Fig. 1.
(A) Experimental setup for microbutton surface rheometry consists of a sample–electromagnet holder placed within a Langmuir trough, a Wilhelmy plate for surface pressure measurements, and bright-field microscopy using a zoom lens and CCD camera; (B) electromagnet and sample holder where microbuttons are added; (C) bright-field image of a 10-μm microbutton. (D) Rotational resistance ζR measured at clean air–water surfaces versus oscillation frequency. Subphase drag for 10-μm probes is 53 = 125 times smaller than for 50-μm probes.