Europhys. Lett., 57 (4), pp. 533–539 (2002) EUROPHYSICS LETTERS 15 February 2002 Polymer transport across isotope-selective interdiﬀusion barriers H. Gr¨ ull 1,2 ( ∗ ), A. R. Esker 1,3 ( ∗∗ ), S. K. Satija 1 and C. C. Han 1 1 Material Science and Engineering Laboratory, National Institute of Standards and Technology (NIST) - Gaithersburg, MD 20899-8542, USA 2 Philips Research Laboratories - 5656 AA Eindhoven, The Netherlands 3 Virginia Polytechnic Institute and State University, Department of Chemistry Blacksburg, VA 24061, USA (received 26 February 2001; accepted in ﬁnal form 19 November 2001) PACS. 66.30.Ny – Chemical interdiﬀusion; diﬀusion barriers. PACS. 68.35.Fx – Diﬀusion; interface formation. PACS. 68.47.Pe – Langmuir-Blodgett ﬁlms on solids, polymers on surfaces, biological molecules on surfaces. Abstract. – Neutron reﬂectivity experiments were performed to study the interdiﬀusion of two compatible polymers, polystyrene and deuterated polystyrene, across a free-standing ultra-thin (60 ˚ A) interstitial membrane. Annealing above the glass transition temperature and quenching back to room temperature allows for a time-dependent study of the changing con- centration proﬁle due to membrane-mediated interdiﬀusion. For the case of matched polymer molecular masses but diﬀerent isotopic labeling, faster transport of the deuterated polymer across the interstitial layer is observed leading to displacement of the membrane. Varying the molecular mass and isotopic labeling of the top polymer layer provides information about the size discrimination and isotopic selectivity of the membrane. Currently, a tremendous technological and scientiﬁc eﬀort is being invested in scaling down feature sizes in modern devices, e.g. microelectronics or hybrid materials such as polymer based microelectronics [1]. New materials on nanometer scales are based on combinations of components with diﬀerent molecular properties. One of the immediate consequences is the need to understand and control interfaces between diﬀerent materials as the material properties are largely governed by interfacial phenomena. The well-known Kirkendall eﬀect [2] in metal composites, dewetting phenomena of metallic or polymeric ﬁlms on surfaces [3], adsorption phenomena in polymer blend thin ﬁlms [4, 5] or controlled drug release through barrier layers [6] are common examples of similar phenomena in very diﬀerent ﬁelds. While interdiﬀusion of compatible materials [7] and the partial interpenetration of incompatible materials (“interfacial width”) [8] were thoroughly studied, the eﬀects of an interstitial barrier layer, sandwiched between two compatible materials, on interdiﬀusion is a less understood problem both experimentally and theoretically [9,10]. Here, we present a study of a diﬀusion barrier formed by a polymeric nanometric membrane between two polymer layers. The interdiﬀusion of two compatible polymers of equal and diﬀerent molecular masses was thoroughly investigated using a variety of diﬀerent techniques [11–16]. The aim of those experiments was to test theoretical models dealing with polymer dynamics as a function of ( * ) E-mail: holger.gruell@philips.com ( ** ) E-mail: aesker@vt.edu c  EDP Sciences