Surface pressure-area (pi-A) isotherms and Maxwell displacement current (MDC) of 10,12-tricosadiynoic acid (TDA) monolayer at the air-water interface were measured. U-V-polymerization was carried out at various surface pressures and polymerization time. After polymerization, larger molecular area expansion, higher collapse pressures and corresponding changes of MDC signals were observed. The flow behavior of TDA monolayer and its resulting polymerized TDA (PTDA) monolayer were studied in detail during the course of monolayer compression and expansion by means of pi-A isotherms and MDC measurements. In-plane molecular flow induced reorientation of TDA monolayer was not reversible, whereas the in-plane molecular flow induced reorientation of PTDA monolayer was reversible. The effects of applied surface pressure and polymerization time on the experimental results of pi-A isotherms and MDC measurements were discussed in association with the conformation change and it was interpreted in terms of molecular packing in the monolayer. (c) 2005 Elsevier B.V. All rights reserved.