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Aschauer U.,Laboratoire Of Technology Des Poudres Ltp | Aschauer U.,Princeton University | Spagnoli D.,University of Bath | Spagnoli D.,Curtin University Australia | And 2 more authors.
Journal of Colloid and Interface Science | Year: 2010

Molecular dynamics simulations were used to investigate possible explanations for experimentally observed differences in the growth modification of calcite particles by two organic additives, polyacrylic acid (PAA) and polyaspartic acid (p-ASP). The more rigid backbone of p-ASP was found to inhibit the formation of stable complexes with counter-ions in solution, resulting in a higher availability of p-ASP compared to PAA for surface adsorption. Furthermore the presence of nitrogen on the p-ASP backbone yields favorable electrostatic interactions with the surface, resulting in negative adsorption energies, in an upright (brush conformation). This leads to a more rapid binding and longer residence times at calcite surfaces compared to PAA, which adsorbed in a flat (pancake) configuration with positive adsorption energies. The PAA adsorption occurring despite this positive energy difference can be attributed to the disruption of the ordered water layer seen in the simulations and hence a significant entropic contribution to the adsorption free energy. These findings help explain the stronger inhibiting effect on calcite growth observed by p-ASP compared to PAA and can be used as guidelines in the design of additives leading to even more marked growth modifying effects. © 2010 Elsevier Inc.


Aschauer U.,Laboratoire Of Technology Des Poudres Ltp | Aschauer U.,Princeton University | Ebert J.,Laboratoire Of Technology Des Poudres Ltp | Aimable A.,Laboratoire Of Technology Des Poudres Ltp | Bowen P.,Laboratoire Of Technology Des Poudres Ltp
Crystal Growth and Design | Year: 2010

Polycarboxylate molecules and oligomers have been investigated as growth modifiers during seeded calcite precipitation. To better understand possible molecular interactions and kinetic effects, additives with different structures and molecular weights have been investigated in this work. All additives show growth modifying effects, albeit less strongly for succinic acid and glutaric acid. This is attributed to a relatively weak interaction with the precipitated particles as well an additive size too small to influence the aggregation phase of the growth mechanism. Poly(acrylic acid) and poly(aspartic acid), on the other hand, led to strong growth modification, with the resulting particles being nanostructured, formed by an assembly of nanosized primary particles and consequently having a high specific surface area. Poly(aspartic acid) showed a stronger growth modifying effect than poly(acrylic acid) at a similar molecular weight and functional group concentration. This was not readily explainable without using molecular dynamics simulations (reported in a separate article), which suggests that the differences originate from the rigidity of the backbone and favorable electrostatic interactions between backbone nitrogen atoms and the surface in the case of poly(aspartic acid). © 2010 American Chemical Society.

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