Light scattering and fluorescence studies of non-ionic surfactant binary mixtures formed by MEGA-10 and C12E8 (original) (raw)
Related papers
Photophysical features of coumarin 120 in reverse micelles
Journal of Molecular Structure, 2018
The photophysical properties of 7-amino 4-methyl coumarin (C120) were investigated in the reverse micelle systems by using molecular UV-Vis absorption, steady-state and timeresolved fluorescence spectroscopy techniques. For this purpose, the fluorescence spectra of C120 dye in reverse micelle systems with different values of W 0 (from 0 to 45) were examined. The bathochromic shift from 400 nm to 439 nm was observed for the fluorescence maxima of C120. It was found that intramolecular arrangements occurred in the structure of C120 molecule due to specific solute-solvent interactions. Fluorescence lifetime measurements were carried out and quantum yield values, radiative (k r) and non-radiative rate constants (k nr) were calculated. The data compared with the values reported in the literature. Steady-state anisotropy (r) studies were done to explain the microenvironment around the C120 molecules. Anisotropy data varying 0.048 to 0.030 with varying W 0 displayed that the microenvironment for the C120 dye in water pools of reverse micelles was different than C120 dye in pure water which is 0.009. The microviscosity and rotational relaxation time values were calculated as a function of W 0. We have determined that C120 dye is a useful probe for the definition the microviscosity of reverse micelles with different water pool sizes.
The Journal of Physical Chemistry A, 2012
The microstructure of mixed micelles containing n-dodecyl-β-Dmaltoside and n-dodecyl-hexaethylene-glycol, two nonionic surfactants belonging to the alkyl polyglucoside and polyoxyethyelene alkyl ether families, respectively, has been investigated. With the aim of understanding how the micellar composition affects the microenvironmental properties of micelles, we have examined the photophysics and dynamics of the neutral probe coumarin 153 in the binary mixtures of the surfactants across the entire composition range. We present data on the steady-state absorption and emission spectra of the probe, as well as fluorescence lifetimes and both steady-state and time-resolved fluorescence anisotropies. These data indicate that the participation of the ethoxylated surfactant in the mixed micelle induces an increasing hydration in the palisade layer of the micelle, which forces the probe to migrate toward the inner micellar region, where it senses a slightly less polar environment. The time-resolved fluorescence anisotropy data were analyzed on the basis of the two-step and wobbling-in-cone model. The average reorientation time of the probe molecule was found to decrease with the presence of the ethoxylated surfactant, in good agreement with steady-state fluorescence anisotropy data, suggesting a reduction of the microviscosity in the solubilization site of the probe. The behavior of all diffusion reorientation parameters was analyzed on the basis of two factors: the micellar hydration and the headgroup flexibility of both surfactants. It was concluded that the increasing participation of the ethoxylated surfactant induces a greater hydration in the micellar palisade layer, producing the formation of a less compact microenvironment where the probe experiences a faster rotational reorientation.
Molecules (Basel, Switzerland), 2015
The photodynamics of Coumarin 6 have been investigated in three nonionic micellar assemblies, i.e., n-dodecyl-β-D-maltoside (β-C12G₂), p-tert-octyl-phenoxy polyethylene (9.5) ether (Triton X-100 or TX100) and n-dodecyl-hexaethylene-glycol (C12E₆), to assess their potential use as encapsulation vehicles for hydrophobic drugs. To evaluate the effect of the micellar size and hydration, the study used a broad temperature range (293.15-323.15 K). The data presented here include steady-state absorption and emission spectra of the probe, dynamic light scattering, together with fluorescence lifetimes and both steady-state, as well as time-resolved fluorescence anisotropies. The time-resolved fluorescence anisotropy data were analyzed on the basis of the well-established two-step model. Our data reveal that the molecular probe in all of the cases is solubilized in the hydration layer of micelles, where it would sense a relatively polar environment. However, the probe was found to undergo a s...
The Journal of Physical Chemistry B, 2014
The solvation dynamics and rotational relaxation of Coumarin 480 (C-480) have been investigated in the micelles of a series of gemini surfactants, 12-4(OH) n-12 (n = 0, 1, and 2), with increasing hydroxyl group substitution within the spacer group. Steady-state and time-correlated single photon counting (TCSPC) fluorescence spectroscopic techniques have been used to carry out such study. Steady-state and TCSPC fluorescence data support the location of probe molecule at the Stern layer. The solvation dynamics is found to be slower on hydroxyl substitution of spacer group due to the formation of hydrogen bonds between water molecules and hydroxyl group(s) of spacer group. Such kind of hydrogen bonding protects the probe molecule from its contact with water molecules and also results in restricted mobility of water molecules. The average rotational relaxation time increases on increasing number of substituted hydroxyl group on a spacer group. It is because of formations of more and more close packed micelles and larger extent of intermolecular hydrogen bonding interactions between C-480 and hydroxyl group(s). For micelles of each of 12-4-12 and 12-4(OH)-12, the slow rotational relaxation is dominated by the lateral diffusion of the fluorophore along the spherical surface of the micelle. However, for 12-4(OH) 2-12, the slow rotational relaxation is mainly due to the rotational motion of the micelle as a whole. Because of high microviscosity of micelles of 12-4(OH) 2-12 and greater extent of hydrogen bonding interactions with C-480, the relaxation time corresponding to the lateral diffusion of the fluorophore is very high in this case.
The Journal of Physical Chemistry B, 2006
Dynamic Stokes' shift and fluorescence anisotropy measurements using coumarin-153 (C153) and coumarin-151 (C151) as the fluorescence probes have been carried out in aqueous poly(ethylene oxide) 20-poly(propylene oxide) 70-poly(ethylene oxide) 20 (P123) and poly(ethylene oxide) 100-poly(propylene oxide) 70-poly(ethylene oxide) 100 (F127) block copolymer micelles with an aim to understand the water structures and dynamics in the micellar corona region. It has been established that the probes reside in the micellar corona region. It is indicated that the corona regions of P123 and F127 micelles are relatively less hydrated than the Palisade layers of neutral micelles like Triton-X-100 and Brij-35. From the appraisal of total Stokes' shift values for the probes in the two block copolymer micelles, it is inferred that the F127 micelle is more hydrated than the P123 micelle. It is observed that the dynamic Stokes' shift values for both of the probes remain more or less similar at all the temperatures studied in the P123 micelle. For C153 in F127, however, the observed Stokes' shift is seen to decrease quite sharply with temperature, though it remains quite similar for C151. Moreover, the fraction of the unobserved initial dynamic Stokes' shift is appreciably higher for both the probes in the F127 micelle compared to that in P123. Over the studied temperature range of 293-313 K, the spectral shift correlation function is described adequately by a bi-exponential function. Rotational relaxation times for C153 in both the micelles show a kind of transition at around 303 K. These results have been rationalized assuming collapse of the poly(ethylene oxide) (PEO) blocks and formation of water clusters in the corona region due to dehydration of poly(ethylene oxide) blocks with an increase in temperature. A dissimilar probe location has been inferred for the differences in the results with C153 and C151 probes in F127. Comparison of the microviscosity and the hydration of the block copolymer micelles has also been made with those of the other commonly used neutral micelles, for a better understanding of the results in the block copolymer micelles.
Fluorescence probing of block copolymeric micelles using Coumarin 153
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009
Coumarin 153 (C-153) was used as a fluorescent probe molecule to monitor the possible micellization of several amphiphilic block copolymers, all of which consist of poly(DMA) (DMA = 2-(dimethylamino)ethyl methacrylate) as the hydrophilic block but otherwise differ in the nature of the hydrophobic block, composition and overall morphology. In case of linear triblock poly(DMA-b-MMA-b-DMA) copolymers (MMA = methyl methacrylate), the fluorescence response of C-153 indicates the formation of micelles at [polymer] ∼0.03%. The probe molecules are preferentially accommodated in the hydrophobic core region of these nano-sized micelles, which is characterized by a strongly non-polar microenvironment and hindered mobility of the probe. In case of copolymers containing long pendant hydrocarbon sidechains attached to the main backbone of the hydrophobic block, the fluorescence response of C-153 is somewhat similar. However, in such systems, micellization at a unique copolymer concentration is not observed within the same concentration range as in poly(DMA-b-MMA-b-DMA), probably due to the emergence of pre-micellar aggregates.
Our aim is to doubly confine a molecule of coumarin C522 in a host–guest supramolecular complex with b-cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n-heptane and polar water solvents. Varying the volumes of coumarin C522 and b-cyclodextrin dissolved in water allows us to control the water-pool diameters of the reverse micelle in n-heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n-heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady-state and time-resolved dependences are compared for the two systems coumarin C522- (water)/AOT(n-heptane), denoted C522/micelle, and coumarin C522/b-cyclodextrin(water)/AOT(n-heptane), referred to as C522/CD/micelle. The formation of the supramolecular host– guest complex CD–C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n-heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n-heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3–5, and w=10–40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3–5 and 10–40 in the steady-state and time-resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60–80) and for bound water (25–60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.
Fluorescence in microemulsions and reversed micelles
Analytica Chimica Acta, 1988
The use of fluorescence to study physicochemical structures of alcohol/surfactant/water systems, microemulsions and reversed micelles is reviewed, and the application of these media in analytical fluorescence spectroscopy is discussed. The sodium dodecylsulfate/l-pentanol/heptane/water system is studied by using pseudo-ternary diagrams. Wide areas of existence of thermodynamically stable and optically clear phases (Winsor IV and two liquid crystals) were found both in the absence and presence of sodium sulfate (0.2 M ) . The influence of the composition of media on the fluorescence characteristics of pyrene, benzo [elpyrene, 2-naphthol and p-aminobenzoic acid is studied.