Journal of Colloid and Interface Science 332 (2009) 477–483 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis Stability and interface properties of thin cellulose ester films adsorbed from acetone and ethyl acetate solutions Jorge Amim Jr. a , Priscila M. Kosaka a , Denise F.S. Petri a,∗ , Francisco C.B. Maia b , Paulo B. Miranda b a Instituto de Quimica, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, 05508-900 São Paulo, Brazil b Instituto de Física, Universidade de São Paulo, São Carlos, Brazil article info abstract Article history: Received 6 November 2008 Accepted 22 December 2008 Available online 25 December 2008 Keywords: Cellulose ester Films Dewetting Atomic force microscopy Sum frequency generation Stability and interface properties of cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) films adsorbed from acetone or ethyl acetate onto Si wafers have been investigated by means of contact angle measurements and atomic force microscopy (AFM). Surface energy (γ total S ) values determined for CAP adsorbed from acetone are larger than those from ethyl acetate. In the case of CAB films adsorbed from ethyl acetate and acetone were similar. Dewetting was observed by AFM only for CAP films prepared from ethyl acetate. Positive values of effective Hamaker constant ( A eff ) were found only for CAP prepared from ethyl acetate, corroborating with dewetting phenomena observed by AFM. On the contrary, negative values of A eff were determined for CAP and CAB prepared from acetone and for CAB prepared from ethyl acetate, corroborating with experimental observations. Sum frequency generation (SFG) vibrational spectra indicated that CAP and CAB films prepared from ethyl acetate present more alkyl groups oriented perpendicularly to the polymer–air interface than those films prepared from acetone. Such preferential orientation corroborates with macroscopic contact angle measurements. Moreover, SFG spectra showed that acetone binds strongly to Si wafers, creating a new surface for CAP and CAB films.  2008 Elsevier Inc. All rights reserved. 1. Introduction Thin polymeric films are largely used in many technological applications, as for instance, as coatings, paint, and sensors. In such situations, stable, continuous and homogeneous layers are required. Polymer surface energy and interface tension between substrate and polymeric film drive the stability of thin polymeric films. If the work of cohesion is larger than the work of adhesion, thin polymer film becomes unstable, resulting in the dewetting phenomena [1,2]. However, the solvents used for film prepara- tion might also affect structure, wettability and stability of thin polymeric films. Special attention has been devoted to the effect of solvent used for spin-coating polymer films on the resulting surface properties [3–9]. Not only the evaporation rate of the sol- vent plays a very import role on the spin-coated [3–9] or cast film [10] uniformity, but also solvent quality and the balance be- tween substrate–polymer interaction and substrate–solvent inter- action [7–9,11]. Nevertheless, there are scarce studies on the ef- fect of solvent on the stability and surface properties of ultrathin (d < 5 nm) adsorbed polymer films. * Corresponding author. Fax: +55 11 3815 5579. E-mail address: dfsp@iq.usp.br (D.F.S. Petri). Cellulose esters are frequently applied as binders, additives, film formers or modifiers in automotive, wood, plastic and leather coatings applications [12]. Cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) find place in the coating in- dustry because they reduce dry time, improve flow and level- ing, control viscosity and gloss, are stable carriers for metallic pigments, improve UV stability and reduce plasticizer migration, among many other benefits [12]. Moreover, cellulose esters films also proved to be efficient supports for adsorption of proteins [13,14] and cell growth [15]. In this work, surface properties and stability of CAP and CAB ultrathin films adsorbed from acetone or ethyl acetate solutions onto Si wafers, when they are heated above their glass transition temperature, has been investigated. Acetone and ethyl acetate are good solvents for CAP and CAB [9]. Surface properties have been determined for adsorbed CAP and CAB films by means of contact angle measurements. Film stabil- ity was predicted with basis on thermodynamic parameters and compared with atomic force microscopy (AFM) analyses. Sum fre- quency generation (SFG) vibrational spectroscopy, a sensitive tool for interfacial analyses, was used to gain insight about molecu- lar orientation at polymer/substrate and solvent/substrate inter- faces. 0021-9797/$ – see front matter  2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2008.12.057