CRITICAL ADSORPTION IN THE UNDERSATURATED REGIME

The interaction between a near-critical binary liquid and a solid subs trate can de modeled by an effective surface field hi. Critical adsorp tion experiments to date have been done in the limit of strong field, but we have been able to produce intermediate-strength fields by chemi cally modifying a surface. We present here an experimental demonstrati on of critical adsorption in this undersaturated regime. Our reflectiv ity data indicate that critical adsorption can remain undersaturated e ven within 3 mK of T-c - a surprising result difficult to reconcile wi th current expectations of the behavior of the critical scaling functi on.