THE TIME OF OBSERVATION OF PI-A ISOTHERMS .2. A POSSIBILITY THAT SO-CALLED SOLID FILMS IN PI-A ISOTHERMS OF MONOLAYERS OF LONG-CHAIN ACIDS MAY NOT CORRESPOND TO THE 2-DIMENSIONAL SOLIDS BUT TO THE 1ST-ORDER PHASE-TRANSITION REGIONS FROM 2-DIMENSIONAL LIQUIDS TO SOLIDS

Monolayers on the water surface are viscoelastic bodies and characteristic times of measurement of pi-A isotherms are necessary. The time of observation of pi-A measurement is defined and a new method of measurement in which the time of observation can be kept constant is proposed. The drastic change of the shape of pi-A isotherms of arachidic acid monolayers even at a constant temperature by changing the time of observation widely and systematically is demonstrated. Some evidence for a possibility that so-called "solid films" of monolayers of long-chain acids may not correspond to the two-dimensional solids but to the two-dimensional first-order phase transition regions from liquids to solids are presented and discussed.