5 research outputs found
Phase Behavior and Molecular Thermodynamics of Coacervation in Oppositely Charged Polyelectrolyte/Surfactant Systems: A Cationic Polymer JR 400 and Anionic Surfactant SDS Mixture
Coacervation in mixtures of polyelectrolytes and surfactants
with
opposite charge is common in nature and is also technologically important
to consumer health care products. To understand the complexation behavior
of these systems better, we combine multiple experimental techniques
to systematically study the polymer/surfactant binding interactions
and the phase behavior of anionic sodium dodecyl sulfate (SDS) surfactant
in cationic JR 400 polymer aqueous solutions. The phase-behavior study
resolves a discrepancy in the literature by identifying a metastable
phase between the differing redissolution phase boundaries reported
in the literature for the surfactant-rich regime. Isothermal titration
calorimetry analyzed within the framework of the simple SatakeāYang
model identifies binding parameters for the surfactant-lean phase,
whereas a calculation for polymer-bound micelles coexisting with free
micelles is analyzed in the surfactant-rich redissolution regime.
This analysis provides a preliminary understanding of the interactions
governing the observed phase behavior. The resulting thermodynamic
properties, including binding constants and the molar Gibbs free energies,
enthalpies, and entropies, identify the relative importance of both
hydrophobic and electrostatic interactions and provide a first approximation
for the corresponding microstructures in the different phases. Our
study also addresses the stability and metastability of oppositely
charged polyelectrolytes and surfactant mixtures
Triblock Copolymer Self-Assembly in Ionic Liquids: Effect of PEO Block Length on the Self-Assembly of PEOāPPOāPEO in Ethylammonium Nitrate
The microstructure and rheological
properties of micellar solutions
of Pluronic block copolymers (PEO<sub><i>x</i></sub>āPPO<sub><i>y</i></sub>āPEO<sub><i>x</i></sub>)
in deuterated ethylammonium nitrate (dEAN, a protic ionic liquid)
are studied by small- and ultrasmall-angle neutron scattering (SANS
and USANS), fluorescence microscopy, and shear rheology. A homologous
series of three Pluronics with similar PPO block length (F127 (PEO<sub>106</sub>āPPO<sub>70</sub>āPEO<sub>106</sub>), P123
(PEO<sub>20</sub>āPPO<sub>70</sub>āPEO<sub>20</sub>),
and L121 (PEO<sub>5</sub>āPPO<sub>70</sub>āPEO<sub>5</sub>)) are examined to explore the effect of the relative balance of
solvophilic to solvophobic block size on the self-assembled microstructure.
Both F127 and P123 form spherical micelles in dEAN that assemble into
face-centered and body-centered cubic supramolecular crystals, respectively,
upon increasing concentration or temperature. The transition from
disordered to crystalline (ordered) structures manifests as a solāgel
rheological transition. A richer phase diagram is observed in the
L121/dEAN system: due to its low solvophilicity in dEAN, L121 self-assembles
into structures with low curvatures, namely, vesicles in the dilute
regime, elongated (wormlike) micelles at intermediate concentrations
and low temperatures, a nematic phase in concentrated solutions, and
multilamellar phases at high temperatures. Highly viscoelastic solutions
are created by the self-assembly of entangled L121 wormlike micelles.
Structural length scales of the three Pluronic/dEAN systems in the
various mesophases are determined from SANS and USANS
Spontaneous Thermoreversible Formation of Cationic Vesicles in a Protic Ionic Liquid
The search for stable vesicular structures is a long-standing
topic
of research because of the usefulness of these structures and the
scarcity of surfactant systems that spontaneously form vesicles in
true thermodynamic equilibrium. We report the first experimental evidence
of spontaneous formation of vesicles for a pure cationic double tail
surfactant (didodecyldimethylammonium bromide, DDAB) in a protic ionic
liquid (ethylammonium nitrate, EAN). Using small and ultra-small angle
neutron scattering, rheology and bright field microscopy, we identify
the coexistence of two vesicle containing phases in compositions ranging
from 2 to 68 wt %. A low density highly viscous solution containing
giant vesicles (<i>D</i> ā¼ 30 Ī¼m) and a sponge
(L<sub>3</sub>) phase coexists with a dilute high density phase containing
large vesicles (<i>D</i> ā¼ 2.5 Ī¼m). Vesicles
form spontaneously via different thermodynamic routes, with the same
size distribution, which strongly supports that they exist in a true
thermodynamic equilibrium. The formation of equilibrium vesicles and
the L<sub>3</sub> phase is facilitated by ion exchange between the
cationic surfactant and the ionic liquid, as well as the strength
of the solvophobic effect in the protic ionic liquid
Spontaneous Thermoreversible Formation of Cationic Vesicles in a Protic Ionic Liquid
The search for stable vesicular structures is a long-standing
topic
of research because of the usefulness of these structures and the
scarcity of surfactant systems that spontaneously form vesicles in
true thermodynamic equilibrium. We report the first experimental evidence
of spontaneous formation of vesicles for a pure cationic double tail
surfactant (didodecyldimethylammonium bromide, DDAB) in a protic ionic
liquid (ethylammonium nitrate, EAN). Using small and ultra-small angle
neutron scattering, rheology and bright field microscopy, we identify
the coexistence of two vesicle containing phases in compositions ranging
from 2 to 68 wt %. A low density highly viscous solution containing
giant vesicles (<i>D</i> ā¼ 30 Ī¼m) and a sponge
(L<sub>3</sub>) phase coexists with a dilute high density phase containing
large vesicles (<i>D</i> ā¼ 2.5 Ī¼m). Vesicles
form spontaneously via different thermodynamic routes, with the same
size distribution, which strongly supports that they exist in a true
thermodynamic equilibrium. The formation of equilibrium vesicles and
the L<sub>3</sub> phase is facilitated by ion exchange between the
cationic surfactant and the ionic liquid, as well as the strength
of the solvophobic effect in the protic ionic liquid
Spontaneous Thermoreversible Formation of Cationic Vesicles in a Protic Ionic Liquid
The search for stable vesicular structures is a long-standing
topic
of research because of the usefulness of these structures and the
scarcity of surfactant systems that spontaneously form vesicles in
true thermodynamic equilibrium. We report the first experimental evidence
of spontaneous formation of vesicles for a pure cationic double tail
surfactant (didodecyldimethylammonium bromide, DDAB) in a protic ionic
liquid (ethylammonium nitrate, EAN). Using small and ultra-small angle
neutron scattering, rheology and bright field microscopy, we identify
the coexistence of two vesicle containing phases in compositions ranging
from 2 to 68 wt %. A low density highly viscous solution containing
giant vesicles (<i>D</i> ā¼ 30 Ī¼m) and a sponge
(L<sub>3</sub>) phase coexists with a dilute high density phase containing
large vesicles (<i>D</i> ā¼ 2.5 Ī¼m). Vesicles
form spontaneously via different thermodynamic routes, with the same
size distribution, which strongly supports that they exist in a true
thermodynamic equilibrium. The formation of equilibrium vesicles and
the L<sub>3</sub> phase is facilitated by ion exchange between the
cationic surfactant and the ionic liquid, as well as the strength
of the solvophobic effect in the protic ionic liquid