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Numerical Investigation of Dewetting Over Topographicaly Srtuctured Substrate on Nanometric Scale

HajiGhasemi, Mustafa | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43919 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Moosavi, Ali
  7. Abstract:
  8. Thin liquid films on solid substrates are of considerable relevance in widespread of natural and technological fields. Examples are eye irrigation, biological cell interaction, tertiary oil recovery, coating, painting, lubrication, integrated circuits, micro- and nano-electronic devices, to name just a few. It is well known that liquid films are not always stable and there are verities of factors that may destabilize and expose the film to dynamical processes which leads to removal of the liquid from the substrate, the phenomenon so-called dewetting, either by nucleation or spinodal mechanisms. In many cases dewetting is destructive but there are several situation in which dewetting turns out to be useful.Although a considerable literature is available that investigates dewetting, the researches predominantly have been focused on homogenous substrates and the case of structured substrates, which encompasses most experimental and technological situations, has been less understood despite recent valuable efforts performed in this area. It has been shown that showed that the details of the physical heterogeneities such as shape and sharpness are important and may appreciably change the dynamics of the rupture.A recent experimental study on dewetting over terraced nanometric steps has revealed a new feature involved in the system. The dewetting front can freely move in the direction of upward steps, while it is blocked by downward steps. It is argued that such a phenomenon may potentially be used in controlling and guiding the liquids, e.g. in micro- and nanofluidic systems.In the present study we theoretically address dewetting on topographically structured substrates. We consider a partially wetting, non-volatile, and incompressible liquid films over different geometries and study time-dependent evolution of the interface. We show that intermolecular forces play a vital role in describing what occurs during the dewetting. In order to generalize the study, most general form of the intermolecular forces is considered. It is shown that by increasing the strength of the intermolecular forces the pinning time decreases. Our results also indicate that as the rate of changes in the geometry of the substrate increases the pinning time increases dramatically
  9. Keywords:
  10. Numerical Solution ; Pinning ; Thin Films ; Nano Sized ; Deweting

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