A Novel Dry Chemical Path Way for Diene and Dienophile Surface Functionalization toward Thermally Responsive Metal-Polymer Adhesion Maryline Moreno-Couranjou,* ,† Anton Manakhov, †,‡ Nicolas D. Boscher, † Jean-Jacques Pireaux, ‡ and Patrick Choquet † † Science and Analysis of Materials Department, Centre de Recherche Public-Gabriel Lippmann, 41 rue du Brill, Belvaux L-4422, Luxembourg ‡ Centre de Recherche en Physique de la Matie ̀ re et du Rayonnement (PMR), University of Namur (FUNDP), 61 rue de Bruxelles, Namur B-5000, Belgium ABSTRACT: In this paper, we report a new and easily up-scalable dry chemical method to functionalize with diene and dienophile groups a large range of surfaces, such as metal, polymer, or glass, and we demonstrate the potentiality of this technique to realize thermally responsive adhesion between these materials. A complete and extensive surface chemistry analysis of the grafted surfaces, based on the deposition of an anhydride-rich thin plasma polymer layer by using an atmospheric pressure dielectric barrier discharge (DBD) plasma process, and its subsequent gas phase aminolysis reaction with specific diene or dienophile compound is discussed. The optimization of the assembling condition for these tailored surfaces has led to achieve a Diels-Alder adhesion force up to 0.6 N/mm at ambient temperature, which can be reduced by a factor of 50 when the retro Diels-Alder is ignited at a heating temperature around 200 °C. The study of the failure interface produced after peeling tests is presented and a mechanism of failure is proposed, based on forensic analyses involving surface analytical techniques such as XPS, ToF-SIMS, and SEM combined to AFM analyses for the retrieving of chemical and morphological information. KEYWORDS: stimuli-responsive materials, functional coatings, surface modifications, plasma polymerization, thermally responsive adhesion 1. INTRODUCTION Because of environmental issues that will be more and more severe in future decades, many industrial sectors such as electronics, transport, or packaging are showing a growing interest in using smart or stimuli-responsive materials such as reversible adhesive systems offering the possibility of easily disassemble or selectively remove manufacturing pieces for maintenance, replacing, or recycling. 1-7 Considering reversible adhesion, different systems have been developed in the past, for example, by incorporating magnetic or electrically conductive micro- or nanoparticles in a shape memory polymer or by exploiting the chemical Diels-Alder (DA) reaction. This latter method seems very attractive and promising as the bonds created are strong covalent chemical linkages that break at high temperature but can reform when the temperature is lowered. Aubert et al. have already developed this kind of original thermal sensitive adhesive and successfully applied it to numerous metals and some foams and polymers. 8 However, an improvement of the method, which will consist of the direct diene and dienophile functionalization of two solid surfaces, could find a larger number of applications. Recently, two main strategies have been developed to functionalize solid surfaces of different natures. In a first step, methods relying wholly on wet chemical treatments based on self-assembled monolayer (SAM) growth, silylation, or electro- chemical reduction reactions have been explored. SAMs have been successfully utilized for the realization of dienophile 9-12 and diene 12 surface functionalization mainly on gold surfaces with the creation of thiol metal bonds. However, such specific groups containing thiol-based molecules do not tend to be commercially available and thus required their custom synthesis. Moreover, this method presents an additional disadvantage in the fact that the thiolate linkages are vulnerable to oxidation and desorption from the gold surface. 13 The silylation technique has also been studied. 14,15 Zhang et al. reported the strong DA adhesion bonding of two functionalized Si wafers annealed for 5 h at 200 °C, with bonding strength up to 1.78 MPa. The chemical grafting was based on a multistep procedure involving the hydroxylization and aminosilylation of the wafers with their subsequent reaction with 2-furaldehyde or maleic anhydride compounds. 15 Maleimide-functionalized gold surfaces were also elaborated by combining the electrochemical reduction of 4-carboxybenzene-diazonium tetrafluoroborate leading to the grafting of benzoic acid moieties and their subsequent activation with 2-ethoxycarbonyl-1,2-dihydroquino- line in order to promote the reaction with first 1,3- diaminopropane and then N-(2-carboxyethyl) maleimide. 16 The substrate-specific and the complex multistep chemistries of these first presented strategies have led to the development of alternative grafting methods based on chemical vapor deposition (CVD) techniques. For example, furan-ring surface functionalization has been achieved by initiated (iCVD) or by Received: May 16, 2013 Accepted: July 15, 2013 Published: July 15, 2013 Research Article www.acsami.org © 2013 American Chemical Society 8446 dx.doi.org/10.1021/am401851y | ACS Appl. Mater. Interfaces 2013, 5, 8446-8456