Figure 6.

Relative adsorption (RA) of 800 μg Survanta on subphases containing 2 mg/mL albumin at varying chitosan concentrations. □ Survanta-albumin-chitosan; ○ Survanta-albumin, which as been plotted at a chitosan concentration of 7×10⁻⁵ mg/mL for comparison purposes. RA is the difference between the sample surface pressure (Π) and the surface pressure of the albumin only isotherm (Π_Alb, red curve in Fig. 1b), divided by the difference between the clean interface isotherm (no albumin), Π_Sat, and Π_Alb, $RA={\frac{\mathrm{\Pi }-{\mathrm{\Pi }}_{\mathit{Alb}}}{{\mathrm{\Pi }}_{\mathit{Sat}}-{\mathrm{\Pi }}_{\mathit{Alb}}}\mid }_{A_0}$. All surface pressures were evaluated by averaging over the same trough area, A₀, denoted by the shaded area in Fig. 2. The relative adsorption increases with chitosan concentration to an optimum value of RA ~ 1 at .001 – 0.005 mg/mL chitosan and then decreases with subsequent increases in chitosan concentration. The dashed box indicates the calculated (Table 1) chitosan concentration range where n₊/n₋ = 1 (0.0005–0.005 mg/mL). The optimum RA occurs in this chitosan concentration range consistent with a chitosan neutralizing the negative surface charge on the albumin and surfactant, thereby eliminating the electrostatic energy barrier to surfactant adsorption. Higher chitosan concentrations above n₊/n₋ = 1 lead to charge reversal as excess chitosan adsorbs to the albumin and surfactant, leading to a net positive charge in the double layer and a restored energy barrier to adsorption (Eqn. 1–3).