Лако-красочные материалы — производство

In this short review, we have presented some results on the behavior of polymer solutions close to surfaces in the context of adhesion phenomena. The emphasis has been placed on the interaction between two flat parallel solid surfaces induced by a polymer solution and more specifically on the bridging effect between the surfaces due to the polymer. Two types of interactions between the surface and the polymer have been considered: grafting and adsorption.

We have not discussed in detail experiments on interaction between surfaces mediated by a polymer solution. There exist now many experiments probing the interac­tion between two surfaces in a polymer solution both when the polymer adsorbs and when the polymer is grafted. The earliest experiments were performed using a surface forces apparatus and measuring the interactions between mica surfaces [38]. More recently, experiments have been performed using other techniques such as atomic force microscopy

[39] , thin film balance, or measuring the interactions between magnetic emulsion droplets

[40] . The theories presented here give in most cases a rather accurate description of the experiments.

Some important effects are ignored by the theoretical models that we have presented. The most important approximation is the thermodynamic equilibrium assumption. All these surface interactions have very long relaxation times and this approximation is in many cases questionable (in some instances, the surface polymer layers are rather dense and become glassy, the thermodynamic description is then not meaningful). In some cases a description in terms of a constrained equilibrium compares favorably with the experi­ments but all these problems would require a kinetic description. Some steps towards a kinetic description have been taken for the structure of the surface layers but the descrip­tion is far from being complete. For the interaction between surfaces and the bridging problem, only very few attempts have been made [41]. The important question here is the role of trapped entanglements that can have a strong influence on the interaction force in cases of both adsorption and grafting. So far this effect has not been included in the theories.

Another important aspect that we have not discussed in this paper is the dynamic properties of the polymer surface layers such as their behavior under steady shear [42] or under an oscillatory stress [43]. This is obviously essential for adhesion studies and theo­retical work in this direction is certainly needed.

Finally, we have considered polymer solutions in good solvents only. For industrial applications, one tends to use more and more water as a solvent. Water soluble polymers have specific properties due to the character of the interactions between monomers in water. Most water soluble polymers, for example, carry ionic charges (they are polyelec­trolytes); if the polymers contain hydrophobic groups, they have interesting associating properties. The surface behavior of polyelectrolytes and associating polymers is the subject of intense experimental and theoretical studies [44].