Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 164

According to Eq. (5.3), the surface energy γ_sv is related to the surface energy of the liquid γ_lv, the solid–liquid interfacial energy γ_sl and the contact angle θ . Whereas γ_lv and θ can be easily measured, γ_sv and γ_sl cannot. Consequently, methods for estimating γ_sv often involve a combination of measuring γ_lv and θ, and estimating γ_sl using theoretical analyses, some of which can be fairly complex. While a variety of methods have been proposed, a useful method for polymers, based on its simplicity and accuracy, involves measuring θ for a single liquid of known surface energy (surface tension) γ_lv and using a theoretical expression for γ_sl (Girifalco and Good 1957):

(5.4)

where Φ is expressed in terms of V_s and V_l, the molar volume (molecular weight divided by the density) of the molecules or molecular segments of the solid and the liquid, respectively, given by

(5.5)

For a polymer, the repeating unit in the polymer chain can be taken to approximate the molecular segment. Using Eqs. (5.3) and (5.4), we get

(5.6)