FIGURE 1.

Variation of π and area during isothermal fast and slow compressions for N&PL. Films were spread on the surface of a captive bubble, heated to 37°C, and compressed either continuously at 0.02 min⁻¹ (experiment 1, black/gray lines), or during a brief pulse at 32 min⁻¹, after which area was expanded and recompressed at 0.04 min⁻¹ (experiment 2, red/blue lines). Rates of compression are expressed as A⁻¹·dA/dt. (A) π (left axis) and area (right axis) versus time after beginning of compression. The subscripts indicate data from the same experiment. Surface area is expressed relative to the initial value (A_o) at the beginning of compression from different initial π values. (B) The same data expressed as π-area isotherms. Surface area is expressed relative to the value at 44 mN/m (A₄₄) during the initial compression to facilitate comparison of different experiments. Arrows indicate the temporal progression of the measurements.