6 research outputs found
A CASE OF PERFORATED PARADUODENAL PAPILLARY DIVERTICULUM AFTER DISTAL GASTRECTOMY RECONSTRUCTION BY THE BILLROTH II METHOD
Peptide-Based Gemini Amphiphiles: Phase Behavior and Rheology of Wormlike Micelles
Aqueous binary phase behavior of a peptide-based gemini
amphiphile
with glutamic acid and lysine as spacer group, acylglutamyllysilacylglutamate
(<i>m</i>-GLG-<i>m</i> where <i>m</i> = 12, 14, and 16), has been reported over a wide range of concentration
and temperature. Lauroylglutamyllysillauroylglutamate, 12-GLG-12,
self-assembles into spherical micelles above critical micelle concentration
(CMC). The micellar region extends up to 32 wt %, and an ordering
of spherical micelles into micellar cubic phase, <i>I</i><sub>1</sub>, takes place at 33 wt % at 25 °C. The phase transition, <i>I</i><sub>1</sub> - hexagonal liquid crystal, (<i>H</i><sub>1</sub>) - lamellar liquid crystal, (<i>L</i><sub>α</sub>) has been observed with further increase in concentration;
moreover, mixed phases are also observed between the pure liquid crystal
domains. Similar phases were observed with 16-GLG-16 above 50 °C
(Krafft temperature). The partial ternary phase behavior shows that
the micellar solutions of <i>m</i>-GLG-<i>m</i> can solubilize a large amount of cationic amphiphile, alkyltrimethylammonium
bromide, C<sub><i>n</i></sub>TAB, (where <i><i>n</i> = </i> 14 (TTAB) and 16 (CTAB)) at 25 °C. An
addition of C<sub><i>n</i></sub>TAB to the aqueous solutions
of 16-GLG-16 in a dilute region forms a transparent solution of viscoelastic
wormlike micelles at very low concentration (0.25 wt %) even at ambient
condition. A mixture of oppositely charged amphiphiles, <i>m</i>-GLG-<i>m</i> and C<sub><i>n</i></sub>TAB, exhibits
synergism as a result the amphiphile layer curvature, becomes less
positive, and favors the transition from sphere to rod to transient
networks (wormlike micelles). The gemini amphiphile, 16-GLG-16, forms
wormlike micelles at relatively low concentrations compared to others
reported so far. Viscosity increases by six orders of magnitude compared
to that of pure solvent. The hydrophobic chain length of <i>m</i>-GLG-<i>m</i> and coamphiphile affects the rheology; the
maximum viscosity achieved with 16-GLG-16/H<sub>2</sub>O/CTAB is higher
than that of 14-GLG-14/H<sub>2</sub>O/CTAB, 12-GLG-12/H<sub>2</sub>O/CTAB, and 16-GLG-16/H<sub>2</sub>O/TTAB systems. These temperature-sensitive
systems exhibited viscoelastic behavior described by the Maxwell mechanical
model with a single stress relaxation mode