Polymer displacement and the role of impurities in homopolymer adsorption: a surface force balance study

Langmuir ◽  
1991 ◽  
Vol 7 (10) ◽  
pp. 2346-2352 ◽  
Author(s):  
David A. Guzonas ◽  
Michael L. Hair
Keyword(s):  
Surface Force ◽  
Force Balance ◽  
Balance Study

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.

scholarly journals Regulation of the normalized rate of driven magnetic reconnection through shocked flux pileup

2021 ◽  
Vol 87 (3) ◽  
Author(s):  
Joseph Olson ◽  
Jan Egedal ◽  
Michael Clark ◽  
Douglass A. Endrizzi ◽  
Samuel Greess ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
System Size ◽  
Force Balance ◽  
Absolute Rate ◽  
Reconnection Rate ◽  
Supersonic Plasma ◽  
Reconnection Layer ◽  
Inflow Conditions ◽  
Theoretical Results

Magnetic reconnection is explored on the Terrestrial Reconnection Experiment (TREX) for asymmetric inflow conditions and in a configuration where the absolute rate of reconnection is set by an external drive. Magnetic pileup enhances the upstream magnetic field of the high-density inflow, leading to an increased upstream Alfvén speed and helping to lower the normalized reconnection rate to values expected from theoretical consideration. In addition, a shock interface between the far upstream supersonic plasma inflow and the region of magnetic flux pileup is observed, important to the overall force balance of the system, thereby demonstrating the role of shock formation for configurations including a supersonically driven inflow. Despite the specialized geometry where a strong reconnection drive is applied from only one side of the reconnection layer, previous numerical and theoretical results remain robust and are shown to accurately predict the normalized rate of reconnection for the range of system sizes considered. This experimental rate of reconnection is dependent on system size, reaching values as high as 0.8 at the smallest normalized system size applied.

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.

Altering the cellular mechanical force balance results in integrated changes in cell, cytoskeletal and nuclear shape

1992 ◽  
Vol 103 (4) ◽  
pp. 1215-1222 ◽  
Author(s):  
J.R. Sims ◽  
S. Karp ◽  
D.E. Ingber
Keyword(s):  
Shape Control ◽  
Nuclear Shape ◽  
Force Balance ◽  
Dependent Manner ◽  
Integrin Receptors ◽  
Permeabilized Cells ◽  
Capillary Endothelial Cells ◽  
Shape Determination ◽  
Dose Dependent

Studies were carried out with capillary endothelial cells cultured on fibronectin (FN)-coated dishes in order to analyze the mechanism of cell and nuclear shape control by extracellular matrix (ECM). To examine the role of the cytoskeleton in shape determination independent of changes in transmembrane osmotic pressure, membranes of adherent cells were permeabilized with saponin (25 micrograms/ml) using a buffer that maintains the functional integrity of contractile microfilaments. Real-time videomicroscopic studies revealed that addition of 250 microM ATP resulted in time-dependent retraction and rounding of permeabilized cells and nuclei in a manner similar to that observed in intact living cells following detachment using trypsin-EDTA. Computerized image analysis confirmed that permeabilized cells remained essentially rigid in the absence of ATP and that retraction was stimulated in a dose-dependent manner as the concentration of ATP was raised from 10 to 250 microM. Maximal rounding occurred by 30 min with projected cell and nuclear areas being reduced by 69 and 41%, respectively. ATP-induced rounding was also accompanied by a redistribution of microfilaments resulting in formation of a dense net of F-actin surrounding retracted nuclei. Importantly, ATP-stimulated changes in cell, cytoskeletal, and nuclear form were prevented in permeabilized cells using a synthetic myosin peptide (IRICRKG) that has been previously shown to inhibit actomyosin filament sliding in muscle. In contrast, both the rate and extent of cell and nuclear rounding were increased in permeabilized cells exposed to ATP when the soluble FN peptide, GRGDSP, was used to dislodge immobilized FN from cell surface integrin receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals A force-balance study of ice flow and basal conditions of Jutulstraumen, Antarctica

1996 ◽  
Vol 42 (142) ◽  
pp. 413-425 ◽  
Author(s):  
Øyvind Armand Høydal
Keyword(s):  
Flow Direction ◽  
Bottom Topography ◽  
Effective Strain ◽  
Great Influence ◽  
Force Balance ◽  
Effect Of Temperature ◽  
Velocity Variation ◽  
Shear Stresses ◽  
Balance Study ◽  
Measured Velocity

Abstract Stresses and velocities at depth are calculated across Jutulstraumen, an ice stream in Dronning Maud Land, draining about 1% of the Antarctic ice sheet. The force-balance study is based on data from kinematic GPS measurements on three strain nets, each consisting of 3 × 3 stakes. The maximum measured velocity is 443 m a−1 and the velocity variation over short distances is large compared with studied ice streams in West Antarctica. The surface topography together with the measured velocities across the profile indicate that the bottom topography has a great influence on the flow direction, even where the ice thickness is more than 2000 m. The basal shear stresses are calculated as 180, 227 and 146 kPa in the three Strain nets, while the corresponding driving stresses are 180, 122 and 111 kPa (±5%). The heat produced by sliding and internal deformation is sufficient to keep the base at the pressure-melting point. The annual basal melting is estimated to be about 60 mm. Investigations on the effect of temperature softening show that the flow parameter’s influence on the effective strain rate is more important than the flow parameter’s direct softening in the flow low alone. The mass flow calculated by the force-balance method is between 87 and 96% of pure plug flow and total discharge is calculated to be 13.3 ± 10 km3a-1.

scholarly journals Early Spindle Assembly in Drosophila Embryos: Role of a Force Balance Involving Cytoskeletal Dynamics and Nuclear Mechanics

2005 ◽  
Vol 16 (10) ◽  
pp. 4967-4981 ◽  
Author(s):  
E. N. Cytrynbaum ◽  
P. Sommi ◽  
I. Brust-Mascher ◽  
J. M. Scholey ◽  
A. Mogilner
Keyword(s):  
Spindle Assembly ◽  
Spindle Pole ◽  
Cortical Reorganization ◽  
Force Balance ◽  
Cell Cortex ◽  
Nuclear Dynamics ◽  
Nuclear Mechanics ◽  
Cytoskeletal Dynamics ◽  
Drosophila Embryos

Mitotic spindle morphogenesis depends upon the action of microtubules (MTs), motors and the cell cortex. Previously, we proposed that cortical- and MT-based motors acting alone can coordinate early spindle assembly in Drosophila embryos. Here, we tested this model using microscopy of living embryos to analyze spindle pole separation, cortical reorganization, and nuclear dynamics in interphase-prophase of cycles 11-13. We observe that actin caps remain flat as they expand and that furrows do not ingress. As centrosomes separate, they follow a linear trajectory, maintaining a constant pole-to-furrow distance while the nucleus progressively deforms along the elongating pole-pole axis. These observations are incorporated into a model in which outward forces generated by zones of active cortical dynein are balanced by inward forces produced by nuclear elasticity and during cycle 13, by Ncd, which localizes to interpolar MTs. Thus, the force-balance driving early spindle morphogenesis depends upon MT-based motors acting in concert with the cortex and nucleus.

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.

Effect of Thermophysical Properties of the Heater Substrate on Critical Heat Flux in Pool Boiling

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Pruthvik A. Raghupathi ◽  
Satish G. Kandlikar
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Temperature Fluctuations ◽  
Operating Conditions ◽  
Force Balance ◽  
Heater Surface ◽  
Monel 400

While the role of the liquid properties, surface morphology, and operating conditions on critical heat flux (CHF) in pool boiling is well investigated, the effect of the properties of the heater material is not well understood. Previous studies indicate that the heater thickness plays an important role on the CHF phenomenon. However, beyond a certain thickness, called the asymptotic thickness, the local temperature fluctuations on the heater surface caused by the periodic bubble ebullition cycle are evened out, and the CHF is not influenced by further increasing the thickness. In the present work, data from literature and pool boiling experiments conducted in this study with seven substrates—aluminum, brass, copper, carbon steel, Monel 400, silver, and silicon—are used to determine the effect of the thermophysical property of the material on CHF for thick heaters that are used in industrial pool boiling applications. The results indicate that the product of density (ρ) and specific heat (cp) represents an important substrate property group that affects the CHF, and that the thermal conductivity is not an important parameter. A well-established force-balance-based CHF model (Kandlikar model) is modified to account for the thermal properties of the substrate. The predicted CHF values are within 15% of the experimental results.

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