Comparison of the Slip of a PDMS Melt on Weakly Adsorbing Surfaces Measured by a New Photobleaching-Based Technique

Hénot, Marceau; Chennevière, Alexis; Drockenmuller, Éric; Léger, Liliane; Restagno, Frédéric

doi:10.1021/acs.macromol.7b00601

Cited by 14 publications

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“…The range of investigated velocities V shear is fixed by the setup limits for high velocities and by a small amount of adsorbed chains of the melt on the surfaces for small velocities, leading to a slip transition [36]. First, we see a significant difference in slip length between the two surfaces as previously observed on the same system [35]. On OTS, on which the slip lengths are larger, they clearly depend on the temperature.…”

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confidence: 66%

“…The contact angle of water on these surfaces was close to 115 • and the advancing contact angle of dodecane was θ a = 34 • with an hysteresis of 1 • . The experimental technique used to measure the slip lengths is described in detail in the supplementary materials and with a discussion on the resolution in [35]. It is an improved version of the velocimetry technique described by Léger et al [36].…”

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confidence: 99%

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Temperature-Controlled Slip of Polymer Melts on Ideal Substrates

et al. 2018

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The temperature dependence of the hydrodynamic boundary condition between a PDMS melt and two different non-attractive surfaces made of either an OTS (octadecyltrichlorosilane) self-assembled monolayer (SAM) or a grafted layer of short PDMS chains has been characterized. A slip length proportional to the fluid viscosity is observed on both surfaces. The slip temperature dependence is deeply influenced by the surfaces. The viscous stress exerted by the polymer liquid on the surface is observed to follow exactly the same temperature dependences as the friction stress of a crosslinked elastomer sliding on the same surfaces. Far above the glass transition temperature, these observations are rationalized in the framework of a molecular model based on activation energies: increase or decrease of the slip length with increasing temperatures can be observed depending on how the activation energy of the bulk viscosity compares to that of the interfacial Navier's friction coefficient.Modeling fluid flows in channels is a general problem in science and engineering. For ideal liquids, the situation is simple: there is no dissipation due to fluid movement. For real liquids, some energy is lost. Navier [1] identified two possible sources of dissipation: bulk dissipation, associated to the friction between layers of liquid, and surface dissipation, associated to the friction of the last layer of liquid molecules sliding on the solid surface. The bulk dissipation can be obtained assuming a linear relation between the shear stress and the velocity gradient, which, for incompressible fluids, gives the Navier-Stokes equation. For surface dissipation, a classical assumption is that a liquid element adjacent to the surface assumes the velocity of the surface, i.e. a non-slip boundary condition, which leads to no surface dissipation. Indeed, Navier, postulated the existence of a slip velocity at the surface. He proposed a linear relation between the shear stress at the solid-liquid interface and the slip velocity: σ fluid→surface = kV , where k is the interfacial friction coefficient, sometimes called the Navier's coefficient, assumed to be independent of the shear rate, and V is the slip velocity. It is thus possible to define the slip length as the distance from the solid surface where the fluid velocity profile extrapolates linearly to zero (see Figure 1a). Balancing the viscous stress exerted by the fluid on the solid σ = ηγ, where η is the fluid viscosity andγ is the shear rate, to the friction stress proposed by Navier gives:The slip length, if it exists, is thus the ratio of two quantities characterizing respectively bulk and surface dissipation mechanisms. In this equation, both η and k should depend on the temperature.Slip length determination in the case of simple fluids has been the subject of intensive experimental [2][3][4][5][6][7] and theoretical/numerical [8][9][10][11][12] research over the last 20 years. Despite this strong activity, there is still no quantitative agreement between experiments and numerical simulatio...

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Temperature-Controlled Slip of Polymer Melts on Ideal Substrates

et al. 2018

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“…Slip was measured using an experimental setup previously described in Hénot et al [57] relying on the analysis of the evolution under shear of the z-integrated fluorescence intensity of a pattern drawn in the sample using photobleaching. The principle of the method is illustrated in Figure 2a.…”

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Sensing adsorption kinetics through slip velocity measurements of polymer melts

et al. 2018

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The evolution over time of the nonlinear slip behavior of a polydimethylsiloxane (PDMS) polymer melt on a weakly adsorbing surface made of short non-entangled PDMS chains densely end-grafted to the surface of a fused silica prism has been measured. The critical shear rate at which the melt enters the nonlinear slip regime has been shown to increase with time. The adsorption kinetics of the melt on the same surface has been determined independently using ellipsometry. We show that the evolution of slip can be explained by the slow adsorption of melt chains using the Brochard-de Gennes's model.

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“…[44][45][46][47][48][49][50] Over the last decade, several studies have been performed based on either near field laser velocimetry or particle tracking velocimetry (PTV) to characterize the wall slip during flow on solid substrates. [51][52][53][54][55][56][57][58][59][60] Relevant parameters such as velocity at the wall (v s ) and extrapolation slip length b ¼ v s dv=dz can be extracted, where dv dz is the velocity gradient in the vicinity of the wall and z is the normal at the wall inwards to the fluid. Despite this large body of work based on velocimetry techniques, it is challenging to gain molecular insights into the nature of slip and understand its dependence on the wall properties.…”

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Microscopic origin of wall slip during flow of an entangled DNA solution in microfluidics: Flow induced chain stretching versus chain desorption

Hemminger

Boukany

2017

Biomicrofluidics

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Despite the relevance and importance of slip, a fundamental understanding of the underlying molecular mechanisms of wall slip in polymer flow is still missing. In this work, we investigate the slip behavior of an entangled DNA solution at a molecular scale using a confocal microscope coupled to a microfluidic device. From microscopic measurement, we obtain both the velocity profile and conformation of polymeric chains by visualizing DNA molecules during flow on various surfaces (ranging from weak to strong interactions with DNA molecules). In channel flow at a low Weissenberg number (Wi = 0.14), we observe a parabolic flow for an APTES-treated glass (with strong interaction with DNA) in the absence of slip, while a significant amount of slip has been observed for a regular glass (with a weak interaction with DNA). At higher flow rates (Wi > 1.0), strong slip appears during flow on APTES-treated surfaces. In this case, only immobile DNA molecules are stretched on the surface and other bulk chains remain coiled. This observation suggests that the flow induced chain stretching at the interface is the main mechanism of slip during flow on strong surfaces. Conversely, for slip flow on surfaces with weak interactions (such as unmodified or acrylate-modified glasses), polymeric chains are desorbed from the surface and a thin layer of water is present near the surface, which induces an effective slip during flow. By imaging DNA conformations during both channel and shear flows on different surfaces, we elucidate that either chain desorption or flow-induced stretching of adsorbed chains occurs depending on the surface condition. In general, we expect that these new insights into the slip phenomenon will be useful for studying the biological flow involving single DNA molecule experiments in micro/nanofluidic devices.

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Comparison of the Slip of a PDMS Melt on Weakly Adsorbing Surfaces Measured by a New Photobleaching-Based Technique

Cited by 14 publications

References 40 publications

Temperature-Controlled Slip of Polymer Melts on Ideal Substrates

Temperature-Controlled Slip of Polymer Melts on Ideal Substrates

Sensing adsorption kinetics through slip velocity measurements of polymer melts

Microscopic origin of wall slip during flow of an entangled DNA solution in microfluidics: Flow induced chain stretching versus chain desorption

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