CRITICAL ADSORPTION IN THE UNDERSATURATED REGIME

The interaction between a near-critical binary liquid and a solid substrate can de modeled by an effective surface field hi. Critical adsorption experiments to date have been done in the limit of strong field, but we have been able to produce intermediate-strength fields by chemically modifying a surface. We present here an experimental demonstration of critical adsorption in this undersaturated regime. Our reflectivity data indicate that critical adsorption can remain undersaturated even within 3 mK of T-c - a surprising result difficult to reconcile with current expectations of the behavior of the critical scaling function.