Figure 10.

Apparent Gibbs’ surface excess scaled as a function of adsorbent surface water wettability (surface energy) as measured by the advancing contact angle θ_a of phosphate buffered saline (PBS) solution, expressed as water (buffer) adhesion tension τ° = γ_lv cosθ_a for incrementally sampling the full range of observable water wettability (where buffer interfacial tension γ_lv = 71.97 mJ/m²; SiO_x = oxidized silicon semi-conductor wafer, APTES = aminopropyltriethoxysilane silanized SiO_x, PS = polystyrene spun-coated onto SiO_x, SAM = 1-hexadecanethiol self-assembled monolayer on gold-coated SiO_x). Symbols and error bars represent mean and standard deviation of ten different proteins spanning three orders of MW (ubiquitin, 10.7 kDa; thrombin (FIIa), 35.6 kDa; FV HSA, 66.3 kDa; Hageman factor (FXII), 78 kDa; fibrinogen, 340 kDa; IgG, 160 kDa; C1q, 400 kDa; IgM, 1000 kDa). See ref. [26] for details. Panel A shows that Gibbs’ surface-excess parameter [Γ_sl − Γ_sv] decreases monotonically with increasing adsorbent-surface hydrophilicity, projecting [Γ_sl − Γ_sv] = 0 near the τ° = 30 mJ/m² pivot point (θ = 65°, see Section 4.2 and Fig. 5). Likewise, the ratio $\left\{\frac{[{\Gamma }_{\mathrm{sl}}-{\Gamma }_{s\nu }]}{{\Gamma }_{l\nu }}\right\}$ decreases from +1 to −1 (Panel B) as [Γ_sl − Γ_sv] decreases from a maximum [Γ_sl − Γ_sv] = −Γ_lv at the liquid-vapor (lv) interface and hydrophobic SAM surface (τ° = −15 mJ/m²) to a minimum [Γ_sl − Γ_sv] = −Γ_lv at the water-wetted (τ° → 73 mJ/m² surfaces. Smoothed curves drawn through the data are guides to the eye.