ORIGINAL CONTRIBUTION Effect of alkali-soluble resin emulsifiers on coalescence and interdiffusion between latex polymer particles Edurne Gonzalez 1 & Christopher Tollan 2 & Andrey Chuvilin 2,3 & María Paulis 1 & María J. Barandiaran 1 Received: 13 January 2015 /Revised: 19 May 2015 /Accepted: 19 May 2015 # Springer-Verlag Berlin Heidelberg 2015 Abstract Coalescence and interdiffusion during film forma- tion of waterborne polymers stabilized by commercial high T g alkali-soluble resins (ASRs) were evaluated through environ- mental scanning electron microscopy and fluorescence reso- nance energy transfer. The observed effects were used to jus- tify the mechanical properties. The presence of a hard barrier between particles that increased the coalescence temperature and hindered interdiffusion was responsible for the poor prop- erties of the films casted at room temperatures and the en- hanced behaviour when films were annealed at much higher temperatures. Keywords Alkali-soluble resin . Latex . Coalescence . Interdiffusion . ESEM . FRET Introduction Macromolecular surfactants are widely employed in emulsion polymerization with the objective of improving colloidal properties [1, 2]. Alkali-soluble resins (ASRs) are a special type of polymeric surfactants that can be classified as hydrophobically modified anionic polyelectrolytes [3]. They are random copolymers of hydrophobic monomers (e.g. sty- rene (S), methyl methacrylate (MMA), butyl methacrylate (BMA)) and monomers containing carboxylic acid groups (e.g. acrylic (AA) and methacrylic acid (MAA)). When neu- tralized, the ASRs become water soluble and act as electrosteric stabilizers (if the pH is higher than the pKa of the carboxylic acid group). Incorporation of ASRs to emulsion polymers provides many advantages such as Newtonian-like flow, low foam production, improved adhesion and wetting properties, excellent mechanical and freeze-thaw stability and good pigment dispersion [4, 5]. Although several authors have studied the effect of ASR surfactants on emulsion polymerization kinetics and latex characteristics [4–14], not many works have been found reporting their influence on film formation and final film prop- erties [15–22]. For a given polymer composition, film forma- tion depends on experimental conditions (such as annealing temperature) as well as on latex characteristics, including col- loidal and microstructural properties and the nature of the surfactant. When performing the polymerization by using dif- ferent ASRs as surfactants, the obtained latexes may have different particle diameters and polymer molecular weights, which in turn could also affect the final film properties. Thus, in order to analyse only the effect of the ASRs on film forma- tion, the additional contribution of the latex characteristics must be excluded. One plausible approach is to prepare the latexes by adsorbing the ASRs on surfactant-free latexes. In this context, Kim and co-workers followed latex film forma- tion by atomic force microscopy (AFM) of an emulsifier-free monodisperse poly(n-butyl methacrylate) (PBMA) latex after the post-addition of commercial ASRs with very different characteristics, namely, poly(styrene/α-methylstyrene/acrylic Electronic supplementary material The online version of this article (doi:10.1007/s00396-015-3635-3) contains supplementary material, which is available to authorized users. * María J. Barandiaran mariaje.barandiaran@ehu.es 1 POLYMAT, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Avda. Tolosa 72, 20018 Donostia-San Sebastián, Spain 2 CIC nanoGUNE Consolider, Av. de Tolosa 76, 20018 Donostia-San Sebastián, Spain 3 IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao, Spain Colloid Polym Sci DOI 10.1007/s00396-015-3635-3