Numerical analysis of compression isotherms of distearoyl monogalactosyl glycerol monolayers

A mathematical method has been developed for the numerical analysis of comp ression isotherms of distearoyl monogalactosyl glycerol (MGDG) monomolecula r films at the air-water interface. The isotherms are given in terms of mea n molecular urea (A. Angstrom (2)) versus surface pressure (pi. mN/m). The numerical analysis by the use of extended cubic spline functions and straig ht lilies of regression describes the compression isotherms and molecular p acking of MGDG in two-dimensions us well as the calculation of two-dimensio nal (surface) compressibility (C-s) of MGDG monolayers with good precision. The phase transition found as a discontinuity in the relationship between the surface compressibility and surface pressure, according to the Ehrenfes t theory, is interpreted as an apparent second-order phase transition from a liquid expanded to a liquid condensed stale in MGDG monolayers in substan tial agreement with our previous findings by electron microscopy.