Adhesion surface energy approach

J. R. Green, K.L. Nevell, T.G. Preventing Bacterial Adhesion onto Surfaces The Low-Surface-Energy Approach. Biomaterials 1999, 20 (13), 1229-1235. 

The adhesion hysteresis and its contribution to the friction have been studied extensively by means of SFA [39], which leads to an important conclusion that it is the adhesion hysteresis or the energy loss during the process of approach/separation, rather than the surface energy itself, that dominates the frictional behavior of boundary films. 

An important consequence resulting from the approach of the interfaces is that Yf, the surface energy of the film, is lowered by the energy of adhesion. When the interfaces are far apart, E(h) is equal to zero and y/ is simply equal to 2yint, where yint is the tension of a single interface. At equilibrium, the surface energy of the film is Yf = 2yint -F E(he). 

A general approach to increase adhesion is for polar groups to be introduced to the surface in order to improve the adhesion of water-borne paints. While the polar groups increase the adhesion characteristics, they also increase the surface energy, which makes the adhesion water sensitive and often increases the water permeability. 

Chiang, M.Y.M., Song R., Crosby, A. J., Karim, A. and Amis, E. J., The combinatorial approach to the thin film adhesion as a function of film thickness and surface energy, in preparation. 

Following the Wulff approach of the equilibrium shape of crystals, some authors have tried to include the presence of a substrate. The solution of this problem has been given by Kaishew [84] and Winterbottom [85]. It is known as the Wulff-Kaishew theorem. The crystal is now truncated at the interface by an amount Ahg, which is related to the adhesion energy of the crystal on the substrate (j ) and to the surface energy of the facet parallel to the interface (cr ) by the following relation ... 

Polymer surface modifications are omnipresent in applications where the surface properties of materials with favorable bulk properties are insufficient. By altering the surface characteristics using physical or chemical modification the desired surface properties may be achieved. Such treatments are required e.g. to enhance printability of films, the adhesion of paints, metal or other coatings, biocompatibility, protein resistances/reduced biofouling, etc. The diverse approaches met in practice include, among others, wet chemical and gas phase chemistry, plasma or corona, UV/ozone and flame treatments. In most cases surface chemical modification reactions take place that alter the surface energy in a desired way. For example,... 

G. Electrostatic Contribution to Adhesion. Surface free energies describe adhesion phenomena once molecular contact has been achieved between the adhering phases. For a cell to come from a distance into molecular contact with a surface requires consideration of long-range forces which influence approach. Two factors are of prime importance to the attachment of microbial cells to solid surfaces 1) electrostatic interactions and 2) fine surface projections. 

These considerations lead to the conclusion that a rational approach to.problems of the adhesion of cells to solid surfaces can be developed from knowledge of the surface properties of both the substrate and the cell. Solid surface energies can be obtained by measurements of contact angles and use of Neumann s equation (Eq. 6), thus allowing calculations of free energy charges associated with adhesion. Zeta potentials and resultant electrostatic contributions to adhesion can also be obtained experimentally. This type of approach should provide insight into microbial adhesion problems in the marine and aquatic environments, disease and infection and in the industrial immobilization of whole cells. 

The analysis of the low adhesive properties of iPP leads to the two different approaches of explanation (Brewis Mathieson, 2002 Chodak Novak, 1999, Kinloch, 1987). By the first explanation the low adhesion of iPP consists in a formation of thin layer of low-molecular substances on the interfacial boundary. The primary function of modification is then a removal of the thin low-molecular substance layer from the polymer surface, while the chemical modification itself is of a secondary importance. The second explanation attributes the low adhesive properties of iPP to its non-polar character and low surface energy, stressing the dependence of the adhesive properties of iPP on their super molecular structure. The chemical changes resulted in the increase of the polarity and surface energy are considering for the most important in the modification of iPP. 

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