Modifying surface forces through control of surface potentials

2017 ◽  
Vol 199 ◽  
pp. 261-277 ◽  
Author(s):  
Ran Tivony ◽  
Jacob Klein
Keyword(s):  
Surface Potential ◽  
Electrolyte Solution ◽  
Strong Electric Field ◽  
Salt Water ◽  
Surface Force ◽  
Adhesion Energy ◽  
Force Balance ◽  
Electrostatic Energy ◽  
Added Salt ◽  
Vdw Interaction

Combining direct surface force measurements with in situ regulation of surface potential provides an exceptional opportunity for investigating and manipulating interfacial phenomena. Recently, we studied the interaction between gold and mica surfaces in water with no added salt, while controlling the metal potential, and found that the surface charge at the metal may vary, and possibly even change its sign, as it progressively approaches the (constant-charge) mica surface [Langmuir, 2015, 31(47), 12845–12849]. Such a variation was found to directly affect the nature of the contact and adhesion between them due to exclusion of all mobile counterions from the intersurface gap. In this work, we extend this to examine the potential-dependent response of the adhesion and interaction between gold and mica to externally applied voltages and in electrolyte solution. Using a surface force balance (SFB) combined with a three-electrode electrochemical cell, we measured the normal interaction between gold and mica under surface potential regulation, revealing three interaction regimes – pure attraction, non-monotonic interaction from electrostatic repulsion to attraction (owing to charge inversion) and pure repulsion. Accordingly, the adhesion energy between the surfaces was found to vary both in no added salt water and, more strongly, in electrolyte solution. We justify this potential-dependent variation of adhesion energy in terms of the interplay between electrostatic energy and van der Waals (vdW) interaction at contact, and attribute the difference between the two cases to the weaker vdW interaction in electrolyte solution. Finally, we showed that through abruptly altering the gold surface potential from negative to positive and vice versa, the adhesion between gold and mica can be reversibly switched on and off. We surmise that the process of bringing the surface into contact is associated with the formation of a strong electric field O (108 V m−1) in the intersurface gap.

Surfactant Impurities Can Explain the Jones-Ray Effect

2018 ◽  
Author(s):  
Timothy Duignan ◽  
Marcel Baer ◽  
Christopher Mundy
Keyword(s):  
Surface Tension ◽  
Electrostatic Potential ◽  
Driving Forces ◽  
Salt Water ◽  
Fundamental Property ◽  
Apparent Contradiction ◽  
Low Salt ◽  
Air Water Interface ◽  
Added Salt ◽  
Effect Of Surface

<div> <p> </p><div> <div> <div> <p>The surface tension of dilute salt water is a fundamental property that is crucial to understanding the complexity of many aqueous phase processes. Small ions are known to be repelled from the air-water surface leading to an increase in the surface tension in accordance with the Gibbs adsorption isotherm. The Jones-Ray effect refers to the observation that at extremely low salt concentration the surface tension decreases in apparent contradiction with thermodynamics. Determining the mechanism that is responsible for this Jones-Ray effect is important for theoretically predicting the distribution of ions near surfaces. Here we show that this surface tension decrease can be explained by surfactant impurities in water that create a substantial negative electrostatic potential at the air-water interface. This potential strongly attracts positive cations in water to the interface lowering the surface tension and thus explaining the signature of the Jones-Ray effect. At higher salt concentrations, this electrostatic potential is screened by the added salt reducing the magnitude of this effect. The effect of surface curvature on this behavior is also examined and the implications for unexplained bubble phenomena is discussed. This work suggests that the purity standards for water may be inadequate and that the interactions between ions with background impurities are important to incorporate into our understanding of the driving forces that give rise to the speciation of ions at interfaces. </p> </div> </div> </div> </div>

scholarly journals The Role of Hyaluronic Acid in Cartilage Boundary Lubrication

Cells ◽  
2020 ◽  
Vol 9 (7) ◽  
pp. 1606 ◽  
Author(s):  
Weifeng Lin ◽  
Zhang Liu ◽  
Nir Kampf ◽  
Jacob Klein
Keyword(s):  
Hyaluronic Acid ◽  
Synovial Fluid ◽  
Surface Force ◽  
Force Balance ◽  
New Paradigm ◽  
Low Friction ◽  
Cartilage Surface ◽  
Boundary Lubricant ◽  
Lipid Layers

Hydration lubrication has emerged as a new paradigm for lubrication in aqueous and biological media, accounting especially for the extremely low friction (friction coefficients down to 0.001) of articular cartilage lubrication in joints. Among the ensemble of molecules acting in the joint, phosphatidylcholine (PC) lipids have been proposed as the key molecules forming, in a complex with other molecules including hyaluronic acid (HA), a robust layer on the outer surface of the cartilage. HA, ubiquitous in synovial joints, is not in itself a good boundary lubricant, but binds the PC lipids at the cartilage surface; these, in turn, massively reduce the friction via hydration lubrication at their exposed, highly hydrated phosphocholine headgroups. An important unresolved issue in this scenario is why the free HA molecules in the synovial fluid do not suppress the lubricity by adsorbing simultaneously to the opposing lipid layers, i.e., forming an adhesive, dissipative bridge between them, as they slide past each other during joint articulation. To address this question, we directly examined the friction between two hydrogenated soy PC (HSPC) lipid layers (in the form of liposomes) immersed in HA solution or two palmitoyl–oleoyl PC (POPC) lipid layers across HA–POPC solution using a surface force balance (SFB). The results show, clearly and surprisingly, that HA addition does not affect the outstanding lubrication provided by the PC lipid layers. A possible mechanism indicated by our data that may account for this is that multiple lipid layers form on each cartilage surface, so that the slip plane may move from the midplane between the opposing surfaces, which is bridged by the HA, to an HA-free interface within a multilayer, where hydration lubrication is freely active. Another possibility suggested by our model experiments is that lipids in synovial fluid may complex with HA, thereby inhibiting the HA molecules from adhering to the lipids on the cartilage surfaces.

Salt, Water and Oilseed Proteins Affect Brine Content of Sausages

1981 ◽  
Vol 44 (1) ◽  
pp. 43-46 ◽  
Author(s):  
R. N. TERRELL ◽  
J. A. BROWN
Keyword(s):  
Salt Water ◽  
Storage Period ◽  
Protein Isolate ◽  
Product Performance ◽  
Cottonseed Protein ◽  
Raw Meat ◽  
Added Water ◽  
Practical Tool ◽  
Microbial Numbers ◽  
Added Salt

Brine contents of commercial sausage products ranged from 3.7 to 5.9% and were different among brands. Frankfurters to which either isolated soy or cottonseed protein isolate were added had greater process shrinkage values and higher moisture, lower fat and lower brine contents than did controls. Frankfurters prepared with oilseed proteins had higher (P &lt; .05) process shrinkage percentages, higher moisture percentages and lower brine contents than did controls (all-meat). Although not significant among all comparisons, as in-going (lb per 100 lb raw meat) salt levels increased from 2.5 to 3.0 to 3.5 lb, brine contents increased regardless of level of added water (25, 30, and 35 lb per 100 lb of meat). Within added-salt levels, brine content generally decreased with increasing level of in-going water but these differences were not significant (P &gt; .05). At the beginning and end of a 6-week storage period, frankfurters with high brine contents (4.50–5.25%) had lower total microbial numbers than did frankfurters with low (2.50–3.49%) or medium (3.50–4.49%) brine contents. Because of simplicity, brine content determinations may be further developed as a practical tool for predicting product performance of cured sausages.

Effects of dielectric decrement on surface potential in a mixed electrolyte solution

2018 ◽  
Vol 27 (12) ◽  
pp. 126801 ◽  
Author(s):  
Jing Peng ◽  
Wen-Xin Zou ◽  
Rui Tian ◽  
Hang Li ◽  
Xin-Min Liu
Keyword(s):  
Surface Potential ◽  
Electrolyte Solution ◽  
Mixed Electrolyte ◽  
Mixed Electrolyte Solution

Practical aspects in the drawing of an optical fiber

1998 ◽  
Vol 13 (2) ◽  
pp. 483-493 ◽  
Author(s):  
S. Roy Choudhury ◽  
Y. Jaluria
Keyword(s):  
Optical Fibers ◽  
Gas Flow ◽  
Surface Force ◽  
Transport Processes ◽  
Operating Conditions ◽  
Force Balance ◽  
Viscous Stress ◽  
Furnace Temperature ◽  
Flow Configuration ◽  
Fiber Radius

The transport processes in the furnace for the continuous drawing of optical fibers have been studied numerically and analytically. Practical circumstances and operating conditions are considered. A peripheral gas flow configuration has been modeled, along with irises at the ends, as employed in practical furnaces. The neck-down profile of the fiber is not chosen, but has been generated on the basis of a surface force balance. The results obtained are validated by comparisons with earlier experimental results. A detailed analysis has been carried out to determine the relative contributions of different forces during the drawing process. Even though the internal viscous stress is shown to be the major contributor to the draw tension, it is found that under certain operating conditions, the force due to gravity is significant, especially at the beginning of the neck-down region. For a peripheral flow configuration, the effect of flow entrance is found to be very important in determining the necking shape. However, the effect of the iris size on the fiber temperature field is found to be negligible. It is found that for a given furnace temperature and fiber radius, there is an upper limit for draw-down speed at which a fiber can be drawn without rupture. Practical ranges of draw speeds and furnace temperature conditions are identified for the process to be feasible.

scholarly journals On the question of whether lubricants fluidize in stick–slip friction

2015 ◽  
Vol 112 (23) ◽  
pp. 7117-7122 ◽  
Author(s):  
Irit Rosenhek-Goldian ◽  
Nir Kampf ◽  
Arie Yeredor ◽  
Jacob Klein
Keyword(s):  
Surface Force ◽  
Lubricant Film ◽  
Force Balance ◽  
Smooth Surfaces ◽  
Stick Slip ◽  
Lubricant Films ◽  
Slip Event ◽  
Stick Slip Motion ◽  
Molecular Layers ◽  
Slip Motion

Intermittent sliding (stick–slip motion) between solids is commonplace (e.g., squeaking hinges), even in the presence of lubricants, and is believed to occur by shear-induced fluidization of the lubricant film (slip), followed by its resolidification (stick). Using a surface force balance, we measure how the thickness of molecularly thin, model lubricant films (octamethylcyclotetrasiloxane) varies in stick–slip sliding between atomically smooth surfaces during the fleeting (ca. 20 ms) individual slip events. Shear fluidization of a film of five to six molecular layers during an individual slip event should result in film dilation of 0.4–0.5 nm, but our results show that, within our resolution of ca. 0.1 nm, slip of the surfaces is not correlated with any dilation of the intersurface gap. This reveals that, unlike what is commonly supposed, slip does not occur by such shear melting, and indicates that other mechanisms, such as intralayer slip within the lubricant film, or at its interface with the confining surfaces, may be the dominant dissipation modes.

Electrohydrodynamics and Surface Force Analysis in AFM Imaging of a Charged, Deformable Biological Membrane in a Dilute Electrolyte Solution

2003 ◽  
Author(s):  
Tai-Hsi Fan ◽  
Andrei G. Fedorov
Keyword(s):  
Cell Membrane ◽  
Double Layer ◽  
Electrolyte Solution ◽  
Electrostatic Field ◽  
Biological Membrane ◽  
Equilibrium Shape ◽  
Surface Force ◽  
Surface Forces ◽  
Contact Mode ◽  
Afm Imaging

Surface forces arising in AFM imaging of a deformable, negatively charged biological membrane in an electrolyte solution are investigated in the limit of continuous electrohydrodynamics. Specifically, we extend our previous analysis [1] of purely hydrodynamic interactions between an AFM tip and the elastic cell membrane by accounting for electric double-layer forces under the assumption of a dilute electrolyte solution and local electrochemical equilibrium. The solution of the problem is obtained by integrating the quasisteady, electrically-forced Stokes equation for the electrohydrodynamic field, the linearized Poisson-Boltzmann equation for the electrostatic field in the electrolyte inside and outside of the cell, and the Laplace equation for the electrostatic field within a dielectric AFM tip. The Helfrich and Zhongcan’s equation for an equilibrium shape of the cell membrane is employed as a quasi-steady, nonlinear boundary condition linking the stress fields on both sides of the cell membrane augmented by the local membrane incompressibility condition in order to find the local tension/compression force acting on the membrane. For the first time, an integrated framework for the dynamic coupling of the membrane double-layer effects and the AFM tip-electrolyte-membrane motion is established that allows for characterizing of the local electrolyte flow field, the electrostatic field, the elastic deformation of the membrane, and the electrohydrodynamic surface force acting on the AFM tip in great detail. The results of the analysis provide information on the motion of the membrane and the surface forces induced by both an electrolyte motion and the Maxwell stresses resulting from the charge double-layer screening effect for a full cycle motion of the AFM tip in a non-contact mode imaging of the cell membrane.

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