Polymer brushes provide the responsive smart surfaces which can be used for fabrication of various devices. In this thesis work, adhesion, friction, and wear of polystyrene (PS) - poly(2-vinyl pyridine) (P2VP) and polystyrene - poly(acrylic acid) (PAA) binary brushes and corresponding monobrushes were investigated in dried state under controlled environment. Spin-coated films were also investigated for comparison. The aim was to explore possibilities to control/tune adhesion, friction, and wear between inorganic or polymeric surfaces by use of polymer brushes. Atomic force microscopy (AFM) with sharp silicon nitride tip and colloidal probes was employed to investigate the nanoscale adhesion and friction forces between different inorganic and polymeric surfaces. Adhesion and friction on the polymer brushes were comparable to that on the spin-coated films. Adhesion and friction force values were correlated, and were in accordance with the wettability of the brush surfaces for most of the samples. Switching in the adhesion and friction forces was observed for the PS+P2VP and PS+PAA binary brushes on treatment with selective solvents. Maximum switching in adhesion force and friction coefficient was by a factor of 2.7 and 5.4, respectively. Furthermore, switching of friction for mixed brush surface was observed during macroscale friction measurements using nanoindenter. Friction coefficients at macroscale were higher than those at the nanoscale. Moreover, adhesion and friction forces between the surfaces were significantly influenced by the humidity, grafting density of polymer brushes, chemical composition of top of the binary brush surface, and tip scan velocity. Nanowear studies were carried out with AFM using sharp silicon nitride tip while macrowear studies were carried out using nanoindenter. Nanowear on the surfaces was affected by molecular entanglements, adhesion and friction forces as well as shape and status of the tip. It was observed that the typical wear mode for PS brushes (treated with toluene) was ripple formation. In case of P2VP brushes (treated with ethanol) and PAA brushes (treated with pH 10 water), wear occurred via removal of the polymeric material. Wear mechanism observed for the monobrushes was similar to that observed for the spin-coated thick films of the same polymeric material. However, extent of the wear on the brush surfaces significantly differed from that on the spin-coated films. In case of PS+P2VP and PS+PAA binary brush samples, change in the wear mode was observed on treatment with the different selective solvents. On treatment with toluene (PS on the top), both of these binary brushes showed the wear by formation of the ripples. On the other hand, when these binary brushes were treated with selective solvent for P2VP or PAA, wear occurred mainly via removal of the polymeric material. The amount of wear increased with the number of scans for all the polymer brush samples. Moreover, wear on the polymer brush surfaces was also increased on increase in the applied load and decrease in the scan speed. Wear behavior on macroscale was averaged due to contact between surfaces at large number of asperities. Our results show that adhesion, friction, and wear of polymer surfaces can be controlled/tuned by the use of binary polymer brushes.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:bsz:14-ds-1226414812035-21826 |
| Date | 11 November 2008 |
| Creators | Vyas, Mukesh Kumar |
| Contributors | Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Technische Universität Dresden, Fachrichtung Chemie und Lebensmittelchemie, Leibniz-Institut für Polymerforschung Dresden e.V.,, Prof. Dr. M. Stamm, Prof. Dr. M. Stamm, Prof. Dr. H.-J. P. Adler, Prof. Dr. H.J. Butt |
| Publisher | Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/pdf |
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