“…For the DC 8 PC pure system shown in panel d, on the other hand, the surface tension is almost constant above the cmc. Taking account of the fact that the ratio of the slope of γ versus log m curve just below and above the cmc is approximately related to the mean aggregation number N̅ by N̅≈false(∂γ/∂lognobreak0em.25emmfalse)m<cmcfalse(∂γ/∂lognobreak0em.25emmfalse)m>cmc N̅ is large for DC 8 PC and comparatively small for DC 6 PC, which is consistent with the previous results of light scattering ( N̅ ≥ 470 for DC 8 PC and N̅ ≈ 30 for DC 6 PC). , …”
The aggregate formation and surface adsorption of aqueous
binary
mixture of short-chain phospholipids, dihexanoyl-phosphatidylcholine
(DC6PC), and dioctanoyl-phosphatidylcholine (DC8PC), were examined by surface tension and dilational viscoelasticity
measurements. The concentration versus composition diagram of aggregate
formation was constructed by analyzing the surface tension data. The
diagram demonstrated a synergetic effect that even when the mole fraction
of DC8PC in the aqueous solution was 0.02, worm-like micelle
was formed and furthermore the addition of DC6PC to DC8PC solution lowered the DC8PC concentration at
which worm-like micelle formation starts, although DC6PC
molecules do not form worm-like micelles solely. The phase diagram
of adsorption was also constructed to elucidate the miscibility of
two components in the adsorbed film. The calculated excess Gibbs energy
of adsorption was negative, again suggesting a synergistic attractive
intermolecular interaction between two species in the adsorbed film.
A staggered arrangement was proposed as a favorable intermolecular
arrangement. The dilational viscoelasticity was also measured by the
electrocapillary wave method, and both storage and loss modulus showed
a maximum at around the surface composition of the minimum of the
excess Gibbs energy of adsorption.
“…For the DC 8 PC pure system shown in panel d, on the other hand, the surface tension is almost constant above the cmc. Taking account of the fact that the ratio of the slope of γ versus log m curve just below and above the cmc is approximately related to the mean aggregation number N̅ by N̅≈false(∂γ/∂lognobreak0em.25emmfalse)m<cmcfalse(∂γ/∂lognobreak0em.25emmfalse)m>cmc N̅ is large for DC 8 PC and comparatively small for DC 6 PC, which is consistent with the previous results of light scattering ( N̅ ≥ 470 for DC 8 PC and N̅ ≈ 30 for DC 6 PC). , …”
The aggregate formation and surface adsorption of aqueous
binary
mixture of short-chain phospholipids, dihexanoyl-phosphatidylcholine
(DC6PC), and dioctanoyl-phosphatidylcholine (DC8PC), were examined by surface tension and dilational viscoelasticity
measurements. The concentration versus composition diagram of aggregate
formation was constructed by analyzing the surface tension data. The
diagram demonstrated a synergetic effect that even when the mole fraction
of DC8PC in the aqueous solution was 0.02, worm-like micelle
was formed and furthermore the addition of DC6PC to DC8PC solution lowered the DC8PC concentration at
which worm-like micelle formation starts, although DC6PC
molecules do not form worm-like micelles solely. The phase diagram
of adsorption was also constructed to elucidate the miscibility of
two components in the adsorbed film. The calculated excess Gibbs energy
of adsorption was negative, again suggesting a synergistic attractive
intermolecular interaction between two species in the adsorbed film.
A staggered arrangement was proposed as a favorable intermolecular
arrangement. The dilational viscoelasticity was also measured by the
electrocapillary wave method, and both storage and loss modulus showed
a maximum at around the surface composition of the minimum of the
excess Gibbs energy of adsorption.
“…This two break point behavior is consistent with the coexistence of micelle and bilayer structures showed by DLLS results in Figure , where two kinds of aggregate appeared at a certain pH value. Similar results were also observed in other surfactants. − We believe that the low surface activity at pH = 2.0 is due to the higher degree of hydrophilicity induced by a protonated NH 2 group. 5 The γ− C plot of C18N3 at three different pH values.…”
Section: Resultssupporting
confidence: 80%
“…Similar results were also observed in other surfactants. [15][16][17][18] We believe that the low surface activity at pH ) 2.0 is due to the higher degree of hydrophilicity induced by a protonated NH 2 group.…”
A novel single-chain surfactant with multi-amine headgroups, bis(amidoethyl-carbamoylethyl) octadecylamine
(C18N3), was synthesized. Electronmicrographic study showed that in aqueous solution C18N3 formed small
micelles (10−20 nm in diameter) at pH 2.0 and changed into much larger globule vesicles sized about 0.6−2.0 μm in diameter at pH 6.8. At pH 12.0 vesicles changed to a much larger continued lyotropic lamella
structure. At pH = 2, the surface tension (γ)−concentration (C) curve at pH 2 was an ordinary one, having
one critical micelle concentration at 2.9 × 10-3 mol L-1 at relatively high surface tension (52 mN m-1).
However, two unique transition points were observed in the γ−C plot at pH = 6.8 and 10.5, showing higher
surface activity that is believed to be associated with the micelle−bilayer structure transition. The protonation
degree pK
a's of the three amine headgroups were found to be 6.6, 10.6, and 10.9, respectively, indicating that
a complete protonation state of the headgroups occurred at pH 2.0, which is consistent with the apparent
surface areas of headgroup calculated according to Gibbs adsorption isotherm. Variation of sizes and
morphologies of C18N3 in aqueous solution at different pH values suggest that our synthetic surfactant may
have great potential applications as a template in fabricating drug delivery, biosensors, and biomolecular
devices.
“…Although the existence of small aggregates is not self-evident from the surface tension curves shown in Figure , the downwardly convex shape of the γ vs log m̂ curves in Figure is probably indicative of the existence of small aggregates because γ of a monomer solution is decreased almost linearly or upward convexly with increasing log m̂ , and on the other hand, γ of a micelle (large aggregates) solution is almost constant above the critical micelle concentration. On the basis of the thermodynamic consideration on adsorption from small aggregate solutions, the average aggregation number was estimated by applying N¯=(∂γ/∂logm̂)m̂<m̂I/(∂γ/∂logm̂)m̂>m̂I to the surface tension curves, and N̅ was around 4−10 for both DDAB and DDAC. , This number is too small for the surface tension curve to show a break point that is observed usually for micelle formation. However, the differential conductivity is usually very sensitive to even such small aggregates described in the literature. , Considering that m̂ I does not change so much with X̂ 2 from the corresponding ones of DDAB and DDAC, designated as m̂ 1 I,0 and m̂ 2 I,0 in the following, as shown in Figure and also that the mixed solutions of small aggregates and monomers are grown up into vesicles at all X̂ 2 at higher concentrations, the small aggregates were inferred to be a kind of embryo of a vesicle bilayer as suggested in our previous studies. , …”
Aggregate formation of a didodecyldimethylammonium bromide (DDAB) and didodecyldimethylammonium chloride (DDAC) mixture in aqueous solution was investigated. The concentration vs composition diagram of aggregate formation was constructed by analyzing the surface tension, turbidity, and electrical conductivity data. The cryogenic transmission electron microscopy was applied to several representative points in the diagram and provided information of the morphology of aggregates. The sequence of monomer (m) - m + small aggregate (A) - m + A + vesicle (V) - m + V was concluded with increasing total concentration of surfactants at all mixing ratios. The compositions of counterions in A and V were estimated on the basis of thermodynamic consideration and examined from the viewpoint of asymmetry of constituents and uneven distribution between outer and inner monolayers of a vesicle bilayer. Vesicle surfaces were suggested to abound in chloride ions compared to bulk solution, which is opposite to spherical micelle surfaces.
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