The interfacial composition of the stable water/C12-s-C12 x 2Br/n-hexanol/n-heptane microemulsions has been studied in detail by dilution method. The results showed a marked maximum amount of the n-hexanol populating on the surfaces of droplets (represented as a = n(a)i/n(s), where n(a)i and n(s) are respectively the moles of n-hexanol and gemini surfactant on the surface of droplets) with increasing water content. At a constant level of water addition (the molar ratio of water to surfactant W0 = 20), a decreased with increasing the spacer length in the C12-s-C12 x 2Br molecule. The structural parameters of a w/o microemulsion were also estimated by analyzing the data of dilution experiments, and we found that the radius of the water pool was very sensitive to the increment of water content. The radius of the water pool varied from 0.74 to 5.35 nm with increasing W0 from 10 to 50. The variation extent reached 4.61 nm. In the cases of water/CPC/n-butanol/isopropyl myristate and water/CTAB/n-butanol/isopropyl myristate, however, the corresponding variation extents were only 1.22 and 1.68 nm, respectively, when increasing comparable water content. The ratio of N(a)/N(2C), where N(a) and N(2C) are respectively the average numbers of n-hexanol and the total average numbers of alkyl chains of gemini surfactant populating on per droplet surface, decreased obviously with increasing water content at W0 > 15. This indicated that C12-2-C12 x 2Br favored to form large droplets that were suitable to solubilize more water.
Two-dimensional
(2D) CsPb2Br5 exhibits intriguing
functions in enhancing the performance of optoelectronic devices in
terms of environmental stability and luminescence properties when
composited with other perovskites in different dimensionalities. We
built a type I three-dimensional (3D) CsPbBr3/2D CsPb2Br5 heterojunction through phase transition where
CsPbBr3 quantum dots in situ grew into 2D CsPb2Br5. A thorough growth mechanism study in combination
with excited state dynamic investigations via femtosecond spectroscopy
and first-principles calculations revealed that the type I hierarchy
enhanced the stability of the heterojunction and spurred its luminous
quantum yield by prolonging the lifetime of photogenerated carriers.
Mixing the heterojunction with other phosphors yielded white-light-emitting
diodes with a color rendering index of 94%. The work thus not only
offered one new avenue for building heterojunctions by using the “soft
crystal” nature of perovskites but also disentangled the enhanced
luminescence mechanism of the heterojunction that can be harnessed
for promising applications in the luminescence and display fields.
Surface tension measurements have been performed on solutions
containing cetyltrimethylammonium
bromide and a bile salt, either sodium cholate or desoxycholate, in 50
mM NaCl. For the individual ionic
surfactants the interfacial area per surfactant molecule
(A
s) and critical micelle concentration
(cmc)
were determined. For bile salt solutions a break in surface
tension before the cmc is explained as an
indication of a change in packing of the anions at the interface from a
flat (A
s > 150 Å2) to an
upright
orientation (A
s ≈ 41−45 Å2) and
is compared with results from the monolayer studies of Ekwall
and
Small. For systems containing binary mixtures of the oppositely
charged surfactants, the experimentally
determined mixed cmc (C*) was used to estimate the mixed
micelle composition and the molecular interaction parameter, β, using the treatment of Rubingh for nonideal
mixtures. The mixtures showed significant deviation from ideal mixing, giving an average β = −4 and
−2.7 for the CTAB−NaC and CTAB−NaDOC systems, respectively. For both bile salts, the mixed cmc has
a minimum when the bile salt
fraction in the mixed micelles is close to 0.3, suggesting that a
particularly favorable packing of the micelles
is obtained in this composition range. However, using the average
value of the interaction parameter in
the theory of Rubingh, the cmc values of the systems are predicted
within the precision of the experimental
findings.
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