Near-field scanning optical microscopy and atomic force microscopy are used
to probe the sub-micrometre phase structure in palmitic acid monolayers co
ntaining the 25 peptide amino terminus of lung surfactant protein B (SP-B1-
25). Monolayers deposited onto mica substrates at a surface pressure of 15
mN m(-1) exhibit a two-phase coexistence across a broad range of SP-B1-25 c
oncentrations, Monolayers containing 5 wt,% SP-B1-25 Or less exhibit an exp
anse of liquid condensed phase in which elliptical liquid expanded (LE) dom
ains with areas of approximately 25 mum(2) coexist. By contrast, monolayers
containing 20 wt.% SP-B1-25 exhibit an expanse of liquid expanded phase in
which circular ii quid condensed domains coexist. The phase distribution d
ependence on SP-B1-25 concentration suggests that the peptide induces disor
der in the monolayer.