TY - JOUR
T1 - A systematic study of equilibrium structure, thermodynamics, and rheology of aqueous CTAB/NaNO3 wormlike micelles
AU - Helgeson, Matthew E.
AU - Hodgdon, Travis K.
AU - Kaler, Eric W.
AU - Wagner, Norman J.
PY - 2010/9
Y1 - 2010/9
N2 - We present a systematic study of the self-assembly of wormlike micelles (WLMs) comprised of cetyltrimethylammonium bromide (CTAB) and sodium nitrate (NaNO3) in aqueous solution as a function of CTAB concentration, NaNO3 concentration, and temperature throughout the dilute and semi-dilute regions of the phase diagram where linear micelles are observed. Combining measurements using isothermal titration calorimetry, rheometry, flow-birefringence, cryo-transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS) enables complete characterization of the structure, thermodynamics, and rheology of CTAB/NaNO3 micelles. The addition of NaNO3 is found to increase the micellization enthalpy as well as the micellar scission energy, resulting in the elongation and growth of WLMs. We find quantitative agreement between the scission energy determined from rheology and the enthalpy of micellization determined from ITC, as well as for contour lengths extracted from rheology and SANS. At fixed molar ratio of NaNO3 and CTAB, the solution rheology exhibits scaling consistent with dilute, semi-dilute overlapping, and semi-dilute entangled regimes typically found in polymer solutions, as confirmed by cryo-TEM and SANS. The transition between these scaling regimes coincides with the structural transitions identified by SANS. The results validate the relationship between structural parameters and rheological behavior underlying theories for ionic WLMs.
AB - We present a systematic study of the self-assembly of wormlike micelles (WLMs) comprised of cetyltrimethylammonium bromide (CTAB) and sodium nitrate (NaNO3) in aqueous solution as a function of CTAB concentration, NaNO3 concentration, and temperature throughout the dilute and semi-dilute regions of the phase diagram where linear micelles are observed. Combining measurements using isothermal titration calorimetry, rheometry, flow-birefringence, cryo-transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS) enables complete characterization of the structure, thermodynamics, and rheology of CTAB/NaNO3 micelles. The addition of NaNO3 is found to increase the micellization enthalpy as well as the micellar scission energy, resulting in the elongation and growth of WLMs. We find quantitative agreement between the scission energy determined from rheology and the enthalpy of micellization determined from ITC, as well as for contour lengths extracted from rheology and SANS. At fixed molar ratio of NaNO3 and CTAB, the solution rheology exhibits scaling consistent with dilute, semi-dilute overlapping, and semi-dilute entangled regimes typically found in polymer solutions, as confirmed by cryo-TEM and SANS. The transition between these scaling regimes coincides with the structural transitions identified by SANS. The results validate the relationship between structural parameters and rheological behavior underlying theories for ionic WLMs.
KW - Entanglement
KW - SANS
KW - Viscoelasticity
KW - Wormlike micelles
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U2 - 10.1016/j.jcis.2010.05.045
DO - 10.1016/j.jcis.2010.05.045
M3 - Article
C2 - 20541217
AN - SCOPUS:77954177289
SN - 0021-9797
VL - 349
SP - 1
EP - 12
JO - Journal of Colloid And Interface Science
JF - Journal of Colloid And Interface Science
IS - 1
ER -