Adhesion And Optical Fibres
ADHESION AND OPTICAL FIBRES
J. Rayss, A. Gorgol
Laboratory of Optical Fibres Technology, Maria Curie-Sklodowska University, 20-031 Lublin, Poland
The optical fibre may be treated to some extent as a special kind of composite material, composed of a „hard” part - fused silica fibre and a soft one - its polymer protective coating. If so, the mechanical properties of the optical fibre should depend on its components properties as well as on the properties of polymer/glass interface. The properties of the interface are responsible for polymer protective coating adhesion to the fused silica surface. As it was shown by Kurkijan and Innis [1], just the adhesion of coating to the glass surface is the most important factor deciding the mechanical reliability of optical fibre and its resistance to the environmental effects, particularly to water corrosion. Of course, adhesion depends on the properties of both surfaces being in contact. The most popular and useful method of investigation of the surface properties is the method proposed by van Oss et al. [2], considering the surface energy in the categories of electron donor and electron acceptor interactions. According to these authors all the components of the solid surface energy may be determined if the contact angles of the three liquids differing in their electron donor and electron acceptor properties are known. Also, the inverse gas chromatography is often used in order to characterise the properties of solid surfaces. We have applied both methods for determine the dispersive and specific components of the free energy of the surfaces of fused silica and polymers used as the protective coatings of optical fibres. We have found, for example, the strong dependency between the electron donor properties of fused silica surface and the surface concentration of the hydroxyl groups and determined the dependencies between the surface character and composition of the polymers used. Measurements of contact angles and inverse gas chromatography gives very similar results, particularly concerning the dispersiv component of surface free energy.
From the other hand, the we have proposed the method of measuring of adhesion (exactly speaking - energy of adjacency) of polymer layer to the
surface of cylindrical objects. This methods permits also to differentiate the „thermodynamic” and „practical” [3] parts of this energy. The knowledge of the practical part of energy of adjacency, caused by the shrinkage of polymer taking place during UV-curing, is very important in the case of optical fibres because to high value of this energy can generate the loses of energy transmitted by the fibre.
References
1. Kurkijan C.R., Innis, D., Optical Engineering, 30 (1991) 681
2. van Oss, J., Chaudhury, K., Good, R.J., Chem. Rev., 88 (1988) 927
3. Mittal, K.L., in: Adhesion Measurements of Films and Coatings, K.L. Mittal Ed., VSP, 1995, pp. 1 - 13
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