Boundary flow on end-grafted PEG brushes

Charrault, Eric; Lee, Thomas; Easton, Christopher D.; Neto, Chiara

doi:10.1039/c5sm02546j

Cited by 23 publications

(36 citation statements)

References 60 publications

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“…The three dashed lines indicate the range of spring parameter and elasticity investigated here. The shaded areas represent experimental configuration of prior experimental studies for reduced modulus of the soft coating between 0.5-10 MPa, where purple: Charrault et al 8 , blue: Kaveh et al 7 red: Wang et al 12 , and grey: Honig et al 39 A slope of 0.8 in log-log scale is illustrated in the bottom right corner. The green regime above the green dashed line indicates…”

Section: Results and Discussion Choice And Relevance Of Parameters Invmentioning

confidence: 99%

“…7,8,12,39 For each experimental configuration ( R ,  , V , k ) the shaded areas show how changing the modulus of the coating, from 0.5 MPa to 10 MPa (elastomers), would change K and  . Lowering the elasticity further would bring most experimental conditions into the K   regime, which is solved here.…”

Section: Results and Discussion Choice And Relevance Of Parameters Invmentioning

confidence: 99%

“…As a result, dynamic AFM measurements would show a decrease in repulsion with an increase in film thickness. 7,8 On the other hand, in the SFA or with other force measurement techniques based on interferometry or profilometry, the raw data is the surface separation, h(t), and an increase in hydrodynamic repulsion would be observed for thicker elastic coatings. 6,12 Finally, the Reynolds' …”

Section: K mentioning

confidence: 99%

“…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 elastohydrodynamic collisions between particles.…”

Section: Introductionmentioning

confidence: 99%

“…[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.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Results and Discussion Choice And Relevance Of Parameters Invmentioning

confidence: 99%

Section: Results and Discussion Choice And Relevance Of Parameters Invmentioning

confidence: 99%

Section: K mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Elastic deformation of soft coatings due to lubrication forces

2017

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Elastic deformation during dynamic force measurements in viscous fluids

Wang

Pilkington

Dhong

et al. 2017

Current Opinion in Colloid & Interface Science

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Understanding and harnessing the coupling between lubrication pressure and elasticity provides materials design strategies for applications such as adhesives, coatings, microsensors, and biomaterials. Elastic deformation of compliant solids caused by viscous forces can also occur during dynamic force measurements in instruments such as the surface forces apparatus (SFA) or the atomic force microscope (AFM). We briefly review hydrodynamic interactions in the presence of soft, deformable interfaces in the lubrication limit. More specifically, we consider the scenario of two surfaces approaching each other in a viscous fluid where one or both surfaces is deformable, which is also relevant to many force measurement systems. In this article the basic theoretical background of the elastohydrodynamic problem is detailed, followed by a discussion of experimental validation and considerations, especially for the role of elastic deformation on surface forces measurements. Finally, current challenges to our understanding of soft hydrodynamic interactions, such as the consideration of substrate layering, poroelasticity, viscoelasticity, surface heterogeneity, as well as their implications are discussed.

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