Metal Ion Induced Adsorption and Ordering of Charged Macromolecules at the Aqueous/Hydrophobic Liquid Interface

Abstract

Whether a charged macromolecule remains solvated or adsorbs to the interface between two immiscible fluids depends on a variety of complex factors. Ions, in particular, have the capacity to affect the degree of polyelectrolyte hydrophobicity and conformation through electrostatic screening and site-specific interactions. Here, surface-specific vibrational spectroscopy is utilized to probe the roles of ions in the oil− water interfacial behavior of a model carboxylic acid-containing macromolecule. Specifically, the adsorption time dependence, conformation, and extent of carboxylate−cation interactions of poly(methacrylic acid) at the carbon tetrachloride−water interface are deduced as a function of CaCl 2 and KCl ionic strength. Additionally, the role of the polymer backbone configuration in interfacial behavior is explored through isomer-specific studies. Results show that ion binding and charge screening induce the adsorption of the isotactic isomer of poly(methacrylic acid) to the oil− water interface under solution conditions unfavorable to surface adsorptivity and that the degree of cation−carboxylate interactions strongly affects the adsorption dynamics and interfacial structure of the adsorbed polymer. The backbone structure of syndiotactic poly(methacrylic acid) does not allow for strong interactions with cations, and therefore, it remains water-solvated in the presence of salt. This work has significance for understanding the role of metal ions in the assembly of natural charged macromolecules at biological and environmental interfaces.

Disentangling Memristive and Memcapacitive Effects in Droplet Interface Bilayers Using Dynamic Impedance Spectroscopy

“…Indeed, ion-pairing and related interfacial interactions are essential to the assembly of soft-matter systems. [38][39][40] For example, vibrational sum frequency spectroscopy measurements have shown that hydrogen bonding [38] and ion pairing/electrostatics [39,40] drive the structure of self-assembled oligomers at oil/aqueous interfaces. However, given the complexity of the system, we cannot specify how lipid structure (e.g., packing, density, etc.)…”

Pilot Performance of Chemical Demulsifier on the Demulsification of Produced Water from Polymer/Surfactant Flooding in the Xinjiang Oilfield

“…It has been reported that the adsorption of HPAM on the oil-water interface increases the steric barriers of dispersed oil droplets, which leads to the enhanced stability of oil/water emulsion [16,[26][27][28]. Polymers (such as polystyrene sulfonate sodium, PSS) have the ability to form complexes with the oppositely charged molecules (such as hexadecanetrimethyl-ammonium bromide, CTAB) by electrostatic attraction or hydrophobic interaction [29,30].…”

Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

“…90 The effect of metal ions on the adsorption behavior of PMA at water/CCl 4 interface was also reported. 91 The electrostatic interaction between cation and carboxylate groups in polymer affected the polymer adsorption dynamics. For isotactic PMA, the presence of cations can induce the adsorption of the PMA to the interface due to ion binding and charge screening.…”

“…This kept the polymer soluble in water and prevented the adsorption of the polymer at the interface. 91 A review paper published in 2014 summarized the SFG-VS studies of the adsorption of PAA and PMA at water/oil interface. 92…”

“…This kept the polymer soluble in water and prevented the adsorption of the polymer at the interface. 91 A review paper published in 2014 summarized the SFG-VS studies of the adsorption of PAA and PMA at water/oil interface. 92 The surface wetting on the polyelectrolyte multilayers, which were obtained by the layer-by-layer alternating deposition of poly(diallyldimethylammonium chloride) (PDDA) and poly(styrene sulfonate) (PSS), was investigated by Liu et al 93 It was found that the PDDA-capped surfaces did not affect the surface hydrophilicity, while the PSScapped surfaces can be translated to either water wetting in hydrophobic environment or water de-wetting in hydrophilic environment, depending on the surface orientation of the benzenesulfonate groups.…”