The change in the wetting behavior of a standard commercially available textile material in response to surface treatment has been thoroughly characterized with conventional laboratory measurement techniques. The characterization was carried out by taking a series of contact angle measurements that allowed for the determination of the corresponding shift in substrate surface energy as a result of the applied treatment. The collected surface energy values were expressed in terms of the spreading parameter S, which was used to describe phase behavior at the substrate/droplet interface. However, these results showed that the use of a coarse parameter S, or even the work of adhesion ( W a ) and the work of cohesion ( W c ) parameters alone did not adequately account for the observed wetting behavior. A proper description of droplet formation on substrate surface was provided only when the interfacial interaction was examined at a more detailed level by involving the individual dispersive ( σ l d , σ s d ) and polar ( σ l p , σ s p ) surface energy components of both the solid and the wetting liquid. The methodology for characterization of interactions between a textile substrate coated with various surface active agents and several functional fluids have been developed. Several practical examples of how this methodology can be applied to describe the substrate surface treatment and the resulting wetting behavior are described herein.

The electrostatic charging behavior of filter elements operating in various hydraulic and lubricating fluids has been re-examined from the perspective of fundamental material properties of the two materials participating in the event. In contrast to the previously proposed mechanisms that focused predominantly on fluid and material conductivities, new evidence strongly suggests that the relative placement of the substrates in the triboelectric series must be taken into account. The positions occupied in the triboelectric series account for the donor/acceptor tendencies exhibited by the materials when brought close together in close proximity ( 10 nm). Nevertheless, this behavior is only an outward manifestation of the deeper underlying characteristics that include material surface energies and, looking even deeper, the associated electron work functions of the interacting materials. Herein we provide several examples of the enhanced understanding of the electrostatic charging/discharging (ESC/ESD) phenomena as they occur in the course of filtration of hydraulic and lubricating fluids through modern filter elements constructed of synthetic glass fiber and polymer materials.