Soft Matter in a Tight Spot: Nanorheology of Confined Liquids and Block Copolymers

Granick, Steve; Demirel, A. Levent; Cai, Lenore; Peanasky, John

doi:10.1002/ijch.199500013

Cited by 99 publications

(108 citation statements)

References 45 publications

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“…The same appears to be true for squalane as shown in figure 7(c). This observation further validates the measurements of Granick et al [33] (using SFA) and lately by Lim and O'Shea [34] (using AFM), showing oscillatory forces exist for branched molecules such as squalane and 3-methylundecane (C12H26).…”

Section: Resultssupporting

confidence: 91%

Frictional characteristics of molecular length ultra-thin boundary adsorbed films

Chong

Reddyhoff

et al. 2015

Meccanica

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The paper presents measurements of friction of any ultra-thin film entrained into the contact of a pair of very smooth specimen subjected to entrainment in a converging micro-wedge of a special-purpose micro-tribometer. An ultra-thin film is expected to form at the boundary solids through adsorption of boundary active molecules. Fluids with linear and branched molecules are used in the investigation. It is found that the frictional characteristics of these films can be adequately described through use of Eyring thermal activation energy and a potential energy barrier to sustain conjunctional sliding motion. The combined experimental measurement and the simple activation energy approach shows that the thin molecular adsorbed films act like hydroLangmuir-Blodgett layers, the formation and frictional characteristics of which are affected by the competing mechanisms of adsorption, forced molecular re-ordering and discrete-fashion drainage through the contact by the solvation effect. This process is a complex function of the contact sliding velocity as well as a defined Eyring activation density (packing density of the molecules within the conjunction). It is shown that the contribution of solvation to friction is in the form of energy expended to eject layers of lubricant out of the contact, which unlike the case of micro-scale hydrodynamic films, is not a function of the sliding velocity.

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Section: Resultssupporting

confidence: 91%

Frictional characteristics of molecular length ultra-thin boundary adsorbed films

Chong

Reddyhoff

et al. 2015

Meccanica

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“…However, recent computer simulations of octane and isooctane did not reveal this unexpected difference in the solvation force profiles [23]. Also recent experiments of 3-methylundecane show that the solvation force show still an oscillatory behaviour, however the amplitudes of the oscillations are smaller than for linear undecane [24]. A similar decrease in the amplitudes of the oscillations has been found in recent computer simulations of n-hexadecane and squalane [25].…”

Section: Introductionmentioning

confidence: 59%

Structure and solvation forces in confined films of alkanes

Dijkstra¹

1998

Thin Solid Films

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We compute by computer simulations the solvation force of a system of linear and branched alkanes confined in a slab geometry. The solvation force for linear decane oscillates with distance with a periodicity close to the width of the molecules. The branched alkanes, 2-methylundecane and 2-methylheptane, show a similar oscillatory behaviour, however the oscillations are decreased with a factor of about three and show a long-range attractive force. In addition, we show that the critical temperature of the liquid-vapour coexistence of npentane shifts to lower temperatures upon confining.

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“…[2][3][4]56 It is generally observed that the properties of thin films go from liquidlike at large film thicknesses and low pressures toward more solidlike at higher confinement. [2][3][4]56 Results Force-Distance Measurements. Static interaction forces (normalized by the mean radius of curvature of the undeformed solid surfaces, R) are plotted against film thickness in Figure 1.…”

Section: Methodsmentioning

confidence: 99%

Tribology of Confined Fomblin-Z Perfluoropolyalkyl Ethers: Role of Chain-End Chemical Functionality

Ruths

Granick

1999

J. Phys. Chem. B

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Strong dependence of the tribological response upon the nature of the polar end groups of perfluorinated linear chains was observed for Fomblin-Z perfluoropolyalkyl ethers of similar length and composition but terminated by a different polar group at both chain ends. The number-average molecular weight of the polymers was M n ≈ 2000 g mol -1 and the chain-end functionality was either carboxylic acid, hydroxyl, piperonyl, or the p-phenoxyanilinium salt of a carboxylic acid. The method of investigation was a surface forces apparatus modified for dynamic oscillatory shear at variable frequency and effective shear rate. Differences were observed as concerns not only the shear forces but also the minimum thickness to which the films could be compressed under a given normal load and the adhesion measured on separation of the surfaces after prior compression. The shear forces were studied at normal pressures of 1 and 3 MPa, both in the linear viscoelastic regime and at high shear amplitudes corresponding to shear rates of 10 -2 -10 5 s -1 . The carboxylic acid terminated polymer displayed solidlike responses to shear, possibly reflecting dimerization owing to hydrogen bonding. This contrasted with the more fluidlike shear rheology of the hydroxyl-and piperonyl-terminated polymers, in which the association from hydrogen bonding and polar interactions is believed to be weaker and result in a different structure. The sample comprised of the p-phenoxyanilinium salt of a carboxylic acid could not be compressed to less than an exceptionally large film thickness, around 100 Å, and did not appear to solidify at the pressures studied. This study suggests that not only the affinity of the functionalized chain ends to a solid surface but also the self-association of polar end groups in the nonpolar environment of fluorinated chains influences the lubricating performance of these films.

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Soft Matter in a Tight Spot: Nanorheology of Confined Liquids and Block Copolymers

Cited by 99 publications

References 45 publications

Frictional characteristics of molecular length ultra-thin boundary adsorbed films

Frictional characteristics of molecular length ultra-thin boundary adsorbed films

Structure and solvation forces in confined films of alkanes

Tribology of Confined Fomblin-Z Perfluoropolyalkyl Ethers: Role of Chain-End Chemical Functionality

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