Abstract
The diffusion kinetics of a molecular probe—rhodamine B—in ternary aqueous solutions containing poly(vinyl alcohol), glycerol, and surfactants was investigated using fluorescence correlation spectroscopy and dynamic light scattering. We show that the diffusion characteristics of rhodamine B in such complex systems is determined by a synergistic effect of molecular crowding and intermolecular interactions between chemical species. The presence of glycerol has no noticeable impact on rhodamine B diffusion at low concentration, but significantly slows down the diffusion of rhodamine B above 3.9% (w/v) due to a dominating steric inhibition effect. Furthermore, introducing surfactants (cationic/nonionic/anionic) to the system results in a decreased diffusion coefficient of the molecular probe. In solutions containing nonionic surfactant, this can be explained by an increased crowding effect. For ternary poly(vinyl alcohol) solutions containing cationic or anionic surfactant, surfactant—polymer and surfactant—rhodamine B interactions alongside the crowding effect of the molecules slow down the overall diffusivity of rhodamine B. The results advance our insight of molecular migration in a broad range of industrial complex formulations that incorporate multiple compounds, and highlight the importance of selecting the appropriate additives and surfactants in formulated products.
Highlights
Poly(vinyl alcohol) (PVA) is widely used in consumer products due to its high degree of water solubility, Received June 12, 2021; accepted September 18, 2021Building upon a well-established theoretical framework [9,10], diffusion is commonly considered as the meansquare displacement of the moving entity, which changes proportionally with its diffusion time [11]
Molecular diffusion in a polymer solution can be measured by a range of techniques, including fluorescence methods such as fluorescence correlation spectroscopy (FCS) [37], dynamic light scattering (DLS) [38,39], pulsedfield gradient spin-echo nuclear magnetic resonance [40], and centrifugation [41,42]
We investigated the effects of crowding and intermolecular interactions on the molecular diffusion in ternary mixtures that replicate PVA based chemical products dissolved in water
Summary
Poly(vinyl alcohol) (PVA) is widely used in consumer products due to its high degree of water solubility, Received June 12, 2021; accepted September 18, 2021. Molecular diffusion in polymer solutions that contain multiple components [12,13] should be considered by more specific models, such as obstruction effect models [14,15], free volume theory-based models [16,17], and hydrodynamic models [18,19] Despite the advancements, these mechanisms do not adequately describe diffusion in complex mixtures of polymers and surfactants [20,21], proving the need for further investigations. Molecular diffusion in a polymer solution can be measured by a range of techniques, including fluorescence methods such as fluorescence correlation spectroscopy (FCS) [37], dynamic light scattering (DLS) [38,39], pulsedfield gradient spin-echo nuclear magnetic resonance [40], and centrifugation (sedimentation) [41,42]. The specific interactions between each component could be characterized, revealing three primary effects: the behavior of the polymer itself, the overall molecular crowding in the system, and specific (charged) interactions between individual species, which could enable a prediction of molecular behavior in complex systems
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