
Sven Holger BehrensGeorgia Institute of Technology | GT · School of Chemical & Biomolecular Engineering
Sven Holger Behrens
PhD
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97
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Introduction
Publications
Publications (97)
Ordered, fibrous, self-seeding aggregates of misfolded proteins known as amyloids are associated with important diseases in
mammals and control phenotypic traits in fungi. A given protein may adopt multiple amyloid conformations, known as variants
or strains, each of which leads to a distinct disease pattern or phenotype. Here, we study the effect...
Vigorous mixing of an aqueous particle dispersion with oil usually produces
a particle-stabilized emulsion (a “Pickering emulsion”), the longevity of which depends on
the particles’ wetting properties. A known exception occurs when particles fail to adsorb to
the oil−water interface created during mixing because of a strong repulsion between
charge...
We study the charging behavior of polystyrene and polymethyl methacrylate particles with different functional surface groups in water and in decane containing either ionic (AOT) or nonionic surfactant (Span 85). Electrophoretic mobilities in the nonpolar media are measured as a function of surfactant concentration and the applied electric field str...
The interaction of solid particles with fluid interfaces in colloidal multiphase systems can lead to a wide range of fascinating and sometimes useful phenomena. Most of the research in this area has focused on ternary systems with two immiscible fluids and one particle species. After a brief review of some common characteristics, this article discu...
Aqueous foams are ubiquitous; they appear in products and processes that span the cosmetics, food, and energy industries. The versatile applicability of foams come as a result of their intrinsic viscous and elastic properties; for example, foams are exploited as drilling fluids in enhanced oil recovery for their high viscosity. Recently so-called c...
We introduce and demonstrate critical steps toward the Geode process for the bottom-up synthesis of semiconductor nanowires. Central to the process is the design and fabrication of an unconventional, high surface area substrate: the interior surface of hollow silica microcapsules, assembled from silica particles via emulsion templating, and featuri...
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We introduce and demonstrate critical steps toward the Geode process for the bottom-up synthesis of semiconductor nanowires. Central to the process is the design and fabrication of an unconventional, high surface area substrate: the interior surface of hollow silica microcapsules, assembled from silica particles via emulsion templating, and f...
Highly hydrophobic, water-insoluble nonionic surfactants are often considered irrelevant to the ionization of interfaces at which they adsorb despite observations that suggest otherwise. In the present study, we provide unambiguous evidence for the participation of a water-insoluble surfactant in interfacial ionization by conducting electrophoresis...
In vitro formation of highly ordered protein aggregates, amyloids, is influenced by the presence of ions. Here, we have studied the effect of anions on amyloid fibril formation by two different amyloidogenic proteins, human Amyloid Beta-42 (Aβ42), associated with Alzheimer disease and produced recombinantly with a N-terminal methionine (Met-Aβ42),...
Air bubbles rising through an aqueous medium have been studied extensively and are routinely used for the separation of particulates via froth flotation, a key step in many industrial processes. Oil-coated bubbles can be more effective for separating hydrophilic particles with low affinity for the air-water interface, but the rise dynamics of oil-c...
Foams are concentrated dispersions of gas bubbles in a continuous liquid phase. They are ubiquitous in nature, and familiar from beer, frothed milk, and bubble baths; moreover, they play important roles in industrial applications ranging from petrochemicals to pharmaceuticals, food and cosmetics. Recently, we reported the discovery of "capillary fo...
Surfactants can adsorb in fluid-fluid interfaces and lower the interfacial tension. Like surfactants, particles with appropriate wettability can also adsorb in fluid-fluid interfaces. Despite many studies of particle adsorption at fluid interfaces, some confusion persists regarding the ability of (simple, non-amphiphilic) particles to reduce the in...
Nanomanufacturing-the fabrication of macroscopic products from well-defined nanoscale building blocks-in a truly scalable and versatile manner is still far from our current reality. Here, we describe the barriers to large-scale nanomanufacturing and identify routes to overcome them. We argue for nanomanufacturing systems consisting of an iterative...
Wetting phenomena are ubiquitous in nature and play key functions in various industrial processes and products. When a gas bubble encounters an oil droplet in an aqueous medium, it can experience either partial wetting or complete engulfment by the oil. Each of these morphologies can have practical benefits, and controlling the morphology is desira...
Charge regulation in the electrical double layer has important implications for ion adsorption, interparticle forces, colloidal stability, and deposition phenomena. While charge regulation generally receives little attention, its consequences can be major, especially when considering interactions between unequally charged surfaces. The present arti...
Amyloid propagation requires high levels of sequence specificity so that only molecules with very high sequence identity can
form cross-β-sheet structures of sufficient stringency for incorporation into the amyloid fibril. This sequence specificity
presents a barrier to transmission of prions between two species with divergent sequences, termed a s...
Electric charging of colloidal particles in nonpolar solvents plays a crucial role for many industrial applications and products, including rubbers, engine oils, toners, or electronic displays. Although disfavored by the low solvent permittivity, particle charging can be induced by added surfactants, even nonionic ones, but the underlying mechanism...
We propose a simple method of characterizing the (Lewis) acid-base behavior of oil-soluble non-ionic surfactants at the interface of nonpolar solvents with a polar phase. Using interfacial tensiometry, we probe the effective acidic and basic response of nonpolar surfactant solutions to contact with a variety of polar reference liquids. The measured...
Aqueous dispersions of polymers which obtained by free radical suspension polymerization or free radical miniemulsion polymerization of ethylenically unsaturated monomers in an oil-in-water emulsion whose disperse phase comprises at least one fluorescent dye dissolved in at least one ethylenically unsaturated monomer and has an average particle dia...
Liquid foams are two-phase systems in which a large volume of gas is dispersed as bubbles in a continuous liquid phase. These foams are ubiquitous in nature. In addition, they are found in industrial applications such as pharmaceutical formulation, food processing, waste water treatment, construction, and cosmetics. Recently, we reported a new type...
Liquid foams are familiar from beer, frothed milk, or bubble baths; foams in general also play important roles in oil recovery, lightweight packaging, and insulation. Here a new class of foams is reported, obtained by frothing a suspension of colloidal particles in the presence of a small amount of an immiscible secondary liquid. A unique aspect of...
Liquid foams are familiar from beer, frothed milk, or bubble baths; foams in general also play important roles in oil recovery, lightweight packaging, and insulation. Here a new class of foams is reported, obtained by frothing a suspension of colloidal particles in the presence of a small amount of an immiscible secondary liquid. A unique aspect of...
Abstracts:
* Abstract for AIChE- Aditi Sharma.pdf (180.6KB) - Uploading Abstracts
Colloidal multi-phase systems, such as foams and emulsions are ubiquitous in our daily life, existing from beer and milk to bubble baths; they also play important roles in industrial processes like enhanced oil recovery, cosmetics and food industries. Long-term stability is desirable for these systems, but often difficult to achieve. Colloidal mult...
Colloidal multi-phase systems, such as foams and emulsions are ubiquitous in our daily life, existing from beer and milk to bubble baths; they also play important roles in industrial processes like enhanced oil recovery, cosmetics and food industries. Long-term stability is desirable for these systems, but often difficult to achieve. Colloidal mult...
Monoclonal antibodies are the fastest growing class of biotherapeutics. Ensuring their colloidal and conformational stability in liquid dispersions is crucial for maintaining therapeutic efficacy and economic viability. Sugars are often added to increase the colloidal and thermal stability of protein; yet, determining which sugar is the most stabil...
A composition for polishing surfaces comprises the following components:
a) at least one inorganic abrasive component (S) comprising a lanthanide oxide,
b) at least one organic dispersing-agent component based on polymer (P),
c) at least one organic gelling agent (G) such as gellan gum,
d) water as solution or dispersing medium, and
e) if appropri...
It has been known for more than a century that colloidal particles with the "right" wetting properties can stabilize emulsions, much like surfactants or amphiphilic polymers do. Today, particle-stabilized emulsions (so-called Pickering emulsions) play an important role in many industrial applications, but our fundamental understanding of the connec...
Measurement of the permeability of microcapsules with Fluorescence Recovery After Photobleaching (FRAP) enables analysis of individual microcapsules, the study of their batch heterogeneity, and the survey of changes in an individual capsule’s transport properties under different environmental conditions. We present a modified protocol and analysis...
Physical stability is critical for any therapeutic protein's efficacy and economic viability. No reliable theory exists to predict stability de novo, and modeling aggregation is challenging as this phenomenon can involve orientation effects, unfolding, and the rearrangement of noncovalent bonds inter- and intramolecularly in a complex sequence of p...
Prion proteins are capable of converting from their soluble, biologically-functional forms into highly ordered, fibrous aggregates, called amyloids. This conversion is associated with certain neurodegenerative conditions, such as Alzheimer's disease. Protein misfolding is strongly influenced by ion-specific solvent effects, known as Hofmeister effe...
Physical stability is critical for any therapeutic protein’s efficacy and economic viability. No reliable theory exists to predict stability de novo, and modeling aggregation is challenging as this phenomenon involves unfolding and rearrangement of non-covalent bonds inter- and intra-molecularly in a complex sequence of poorly understood events. De...
Colloidosomes are semipermeable microcapsules with external shell formed by colloidal particles, providing promising technique for encapsulations with controllable permeability, mechanical properties and bio-compatibility. Our work explores double Pickering emulsion, also known as particle stabilized emulsions, as precursors to synthesize composite...
The wetting behavior of solid surfaces can be altered dramatically by introducing surface roughness on the nanometer scale. Some of nature's most fascinating wetting phenomena are associated with surface roughness; they have inspired both fundamental research and the adoption of surface roughness as a design parameter for man-made functional coatin...
Colloidal particles can strongly adsorb to liquid interfaces and
stabilize emulsions against droplet coalescence, the effectiveness of
which depends crucially on the particle wettability. From the study of
macroscopic solids, surface wetting is known to be influenced strongly
by nano-scale roughness (as seen e.g. in the ``Lotus effect'' or in
anti-...
The addition of salt to a colloidal dispersion reduces the energetic barrier for aggregation; however, in the context of protein, salts do not all have the same effect. The Hofmeister series is a qualitative ranking system for ions describing the extent to which an ion will affect a variety of phenomena in solution including (but not limited to) pr...
The thermostability of cellobiohydrolase I Cel7A from Trichoderma reesei was investigated using dynamic light scattering. While the whole enzyme displayed a melting point of 59°C, the catalytic domain obtained via papain-catalyzed proteolysis was shown to denature at 51°C and the cellulose-binding domain (with linker attached) melted at 65-66°C. Th...
The aggregation of therapeutic proteins in solution represents a major challenge in pharmaceutical development, as the mid- and long-term stability of these proteins is crucial for their efficacy and for compliance with FDA requirements. Monitoring slow aggregation experimentally is notoriously time-consuming, yet often unavoidable, since no theory...
Self-assembly of colloidal particles in the liquid interface of double emulsion droplets can be used to fabricate "colloidosome" microcapsules, which have great potential as vehicles for the controlled delivery of drugs or other cargoes. Here we present a novel class of aqueous core colloidosomes that combine the benefit of low capsule permeability...
The electrostatic stabilization of colloidal dispersions is usually considered the domain of polar media only, but some surfactants are known to raise the conductivity of liquids with low electric permittivity and to mediate charge-stabilization of nonpolar dispersions. Here we report an example of the counterintuitive electrostatic effects of noni...
Self-assembly of colloidal particles in the liquid interface of double emulsion droplets can be used to fabricate “colloidosome” microcapsules, which have great potential as vehicles for the controlled delivery of drugs or other cargoes. Here we present a novel class of aqueous core colloidosomes that combine the benefit of low capsule permeability...
Nanogels are small, highly crosslinked networks of a soluble polymer. In the case of water-soluble polymers these networks (hydrogels) can reach a very high water content by swelling in aqueous environments. The design and fabrication of functionalized nanogels as carriers of biomolecules have drawn great interests in nanotechnology and pharmaceuti...
The aggregation of therapeutic proteins in solution represents a major challenge in pharmaceutical development, as the mid- and long-term stability of these proteins is crucial for their efficacy and for compliance with FDA requirements. Monitoring slow aggregation experimentally is notoriously time-consuming, yet often unavoidable, since no theory...
The electrostatic stabilization of colloidal dispersions is usually considered the domain of polar media only because of the high energetic cost associated with introducing electric charge in nonpolar environments. Nevertheless, some surfactants referred to as "charge control agents" are known to raise the conductivity of liquids with low electric...
This paper reports the assembly and pH-triggered dissolution of a novel type of colloidosome microcapsules formed by self-assembly of responsive particles made from enteric coating polymers onto double emulsion templates; measurements of the capsules' permeability are complemented by evidence for fast and complete capsule dissolution in response to...
Nonpolar liquids do not easily accommodate electric charges, but surfactant additives are often found to dramatically increase the solution conductivity and promote surface charging of suspended colloid particles. Such surfactant-mediated electrostatic effects have been associated with equilibrium charge fluctuations among reverse surfactant micell...
This paper compares two manifestations of electrolyte-mediated interaction between globular proteins. Salt-induced protein aggregation is studied with dynamic light scattering (DLS) in solutions of lysozyme and bovine serum albumin (BSA) containing different types of sodium salts. The same types of ions are used in a second measurement series asses...
The behavior of colloidal particles in liquid-liquid interfaces is relevant to numerous commercial products and industrial processes, such as food processing, pharmaceutical formulation, flotation, oil extraction and materials fabrication. Over the past century, colloid and surface forces have been well understood in bulk phase, but the presence of...
It is well known that ionic surfactants such as AOT are able to induce strong charging effects in nonpolar liquids. They avoid the large energetic barrier associated with the introduction of small ions in low dielectric media by forming charged micellar aggregates. Here we report evidence that nonionic surfactants have a very similar effect on nonp...
It is well known that colloidal particles can strongly adsorb to an oil-water interface and stabilize emulsion droplets. The properties of any particle stabilized liquid-liquid interface can be further tuned with surfactant additives, and the effects of added surfactant can be surprisingly varied and complex. Surfactant molecules can adsorb to the...
The interaction of charged colloidal particles adsorbed to oil-water interfaces is still a subject of intensive research and scientific debate. The relative stability of such particles against aggregation compared to particles in aqueous bulk solution or in air-water interfaces has led to the controversial proposition that particles can sustain ele...
Particles adsorbed to the surface of emulsion droplets act as emulsifiers and stabilizers in so-called Pickering emulsions. Surface roughness has been proposed as one of the key parameters determining the particles' emulsifying properties, but some confusion persists about its true impact: although surface roughness reportedly lessens a particle's...
Nonpolar liquids do not easily accommodate electric charges, but it is known that surfactant additives can raise the conductivity and lead to electric charging of immersed solid surfaces. Here, we study the rarely considered conductivity effects induced by surfactant molecules without ionizable groups. Precision conductometry, light scattering, and...
The stabilization of complex microscale emulsions can lead to the development of new stimulus-responsive materials. Understanding the interfacial tension of such an emulsion can help interpret its relative stability, as well as provide insight about surface chemical interactions and other phenomena. Few conventional IFT instruments have the sophist...
It is well known that surfactants and amphiphilic copolymers commonly used to stabilize emulsions can often be substituted, as emulsifiers, by solid colloidal particles. Long after their original discovery, particle-stabilized emulsions ("Pickering emulsions") are currently attracting renewed interest for their potential role as precursors in the f...
According to conventional wisdom, ionization processes do not occur in media of low electric permittivity, where they require a higher energy input than thermal motion can provide (equivalently, the Bjerrum length is much larger than a typical ion size), and thus electric charge is not commonly considered relevant for particle interaction in nonpol...
We analyze the interaction forces between charged surfaces across aqueous solutions under the conditions of extreme charge regulation. Under such conditions, interactions may be weaker than those given by the constant potential (CP) boundary conditions. Thermodynamically, even vanishing electrostatic interactions are conceivable. Within the constan...
Interactions between preadsorbed films of poly(vinyl amine) (PVA) of two different line charge densities on silica substrates were studied with the colloidal probe technique based on the atomic force microscope (AFM). The preadsorbed films were prepared by adsorption of PVA from a pH 4 solution without any added salt. The highly charged PVA adsorbs...
Charging and swelling of cellulose in aqueous environments are of highest interest with respect to the performance of cellulose based products and applications. To unravel the interplay between ionization and structural features of the biopolymer hydrogel we compared non-crosslinked and crosslinked cellulose thin films based on a determination of t...
The pH- and electrolyte-dependent charging of collagen I fibrils was analyzed by streaming potential/streaming current experiments using the Microslit Electrokinetic Setup. Differential scanning calorimetry and circular dichroism spectroscopy were applied in similar electrolyte solutions to characterize the influence of electrostatic interactions o...
Using stimulus-sensitive microgel particles as an emulsifier, we have prepared a new type of emulsion responsive to pH, ionic strength, and temperature changes. Each of these environmental changes can trigger a volume phase transition in poly(N-isopropylacrylamide) (PNIPAM) microgel particles containing some carboxylic groups. Depending on their hy...
Interaction forces between pre-adsorbed layers of branched poly(ethylene imine) (PEI) of different molecular mass were studied with the colloidal probe technique, which is based on atomic force microscopy (AFM). During approach, the long-ranged forces between the surfaces are repulsive due to overlap of diffuse layers down to distances of a few nan...
The stability of colloidal dispersions hinges on the repulsive interaction between the particle surfaces. This interaction can be modified by adsorbed polymer and further tuned by the response of the adsorbate layer to changes in the surrounding solution.Total internal reflection microscopy has been used in this study to investigate the effect of c...
Thin films of cellulose are advantageous for analytical studies in aqueous environments to investigate various factors determining the performance of cellulose-based products. However, the weak fixation of cellulose layers on common carrier materials often limits this approach. To address this problem, we suggest a novel maleic anhydride copolymer...
Surfactant-free oil-in-water emulsions prepared with temperature and pH sensitive poly(N-isopropylacrylamide)
(PNIPAM) microgel particles offer unprecedented control of emulsion stability.
Interaction forces between ionizable surfaces across an electrolyte solution on the Poisson-Boltzmann level are discussed within the constant regulation approximation. The chemical response of each surface is expressed in terms of two parameters, namely, the diffuse layer potential and the regulation parameter p. Both parameters are easily availabl...
Conformational changes of poly(vinylamine) (PVA) upon adsorption onto mica were determined by AFM. The polyelectrolyte charge can be tuned through the solution pH. At pH 3, where the PVA is highly charged, an extended coil conformation is observed. When the pH is increased, the polyelectrolyte charge decreases and induces a segmental collapse throu...
A new and general approach is proposed to analyze the dynamics of a colloidal particle interacting with a nearby wall. This analysis can be used to determine the acting forces even when the system is non-stationary. As an illustration, we use total internal reflection microscopy to investigate the forces acting on a polystyrene sulfate latex partic...
These lecture notes address some recent advances in our understanding of macroionic interactions inspired in part by the evolution
of new techniques for studying macroions’ dynamics.
Although equally charged colloidal particles dispersed in clean water are expected to repel each other, an unexplained long-range attraction has consistently been reported for charged colloidal spheres confined by charged macroscopic surfaces. We present an alternative equilibrium measurement of the pair interaction energy for charged spheres near...
A model incorporating electrostatic and van der Waals forces was used to predict the wetting behavior of several systems containing a quartz surface, water, and a dense nonaqueous phase liquid (DNAPL). The disjoining pressure between the quartz/water and a water/DNAPL interface as a function of their separation was calculated from a full solution o...
The electric charge density of glass and silica surfaces in contact with aqueous electrolytes were analyzed. The surfaces had low specific area at low ionic strength and the surfaces interacted strongly with a second anionic surface. The regulated charge of silica and glass surfaces near the contact with a second anionic surface and the strength of...
The pair interaction energy of charged colloidal particles in electrolyte solutions can exhibit a large barrier as well as a pronounced secondary minimum. We discuss the effect of a secondary energy minimum on aggregation kinetics by modeling irreversible dimer formation as a two-step process in which charged colloidal particles in electrolyte solu...
Electrophoretic mobility studies of highly charged amidine latex particles were carried out to validate the standard electrokinetic model. The electrophoretic mobilities were measured on a standard commercial laser Doppler velocimetry electrophoresis apparatus. In a plot against the salt concentration, a pronounced mobility maximum was observed. Th...
Carboxyl latex particles of two different sizes were used to study the early stages of aggregation in dilute colloidal suspensions. The charging behavior as a function of solution pH was characterized in acid−base titration and electrophoresis experiments at fixed ionic strength; absolute aggregation rate constants were measured by combined static...
An efficient method is proposed to calculate the electric double layer force between two flat surfaces of dissimilar composition and ionization properties. The approach is based on explicit expressions for the solution of the (nonlinear) Poisson-Boltzmann equation and allows for boundary conditions of charge regulation, i.e., chemical equilibrium o...
Electrostatic interactions between charged surfaces across an electrolyte solution are commonly described by boundary conditions of constant charge or constant surface potential. These two extremes are in general not appropriate for an equilibrium description of materials with ionizable surface groups, but do provide an upper and lower bound for th...
When two surfaces with ionizable groups interact across an electrolyte solution, both their equilibrium charge density and the corresponding electrostatic surface potential will depend on the surface separation (charge regulation). The corresponding nonlinear boundary conditions are often replaced, for simplicity, by the limiting conditions of cons...
The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory commonly used to describe interactions bf charged surfaces across liquids has traditionally been reported to fail when used for quantitative predictions of deposition and aggregation in aqueous colloidal suspensions. Yet direct force measurements have recently confirmed the theory down to surface s...
Measurements of absolute aggregation rate constants were performed for two samples of well-characterized spheroidal hematite particles with rather different surface morphology. At high ionic strength, the system is in the fast aggregation regime with pH independent rate constants around (1-4) x 10(-18) m3/s. At low ionic strengths, the rate constan...
It is commonly reported that the classical aggregation theory by Derjaguin, Landau, Verwey and Overbeek (DLVO) fails to predict
quantitatively the dependence of colloid stability on the electrolyte concentration of the solution and on the particle size.
A connection of such problems to the typical surface charge density of model particles was indic...
These lecture notes address some recent advances in our understand- ing of macroionic interactions inspired in part by the evolution of new techniques for studying macroions' dynamics.
Charging and swelling of cellulose and collagen in aqueous environments are of highest interest with respect to the performance of cellulose and collagen based products and applications. To unravel the interplay between ionization and structural features of the biopolymers we compared reconstituted cellulose and collagen thin films based on a deter...
Diss. Nr. 13230 Naturwiss. ETH Zürich. Literaturverz.