Surface force measurements at the basal planes of ordered kaolinite particles

Chemical Force Microscopy Study on the Interactions of COOH Functional Groups with Kaolinite Surfaces: Implications for Enhanced Oil Recovery

“…The trend observed can be explained by looking into the protonation of -COOH groups-at pH 5-6, a large number of groups in the tip will be protonated, and therefore be able to bond to the kaolinite surface by the aforementioned hydrogen bonding mechanism; on the contrary, at pH ≥ 7, most carboxylate groups will be deprotonated and will not form strong bonds in the absence of bridging cations such as Ca 2+ . Neither the variation in the relative amount of H + to Na + -surface bound ions nor the previously reported decrease in surface potential [11] above pH 8 show any effect in modifying the adhesion. The contrast between this result and that observed from the Ca 2 experiments once again reinforces the critical role of Ca 2+ in controlling -COOH adhesion.…”

“…The presence of Ca 2+ , however, complicates this picture as there will be competition with protons for surface sites, which may lead to the At the experimental conditions (constant pH), the protonation state of the -COOH will remain unchanged and, therefore, should be critical in determining the adhesion to the kaolinite surface. In addition, as has been established by numerous authors, the overall charge of the kaolinite siloxane surface is negative, although some authors have found it to vary, to some extent, as a function of pH [10,11], and to also be affected by the ionic strength of the electrolyte on which its immersed, although always maintaining its negative value [13].…”

“…In order to study the adhesion over a particular kaolinite face, it was imperative to prepare films of oriented kaolinite crystals (KGa-1b from the Clay Minerals Society Source Clay Repository) To this end, a modified version of method originally developed by Gupta and Miller [11] was used. This method is based on the fact that the negatively charged surface of siloxane is attracted to a positively charged surface (for example, sapphire), whereas the positively charged alumina face is attracted to a negatively charged surface (like muscovite mica).…”

“…An additional mechanism that could contribute to the large increase in adhesion may be related to a decrease in the electric double layer repulsive forces. Recently, Gupta et al [11] measured the change in surface charge and potential of siloxane and alumina surfaces and reported a decrease in both quantities when solution pH increased from 8 to 9. Although their experiments were conducted with a KCl electrolyte, it is feasible to assume a similar reduction on our experiments with Ca 2+ , and even expect a larger decrease in surface potential due to the larger affinity of Ca 2+ for the siloxane surface.…”

“…This behaviour is the same as that observed for the experiments performed on the siloxane face at the same pH ( Figure 3 and Figure S1) and can be explained by looking into the protonation state of the -COOH groups and the surface charge of the kaolinite surface. At a pH ≈ 5.5, the overall surface charge of the alumina surface will be positive [11], whereas the tip, having a pKa ≈ 5.5 [34], will be composed of approximately the same amount of protonated -COOH groups and deprotonated -COO-groups (i.e., it will have an overall negative charge). At low CaCl2, only a relatively amount of Cl − counter ions will be present at the surface and, therefore, electrostatic attraction between tip and surface will occur.…”