FIGURE 4.

Rapid initial compression followed immediately by isobaric compression. Monolayers of POPC spread to <42 mN/m were first compressed at 26°C and <0.005 min⁻¹ to 46 mN/m and then at 23 ± 5 min⁻¹ to different target surface pressures. Isobaric compression then maintained the final surface pressure achieved at the end of the rapid compression. Experiments lasted at least 15 min or until hydrostatic pressure exceeded the limits of the apparatus (3.5 atm). (A) Variation of surface area (lower left axis) and surface pressure (upper right axis) with time. Area is normalized to the initial value at 46 mN/m (A_o). (B) Surface pressure-surface area isotherms. Curves of the same color in Fig. 4, A and B, indicate presentations of the same data. For purposes of clarity, results are presented for individual experiments. Symbols in Fig. 4 B give mean area ± SD at specific surface pressures during the rapid compression for at least five experiments in each case. Error bars that are not evident are less than the size of the symbols. Error of the measurements during the isobaric compressions is given in Fig. 5.