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Silica Vs Calcite – A DLVO story Saravana Kumar, Dirk van den Ende, Igor Siretanu, Frieder Mugele
Physics of Complex Fluids, University of Twente
IntroductionMineral interfaces are important in many areas such as geology, mineral synthesis, carbon capture, oil-recovery, nuclear waste storage etc… Understanding the physics that takes place at the mineral-liquid interface is of great importance in these fields.
Here, we study calcite and silica interfaces using an atomic force microscopy to compare and contrast between the two and to answer some of the recent theories out there in the field of interfacial science.
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Outlook The silica interface behaves as expected(DLVO theory). Even at high concentrations of 4M, we do not see any unusual decay length
for both calcite and silica. The calcite on the other hand, does not show any discernable DLVO interaction even at 1mM NaCl. We ruled out the effect of
roughness by measuring interactions locally The calcium ions which are released from the surface might have screened the charge effectively and hence we see no interaction.
This needs to tested
DLVO
The silica exhibits DLVO behavior over all concentrations and temperature ranges
The magnitude of force changes with temperature indicating surface charge density(increased deprotonation) changes with change temperature
We did not see any long range decay lengths at high salt concentrations and is true for all temperatures probed, indicating no relation between decay length and permittivity of the intervening medium[1]
???? In order to rule out the effect of roughness on the probed force[2], we did force maps using blunted sharp probes
Topography shows calcite with atomic steps
Again, no discernable interactions observed for local averaged and total averaged spots except for the noise
R = 10 nmk = 0.58 N/m
Colloidal probe
Substrate
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References1. Smith, A. et al, J Phys Chem Letters 7.12 (2016): 2157-2163.2. Ozcelik, H. G. et al, Phys Chem Chem Phys 21.14 (2019): 7576-7587.
How Silica behaves
The plot shows the interaction force between two silica surfaces across NaCl of varying concentration
As can be clearly seen the interaction length goes down as the concentration increases
Silica obeys the DLVO theory and we observe no long range force at high concentrations
How Calcite behaves
The plot shows interaction force between silica and calcite across NaCl at pH ~ 8.5
The pH is elevated to minimize calcite dissolution. The calcite shows no discernable decay length even in low concentrations
Calcite does not seem to be obeying the DLVO theory and we also don’t observe any longer decay lengths at high concentration
R = 750 nm k = 3.0 N/m
