Adhesion and Friction of Polystyrene Surfaces around T g (original) (raw)
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Variable temperature Scanning Force Microscopy of mixed polystyrene (2000-100000 g/mol) and poly(methylmethacrylate) (100000 g/mol) thin films was used to probe mechanical properties such as surface stiffness and pull-offforces. Adhesion data can be explained by the molecular properties of the constituents. The adhesion of Polystyrene samples was measured by force distance curves and using the Pu!sed Force Mode. lt can be shown that surface tension is not the dominant part ofthe tip-surface interaction, but the mechani ca! properties of the material will influence the measured adhesive force. Wetting of the tip by polymer molecules at higher temperatures due to increasing mobility is one possible model .
Temperature and Time Effects on the “Adhesion Dynamics” of Poly(butyl methacrylate) (PBMA) Surfaces
Langmuir, 1998
We present a surface force apparatus (SFA) study of the effects of time and loading-unloading rates on the adhesion of solid polymeric surfaces of poly(butylmethacrylate). We used the equilibrium JKR theory of adhesion or contact mechanics as a framework for analyzing the "adhesion dynamics" of two surfaces during nonequilibrium (viscoelastic, plastic) adhesion and separation. PBMA films of thickness ∼2 µm were prepared on curved mica surfaces by casting from a solution of methyl ethyl ketone. Pull-off forces from adhesive contact were measured at different temperatures around the glass-rubber transition temperature (Tg ≈ 25°C) at different loads and contact times, and hysteretic loading-unloading cycles were measured at different rates. On entering the rubber regime, the effective surface energies deduced from the pull-off forces increase dramatically, by up to 3 orders of magnitude above the "equilibrium" value, with increasing contact time and load. Strong entanglements across the interface, probably through reptation, increase the effective area of contact with time, giving rise to the high pull-off forces observed. Bulk viscoelastic deformations of the surface profiles accompany the time-dependent adhesion processes. The existence of at least two different relaxation (energy dissipating) processes, one at the molecular level and the other at the microscopic to macroscopic level, can be inferred from these experiments. The implications of the results for understanding the adhesion, fracture strength, and crack-propagation of elastic versus viscoelastic materials are discussed.
Temperature dependent surface properties of thin polymer films
1998
Variable temperature Scanning Force Microscopy of mixed polystyrene (2000-100000 g/mol) and poly(methylmethacrylate) (100000 g/mol) thin films was used to probe mechanical properties such as surface stiffness and pull-offforces. Adhesion data can be explained by the molecular properties of the constituents. The adhesion of Polystyrene samples was measured by force distance curves and using the Pu!sed Force Mode. lt can be shown that surface tension is not the dominant part ofthe tip-surface interaction, but the mechani ca! properties of the material will influence the measured adhesive force. Wetting of the tip by polymer molecules at higher temperatures due to increasing mobility is one possible model .
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The bonding of polystyrene (PS) surfaces below T g was investigated by two different fracture tests: the lap-shear joint method and the cantilever beam method. Adhesion energy values obtained by the two methods are in agreement and develop with (time) 1/2 , at temperatures as low as T g 2 16 8C. Even if the double cantilever method is the most common test found in the literature for adhesions above T g , for low adhesion values, below T g , the lap-shear joint geometry is more appropriate. Moreover, when the glass transition temperature is used as a reference temperature, polydisperse and monodisperse PS adhesion energy curves are superposable, suggesting that the auto-adhesion is not significantly favored by the presence of numerous chain ends at the surface (due to the low molecular weight chains provided by the polydisperse PS).
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Force-distance profiles were strikingly sensitive to small differences in temperature and solvent composition. Surfaces forces were measured at 18 and 28 "C between mica surfaces bearing polystyrene (M, = 490000 gmol-l) adsorbed from dilute cyclopentane solution (0 temperature TO = 19.5 "C). Forces at long range were monotonically repulsive at 28 "C and mildly attractive at 18 "C provided that a cyclopentane containing 5% linear pentanes was used. This contrasts with experiments in 99% pure cyclopentane, in which the range of detectable forces was (2-3) R~ (unperturbed radius of gyration) at 18 "C and (5-6) R~ at 28 "C, and the forces at long range were strongly attractive at 18 "C and weakly attractive even at 28 "C. A change of sign of the long-range interactions between adsorbed homopolymers, over a small range of temperature, does not appear to have been reported previously.
Adhesion and Friction of Polymers
Polymer Tribology, 2009
Surface phenomena and the structure of polymers affect essentially their tribological characteristics, the adhesion of polymers to solids being one of the dominating factors. The latter is explained, in particular, by the adsorption (chemisorption) of the functional groups, variations in the polymer crystallinity and morphology, constrained molecular mobility, and catalytic effects of the additives on the reactions occurring in the contact zone. It is shown how load, sliding velocity, and temperature affect friction. Different modes of wear of polymers and friction transfer are considered.
Adhesion mechanisms at soft polymer interfaces
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 2008
Based on several significant examples, we analyse the adhesion mechanisms at soft polymer interfaces with a special emphasis first on the role of connector molecules, that is, polymer chains bound to the interface and which transmit stress through a stretching and extraction mechanism, and second on the necessary relay that must be taken by additional dissipation mechanisms acting at larger scales if one wants to reach typical fracture toughnesses in the range of a few 10 J m(-2). Examples of such bulk dissipation mechanisms will be discussed for interfaces between polymer melts and for pressure-sensitive adhesives in contact with a solid surface. We shall particularly point out the fact that the level of adhesion results from a competition between adhesive failure usually driven by both the interactions and the friction properties of the interface and bulk strong deformations which take place in the bulk of the adhesive layer. Controlling the friction properties of the interface th...
International Journal of Adhesion and Adhesives, 1993
Contact angles have been measured for a number of liquids against the surfaces of dried films from various emulsion adhesives. From the results have been calculated the dispersive and polar components of the surface free energies of the film surfaces, and also the thermodynamic work of adhesion to polystyrene in dry conditions and in the presence of water. The properties of the surfaces of adhesives dried against air, polystyrene and polytetrafluoroethylene are very similar. One of the adhesives was found to have a particularly polar surface. This causes the thermodynamic work of adhesion to become negative in the presence of water, implying that the particular adhesive bond to polystyrene is unstable in the presence of water. This prediction has been confirmed experimentally, in that expanded polystyrene beads bonded with this adhesive disintegrated when immersed in water.