Design of Surfactant Tails for Effective Surface Tension Reduction and Micellization in Water and/or Supercritical CO₂

Abstract

Interfacial properties and water-in-CO2 (W/CO2) microemulsion (μE) formation with double and novel triple tail surfactants bearing trimethylsilyl (TMS) groups in the tails are investigated.Comparisons of these properties are made with those for analogous hydrocarbon (HC) and fluorocarbon (FC) tail surfactants. Surface tension measurements allowed for critical micelle concentrations (CMC) and surface tensions at the CMC (γCMC) to be determined, resulting in the following trend in surface activity FC > TMS > HC. Addition of a third surfactant tail gave rise to increased surface activity, and very low γCMC values were recorded for the double/ triple tail TMS and HC surfactants. Comparing effective tail group densities (layer) of the respective surfactants allowed for understanding of how γCMC is affected by both the number of surfactant tails and the chemistry of the tails. These results highlight the important role of tail group chemical structure on ρlayer for double tail surfactants. For triple tail surfactants, however, the degree to which ρlayer is affected by tail group architecture is harder to discern, due to the formation of highly dense layers.Stable W/CO2 μEs were formed by both the double and triple tail TMS surfactants. High pressure small-angle neutron scattering (HP-SANS) has been used to characterize the nanostructures of W/CO2 μEs formed by the double and triple tail surfactants, and at constant pressure and temperature, the aqueous cores of the microemulsions were found to swell with increasing water-to-surfactant ratio (W0). A maximum W0 value of 25 was recorded for the triple tail TMS surfactant, which is very rare for non-fluorinated surfactants. These data therefore highlight important parameters required to design fluorine-free environmentally responsible surfactants for stabilizing W/CO2 μEs formation.

Using Microemulsions: Formulation Based on Knowledge of Their Mesostructure

“…SANS experiments allowed to link this directly to the effective packing parameter of the system and the concomitant change of the hydrophilic/CO 2 -philic balance. 411 Still more recently doubleand triple-tailed surfactants containing trimethylsily (TMS) groups in their tail were shown to also be able to form microemulsions with water and CO 2 , 412 which is interesting as it allows to formulate fluorine-free microemulsions, which is relevant from an environmental point of view.…”

Effects of Shale Pore Size and Connectivity on scCO2 Enhanced Oil Recovery: A Molecular Dynamics Simulation Investigation

“…The consequences show that the interaction energy between CO 2 and the wall increases significantly with the injection of CO 2 and is far greater than that between the oil and the wall. This is mainly caused by the properties of rock surface and CO 2 , which supercritical CO 2 becomes more polar while CO 2 is usually non-polar . This mechanism contributes to enhancing the electrostatic interaction between CO 2 and the wall, causing more CO 2 to desorb oil .…”

“…This is mainly caused by the properties of rock surface and CO 2 , which supercritical CO 2 becomes more polar while CO 2 is usually non-polar. 42 This mechanism contributes to enhancing the electrostatic interaction between CO 2 and the wall, causing more CO 2 to desorb oil. 43 As shown in Figure 5a, due to the presence of notches in the connected pore, the interaction energy of oil and wall in the 3 nm pore at the initial moment is less than that of the small pores in the double pore and the single pore systems.…”

Controlling water adhesion on superhydrophobic surfaces with bi-functional polymers

“…In earlier studies, surfactants having TMS-terminated tails were found to generate very low surface energies (surface tensions), and comparable to short fluorocarbons in water (the limiting aqueous surface tension is 22.8 mN/m for the double TMS-chain terminated surfactant AOTSiC) [39]. As an example application of low surface energy surfactants, superspreading of aqueous solution on polyvinylidene difluoride (PVDF) surface was demonstrated by using the TMS surfactant [40,41]. Therefore, combining these two functions together, polymer films prepared with TMS-bearing ProDOTSiMe3 and ProDOT(SiMe3)2 thiophene monomers are expected to exhibit superhydrophobicity as well as oleophobicity as found uniquely with fluoro-polymers [41 42].…”