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Title: Polydimethylsiloxane (PDMS) monolayers : morphology, nanostructure, adhesive and frictional properties
Author: Madani, Frederic
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2005
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In this work polymer and other organic films deposited on silica substrates were studied. Special attention was given to adsorbed polydimethylsiloxane (PDMS) monolayers. Scanning White Light Interferometry (SWLI) is shown to provide direct three-dimensional imaging of thin films with a thickness higher than – 0.5nm. The thickness values are precise (± 0.1 nm) if the system is covered with a metal layer of thickness ~80nm. The lateral resolution is in the sub-microwave range. This makes SWLI a credible alternative to imaging ellipsometry, the standard technique for global imaging of thin and ultra-thin films. SWLI has been used to establish the irreversible nature of adsorption of PDMS on silica. It has also been to judge whether or not a film is a true monolayer through height measurement across the layer. A leap in lateral resolution of two or three orders of magnitude is obtained by using Intermittent Contact Scanning Force Microscopy (IC-SFM). A dense dry PDMS monolayer consists of a bimodal system: a smooth layer made of chains with a flat conformation topped by upright chain segments of poorly adsorbed chains that aggregate to form large spots. The presence of the smooth base layer was verified by means of an SFM tip used as a ‘nanodigger’. Pull-off force experiments carried out in bad solvent conditions between an SFM tip and a PDMS monolayer (contact area ~10nm) have shown two main energy dissipation mechanisms: chain or chain segment stretching, long range adhesive plateaus the length of which is related to chain length. Their height is related to the surface energy of PDMS that was estimated through contact angle goniometry. This phenomenon has been interpreted as the elongation of a collapse chain going from a globule to coil state.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available