A monolayer film of poly(hexamethylene adipamide) (nylon 66) was obtained by spreading N-trifluoroacetic anhydride (NTF)- modified nylon 66 in chloroform solution on an air-water interface at 14.7 °C. The pressure relaxation in a constant area and hysteresis of the film were measured. The surface moment versus surface area isotherm shows that the film holds the same conformation over the surface area region between 120 and 52.6 A ̊2 repeat-unit, and collapses at 52.6 A ̊2 repeat-unit. However, pressure relaxation at a constant surface area smaller than some transition value between 85 and 70 A ̊2 repeat-unit and significant hysteresis were observed. These phenomena were attributed to the effect of intermolecular interaction of hydrogen bonding. The mechanism of collapse was evaluated using the Avrami crystallization equation. Two-step crystallization was observed.
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