Shear Response of Molecularly Thin Liquid Films to an Applied Air Stress

Mate, C. Mathew; Marchon, B.

doi:10.1103/physrevlett.85.3902

Cited by 51 publications

(40 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[1][2][3][4][5][6][7][8][9][10] Further advances in these fields depend on understanding the mechanisms that control the kinetics of flow. [11][12][13][14] However, one of the problems in flowing monolayers is the independent characterization of the driving and frictional forces that are intimately coupled through the molecular interactions between the fluid and the substrate. In this regard, the visualization of compressible macromolecules during flow provides an exceptional opportunity to study these forces.…”

mentioning

confidence: 99%

Molecular Pressure Sensors

Sun

Shirvanyants

et al. 2007

Advanced Materials

View full text Add to dashboard Cite

Flow properties of molecularly thin films are at the foundation of many practical applications such as lithography, microfluidics, coatings, and lubrication. [1][2][3][4][5][6][7][8][9][10] Further advances in these fields depend on understanding the mechanisms that control the kinetics of flow. [11][12][13][14] However, one of the problems in flowing monolayers is the independent characterization of the driving and frictional forces that are intimately coupled through the molecular interactions between the fluid and the substrate. In this regard, the visualization of compressible macromolecules during flow provides an exceptional opportunity to study these forces.[15] Here we report on the monitoring of brush-like macromolecules as they change their shape in response to variations in the film pressure during flow. After appropriate calibration, these molecular sensors can be used to gauge both the pressure gradient and the friction coefficient at the substrate. We anticipate the utilization of such miniature sensors for probing flow properties on nanometer length scales. The design of the pressure-responsive macromolecules is based on brush-like polymer architectures comprised of a flexible backbone surrounded by a dense shell of side chains (Fig. 1a). The characteristic property of these macromolecules is their ability to change shape upon lateral compression on a substrate. [16][17][18] If the film pressure increases, the number of side chains adsorbed to the surface decreases allowing the backbone to coil. This causes the macromolecules to become more compact and occupy less area on the substrate. Therefore, the area per molecule can be used as a pressure sensitive parameter to gauge the variations of film pressure within flowing monolayers. Molecular brushes (Fig. 1a) with the same degree of polymerization of a poly(2-hydroxyethyl methacrylate) backbone (n = 570 ± 50) and different degrees of polymerization of poly(n-butyl acrylate) (pBA) side chains (n = 35 ± 5 and n = 51 ± 5) were synthesized by atom transfer radical polymerization. [19,20] At room temperature, the materials are fluid melts that spontaneously spread when placed on higher surface energy substrates such as mica and graphite.[21] Small drops of molecular brushes (volume ∼ 1 nl, radius ∼ 100 lm) were deposited on a substrate inside an environmental chamber under controlled temperature (T = 25°C) and relative humidity (RH = 30-99 %). Like many other fluids, the drops first spread by generating a molecularly thin precursor film moving ahead of the macroscopic drop (Fig. 1b). [22] Using an atomic force microscope (Multimode, Nanoscope 3A, Veeco Metrology Group), we monitored the spreading process over a broad range of length scales ranging from the motion of the film front all the way down to the movements of the individual molecules within the film.[15,23] Figure 1c shows the time dependence of the film length L= R -R 0 observed on mica at a high relative humidity (RH = 99 %), where R 0 = 63 lm is the initial drop radius and R is the total radiu...

show abstract

mentioning

confidence: 99%

Molecular Pressure Sensors

Sun

Shirvanyants

et al. 2007

Advanced Materials

View full text Add to dashboard Cite

show abstract

“…7c. Such air shear-induced slippage of sub-monolayer films has been observed previously in blow-off experiments with films of perfluoropolyether lubricants with neutral -CF 3 end groups [22,23]. At sub-monolayer coverages, the air shear-induced migration of polymers molecules should occur from isolated molecules being slid across the surface under the action of the air shear stress r, as illustrated in Fig.…”

Section: Diffusion Migration Modelmentioning

confidence: 79%

Lubricant-Induced Spacing Increases at Slider–Disk Interfaces in Disk Drives

et al. 2009

Self Cite

View full text Add to dashboard Cite

In this article, we explore the physical mechanisms for lubricant migration on recording head slider surfaces and how this migration leads to increased sliderdisk spacing during disk drive operations. This is done using both a new experimental methodology, called the ''droplet stress test,'' and through simulation. In our simulations, we compare the air shear-induced lubricant migration modeled either as viscous flow of a continuum liquid film with zero slip or as wind driven slippage of molecules across the surface. The experimental data are best fitted using the viscous flow model to determine an effective viscosity for the sub-nanometer thick lubricant films. This effective viscosity tends to be somewhat less than the lubricant bulk viscosity due to air shear promoting the slippage of lubricant molecules across the surface. Our experimental results also indicate that the potential spacing increase from the pickup of disk lubricant on the slider is limited by the mobile fraction of the dewetting thickness of the lubricant film on the slider.

show abstract

“…Blow-off experiment provides a much higher shear stress than the spin-off. This method stemmed from the blow-off measurement proposed firstly by Deryguin et al [8,9], and recently modified by Mate et al [10]. The layer structure was also observed in blow-off experiment.…”

Section: List Of Symbolsmentioning

confidence: 96%

Blow-Off Flow of Nano PFPE Liquid Film at Hard Disk Surfaces

2010

View full text Add to dashboard Cite

Blow-off test was conducted for two different types of perfluoropolyether (PFPE): non-functional PFPE Z25 and functional PFPE Zdol3000. The film thickness of PFPE during the blow-off test was monitored intermittently in terms of ellipsometry. It is found that the two types of PFPE show completely different rheological behavior; micro-slip at the hard disk surface was observed for the non-functional PFPE Z25, while there was no micro-slip for the functional PFPE Zdol3000. Experimental results were analyzed theoretically, and it is found that micro-slip velocity of Z25 decreases steeply at first with the increases in the distance from the front end and then reaches a constant value, the film thickness in the front region increases with time due to the different micro-slip velocity, and a pileup layer is formed in the region. The pileup layer has a much lower viscosity than the original layer.

show abstract

Shear Response of Molecularly Thin Liquid Films to an Applied Air Stress

Cited by 51 publications

References 28 publications

Molecular Pressure Sensors

Molecular Pressure Sensors

Lubricant-Induced Spacing Increases at Slider–Disk Interfaces in Disk Drives

Blow-Off Flow of Nano PFPE Liquid Film at Hard Disk Surfaces

Contact Info

Product

Resources

About