Measurement of the mechanical properties of thin films mechanically confined within contacts

Gacoin, Eric; Frétigny, Christian; Chateauminois, A.; Barthel, Étienne

doi:10.1007/s11249-006-9030-y

Cited by 57 publications

(58 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For this case, a closed form for the surface deformation, which is needed to calculate ℎ( , ) in Equation 1 was derived previously in the context of indentation, 30,31 and used by others in the context of elastohydrodynamics. 20,32 The surface deformation can be calculated from: (1 ) 4 ( ) Leroy and Charlaix used the approach outlined in Equations 2-4 to characterize the force response of an oscillatory motion on a thin or a thick coating mediated by a liquid. 20 Here we rely on Equations 2-4, but applied them into an unsteady continuous approach model to update the surface separation.…”

Section: Problem Formulationmentioning

confidence: 99%

Elastic deformation of soft coatings due to lubrication forces

2017

View full text Add to dashboard Cite

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...

show abstract

Section: Problem Formulationmentioning

confidence: 99%

Elastic deformation of soft coatings due to lubrication forces

2017

View full text Add to dashboard Cite

show abstract

“…As for polymer gels [51], the modulus of a brush scales as M ∼ 1/ξ 3 (see Supplemental Material). From previous measurements of the mechanical response of HA brushes [27,52], we determine M ref ≃ 100 Pa for a brush of ξ ref = 57 nm (see Supplemental Material and references [53,54]). We can thus compute the expected moduli of the brushes from…”

mentioning

confidence: 99%

Elastohydrodynamic Lift at a Soft Wall

et al. 2018

View full text Add to dashboard Cite

We study experimentally the motion of non-deformable microbeads in a linear shear flow close to a wall bearing a thin and soft polymer layer. Combining microfluidics and 3D optical tracking, we demonstrate that the steady-state bead/surface distance increases with the flow strength. Moreover, such lift is shown to result from flow-induced deformations of the layer, in quantitative agreement with theoretical predictions from elastohydrodynamics. This study thus provides the first experimental evidence of "soft lubrication" at play at small scale, in a system relevant e.g. to the physics of blood microcirculation.

show abstract

“…However, upon contact with another surface such as the spherical diamond probes used in our experiments, this highly mobile region existing within 5 nm of PS free surfaces has the potential for significantly enhanced intermolecular interactions at the geometrically confined interface induced by the indenter probe [41] . Mechanical loading at this interface induces hydrostatic stress beneath the probe, which is well established to increase T g by 0.3°C/MPa (for PS and PMMA [6,42] ) to 0.4°C/MPa (for PC [43] ). For the range of contact pressures in our experiments on these polymers, the hydrostatic stress beneath the spherical probes ranged from 250 to 400 MPa.…”

mentioning

confidence: 99%

Enhanced Stiffness of Amorphous Polymer Surfaces under Confinement of Localized Contact Loads

et al. 2007

View full text Add to dashboard Cite

Although there is an increasing appreciation that physical properties of amorphous (glassy) polymer surfaces and interfaces can differ substantially from those of the bulk, the mechanisms and implications for mechanical performance of thin films, surfaces of bulk polymers, and nanocomposites are unclear. For example, several natural and synthetic nanocomposites exhibit markedly enhanced stiffness and strength that cannot be explained via two-phase composite rules-of-mixtures. Here we apply recent advances in contact deformation to determine the apparent elastic (or storage) moduli over 5 to 200 nanometers from the free surface of amorphous polystyrene, poly(methyl methacrylate), and polycarbonate. We observe that the apparent stiffness of the surface under contact can exceed that of the bulk by up to 200%, independent of processing scheme, macromolecular structural characteristics, and relative humidity. We attribute this enhanced apparent stiffness at the surface to the contact stress-induced formation of a mechanically confined phase at the probepolymer interface. These observations are consistent with the increased macromolecular mobility of glassy polymer free surfaces, and relate directly to the material physics of the interphase in synthetic and biological polymer nanocomposites.Most experimental investigations of amorphous polymer surfaces have focused on thermally activated behavior such as the glass transition temperature T g [1][2][3] and structural relaxation. [4,5] However, few overarching conclusions exist regarding surface and interface properties, [6] in large part because experimental and sample preparation capabilities have not yet been optimized for the nanometer-length scales over which these surface-specific phenomena are observed. There are two generally accepted conclusions regarding amorphous polymer surface behavior: that T g is a function of polymer film thickness t f for t f < 100 nm, and that the magnitude and direction of the T g shift depends on the polymer and/or substrate [7] . For example, the T g of amorphous polystyrene (PS) films has been found to be depressed by 35°C in spin-coated films of t f < 20 nm on Si substrates [1] and by 70°C for free standing films of t f < 30 nm, [2] while amorphous poly(2-vinylpyridine) has demonstrated a 35°C elevation in T g for t f = 10 nm that is attributed to secondary bonding with the Si substrate.[8]Here, we sought to consider the consequences of such a physical property variation on the resistance of amorphous polymer surfaces to localized contact deformation. Depression of T g in polymers such as PS and PMMA suggests that, over distances < 100 nm from the free surface of these socalled glassy polymers, the macromolecular chains are more mobile than those located within the bulk. This conceptualization is consistent with computational simulations of molecular mobility of free surfaces and confined volumes, [9][10][11] as well as recent experimental observations for PS thin films of t f < 40 nm, including broadened structural relaxation times...

show abstract

Measurement of the mechanical properties of thin films mechanically confined within contacts

Cited by 57 publications

References 26 publications

Elastic deformation of soft coatings due to lubrication forces

Elastic deformation of soft coatings due to lubrication forces

Elastohydrodynamic Lift at a Soft Wall

Enhanced Stiffness of Amorphous Polymer Surfaces under Confinement of Localized Contact Loads

Contact Info

Product

Resources

About