Articolo in rivista, 2023, ENG, 10.1016/j.jcis.2023.01.012

Physicochemical characterization of green sodium oleate-based formulations. Part 3. Molecular and collective dynamics in rodlike and wormlike micelles by proton nuclear magnetic resonance relaxation

Lucia Calucci, Silvia Borsacchi, Federica Balzano, Rachele Volpi, Duccio Tatini, Gloria Uccello Barretta, Pierandrea Lo Nostro, Marco Geppi

a Istituto di Chimica dei Composti OrganoMetallici (ICCOM), Consiglio Nazionale delle Ricerche - CNR, via G. Moruzzi 1, 56124 Pisa, Italy b Centro per l'Integrazione della Strumentazione Scientifica dell'Università di Pisa - CISUP, Lungarno Pacinotti 43/44, 56126 Pisa, Italy c Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi 13, 56124 Pisa, Italy d Dipartimento di Chimica ''Ugo Schiff", Università di Firenze, 50019 Sesto Fiorentino, Italy e Consorzio per lo Sviluppo dei Sistemi a Grande Interfase - CSGI, Università di Firenze, 50019 Sesto Fiorentino, Italy

Hypothesis Sodium oleate (NaOL) self-aggregates in water forming rodlike micelles with different length depending on NaOL concentration; when KCl is added wormlike micelles form, which entangle giving rise to a viscoelastic dispersion. It is expected that aggregates with different size and shape exhibit different internal and overall molecular motions and collective dynamics. Experiments Two low viscosity NaOL/water and two viscoelastic NaOL/KCl/water formulations with different NaOL concentration (0.23 and 0.43 M) were investigated by 1H fast field cycling NMR relaxometry over broad temperature and Larmor frequency ranges, after a first screening by 1H and 13C NMR spectroscopy at high frequency. Findings The analysis of the collected data indicated that fast conformational isomerization and rotation of NaOL about its long molecular axis and lateral diffusion of NaOL around the axis of the cylindrical aggregates are slightly affected by the aggregate shape and length. On the other hand, fluctuations of the local order director are quite different in the fluid and viscoelastic systems, reflecting the shape and size of the aggregates. Quantitative information was obtained on activation energy for fast internal and overall motions, correlation times and activation energy for lateral diffusion, and coherence length for collective order fluctuations.

Journal of colloid and interface science (Online) 636 , pp. 279–290

Keywords

13C NMR spectroscopy; 1H FC NMR relaxometry; 1H NMR spectroscopy; Green formulation(s); Lateral diffusion; Order director fluctuations; Reorientational motions; Sodium oleate; Viscoelasticity; Wormlike micelles

CNR authors

Geppi Marco, Calucci Lucia, Borsacchi Silvia

CNR institutes

ICCOM – Istituto di chimica dei composti organo metallici