Slip effects in polymer thin films

Department of Experimental Physics, Saarland University, D-66041 Saarbrücken, Germany.
Journal of Physics Condensed Matter (Impact Factor: 2.35). 01/2010; 22(3):033102. DOI: 10.1088/0953-8984/22/3/033102
Source: PubMed


Probing the fluid dynamics of thin films is an excellent tool for studying the solid/liquid boundary condition. There is no need for external stimulation or pumping of the liquid, due to the fact that the dewetting process, an internal mechanism, acts as a driving force for liquid flow. Viscous dissipation, within the liquid, and slippage balance interfacial forces. Thus, friction at the solid/liquid interface plays a key role towards the flow dynamics of the liquid. Probing the temporal and spatial evolution of growing holes or retracting straight fronts gives, in combination with theoretical models, information on the liquid flow field and, especially, the boundary condition at the interface. We review the basic models and experimental results obtained during the last several years with exclusive regard to polymers as ideal model liquids for fluid flow. Moreover, concepts that aim to explain slippage on the molecular scale are summarized and discussed.

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Available from: Oliver Bäumchen, Oct 10, 2015
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    • "In order to test the self-similarity of the form of the rim, the rim width w (the distance between three-phase contact line and the point, where the rim height has dropped to 110% of the initial film thickness) is plotted as function of the maximum rim height H, c.f. Fig. 9b. The linear dependence indicates that self-similarity can safely be assumed and w ∝ √ R (where R denotes the radius of the hole) is obtained from the conservation of volume for growing holes (see Ref. [44]). "
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    ABSTRACT: Thin liquid films on surfaces are part of our everyday life; they serve, e.g., as coatings or lubricants. The stability of a thin layer is governed by interfacial forces, described by the effective interface potential, and has been subject of many studies in recent decades. In recent years, the dynamics of thin liquid films has come into focus since results on the reduction of the glass transition temperature raised new questions on the behavior of especially polymeric liquids in confined geometries. The new focus was fired by theoretical models that proposed significant implication of the boundary condition at the solid/liquid interface on the dynamics of dewetting and the form of a liquid front. Our study reflects these recent developments and adds new experimental data to corroborate the theoretical models. To probe the solid/liquid boundary condition experimentally, different methods are possible, each bearing advantages and disadvantages, which will be discussed. Studying liquid flow on a variety of different substrates entails a view on the direct implications of the substrate. The experimental focus of this study is the variation of the polymer chain length; the results demonstrate that inter-chain entanglements and in particular their density close to the interface, originating from non-bulk conformations, govern the liquid slip of a polymer.
    Journal of Physics Condensed Matter 05/2012; 24(32):325102, 1-17. DOI:10.1088/0953-8984/24/32/325102 · 2.35 Impact Factor
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    • "Up to date many factors have been found that seem to influence the boundary conditions [20] [21] [22]. The least controversially discussed amongst them is the fluid-wall interaction [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]. Shear rates beyond a critical value are supposed to induce slip, too [35] [36] [37] [38]. "
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    ABSTRACT: We present, along with some fundamental concepts regarding imbibition of liquids in porous hosts, an experimental, gravimetric study on the capillarity-driven invasion dynamics of water and of the rod-like liquid crystal octyloxycyanobiphenyl (8OCB) in networks of pores a few nanometers across in monolithic silica glass (Vycor). We observe, in agreement with theoretical predictions, square root of time invasion dynamics and a sticky velocity boundary condition for both liquids investigated. Temperature-dependent spontaneous imbibition experiments on 8OCB reveal the existence of a paranematic phase due to the molecular alignment induced by the pore walls even at temperatures well beyond the clearing point. The ever present velocity gradient in the pores is likely to further enhance this ordering phenomenon and prevent any layering in molecular stacks, eventually resulting in a suppression of the smectic phase in favor of the nematic phase.
    Journal of Physics Condensed Matter 05/2011; 23(18):184109. DOI:10.1088/0953-8984/23/18/184109 · 2.35 Impact Factor
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    ABSTRACT: The interface between two immiscible polymers, polystyrene (PS) and polydimethylsiloxane (PDMS), was studied by neutron reflectivity and dewetting by using free PS chains and PDMS brushes. Unexpectedly, we found that the PS chains diffuse in the PDMS brushes at temperatures well below the glass transition temperatures of PS, the dynamics being largely determined by the grafting density of the brush. By this study, we demonstrate the major influence of the chains interdiffusion on the friction properties for a couple of immiscible polymers. By the way, the puzzling ageing of PS thin films observed from dewetting experiments is found to be directly related to modifications of the PS/PDMS interface.
    Soft Matter 05/2009; 7(21). DOI:10.1039/C1SM05486D · 4.03 Impact Factor
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