Spontaneous curvature of polydimethylsiloxane thin films : Mechanisms and applications : A new route for the low cost fabrication of new functionalities for microfluidics

Abstract : The guideline of this work is the spontaneous rolling of oxidized polydimethylsiloxane (PDMS) thin films in organic solvant vapors. Briefly, thin films of PDMS are produced by spin coating. Those films are then exposed to oxygen plasma which oxidizes and hardens their surfaces. When those systems are immersed in appropriate solvent vapors, non oxidized PDMS selectively swells. This leads to the spontaneous rolling of the films and thus to the formation of capillaries. This mechanism is of great interest for the fabrication of microfluidic channels because what is to become the inner surface of those channels can be characterized and functionalized prior to rolling.In a first chapter, different aspects of spontaneous rolling are reviewed theoretically and numerically.A second chapter is dedicated to the investigation of the oxide layer by AFM nanoindentation. The mechanical properties of the composite system (hard layer on a soft substrate) are measured and interpreted with a new model in order to extract in particular the thickness of the oxide layer.A third chapter dwells on engineering of the rolled-up tubes. The inner diameter of the capillaries as a function of experimental parameters is measured and confronted to theory. We present tubes with various inner surface functionalizations as a proof of concept of the method.Finally, in order to solve the issue of the integration of the system in a wider structure, an innovative method is proposed in a final fourth chapter. Based on the fabrication of a sacrificial mold by inkjet printing, the method is first established and implemented. Several proof-of-concept systems are then displayed in order to demonstrate the great potential of that idea.
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Rémy Brossard. Spontaneous curvature of polydimethylsiloxane thin films : Mechanisms and applications : A new route for the low cost fabrication of new functionalities for microfluidics. Materials Science [cond-mat.mtrl-sci]. Université Paris-Saclay, 2017. English. ⟨NNT : 2017SACLV103⟩. ⟨tel-01735251⟩

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