Adsorption of poly acrylic acid onto the surface of calcite: an experimental and simulation study

Abstract

Macromolecular binding to minerals is of great importance in the formation of biofilms, and carboxylate functional groups have been found to play a pivotal role in the functioning of these macromolecules. Here we present both fluorescence time-resolved anisotropy measurements and simulation data on the conformational behaviour and binding of a poly acrylic acid polymer. In solution the polymer exhibits a pH dependent behaviour, with a coiled conformation at a low pH and extended conformation at higher pH values. The polymer is readily adsorbed on the surface of calcite, preferring to bind in an extended conformation, with the strength of the adsorption dependent on the pH and presence of counter ions. We discuss the reasons why the calculated adsorption free energy differs from that obtained from a Langmuir isotherm analysis, showing that they refer to different quantities. The enhanced binding of the extended conformations shows the importance of flexibility in the binding of macromolecules.

Molecular Dynamics Simulation to Understand the Ability of Anionic Polymers to Alter the Morphology of Calcite

“…This is in accordance with the experimental observation of PAA and PMAA frustrating the normal growth of calcite to form staircase-like crystal morphologies [11]. (We note here that the similar studies reported a diverse range of binding energies for several carboxylic acid-containing adsorbates probably because of the various stages of energy minima found in the particular studies [13,15,16]; e.g., simple tartrate showed preferred adsorption on (1-10) (−9.1 kcal/mol) over (104) (−1.6 kcal/mol), and nonanoic acid with one carboxylic acid showed interaction energy of −40 kcal/mol with (110) [13,16].) In contrast, PEI showed weak preferential binding on (104) (ca.…”

“…While this model appeared qualitatively reasonable to explain the varying degree of the macromolecular interactions, it could be too simplistic not considering the dynamic nature of mineral surfaces in the presence of water molecules. On the other hand, approaches using molecular dynamics have been successfully utilized to explain the interactions of various organic molecules on the calcite surfaces [12][13][14][15][16]. Similarly, the present molecular dynamics study could generate a more realistic model to clarify the mechanism of the cooperative effects.…”

Pilot plant experiments and modeling of CaCO3 growth inhibition by the use of antiscalant polymers in recirculating cooling circuits

“…5 (bottom). These two observations, already observed previously [1,38], reinforce the choice of an adsorption model as adsorption is favored at low temperature, and Fig. 5 (top) is similar to a type I adsorption isotherm.…”

“…7) suggest the dependency of the pH on the polymer efficiency. For instance, Wisniewska et al [42] have reported the effects of solution pH on the adsorption isotherms of polyacrylic acid (PAA) on mixed silica alumina, caused by the modification of surface charge density; Sparks et al [38] have reported the effect of pH on the energies of adsorption of PAA on calcite. Hence, the adsorption model could include such dependencies, in addition to temperature and polymer concentration.…”

The Effect of Additives on the Early Stages of Growth of Calcite Single Crystals

“…However, rough estimates can be made based on simulations of the binding of methanoic acid and poly(acrylic acid) (PAA) to calcite, where the free energy of binding for Ca 2+ and methanoic acid to a {104} face was estimated to be −7 kJ mol −1   25a and −1.58 kJ mol −1 ,25b respectively. The fact that polymeric additives adsorb and modify crystal habits much more strongly than the corresponding monomers was considered using simulations that showed that about 15 % of the functional groups of PAA were bound to calcite at any given time 26. Hence, 58 of the 385 sulfonate groups in each of the PSS chains used here would be expected to bind.…”