adsorption phenomena and high-frequency relaxations at liquid interfaces particular experimental techniques are needed. The most suitable method for respective studies is the capillary pressure tensiometry. However, under gravity conditions there are rather strong limitations, in particular due to convections and interfacial deformations. This manuscript provides an overview of the state of the art of experimental tools developed for short-time and high-frequency investigations of liquid drops and bubbles under microgravity. Besides the brief description of instruments, the underlying theoretical basis will be presented and limits of the applied methods under ground and microgravity conditions will be discussed. The results on the role of surfactants under highly dynamic conditions will be demonstrated by some selected examples studied in two space shuttle missions on Discovery in 1998 and Columbia in 2003. © 2010 Elsevier B.V. All rights reserved.

Mucic N.,MPI of Colloids and Interfaces | Moradi N.,MPI of Colloids and Interfaces | Javadi A.,MPI of Colloids and Interfaces | Javadi A.,University of Tehran | And 3 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2015

The adsorption of surfactants from aqueous solution at the water/air interface is changed when the air phase contains hexane vapor. This co-adsorption of surfactant and hexane depends on the hexane vapor pressure. A thermodynamic model developed for the adsorption of surfactant mixtures can be adapted to the present situation. The surfactants studied were SDS, C12TAB and C12DMPO, and the dependence of their adsorption characteristics on the partial hexane vapor pressure was determined. The co-adsorption of hexane from the vapor phase increases the surface activity of the adsorbing surfactants. © 2015 Elsevier B.V.

PubMed | Fraunhofer Institute for Mechanics of Materials, MPI of Colloids and Interfaces, MPI of Microstructure Physics and University Pierre and Marie Curie
Type: Journal Article | Journal: Journal of structural biology | Year: 2015

We report on a structural analysis of several basal spicules of the deep-sea silica sponge Monorhaphis chuni by electron microscope techniques supported by a precise focused ion beam (FIB) target preparation. To get a deeper understanding of the spicules length growth, we concentrated our investigation onto the apical segments of two selected spicules with apparently different growth states and studied in detail permanent and temporary growth structures in the central compact silica axial cylinder (AC) as well as the structure of the organic axial filament (AF) in its center. The new findings concern the following morphology features: (i) at the tip we could identify thin silica layers, which overgrow as a tongue-like feature the front face of the AC and completely fuse during the subsequent growth state. This basically differs from the radial growth of the surrounding lamellar zone of the spicules made of alternating silica lamellae and organic interlayers. (ii) A newly detected disturbed cylindrical zone in the central region of the AC (diameter about 30 m) contains vertical and horizontal cavities, channels and agglomerates, which can be interpreted as permanent leftover of a formerly open axial channel, later filled by silica. (iii) The AF consists of a three-dimensional crystal-like arrangement of organic molecules and amorphous silica surrounding these molecules. Similar to an inorganic crystal, this encased protein crystal is typified by crystallographic directions, lattice planes and surface steps. The 001 growth direction is especially favored, thereby scaffolding the axial cylinders growth and consequently the spicules morphology.

Ponader D.,MPI of Colloids and Interfaces | Wojcik F.,MPI of Colloids and Interfaces | Beceren-Braun F.,Charité - Medical University of Berlin | Dernedde J.,Charité - Medical University of Berlin | Hartmann L.,MPI of Colloids and Interfaces
Biomacromolecules | Year: 2012

We present for the first time the synthesis of sequence-defined monodisperse glycopolymer segments via solid-phase polymer synthesis. Functional building blocks displaying alkyne moieties and hydrophilic ethylenedioxy units were assembled stepwise on solid phase. The resulting polymer segments were conjugated with mannose sugars via 1,3-dipolar cycloaddition. The obtained mono-, di-, and trivalent mannose structures were then subject to Con A lectin binding. Surface plasmon resonance studies showed a nonlinear increase in binding regarding the number and spacing of sugar ligands. The results of Con A lectin binding assays indicate that the chemical composition of the polymeric scaffold strongly contributes to the binding activities as well as the spacing between the ligands and the number of presented mannose units. Our approach now allows for the synthesis of highly defined glycooligomers and glycopolymers with a diversity of properties to investigate systematically multivalent effects of polymeric ligands. © 2012 American Chemical Society.

A model for chemists: mussel attachment fibers, also known as byssus threads, sticks underwater better than any glue from a tube. The filaments are strong, elastic, hard and self-healing. They also partly self-assemble. The chemical industry could imitate the process to produce plastics in an environmentally friendly manner. Credit: Tobias Priemel / MPI of Colloids and Interfaces The chemical industry can learn a lot from the common mussel. Not only are the mollusc's mother of pearl and tough threads with which it clings to the seafloor remarkable, but the way in which these materials are produced could also serve as a blueprint for the environmentally friendly production of complex polymer structures. Scientists at the Max Planck Institute of Colloids and Interfaces have gained the first insights into how mussel attachment fibres, known as byssus threads, are produced in the mollusc foot. They discovered that many steps in this process proceed autonomously, i.e. without any active intervention by the mussel. These findings could reveal new insights into how polymers can technically be assembled to more complex structures. You probably won't see them at the fish counter, but when mussels are hauled in fresh from the sea, their byssus threads – forming a yellowish mat of fine hairs – are sometimes still hanging from the shells. Despite its unremarkable appearance, the properties of mussel byssus have caused excitement among material scientists. The small adhesive plaque at the end of the thread, which mussels use to cling to stones on the seafloor, is unsurpassed in their ability to adhere underwater. The biopolymer that forms the core of the thread is extremely tough and also heals itself when damaged. The cuticle of the thread is as hard as the epoxide resin used to manufacture printed circuit boards, but is still highly extensible. These qualities have inspired chemists to mimic the materials produced by these molluscs. As it turns out, the process by which the threads are produced could also serve as an inspiration to chemists. "Many of the starting materials of the biopolymers self-assemble into complex structures simply because the mussel releases them in a coordinated fashion at specific locations," says Matt Harrington, whose research group at the Max Planck Institute of Colloids and Interfaces has gained the first insights into the mollusc's polymer factory. Dedicated glands for each part of the thread Scientists have long known that mussels spin byssus threads in a fine groove in their foot. This occurs when glands secrete the starting substances into the groove. However, Matt Harrington and his coworkers have now found that the glands can be differentiated according to the three parts of the byssal thread. This means, there are separate glands for the adhesive plaque at the end of a thread, for the core and for the cuticle. The starting substances are then mixed in appropriate ratios in small sacs called vesicles. Differentiation of the glands, their position and the point in time when they release their content, are crucial to ensure that the three parts of the filament are formed at the correct sites. A perfectly choreographed series of vesicles containing the polymer components for the core, the cuticle and the plaque flow into the groove, where they autonomously assemble into a material with very complex structure. The Potsdam team observed this by artificially stimulating the glands in the mussel foot to release vesicles but otherwise paralyzed the foot so that they could study it. They then froze several feet in various phases of thread production and analyzed sections of them using a spectroscopic method that shed light on the chemical composition of the substances. They compared the results of these analyses with the results of experiments in which they selectively stained various chemical components in the threads. "Because only the glands function in the paralyzed foot, we were able to distinguish precisely which steps of the biopolymerization process are self-organized and where the mussel has to intervene to regulate the process," Tobias Priemel, who performed most of the experiments, explains. The different effects of self-organized and biologically regulated steps were particularly obvious in the case of the thread core. The artificially spun threads emerged from the foot groove looking rather shapeless. Examining the internal structure, the researchers noticed that the core polymers in their experiments were highly aligned only over short segments and not over the full length of the thread, as is the case with naturally produced byssus. "It's possible that the mussel foot shapes the threads so that the polymers are aligned along their entire length," Tobias Priemel surmises. Self-assembly of polymers in the chemical industry When synthesis is artificially initiated and the mussel is unable to intervene, flaws also appear in other parts of the byssus thread. Matt Harrington and his coworkers want to find out how mussels produce threads without the observed flaws and why they do not have to actively intervene in other byssus production steps. "If we knew which factors favour self-assembly of the biological polymers, the chemical industry might be able to produce complex polymer structures in a similar manner, Harrington says. For example, the pH level in and around the vesicles might play a role in self-assembly in the mussel foot. "But it's just as interesting to learn more about the underlying biological regulation," Harrington says. It might be explained by simple mechanisms, for example that the foot squeezes the polymers into the desired shape or that the mussel after the formation of the protein structure adds metal ions which crosslink the proteins. Such tricks could also be harnessed for the industrial synthesis of polymers. "My dream is to create – with the help of what we learn from byssus threads – self-healing materials in an environmentally friendly process that have similar physical properties to byssus threads," Harrington says. More information: Rapid self-assembly of complex biomolecular architectures during mussel byssus biofabrication. Nature Communications, 28 February 2017; DOI: 10.1038/ncomms14539

Gaponik N.,TU Dresden | Shchukin D.G.,MPI of Colloids and Interfaces | Sviridov D.V.,Belarussian State University
Zeitschrift fur Physikalische Chemie | Year: 2011

A facile method of patterning of various dielectric substrates (glass, quartz, and polyimide) with thin films of conducting polyaniline with at least 10 μm resolution is demonstrated. This method can be applied for the fabrication of functional conducting polymer interconnections between microelectrode arrays separated by dielectric gaps. Such interconnections may find applications in microelectrochemical sensors and electrocatalytic systems. © by Oldenbourg Wissenschaftsverlag, München.

Liggieri L.,CNR Institute of Neuroscience | Miller R.,MPI of Colloids and Interfaces
Current Opinion in Colloid and Interface Science | Year: 2010

The relaxation behaviour of surfactant layers provides a deep insight into the composition and structure of adsorbed layers at liquid interfaces. The development of professional experimental tools created a helpful basis for an increasing interest in these studies. In addition, the theoretical basis has been improved in many aspects such that for several surfactant systems a quantitative understanding is already possible. In particular the consideration of the changes in molar area of adsorbed molecules, introduced into the thermodynamics of adsorbed layers first by Fainerman in 1995, due to changes in the surface coverage allowed a considerably better, in many cases even quantitative understanding of the surface relaxation. Another important additional property, introduced into the thermodynamics and consequently also into the mechanisms of relaxation processes in interfacial layers, is the two-dimensional compressibility, important for the response to deformations of rather packed interfacial layers. The experimentally observed negative dilational viscosity is discussed only briefly and considered essentially in terms of experimental and theoretical shortcomings. The relaxation behaviour of nano- and microparticles, in literature often addressed is compounds able to act "instead of surfactants" are also addressed and some peculiarities discussed, while the obvious interrelation between the dilational rheology and stability of foams and emulsions is not analysed in detail. © 2010 Elsevier Ltd.

Pussak D.,MPI of Colloids and Interfaces | Behra M.,MPI of Colloids and Interfaces | Schmidt S.,Fraunhofer Institute for Biomedical Engineering | Hartmann L.,MPI of Colloids and Interfaces
Soft Matter | Year: 2012

We report on the synthesis and operation of new soft colloidal probes (SCPs) as sensors for adhesion energy measurements. The measurements involve determination of the thermodynamic work of adhesion using the Johnson-Kendall-Roberts (JKR) approach. To maximize the sensitivity as well as the specificity of adhesion measurements in aqueous media we use highly compliant poly(ethylene glycol) (PEG) microparticles as SCPs. The chemical inertness of PEG offers advantages as probe material, but at the same time complicates the integration of functional groups. Consequently, we focus on the development of a straightforward yet variable surface modification procedure involving radical surface chemistry using benzophenone as the photoinitiator. With this highly versatile method we are able to introduce various functionalities like carboxy or amine groups directly to the PEG network. These functionalized SCPs can then be further modified with more complex structures such as dendritic oligo(amidoamines). With a first set of SCPs, adhesion energies were measured on model surfaces revealing the contributions due to acid-base, electrostatic and hydrophobic interactions in water. We successfully showed that the developed PEG probes allow for the study of contact behaviour without expensive instrumentation and with high sensitivity suitable to detect very weak (biological) interactions. © 2012 The Royal Society of Chemistry.

Ulaganathan V.,MPI of Colloids and Interfaces | Bergenstahl B.,Lund University | Kragel J.,MPI of Colloids and Interfaces | Miller R.,MPI of Colloids and Interfaces
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2012

The adsorption and shear rheological behavior is studied of β-lactoglobulin (BLG) alone and in mixtures with sodium dodecyl sulphate (SDS) at water/hexane and water/MCT interface. At a low ratio of SDS in the mixture, the adsorbed layer at the interface comprises mostly of protein-surfactant complexes while at a higher SDS/BLG mixing ratio the surfactant dominates at the interface and governs the interfacial properties. The adsorption and shear rheological behavior complement each other and confirm the stepwise replacement of BLG by SDS. The molecular scheme at the two studied interfaces is similar, but the quantitative properties differ due to the differences in the polarity of the oils. © 2012 Elsevier B.V.

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