Abstract:Double-chain ammonium amphiphiles that contain the carbazole ring formed stable monolayers on water. Their fluorescence patterns indicated different packing modes of the chromophore which depended on chemical structure and component distribution.
“…It has been reported that the isotherm of DDOAB is sensitive to experimental conditions and, in particular, the concentration and type of counterion . A comparison of the isotherm of DDOAB on pure water given in Figure with others reported in the literature ,, reveals good agreement. Although there is some difference between the isotherm presented here and that of Marra, this may be understood by the different electrolyte concentration and spreading solvent. 3 Surface pressure−area isotherms of DDOAB on water and polyion solution subphases at various pH values.…”
The nature of an azobenzene moiety incorporated into a polyion
complex Langmuir−Blodgett (LB) film
over a range of subphase pH values was investigated by UV−visible
spectroscopy. The azobenzene unit
was substituted with both carboxyl, and hydroxyl groups and the charge
per polymer segment was varied
by altering the pH of the subphase. The trans isomer of the
azobenzene is present in films transferred
from a neutral pH subphase. At a higher pH where both the carboxyl
and hydroxyl groups are ionized
in aqueous solution, the complex LB film formed from this subphase
exhibits the cis isomer of the singly
charged polymer segment. By comparison with a water-soluble
polyion−surfactant complex for which the
cis isomer is not observed, it is concluded that the LB film has
considerable rigidity which stabilizes the
cis isomer. The severely limited photoisomerization of the trans
isomer in the film is further indication
of the restricted molecular motion within the polyion complex LB
film.
“…It has been reported that the isotherm of DDOAB is sensitive to experimental conditions and, in particular, the concentration and type of counterion . A comparison of the isotherm of DDOAB on pure water given in Figure with others reported in the literature ,, reveals good agreement. Although there is some difference between the isotherm presented here and that of Marra, this may be understood by the different electrolyte concentration and spreading solvent. 3 Surface pressure−area isotherms of DDOAB on water and polyion solution subphases at various pH values.…”
The nature of an azobenzene moiety incorporated into a polyion
complex Langmuir−Blodgett (LB) film
over a range of subphase pH values was investigated by UV−visible
spectroscopy. The azobenzene unit
was substituted with both carboxyl, and hydroxyl groups and the charge
per polymer segment was varied
by altering the pH of the subphase. The trans isomer of the
azobenzene is present in films transferred
from a neutral pH subphase. At a higher pH where both the carboxyl
and hydroxyl groups are ionized
in aqueous solution, the complex LB film formed from this subphase
exhibits the cis isomer of the singly
charged polymer segment. By comparison with a water-soluble
polyion−surfactant complex for which the
cis isomer is not observed, it is concluded that the LB film has
considerable rigidity which stabilizes the
cis isomer. The severely limited photoisomerization of the trans
isomer in the film is further indication
of the restricted molecular motion within the polyion complex LB
film.
The efficient energy transfer from 11‐(9‐carbazolyl)undecanoic acid to a very small fraction (470 ppm) of benzocarbazolyl derivatives in mixed monolayer assemblies with long‐chain fatty acids was observed when the molar fraction of chromophore‐containing amphiphiles (fc) was higher than about 0.05. The fluorescence intensity ratio of acceptors and donors increased with the molar fraction. It tended to saturate when fc is larger than about 0.2. Such fraction dependence was not explained by the Förster energy transfer among randomly distributed chromophores, but was analyzed by the exciton migration model. Our results show that aggregation of chromophores in mixed monolayer assemblies does occur depending on the molar fraction fc.
The surface pressure‐molecular area isotherms for various mixtures of 11‐(9‐carbazolyl)undecanoic acid (CUA) and palmitic acid (PA) showed plateau at about 13 mN · m−1 at 15°C. The width of plateau increased with the molar fraction of CUA. A bilayer structure due to the squeezing‐out of CUA from mixed monolayers at the air/water interface was suggested from π‐A isotherms and the limiting area. The structure of Langmuir‐Blodgett (LB) films of a 1:2.7 mixture of CUA and PA deposited at 15°C and 20 mN · m−1 by a vertical dipping method was studied by the small‐angle X‐ray scattering, absorption, and capacitance measurements These results showed that LB films deposited at 20 mN · m−1 were usual Y‐type composed of a monolayer unit. It was strongly suggested that CUA partially squeezed‐out at the air/water interface was reorganized to mixed monolayers during a transfer process.
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