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Dive into the research topics where Kai Kristiansen is active.

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Featured researches published by Kai Kristiansen.


Reports on Progress in Physics | 2010

Recent advances in the surface forces apparatus (SFA) technique

Jacob N. Israelachvili; Younjin Min; Mustafa Akbulut; Anna R. Godfrey Alig; G Carver; W Greene; Kai Kristiansen; Ernst Meyer; Noshir S. Pesika; K Rosenberg; Hongbo Zeng

The surface forces apparatus (SFA) has been used for many years to measure the physical forces between surfaces, such as van der Waals (including Casimir) and electrostatic forces in vapors and liquids, adhesion and capillary forces, forces due to surface and liquid structure (e.g. solvation and hydration forces), polymer, steric and hydrophobic interactions, bio-specific interactions as well as friction and lubrication forces. Here we describe recent developments in the SFA technique, specifically the SFA 2000, its simplicity of operation and its extension into new areas of measurement of both static and dynamic forces as well as both normal and lateral (shear and friction) forces. The main reason for the greater simplicity of the SFA 2000 is that it operates on one central simple-cantilever spring to generate both coarse and fine motions over a total range of seven orders of magnitude (from millimeters to angstroms). In addition, the SFA 2000 is more spacious and modulated so that new attachments and extra parts can easily be fitted for performing more extended types of experiments (e.g. extended strain friction experiments and higher rate dynamic experiments) as well as traditionally non-SFA type experiments (e.g. scanning probe microscopy and atomic force microscopy) and for studying different types of systems.


Langmuir | 2015

Developing a general interaction potential for hydrophobic and hydrophilic interactions.

Stephen H. Donaldson; Anja Røyne; Kai Kristiansen; Michael V. Rapp; Saurabh Das; Matthew A. Gebbie; Dong Woog Lee; Philipp Stock; Markus Valtiner; Jacob N. Israelachvili

We review direct force measurements on a broad class of hydrophobic and hydrophilic surfaces. These measurements have enabled the development of a general interaction potential per unit area, W(D) = -2γ(i)Hy exp(-D/D(H)) in terms of a nondimensional Hydra parameter, Hy, that applies to both hydrophobic and hydrophilic interactions between extended surfaces. This potential allows one to quantitatively account for additional attractions and repulsions not included in the well-known combination of electrostatic double layer and van der Waals theories, the so-called Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The interaction energy is exponentially decaying with decay length D(H) ≈ 0.3-2 nm for both hydrophobic and hydrophilic interactions, with the exact value of D(H) depending on the precise system and conditions. The pre-exponential factor depends on the interfacial tension, γ(i), of the interacting surfaces and Hy. For Hy > 0, the interaction potential describes interactions between partially hydrophobic surfaces, with the maximum hydrophobic interaction (i.e., two fully hydrophobic surfaces) corresponding to Hy = 1. Hydrophobic interactions between hydrophobic monolayer surfaces measured with the surface forces apparatus (SFA) are shown to be well described by the proposed interaction potential. The potential becomes repulsive for Hy < 0, corresponding to partially hydrophilic (hydrated) interfaces. Hydrated surfaces such as mica, silica, and lipid bilayers are discussed and reviewed in the context of the values of Hy appropriate for each system.


Proceedings of the National Academy of Sciences of the United States of America | 2009

Interaction forces and adhesion of supported myelin lipid bilayers modulated by myelin basic protein

Younjin Min; Kai Kristiansen; Joan M. Boggs; Cynthia Husted; Joseph A. Zasadzinski; Jacob N. Israelachvili

Force–distance measurements between supported lipid bilayers mimicking the cytoplasmic surface of myelin at various surface coverages of myelin basic protein (MBP) indicate that maximum adhesion and minimum cytoplasmic spacing occur when each negative lipid in the membrane can bind to a positive arginine or lysine group on MBP. At the optimal lipid/protein ratio, additional attractive forces are provided by hydrophobic, van der Waals, and weak dipolar interactions between zwitterionic groups on the lipids and MBP. When MBP is depleted, the adhesion decreases and the cytoplasmic space swells; when MBP is in excess, the bilayers swell even more. Excess MBP forms a weak gel between the surfaces, which collapses on compression. The organization and proper functioning of myelin can be understood in terms of physical noncovalent forces that are optimized at a particular combination of both the amounts of and ratio between the charged lipids and MBP. Thus loss of adhesion, possibly contributing to demyelination, can be brought about by either an excess or deficit of MBP or anionic lipids.


Langmuir | 2012

The Electrochemical Surface Forces Apparatus: The Effect of Surface Roughness, Electrostatic Surface Potentials, and Anodic Oxide Growth on Interaction Forces, and Friction between Dissimilar Surfaces in Aqueous Solutions

Markus Valtiner; Xavier Banquy; Kai Kristiansen; George W. Greene; Jacob N. Israelachvili

We present a newly designed electrochemical surface forces apparatus (EC-SFA) that allows control and measurement of surface potentials and interfacial electrochemical reactions with simultaneous measurement of normal interaction forces (with nN resolution), friction forces (with μN resolution), and distances (with Å resolution) between apposing surfaces. We describe three applications of the developed EC-SFA and discuss the wide-range of potential other applications. In particular, we describe measurements of (1) force-distance profiles between smooth and rough gold surfaces and apposing self-assembled monolayer-covered smooth mica surfaces; (2) the effective changing thickness of anodically growing oxide layers with Å-accuracy on rough and smooth surfaces; and (3) friction forces evolving at a metal-ceramic contact, all as a function of the applied electrochemical potential. Interaction forces between atomically smooth surfaces are well-described using DLVO theory and the Hogg-Healy-Fuerstenau approximation for electric double layer interactions between dissimilar surfaces, which unintuitively predicts the possibility of attractive double layer forces between dissimilar surfaces whose surface potentials have similar sign, and repulsive forces between surfaces whose surface potentials have opposite sign. Surface roughness of the gold electrodes leads to an additional exponentially repulsive force in the force-distance profiles that is qualitatively well described by an extended DLVO model that includes repulsive hydration and steric forces. Comparing the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer allowed the identification of its chemical structure as a hydrated Au(OH)(3) phase formed at the gold surface at high positive potentials. The EC-SFA allows, for the first time, one to look at complex long-term transient effects of dynamic processes (e.g., relaxation times), which are also reflected in friction forces while tuning electrochemical surface potentials.


Advanced Materials | 2011

Effect of Surface Roughness and Electrostatic Surface Potentials on Forces Between Dissimilar Surfaces in Aqueous Solution

Markus Valtiner; Kai Kristiansen; George W. Greene; Jacob N. Israelachvili

The first surface force measurements under electrochemical potential control between a metal and a ceramic surface across a liquid medium (water) are reported. Our experiments also investigate and reveal how increasing levels of surface roughness and dissimilarity between the potentials of the interacting surfaces influence the strength and range of electric double layer, van der Waals, hydration, and steric forces and how this contributes to deviations from DLVO theory at small distances within aqueous solution.


Proceedings of the National Academy of Sciences of the United States of America | 2014

Lipid domains control myelin basic protein adsorption and membrane interactions between model myelin lipid bilayers

Dong Woog Lee; Xavier Banquy; Kai Kristiansen; Yair Kaufman; Joan M. Boggs; Jacob N. Israelachvili

Significance The proper functioning of multilayer membrane systems, such as myelin, requires the multilamellar membranes to be tightly wrapped around the axon fibers, thereby allowing efficient electric signal transmission. Slight changes in lipid composition in myelin membranes will alter their domain sizes and distributions, and the intermembrane adhesive properties. Using the surface forces apparatus and atomic force microscope, we studied the adsorption of myelin basic protein (MBP) to model myelin lipid bilayer membranes of varying compositions, and their effects on the structure, equilibrium spacing (swelling), and adhesion force between them. We find that MBP preferentially adsorbs to “disordered” submicron domains, affecting regular spacing and adhesion. These findings provide insights into lipid–protein interactions and membrane-associated (e.g., demyelinating) diseases. The surface forces apparatus and atomic force microscope were used to study the effects of lipid composition and concentrations of myelin basic protein (MBP) on the structure of model lipid bilayers, as well as the interaction forces and adhesion between them. The lipid bilayers had a lipid composition characteristic of the cytoplasmic leaflets of myelin from “normal” (healthy) and “disease-like” [experimental allergic encephalomyelitis (EAE)] animals. They showed significant differences in the adsorption mechanism of MBP. MBP adsorbs on normal bilayers to form a compact film (3–4 nm) with strong intermembrane adhesion (∼0.36 mJ/m2), in contrast to its formation of thicker (7–8 nm) swelled films with weaker intermembrane adhesion (∼0.13 mJ/m2) on EAE bilayers. MBP preferentially adsorbs to liquid-disordered submicron domains within the lipid membranes, attributed to hydrophobic attractions. These results show a direct connection between the lipid composition of membranes and membrane–protein adsorption mechanisms that affects intermembrane spacing and adhesion and has direct implications for demyelinating diseases.


ACS Nano | 2014

Influence of molecular dipole orientations on long-range exponential interaction forces at hydrophobic contacts in aqueous solutions

Kai Kristiansen; Philipp Stock; Theodoros Baimpos; Sangeetha Raman; Jaye K. Harada; Jacob N. Israelachvili; Markus Valtiner

Strong and particularly long ranged (>100 nm) interaction forces between apposing hydrophobic lipid monolayers are now well understood in terms of a partial turnover of mobile lipid patches, giving rise to a correlated long-range electrostatic attraction. Here we describe similarly strong long-ranged attractive forces between self-assembled monolayers of carboranethiols, with dipole moments aligned either parallel or perpendicular to the surface, and hydrophobic lipid monolayers deposited on mica. We compare the interaction forces measured at very different length scales using atomic force microscope and surface forces apparatus measurements. Both systems gave a long-ranged exponential attraction with a decay length of 2.0 ± 0.2 nm for dipole alignments perpendicular to the surface. The effect of dipole alignment parallel to the surface is larger than for perpendicular dipoles, likely due to greater lateral correlation of in-plane surface dipoles. The magnitudes and range of the measured interaction forces also depend on the surface area of the probe used: At extended surfaces, dipole alignment parallel to the surface leads to a stronger attraction due to electrostatic correlations of freely rotating surface dipoles and charge patches on the apposing surfaces. In contrast, perpendicular dipoles at extended surfaces, where molecular rotation cannot lead to large dipole correlations, do not depend on the scale of the probe used. Our results may be important to a range of scale-dependent interaction phenomena related to solvent/water structuring on dipolar and hydrophobic surfaces at interfaces.


Nature Communications | 2015

Real-time intermembrane force measurements and imaging of lipid domain morphology during hemifusion

Dong Woog Lee; Kai Kristiansen; Stephen H. Donaldson; Nicholas Cadirov; Xavier Banquy; Jacob N. Israelachvili

Membrane fusion is the core process in membrane trafficking and is essential for cellular transport of proteins and other biomacromolecules. During protein-mediated membrane fusion, membrane proteins are often excluded from the membrane–membrane contact, indicating that local structural transformations in lipid domains play a major role. However, the rearrangements of lipid domains during fusion have not been thoroughly examined. Here using a newly developed Fluorescence Surface Forces Apparatus (FL-SFA), migration of liquid-disordered clusters and depletion of liquid-ordered domains at the membrane–membrane contact are imaged in real time during hemifusion of model lipid membranes, together with simultaneous force–distance and lipid membrane thickness measurements. The load and contact time-dependent hemifusion results show that the domain rearrangements decrease the energy barrier to fusion, illustrating the significance of dynamic domain transformations in membrane fusion processes. Importantly, the FL-SFA can unambiguously correlate interaction forces and in situ imaging in many dynamic interfacial systems.


Langmuir | 2015

Adsorption Mechanism of Myelin Basic Protein on Model Substrates and Its Bridging Interaction between the Two Surfaces

Dong Woog Lee; Xavier Banquy; Kai Kristiansen; Younjin Min; Joan M. Boggs; Jacob N. Israelachvili

Myelin basic protein (MBP) is an intrinsically disordered (unstructured) protein known to play an important role in the stability of myelins multilamellar membrane structure in the central nervous system. The adsorption of MBP and its capacity to interact with and bridge solid substrates has been studied using a surface forces apparatus (SFA) and a quartz crystal microbalance with dissipation (QCM-D). Adsorption experiments show that MBP molecules adsorb to the surfaces in a swollen state before undergoing a conformational change into a more compact structure with a thickness of ∼3 nm. Moreover, this compact structure is able to interact with nearby mica surfaces to form adhesive bridges. The measured adhesion force (energy) between two bridged surfaces is 1.0 ± 0.1 mN/m, (Ead = 0.21 ± 0.02 mJ/m(2)), which is slightly smaller than our previously reported adhesion force of 1.7 mN/m (Ead = 0.36 mJ/m(2)) for MBP adsorbed on two supported lipid bilayers (Lee et al., Proc. Natl. Acad. Sci. U.S.A. 2014, 111, E768-E775). The saturated surface concentration of compact MBP on a single SiO2 surface reaches a stable value of 310 ± 10 ng/cm(2) regardless of the bulk MBP concentration. A kinetic three-step adsorption model was developed that accurately fits the adsorption data. The developed model is a general model, not limited to intrinsically disordered proteins, that can be extended to the adsorption of various chemical compounds that undergo chemical reactions and/or conformational changes upon adsorbing to surfaces. Taken together with our previously published data (Lee et al., Proc. Natl. Acad. Sci. U.S.A. 2014, 111, E768-E775), the present results confirm that conformational changes of MBP upon adsorption are a key for strong adhesion, and that such conformational changes are strongly dependent on the nature of the surfaces.


Proceedings of the National Academy of Sciences of the United States of America | 2017

In situ nano- to microscopic imaging and growth mechanism of electrochemical dissolution (e.g., corrosion) of a confined metal surface

Claudia Merola; Hsiu-Wei Cheng; Kai Schwenzfeier; Kai Kristiansen; Ying-Ju Chen; Howard A. Dobbs; Jacob N. Israelachvili; Markus Valtiner

Significance A surface forces apparatus was used with an electrochemical attachment to directly visualize electrochemical reactions, dissolution, and pitting on surfaces when confined in nanoscale gaps (or “crevices”) in real time. The results provide unique insights into how two closely apposed surfaces degrade under confinement, which is different from degradation of surfaces exposed to bulk solution. Degradation proceeds via local nucleation of “pits” at the periphery or center of the “contact area” that rapidly grow outward (in radius) and, more slowly, in depth, until the pits converge and the whole area has become one large pit. The results on a metal–inorganic interface are similar to previous observations on inorganic interfaces, and support a general mechanism of “pitting corrosion” at confined interfaces. Reactivity in confinement is central to a wide range of applications and systems, yet it is notoriously difficult to probe reactions in confined spaces in real time. Using a modified electrochemical surface forces apparatus (EC-SFA) on confined metallic surfaces, we observe in situ nano- to microscale dissolution and pit formation (qualitatively similar to previous observation on nonmetallic surfaces, e.g., silica) in well-defined geometries in environments relevant to corrosion processes. We follow “crevice corrosion” processes in real time in different pH-neutral NaCl solutions and applied surface potentials of nickel (vs. Ag|AgCl electrode in solution) for the mica–nickel confined interface of total area ∼0.03 mm2. The initial corrosion proceeds as self-catalyzed pitting, visualized by the sudden appearance of circular pits with uniform diameters of 6–7 μm and depth ∼2–3 nm. At concentrations above 10 mM NaCl, pitting is initiated at the outer rim of the confined zone, while below 10 mM NaCl, pitting is initiated inside the confined zone. We compare statistical analysis of growth kinetics and shape evolution of individual nanoscale deep pits with estimates from macroscopic experiments to study initial pit growth and propagation. Our data and experimental techniques reveal a mechanism that suggests initial corrosion results in formation of an aggressive interfacial electrolyte that rapidly accelerates pitting, similar to crack initiation and propagation within the confined area. These results support a general mechanism for nanoscale material degradation and dissolution (e.g., crevice corrosion) of polycrystalline nonnoble metals, alloys, and inorganic materials within confined interfaces.

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Xavier Banquy

Université de Montréal

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Dong Woog Lee

University of California

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Younjin Min

Massachusetts Institute of Technology

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James R. Boles

University of California

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