Serge Rebouillat

Wettability of single fibres : beyond the contact angle approach

Abstract To know the wettability of fibres is useful to predict their adhesion potential to the matrices which they strengthen. The contact angle on a single fibre can characterise its wettability by the contacting liquid in a given environment. In this paper, the theoretical model proposed by Carroll (J Colloid Interface Sci 1976;57:488) and Yamaki and Katayama (J Appl Polym Sci 1975;19:2897) is reviewed. Using a modified version of their model and a modern image analysis approach, a computer assisted measurement of the inflection angle of the drop profile leads to a more accurate and faster calculation of the contact angle. Experiments on Kevlar ® fibre were conducted and statistics are presented. These provide a comparison between the traditional wetted length approach and the new one involving the inflection angle of the drop profile which appears to be a useful parameter for characterising fiber–liquid interactions of various wettability situations.

Hydrodynamics of high-speed fibre impregnation: the fluid layer formation from the meniscus region

Abstract Coating and fibre impregnation are studied from the theory of Landau and Levich (Acta Physicochem. USSR 17 (1942) 42), Deryagin (Acta Physicochem USSR 39 (1943) 13) and more recent approaches of De Ryck and Quere (J. Fluid Mech 311 (1996) 219) and Rebouillat et al. (2000). Chemical and physical effects as well as hydrodynamic influence the impregnation. To study fibre impregnation at speeds higher than 2 m s −1 , a high-speed impregnation unit was developed to reach fibre velocities of 5 m s −1 and above. The wettability and the hydrodynamic phenomena associated with impregnation at high fibre velocity have been investigated on mono- and multi-filaments yarn structures passing through a bath of liquid. The negligibility of gravity in comparison with inertia at high velocities has been experimentally observed by studying the effect of fibre inclination on the fluid thickness and by processing dimensional analysis. Moreover, the impregnation phenomena have been studied owing to a new image analysis set-up, which allows to measure directly the fluid thickness on fibres and to study the dynamic meniscus region, which has been successfully modelled to allow back calculations under specific conditions.

Hydrodynamics of high speed fibre impregnation

Abstract Coating and fibre impregnation are studied from the theory of Landau and Levich (1942) (Acta. physicochimica USSR, 17, 42–54) Deryagin (1943) (Acta physicochemica USSR, 39,13–16) and more recent approaches of De Ryck and Quere (1996) (Journal of fluid Mechanics, 311, 219–237). Chemical and physical effects influence the impregnation. To study fibre impregnation at speeds higher than 2xa0m/s, a high-speed impregnation unit was developed to reach fibre velocities of 5xa0m/s and above. Two wetting applicators were set up and experiments on mono- and multi-filaments yarn structures were conducted in order to understand the wettability and the hydrodynamic phenomena associated with impregnation at high fibre velocities. The results for the impregnation with water both in the case of the mono-filament and the multi-filament fibres differ significantly. Three hydro-capillary regimes have been identified in the case of the single fibre whereas multi-filament impregnation seems to vary in a way comparable to the Landau theoretical prediction.

Optical diffractive properties of UV-treated polyamide films

Optical gratings were generated by spatially controlled UV irradiation of suitable polyamide films coated on a glass slide. The details of the writing process are given and preliminary microtopographical characterization of the relief structure is observed. The diffractive properties have also been established.