Elastic deformation during dynamic force measurements in viscous fluids

Wang, Yumo; Pilkington, Georgia A.; Dhong, Charles; Fréchette, Joëlle

doi:10.1016/j.cocis.2016.09.009

Cited by 37 publications

(46 citation statements)

References 56 publications

(104 reference statements)

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“…Previous theoretical works have studied confined flows in the soft lubrication approximation and accounted for the roles of elasticity [11][12][13][14][15][16], fluid compressibility [17], the inertia of the fluid and the elastic medium [18], and viscoelasticity of the substrate [19]. More recent works have focused on elastohydrodynamic effects for liquids confined at the micro and nano scales [20][21][22], which has important consequences for surface mechanical characterization [23,24]. For symmetrical objects, the results show that elastic deformations lead to a non-symmetric pressure field and to the emergence of a friction-reducing lift force.…”

Section: Introductionmentioning

confidence: 99%

Rotation of a submerged finite cylinder moving down a soft incline

et al. 2020

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A submerged finite cylinder moving under its own weight along a soft incline lifts off and slides at a steady velocity while also spinning. Here, we experimentally quantify the steady spinning of the cylinder and show theoretically that it is due to a combination of an elastohydrodynamic torque generated by flow in the variable gap, and the viscous friction on the edges of the finitelength cylinder. The relative influence of the latter depends on the aspect ratio of the cylinder as well as the deformability of the substrate, which we express in term of a single scaled compliance parameter. By varying this compliance parameter, we show that our experimental results are consistent with a transition from an edge-effect dominated regime for short cylinders to a gapdominated elastohydrodynamic regime when the cylinder is very long.

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Section: Introductionmentioning

confidence: 99%

Rotation of a submerged finite cylinder moving down a soft incline

et al. 2020

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“…Despite the above theoretical literature, experimental evidence for such an elastohydrodynamic lift force remains recent and scarce 28,29 . A preliminary qualitative observation was reported in the context of smart lubricant and polyelectrolytes 30 .…”

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confidence: 99%

Direct Measurement of the Elastohydrodynamic Lift Force at the Nanoscale

et al. 2020

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Friction in soft and wet contacts is crucial for industry and engineering, but it might also play a central role for the motion of various physiological and biological entities, as well as for the nanorheology of very soft materials. Here, we report on the first direct measurement of the elastohydrodynamic lift force acting on a sphere moving within a viscous liquid, near and along a soft substrate under nanometric confinement. Using atomic force microscopy, the lift force is probed as a function of the gap size, for various driving velocities, viscosities, and stiffnesses. The results are in excellent agreement with scaling arguments and a novel quantitative model developed from the soft lubrication theory, in linear elasticity, and for small compliances. For larger compliances, or equivalently for smaller confinement length scales, a saturation of the lift force is observed and its empirical scaling law is discussed.

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“…More specifically, lubrication forces can lead to elastic deformation, also known as elastohydrodynamic deformation or EHD, which can prevent contact formation as fluid drains from a gap separating compliant materials. [5][6][7] If unaccounted for, EHD can lead to the misinterpretation of dynamic surface forces measurements. The surface forces apparatus (SFA) 6 or the atomic force microscope (AFM) 8 are commonly employed under dynamic conditions and can be used with soft materials.…”

Section: Introductionmentioning

confidence: 99%

Elastic deformation of soft coatings due to lubrication forces

2017

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Elastic deformation of rigid materials with soft coatings (stratified materials) due to lubrication forces can also alter the interpretation of dynamic surface forces measurements and prevent contact formation between approaching surfaces. Understanding the role of elastic deformation on the process of fluid drainage is necessary, and the case where one (or both) of the interacting materials consists of a rigid substrate with a soft coating is still limited. We combine lubrication theory and solid linear elasticity to describe the dynamic of fluid drainage past a compliant stratified boundary. The analysis presented covers the full range of coating thicknesses, from an elastic foundation to a half-space for an incomressible coating. We decouple the individual contributions of the coating thickness and material properties on the elastic deformation, hydrodynamic forces, and fluid film thickness. We obtain a simple expression for the shift in contact position during force measurements that is valid for many experimental conditions. We compare directly the effect of stratification on the out-of-contact deformation to the well-known effect of stratification on indentation. We show that corrections developed for stratification in contact mechanics are not applicable to elastohydrodynamic deformation. Finally, we provide generalized contour maps that can be employed directly to estimate the elastic deformation present in most dynamic surface force measurements. IntroductionRigid materials with soft coatings are ubiquitous in tribology, 1 microfluidic devices, 2 biomaterials, 3 or colloidal and particulate systems. 4 Under many practical settings they are employed in fluid environments where they are in close proximity to another surface. Under these conditions viscous forces due to the relative movement of the two surfaces can exert fluid pressures and cause elastic deformation (see Figure 1). More specifically, lubrication forces can lead to elastic deformation, also known as elastohydrodynamic deformation or EHD, which can prevent contact formation as fluid drains from a gap separating compliant materials. [5][6][7] If unaccounted for, EHD can lead to the misinterpretation of dynamic surface forces measurements. The surface forces apparatus (SFA) 6 or the atomic force microscope (AFM) 8 are commonly employed under dynamic conditions and can be used with soft materials. In particular, an exact description of lubrication forces is necessary to rely on dynamic surface forces measurements for the characterization of, for example, conservative surface forces, 9 fluid structure, 10 or surface slip 11 on compliant materials. In addition, recent reports show that ignoring the effect of elastic deformation can lead to a misinterpretation of the force data, contact position, and slip at the solid-liquid surfaces. 8,12 Most previous efforts to describe unsteady normal fluid drainage past an elastic boundary studied the case where the soft materials could be considered a half-space. For instance, Davis et al. studied normal e...

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Elastic deformation during dynamic force measurements in viscous fluids

Cited by 37 publications

References 56 publications

Rotation of a submerged finite cylinder moving down a soft incline

Rotation of a submerged finite cylinder moving down a soft incline

Direct Measurement of the Elastohydrodynamic Lift Force at the Nanoscale

Elastic deformation of soft coatings due to lubrication forces

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