Colloids and Surfaces A: Physicochem. Eng. Aspects 330 (2008) 227–233 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Study on the interaction between anionic and cationic latex particles and Portland cement J. Plank ∗ , M. Gretz Institute for Inorganic Chemistry, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany article info Article history: Received 3 April 2008 Received in revised form 1 August 2008 Accepted 3 August 2008 Available online 15 August 2008 Keywords: Latex adsorption Cement Streaming potential Zeta potential abstract The interaction between organic latex polymers and the surface of hydrating cement was investigated by measuring the zeta potential and adsorbed amount of polymer on cement. First, differently charged model latex particles were synthesized in aqueous media by well-known emulsion polymerization technique. The latex polymers were characterized by differential scanning calorimetry (DSC), dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM). Electrokinetic latex surface properties were investigated by means of streaming potential measurements using a particle charge detector (PCD). It is shown that the anionic latexes adsorb a considerable amount of Ca 2+ from the cement pore solution. Next, adsorption of the latex polymers on the surface of hydrating cement was confirmed by zeta potential measurements using the electroacoustic method. A water to cement ratio in the cement paste as low as 0.5 was studied, representing actual conditions in mortar and concrete. Additionally, adsorption isotherms were determined in a sedimentation test using the depletion method. For all latex polymers, Langmuir type adsorption isotherms were found. The latex dosages required to achieve saturated adsorption on the cement surface obtained from zeta potential measurements correspond well with those determined in the sedimentation test. Electron microscopy photographs confirm that the charged latex polymers adsorb selectively on surface areas of hydrating cement showing opposite charge. This way, domains of organic latex polymers exist on the cement surface. They provide adhesion between the inorganic cement matrix and the organic polymer film formed later on by particle coalescence as a result of cement hydration and drying. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The modification of ordinary Portland cement (OPC) based systems with latex dispersions is well known in construction appli- cations. It allows to improve important properties of fresh and hardened mortars and concretes such as cohesion, adhesion, and flexural strength [1,2]. Studies on the interaction of polymers and in particular latexes with cement represent a field of intense research since many years [3–5]. Many articles can be found in the literature dealing with the material properties of cementitious systems containing a latex polymer [6–10]. Nonetheless, little information is available on the mode of the interaction between the colloidal latex particles and the surface of the inorganic binder, especially before polymer films are formed. This might be ascribed to the complexity of the sys- tem since both cement and latex are heterogeneous components. Latex is mainly composed of the continuous phase, of polymer ∗ Corresponding author. Tel.: +49 89 289 13151; fax: +49 89 289 13152. E-mail address: sekretariat@bauchemie.ch.tum.de (J. Plank). particles and additives such as emulsifiers (surfactants). Ordinary Portland cement represents a reactive multi phase system consist- ing of calcium silicate, calcium aluminate and calcium aluminate ferrite phases, lime and gypsum. The interaction of latex particles with cement is of great impor- tance regarding its influence on the cement hydration, particularly in the early stage (0–2 h), on distribution of the latex particles in the cement paste, and on the resulting properties of the hardened cementitious matrix. Several models describing the dispersion and the behaviour of latexes in the cement paste have been proposed [11]. Recently, van Damme et al. confirmed the adsorption of a methyl methacrylate/butyl acrylate based latex copolymer on pure tricalcium silicate, portlandite and gypsum. After sedimentation of the mineral particles, they determined the depletion of the latex concentration in the pore solution resulting from adsorption [12]. A disadvantage of this study is that it used a water to solids ratio of 3 which is considerably higher than conventional building materi- als where the water to cement (w/c) ratio typically is <1, and more often about 0.5. The electrokinetic properties of colloidal suspen- sions such as cement pastes, though, are much affected by the water to solids ratio. 0927-7757/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2008.08.005