Effect of Solvent Condition on the Dynamic Response of Polymer Brushes

1998 ◽  
Vol 543 ◽  
Author(s):  
S. M. Kilbey ◽  
P. Schorr ◽  
M. Tirrell
Keyword(s):  
Polymer Brushes ◽  
Surface Forces ◽  
Polymer Chains ◽  
Lateral Motion ◽  
Dilute Solution ◽  
Surface Forces Apparatus ◽  
Effect Of Solvent ◽  
Preferential Adsorption ◽  
Frictional Forces ◽  
Theta Solvent

AbstractThe frictional response of two opposing polymer brushes subjected to steady shear was studied as a function of solvent condition and degree of compression using the Surface Forces Apparatus (SFA). The brushes were made by preferential adsorption of polyvinylpryridinepolystyrene (PVP-PS) block copolymers adsorbed onto atomically smooth surfaces from a dilute solution of toluene. Extremely parallel lateral motion was imparted to one surface and the response was detected at the opposing brush-covered surface. When the brushes were bathed in a good solvent, it was necessary to strongly compress the layers in order to observe frictional forces transmitted between the surfaces. However, when the solvent was changed to a near-theta solvent, large frictional forces were measured at weaker compressions. The onset of these frictional forces occurred at distances comparable to the distance at which the opposing layers contact one another and rapidly increase as the brushes are compressed. Arguments are advanced that this behavior is attributable to frictional interactions between the polymer chains and the solvent.

Nanotribological Investigation of the Role of Proteoglycans in Biolubrication

2008 ◽  
Author(s):  
Jasmine Seror ◽  
Nir Kampf ◽  
Alice Maroudas ◽  
Jacob Klein
Keyword(s):  
Polymer Brushes ◽  
Surface Force ◽  
Polymer Chains ◽  
Force Balance ◽  
Superficial Zone ◽  
Prosthetic Devices ◽  
Atomic Force ◽  
Frictional Forces ◽  
Human Joints ◽  
Hydration Layers

Articular joints in human body are uniquely efficient lubrication systems. While the cartilage surfaces slide past each other under physiological working conditions (pressure of tens of atmospheres and shear rates up to 106 – 107 Hz), the friction coefficient (μ) achieves extremely low values (down to 0.001) never successfully reached by mechanical prosthetic devices. Friction studies on polymer brushes attached to surfaces have recently demonstrated (17) their ability to reduce friction between the rubbing surfaces to extremely low values by means of the hydrated ions and the charges on the polymer chains. We propose that the extremely efficient lubrication observed in living joints arises from the presence of a brush-like phase of charged macromolecules at the surface of the cartilage superficial zone: hydration layers which surround the charges on the cartilage macromolecules might provide a lubricating ball-bearing-like effect as demonstrated for the synthetic polyelectrolytes (17). In this work macromolecules of the cartilage superficial zone (aggrecans) are extracted from human femoral heads and purified using well developed biochemical techniques (20). The extracted molecules are then characterized with atomic force microscope (AFM). By means of a surface force balance (SFB) normal and shear interactions between mica surfaces coated with these molecules are examined focusing on the frictional forces between such surfaces at normal stresses similar to those in human joints.

Effect of Solvent Quality on the Friction Forces Between Polymer Brushes

2001 ◽  
Vol 707 ◽  
Author(s):  
Aaron M. Forster ◽  
S. Michael Kilbey
Keyword(s):  
Frictional Force ◽  
Polymer Brushes ◽  
Diblock Copolymers ◽  
Surface Forces Apparatus ◽  
Friction Forces ◽  
Molecular Weights ◽  
Solvent Quality ◽  
Frictional Forces ◽  
Theta Point ◽  
Force Profiles

ABSTRACTWe have used the surface forces apparatus to measure the structural and frictional force profiles between opposing, solvated brush layers as a function of temperature. Two different polyvinylpyridine-polystyrene [PVP-PS] diblock copolymers were used to make PS brushes. The molecular weights (in thousands) of these PVP-PS materials were [114/103]k, [30/70]k, respectively. Structural and frictional force profiles in toluene and cyclohexane were measured, and the cyclohexane experiments were conducted at temperatures ranging from the theta-point to 50 C. In toluene the PS brushes needed to be compressed to ∼1/5th of their equilibrium height before frictional forces were measured, but this onset of frictional forces was detected at a much lower level of compression in near-theta cyclohexane. In cyclohexane the structural force profiles were basically insensitive to the temperature change, but the frictional forces depended strongly on the solvent temperature. When the cyclohexane temperature was raised, the onset of frictional forces decreased toward the good-solvent onset. We also discuss the dependence of frictional force on shearing parameters.

Effect of Solvent Quality on the Friction Forces Between Polymer Brushes

2001 ◽  
Vol 710 ◽  
Author(s):  
Aaron M. Forster ◽  
S. Michael Kilbey
Keyword(s):  
Frictional Force ◽  
Polymer Brushes ◽  
Diblock Copolymers ◽  
Surface Forces Apparatus ◽  
Friction Forces ◽  
Molecular Weights ◽  
Solvent Quality ◽  
Frictional Forces ◽  
Theta Point ◽  
Force Profiles

ABSTRACTWe have used the surface forces apparatus to measure the structural and frictional force profiles between opposing, solvated brush layers as a function of temperature. Two different polyvinylpyridine-polystyrene [PVP-PS] diblock copolymers were used to make PS brushes. The molecular weights (in thousands) of these PVP-PS materials were [114/103]k, [30/70]k, respectively. Structural and frictional force profiles in toluene and cyclohexane were measured, and the cyclohexane experiments were conducted at temperatures ranging from the theta-point to 50°C. In toluene the PS brushes needed to be compressed to ∼1/5th of their equilibrium height before frictional forces were measured, but this onset of frictional forces was detected at a much lower level of compression in near-theta cyclohexane. In cyclohexane the structural force profiles were basically insensitive to the temperature change, but the frictional forces depended strongly on the solvent temperature. When the cyclohexane temperature was raised, the onset of frictional forces decreased toward the good-solvent onset. We also discuss the dependence of frictional force on shearing parameters.

scholarly journals Stick–slip friction of gecko-mimetic flaps on smooth and rough surfaces

2015 ◽  
Vol 12 (104) ◽  
pp. 20141346 ◽  
Author(s):  
Saurabh Das ◽  
Nicholas Cadirov ◽  
Sathya Chary ◽  
Yair Kaufman ◽  
Jack Hogan ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Silica Surface ◽  
Surface Forces ◽  
Surface Forces Apparatus ◽  
Stick Slip ◽  
Theoretical Approaches ◽  
Frictional Forces ◽  
Modified Surface ◽  
Glass Surfaces ◽  
Effect Of Surface

The discovery and understanding of gecko ‘frictional-adhesion’ adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick–slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick–slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick–slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems.

scholarly journals Investigation of Ring and Star Polymers in Confined Geometries: Theory and Simulations

Entropy ◽  
2021 ◽  
Vol 23 (2) ◽  
pp. 242
Author(s):  
Joanna Halun ◽  
Pawel Karbowniczek ◽  
Piotr Kuterba ◽  
Zoriana Danel
Keyword(s):  
Star Polymers ◽  
Polymer Chains ◽  
The Other ◽  
Nano Particles ◽  
Dilute Solution ◽  
Confined Geometries ◽  
Density Profiles ◽  
Ideal Ring ◽  
Ring Polymer ◽  
Monomer Density

The calculations of the dimensionless layer monomer density profiles for a dilute solution of phantom ideal ring polymer chains and star polymers with f=4 arms in a Θ-solvent confined in a slit geometry of two parallel walls with repulsive surfaces and for the mixed case of one repulsive and the other inert surface were performed. Furthermore, taking into account the Derjaguin approximation, the dimensionless layer monomer density profiles for phantom ideal ring polymer chains and star polymers immersed in a solution of big colloidal particles with different adsorbing or repelling properties with respect to polymers were calculated. The density-force relation for the above-mentioned cases was analyzed, and the universal amplitude ratio B was obtained. Taking into account the small sphere expansion allowed obtaining the monomer density profiles for a dilute solution of phantom ideal ring polymers immersed in a solution of small spherical particles, or nano-particles of finite size, which are much smaller than the polymer size and the other characteristic mesoscopic length of the system. We performed molecular dynamics simulations of a dilute solution of linear, ring, and star-shaped polymers with N=300, 300 (360), and 1201 (4 × 300 + 1-star polymer with four arms) beads accordingly. The obtained analytical and numerical results for phantom ring and star polymers are compared with the results for linear polymer chains in confined geometries.

Imaging the condensation and evaporation of molecularly thin ethanol films with surface forces apparatus

2014 ◽  
Vol 85 (1) ◽  
pp. 013702 ◽  
Author(s):  
Gutian Zhao ◽  
Qiyan Tan ◽  
Li Xiang ◽  
Di Zhang ◽  
Zhonghua Ni ◽  
...  
Keyword(s):  
Surface Forces ◽  
Surface Forces Apparatus

Lubrication mechanism of concentrated polymer brushes in solvents: effect of solvent viscosity

2012 ◽  
Vol 3 (1) ◽  
pp. 148-153 ◽  
Author(s):  
Akihiro Nomura ◽  
Kohji Ohno ◽  
Takeshi Fukuda ◽  
Takaya Sato ◽  
Yoshinobu Tsujii
Keyword(s):  
Polymer Brushes ◽  
Lubrication Mechanism ◽  
Solvent Viscosity ◽  
Effect Of Solvent

scholarly journals Self-restoring polymer brushes under tribological stress and the biomedical applications

MRS Advances ◽  
2016 ◽  
Vol 1 (27) ◽  
pp. 1971-1976
Author(s):  
Troels Røn ◽  
Irakli Javakhishvili ◽  
Søren Hvilsted ◽  
Katja Jankova ◽  
Seunghwan Lee
Keyword(s):  
Polymer Brushes ◽  
Diblock Copolymers ◽  
Polymer Chains ◽  
Aqueous Environment ◽  
Pdms Film ◽  
Pdms Surface ◽  
Tribological Application ◽  
Optimal Functions ◽  
Amphiphilic Diblock Copolymers

ABSTRACTFor biological and mechanical systems involving moving parts, surface slipperiness is often a critical attribute for their optimal functions. Surface grafting with hydrophilic polymers is a powerful means to render materials slippery in aqueous environment. In “inverted grafting-to approach”, the hydrophilic polymer chains of amphiphilic diblock copolymers dispersed within a poly(dimethylsiloxane) (PDMS) network are selectively segregated upon exposure to aqueous solution. This allows formation of extremely stable brush-like polymer layers. Tribological application of inverted grafting-to approach was successfully demonstrated with PDMS-block-poly(acrylic acid) (PDMS-b-PAA) dispersed within thin PDMS films on PDMS blocks by showing friction coefficients (µ) of ca 10-2 to 10-3, depending on the load, pH and buffer salinity in the absence of other external re-supply of PAA chains. Further manipulations of the thin PDMS film incorporating PDMS-b-PAA to optimize the tribological properties are presented. Lastly, first trials to employ PAA-grafted PDMS surface to generate in-vitro mucosae model are also presented and discussed.

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