Surface and Interfacial Interactions in Dodecane/Brine Pickering Emulsions Stabilized by the Combination of Cellulose Nanocrystals and Emulsifiers

Abstract

Interfacial properties of cellulose nanocrystals (CNC) and surfactants were studied in high ionic strength (I) brines and correlated to the stability of dodecane/brine Pickering emulsions. Bis-(2-hydroxyethyl) cocoalkylamine (CAA), dodecyltrimethylammonium bromide (DTAB), and octyl-β-d-glucopyranoside (OGP) were adsorbed onto CNC in American Petroleum Institute (API) brine (I = 1.9 M) and synthetic seawater (SSW), with I = 0.65 M. Raman spectroscopy indicated that hydroxyl groups on the CNC surface interact with all three surfactants in high ionic strength media. Ionic interactions still play a role at the very large ionic strengths studied herein. Despite all surfactants adsorbing onto CNC, only the surface tension of CAA solutions in both brines was increased by the addition of 0.5 wt % CNC. The effect was much more prominent in API than in SSW. Contact angle measurements indicated that CAA increased the wettability of CNC by both brines in dodecane; DTAB, on the other hand, decreased wettability. Emulsion stability studies revealed that ionic strength, wettability, adsorption energy, and oil content strongly affect emulsion stability, more so than surfactant adsorption. In API, CNC aggregates alone stabilized the emulsions better compared to samples with additional emulsifiers; the same was true in SSW for oil contents below 50% v/v. For oil contents above 50% v/v in SSW, CAA was either detrimental or failed to improve emulsion stability. On the other hand, DTAB increased the stability of dodecane in SSW emulsions. Emulsions stable for over 21 months were prepared with oil contents of 75% v/v. The adsorption of CAA onto CNC limits the migration of both CNC and CAA to the dodecane/brine interface, while DTAB adsorption has the opposite effect.

Cellulose Nanocrystal-Stabilized Dispersions of CO2, Heptane, and Perfluorooctane at Elevated Temperatures and Pressures for Underground CO2Sequestration

“…This result was surprising since the adsorption onto the CNC surface was expected to drive DTAB away from the interface and increase its γ ow . Previous surface tension measurements in the air indicated a critical micelle concentration (CMC) of DTAB in API brine of 0.16 ± 0.03 g/L, thus at the 0.45 g/L used herein, adsorption onto CNC likely removed surfactant from micelles instead of the interface . The same concentration was used for the heptane/brine interface; however, we speculate that heptane may shift the CMC to a higher concentration due to having a polarity closer to the linear alkyl chain of DTAB, compared to the more hydrophobic PFO.…”

“…CNC and CNC + DTAB conjugates in high ionic strength brine ( I = 1.9 M) have their surface charge screened due to the collapse of the electric double layer causing them to aggregate. This results in the formation of CNC and CNC + DTAB networks contributing to increased viscosity of the aqueous phase and thereby forming stable gel-like emulsions. ,, A previous study with dodecane/brine emulsions indicated that adsorption of DTAB onto the surface of CNC aggregates increased their hydrophobicity, thus facilitating the migration of CNC onto the oil–water interface. , However, this does not appear to be enough to stabilize PFO/brine interfaces (Supporting Information, Figure S3).…”

“…37−39 Our earlier study indicates that short-range electrostatic and ion−dipole interactions between negatively charged CNC and cationic DTAB could act as a driving force for the adsorption of DTAB molecules onto the surface of CNC, even at high ionic strengths. 39 The PFO-brine interfacial tension was unaffected by the presence of CNC, while DTAB lowered it to 13.1 ± 0.1 mN/m from 50.7 ± 0.6 mN/m at 298 K, suggesting that due to their lower polarity, CNCs do not adsorb as readily onto the PFO/ brine interface. Contrary to the heptane/brine interface, the addition of CNC did not change the γ ow between PFO and the DTAB-brine solution.…”

“…Previous surface tension measurements in the air indicated a critical micelle concentration (CMC) of DTAB in API brine of 0.16 ± 0.03 g/ L, thus at the 0.45 g/L used herein, adsorption onto CNC likely removed surfactant from micelles instead of the interface. 39 The same concentration was used for the heptane/brine interface; however, we speculate that heptane may shift the CMC to a higher concentration due to having a polarity closer to the linear alkyl chain of DTAB, compared to the more hydrophobic PFO. Further studies are needed to fully comprehend this phenomenon and its effect on DTAB and CNC migration to the oil/brine interface.…”

Polymer-Decorated Cellulose Nanocrystals as Environmentally Friendly Additives for Olefin-Based Drilling Fluids

“…All the fluids showed elevated electrical stability values ( Table 2 ). Probably, the amount of modified cellulose nanocrystals was not enough to result in a substantial difference in the electrical stability [ 31 ].…”