Figure 1.

(a) Cyclic isotherms of 800 μg Survanta deposited from an aqueous buffer onto a saline-buffered subphase containing no albumin or chitosan. On compression, the isotherm exhibits a characteristic shoulder at 45 mN/m and a collapse plateau at Π_max ~ 69 mN/m. On expansion, the surface pressure drops rapidly, reaching a minimum surface pressure of ~5–10 mN/m until compression is resumed.

(b) Black curve: 800 μg Survanta added to a saline-buffered subphase containing 2 mg/mL albumin. The characteristic shoulder and collapse plateau on compression seen in (a) cannot be reached with albumin in the subphase regardless of the compression. Red Curve: The isotherm of a subphase containing 2 mg/ml albumin, with no added Survanta or chitosan. The two curves trace over each other, indicating that the interfacial film is dominated by albumin and that Survanta is not adsorbing to the interface.

(c) 800 μg Survanta deposited on a subphase containing 2 mg/ml albumin and 0.005 mg/mL chitosan. By the second compression cycle, the characteristic shoulder and collapse plateau have been restored at similar trough areas as in (a) showing that the presence of 0.005 mg/mL chitosan completely reverses the surfactant adsorption inhibition. The only difference with the Survanta isotherms in Fig. 1a is that the minimum surface pressure in the presence of albumin never drops below about 15 mN/m on full expansion, which corresponds to the equilibrium spreading pressure of the albumin.

(d) 800 μg Survanta deposited on a subphase containing 2 mg/ml albumin and 0.5 mg/mL chitosan. At high trough areas, the isotherm resembles that of albumin (Fig. 1b), while at low trough areas, the characteristic shoulder is evident as in Fig. 1a. However, the isotherm only reaches a surface pressure of ~ 60 and the collapse plateau does not form at the limiting compression. This indicates that the increased chitosan concentration decreases surfactant adsorption compared to Fig. 1c.