COMPRESSION EXPANSION HYSTERESIS OF POLY(L-GLUTAMIC ACID) MONOLAYERS SPREAD AT THE AIR/WATER INTERFACE/

In order to study Che conformational behavior of poly(L-glutamic acid) (PGA) at the air/water interface under the influence of compression a nd expansion forces, PGA was spread on an aqueous acidic subphase and. studied by the Langmuir technique. Several distinct regions of the fi rst compression surface pressure! area (pi/A) isotherm could be identi fied by the starting and inflection point of the isotherm and by the b eginning and the center of the pseudoplateau. The interpretation of th e characteristic shape of the pi/A isotherms in the sense of a side-by -side and an interdigitated organization of helical rods is strongly s upported by molecular modeling calculations. But the helical surface l ayer is sensitive to repeated expansion and compression. A well-define d and reaction-kinetic demonstrable change occurs. The reasons for thi s transformation are discussed. Solidified regions are forming in the layer. Finally, after several compression/expansion cycles a. more rig id monolayer results than that formed by helical rods exclusively. The se monolayer ruptures on expansion and clods of PGA molecules were obs erved using Brewster angle microscopy and ellipsometry.