Re-Evaluating the Surface Tension Analysis of Polyelectrolyte-Surfactant Mixtures Using Phase-Sensitive Sum Frequency Generation Spectroscopy

Abstract

Surface tension (ST) has been the most important measure of a molecule's surface activity. However, in many cases the complex behaviors of ST are challenging to interpret. For example, aqueous solutions of sodium docecyl sulfate (SDS) and poly(diallyldimethylammonium chloride) (PDADMAC) show dramatic changes in ST when the concentration of SDS varies. Although surfactants are generally described as "substances that reduce surface tension", new evidence shows that ST may have little changes when a significant amount of SDS is present at the water surface. The decrease of surface entropy resulting from a better ordering of interfacial molecules, such as water, counteracts the decrease of surface enthalpy and is able to keep the ST nearly unchanged. The dramatic ST decrease and recovery of the SDS-PDADMAC mixtures was discovered to be a result of a surface charge reversal. Similar surface charge reversal was also observed in cationic surfactant and anionic polyelectrolyte mixtures.

Design rules for encapsulating proteins into complex coacervates

“…1 In contrast, we examine the use of polymer-based complex coacervation as a gentle and fully aqueous strategy for achieving high levels of protein encapsulation. Complex coacervation is an associative, liquid-liquid phase separation phenomenon driven by an initial electrostatic attraction between oppositely charged macroions [2][3][4][5][6][7][8][9][10][11][12][13] such as polymers, [14][15][16][17][18][19][20] surfactant micelles, [21][22][23][24][25][26][27][28] and colloids, 29 followed by entropic gains associated with the release of small, bound counter-ions and the restructuring of water. [2][3][4][5] The utility of complex coacervation as an encapsulation strategy has been highlighted, particularly in the areas of food science, 30,31 personal care products, 32,33 and medicine, 34 because of the ability to generate formulations and drive encapsulation without the need of organic solvents.…”

Complex coacervate‐based materials for biomedicine

“…Building on this foundational research, coacervates have found utility as encapsulants, additives, emulsifiers, and viscosity modifiers in food science and personal care products . The scope of coacervation has expanded from proteins and polysaccharides to include polynucleotides, synthetic polymers, surfactants, nanoparticles, and other hierarchical assemblies . Furthermore, the utility of coacervates has extended into fields such as adhesives, drug delivery, nano/bioreactors, and cellular biology …”

Structure of Polystyrenesulfonate/Surfactant Mixtures at Air–Water Interfaces and Their Role as Building Blocks for Macroscopic Foam

“…Vibrational sum-frequency generation (SFG) spectroscopy has been previously applied to study interfaces of polymers, 34 surfactant, 35 and proteins, 36 however, only a few studies exist that address polyelectrolyte/surfactant mixtures 37,38 and none of these show specific bands of each component in different spectral regions. By addressing both solvent and adsorbate specific bands, we gain detailed information on the molecular composition, charging state, and structure of the interfacial layer.…”