Polymer Communication Novel method for preparing cellulose model surfaces by spin coating E. Kontturi * , P.C. Thu ¨ne, J.W. Niemantsverdriet Schuit Institute of Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Received 20 November 2002; received in revised form 13 March 2003; accepted 27 March 2003 Abstract A new, simplified method for preparing model surfaces of cellulose is introduced. Non-polar cellulose derivative trimethylsilyl cellulose (TMSC) was deposited onto untreated silicon substrate by spin coating, after which the coated TMSC was regenerated back to cellulose by vapour phase acid hydrolysis. By optimising the parameters of spin coating, a smooth cellulose film of ca 20 nm was obtained with roughness variation of max. 3 nm. With the well-defined morphology and chemical structure, combined with easy preparation, these model surfaces provide excellent means to explore the molecular level phenomena, taking place during various processes involving cellulose. Films were characterized using atomic force microscopy to illustrate the morphology and X-ray photoelectron spectroscopy to determine the chemical structure of the layers. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Atomic force microscopy; Cellulose model surface; Spin coating 1. Introduction Despite the abundance of cellulose and its importance for the human culture, ultrathin films of cellulose are a relatively new and surprisingly rare field of interest. To our knowledge, the only established way to manufacture ultrathin model surfaces from cellulose is the preparation of Langmuir–Blodgett films from trimethylsilyl cellulose (TMSC) which, once deposited on a smooth substrate, can be easily hydrolysed to cellulose by a simple acid hydrolysis. The method was introduced in the early 1990s by Wegner and co-workers [1,2] and developed further in studies with surfaces forces [3,4] and hydroxyl accessibility [5]. Smooth, ultrathin model surfaces provide excellent means to examine the chemical and morphological changes, taking place in various processes and phenomena involving cellulose, e.g. interactions with water (papermaking, paper recycling), photochemistry (yellowing of paper), thermal degradation (biomass gasification), etc. We feel that model surfaces have not been exploited to their full potential in cellulose research. The purpose of this paper is to describe a simplified procedure to prepare cellulose films with a thickness of the order of 10–50 nm. The seminal difficulty of creating model surfaces from cellulose has been its reluctance of to dissolve into conventional organic and inorganic solvents. There is a number of solvents available, such as lithium chloride in dimethylacetamide [6], N-methylmorpholine- N-oxide (NMMO) monohydrate [7], or the cadmium complex with ethylenediamine (Cadoxen) [8] but while they are suitable for the analytical and synthetic purposes, they are very difficult to work with from the point of view of model surface preparation. This is also the reason why easily dissolving cellulose derivatives have been subjects for model surfaces with a wider interest than cellulose itself [9–12]. The elegance of the LB technique [1,2] lies in the easy transformation of the TMSC derivative to cellulose with vapour phase acid hydrolysis after the TMSC has already been deposited on the substrate (Scheme 1). The LB technique, however, requires special equipment like the Langmuir-trough, and rather demanding conditions, e.g. a computer controlled thermostat. Therefore, we set out to establish spin coating as a new, simplified method to prepare smooth ultrathin films of cellulose. Spin coating is a process, in which a polymer or colloid containing liquid film is spread by centrifugal forces on a rotating substrate and the liquid is evaporated with the help of high speed spinning leaving a smooth, uniform film with thickness that can be modified by altering parameters such as original solution concentration, spinning speed, and choice of solvent 0032-3861/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0032-3861(03)00283-0 Polymer 44 (2003) 3621–3625 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 31-40-2473068; fax: þ 31-40-2473481. E-mail address: e.j.kontturi@tue.nl (E. Kontturi).