A new method for the quantification of adsorbed styrene acrylate copolymer particles on cementitious surfaces: a critica
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A new method for the quantification of adsorbed styrene acrylate copolymer particles on cementitious surfaces: a critical comparative study Ulrike Schirmer1 · Andrea Osburg1 Received: 7 April 2020 / Accepted: 3 November 2020 © The Author(s) 2020 OPEN
Abstract The amount of adsorbed styrene acrylate copolymer (SA) particles on cementitious surfaces at the early stage of hydration was quantitatively determined using three different methodological approaches: the depletion method, the visible spectrophotometry (VIS) and the thermo-gravimetry coupled with mass spectrometry (TG–MS). Considering the advantages and disadvantages of each method, including the respectively required sample preparation, the results for four polymer-modified cement pastes, varying in polymer content and cement fineness, were evaluated. To some extent, significant discrepancies in the adsorption degrees were observed. There is a tendency that significantly lower amounts of adsorbed polymers were identified using TG-MS compared to values determined with the depletion method. Spectrophotometrically generated values were lying in between these extremes. This tendency was found for three of the four cement pastes examined and is originated in sample preparation and methodical limitations. The main influencing factor is the falsification of the polymer concentration in the liquid phase during centrifugation. Interactions in the interface between sediment and supernatant are the cause. The newly developed method, using TG–MS for the quantification of SA particles, proved to be suitable for dealing with these revealed issues. Here, instead of the fluid phase, the sediment is examined with regard to the polymer content, on which the influence of centrifugation is considerably lower. Keywords Polymer adsorption · Cement · Visible spectrophotometry · Depletion method · Mass spectrometry
1 Introduction Beside the cement hydration, the polymer particle adsorption is the main driving process in microstructure formation of polymer-modified mortars and concretes. The adsorption of polymer particles is to be understood as the result of attractive intermolecular and interparticlular interactions taking place within the suspension between organic, inorganic components and the constitution of cement paste pore solution at early stages of the cement hydration. The physicochemical processes leading to the destabilization of colloidal polymer particles and the effect
of these interactions on macroscopic properties were subject of numerous studies in the last 25 years (e.g. [1–13].). There are numerous methods for quantifying macromolecules on inorganic surfaces. For example the adsorption of macromolecules on mesoporous materials can be studied by using the isothermal titration calorimetry [14] and the differential scanning calorimetry [15]. To characterize the adsorption behavior of particulate polymers on cementitious surfaces, beside qualitative observation methods like zeta potential measurements [7, 9], confocal laser scanning microscopy [10] or cryo-S
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