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ABSTRACT: The structure of water in aqueous solutions of polyoxyethylene nonionic amphiphiles C10E5 is studied by Raman scattering along an isothermal path crossing the isotropic one-phase region from 0 to 1 amphiphile volume
fraction φ. The isotropic OH stretching vibration spectrum evidences a behavior that depends on the amphiphile concentration. The interpretation
of such scattering data leads to the following structural picture for the water in the systems; for φ lower than 0.75, water is partially bound to the oxyethylene groups of the amphiphile; above φ=0.75 all water present in the system is bound. The structure of such bound water presents a local, low dense, four coordinated
environment.
03/2008: pages 130-134;
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ABSTRACT: The phase separation process in a one-phase microemulsions has been examined in an unstable region above its lower cloud point
temperature by light-scattering measurements. The three time stages of the spinodal decomposition, i.e., early, intermediate,
and late, has been observed. The scaling behavior of the peak in the structure factor, and the scaled structure function,
have been studied and compared with the recent theoretical predictions of spinodal decomposition.
02/2008: pages 311-316;
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02/2008: pages 311-311;
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ABSTRACT: In order to elucidate the aggregation phenomena in alcoholic aqueous solutions, we present some experimental results from
small-angle neutron scattering (SANS), elastic and quasielastic light scattering and ultrasonic spectroscopy. We find that,
by increasing the alkyl chain length of the alcohol, the molecular aggregates change from small fluctuating wateralcohol groups
to micelle-like structures. The role of temperature and concentration is also discussed.
12/2007: pages 177-183;
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ABSTRACT: We report extensive measurements of hypersonic sound velocity in an AOT-water-decane system in the one-phase region where
it forms water-in-oil microemulsions. The experiments were performed as a function of the droplets volume fraction ϕ in the range 0 to 0.75, and for several temperatures. A comparison of these results with ultrasonic data shows the presence
of dispersion effects strongly dependent on the temperature for ϕ ≥ 0.3. The overall analysis of the data in terms of a static effective-medium-approach indicates that the observed effects
are related to the dynamics of the aggregation process near the percolation threshold.
12/2007: pages 159-162;
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ABSTRACT: Viscosity measurements as a function of the volume fraction on a dilute colloidal water solution of polystyrene particles
are performed in deionized water suspensions at several ionic strengths. The analysis of the data confirms the idea that in
such systems their rheological behavior can be completely explained in terms of the interparticle potential energy of interaction.
11/2007: pages 428-431;
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04/2002;
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ABSTRACT: A series of polyamidoamine dendrimers (generations 1.5–4.0, with ethylenediamine as the central core) has been investigated
in methanol solution by means of the small-angle X-ray scattering technique. The comparative analysis of the structural properties
of integer and half-integer generations of the dendrimers seems to be dominated by rather different trends.
While the integer generations, bearing terminal amino groups, approach a compact space-filling structure, the presence of
residue charges on the terminal carboxylate groups in the half-integer generations leads to a less compact internal structure
and a long-range electrostatic interaction (structural order) in the system.
06/1999: pages 152-156;
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ABSTRACT: We have performed extensive small-angle light scattering (SALS) measurements on a three-component microemulsion (AOT/decane/water)
as a function of the dispersed phase concentration and the temperature. All samples have a water/AOT molar fraction w=40.8. Such a system presents a very complex phase diagram with many structural configurations. With the SALS technique, we
have been able to observe all the phase separation lines. In particular we give details on the system structure on the percolation
phenomenon and on the bicontinuous phase recently observed. In particular we show that the percolation is driven by a long-scale
aggregation between microemulsion droplets.
Il Nuovo Cimento D 08/1994; 16(9):1627-1633.
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ABSTRACT: A water/butoxyethanol solution has been investigated by means of several techniques (viscosity, ultrasound and hypersound)
as a function of concentration and temperature. The butoxyethanol molar fraction range investigated was situated between 0.015
and 0.09, while temperature ranged between −10°C and +45°C. We observed the building-up of large structures lowering the temperature,
in particular below +15°C. All data coming from different techniques seem to confirm such a picture and indicate that this
aggregation phenomenon is a percolation-like process.
Il Nuovo Cimento D 08/1994; 16(9):1619-1625.
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ABSTRACT: We have performed Brillouin and depolarized Rayleigh light scattering on water-methanol solutions as a function of methanol
molar fraction and temperature. For this system, molecular-dynamics (MD) simulation predicts that a shell of water forms around
a methanol molecule, prediction which has been recently confirmed by neutron diffraction experiments. The results obtained
by light scattering and presented here confirm previous observations and show, in addition, an increase of the stability in
time of the water structure in the shells when temperature decreases and methanol concentration approaches a particular value.
Il Nuovo Cimento D 06/1994; 16(7):923-931.
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ABSTRACT: We report the results of different light scattering experiments, both elastic and quasi-elastic, performed as a function of
temperature at different concentrations on a water-butoxyethanol (C4E1) mixture. The comparison of the obtained data with the results of SANS gives evidence of the amphiphilic character of the
alcohol molecules. In particular, we observe such a property gives rise to a well-defined micellarlike structure. At low temperatures
(T≤5°C) we find that the mixture exhibits a surprising behaviour, namely very large structures (of the order of 2000 Å) built
by an intermicellar aggregation process. In addition when the light scattering data show the presence of such large aggregates,
neutron data reveal the persisting presence of micelles of about 20 Å. Such a structural picture agrees with the behaviour
of the viscosity data.
Il Nuovo Cimento D 02/1992; 14(3):333-341.
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ABSTRACT: All parameters of a spectrometer, signal detection, and normalization of the recorded Raman signal were controlled by a compatible IBM PC/XT computer which was connected to a Spex Ramalog 5 system. By the use of a motor‐driven polarizer, we are able for each single step time of the instrument, to monitor simultaneously the contributions I VV and I VH of the spectrum. Moreover, the simultaneous normalization of the signal with the intensity of the exciting laser light allows one to avoid the effects of the unwanted laser instability. The program can be requested by electronic mail.
Review of Scientific Instruments 09/1990; · 1.37 Impact Factor
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ABSTRACT: We report measurements of viscosity and light scattering in an aqueous solution of BSA. Like the lysozyme solutions, previously investigated, the BSA solutions show thixotropic properties. Optical measurements of both elastic and inelastic light scattering indicate the existence of a structure in which the BSA molecule tends to clusterize, each cluster being correlated to the others. A k‐dependent diffusion coefficient D(k) is found. The static structure factor deduced from the values of DL(k) agrees well with the indications given by the elastically scattered intensity J(k). Also, the statical properties of scattered light appear to be consistent with the proposed model. A qualitative explanation, in terms of a dominant component in the fluctuations of concentration, is briefly sketched.
The Journal of Chemical Physics 11/1981; 75(10):4770-4775. · 3.33 Impact Factor
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ABSTRACT: We have studied the aggregation of the porphyrin trans-bis(N-methylpyridinium-4-yl)-diphenylporphyrine (t−H2Pagg) in aqueous solutions by means of light scattering (elastic and quasielastic) and UV-visible absorption measurements. Elastic and dynamic light scattering indicate that the aggregation produces large monodisperse clusters having a fractal structure driven by diffusion limited aggregation (DLA). UV-visible absorption measurements have been applied to study the corresponding kinetics, obtaining the time dependence of the monomer concentration and of the mean cluster size. The obtained findings are in agreement with the picture proposed by current theoretical models and molecular dynamics (MD) simulations on DLA.
Physica A: Statistical Mechanics and its Applications. 249:501-510.
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ABSTRACT: Quasielastic light scattering measurements give evidence that in concentrated microemulsions of water in oil a strong interaction among the constitutive droplets is present. This interaction is attractive and therefore can originate aggregation processes. In the frame of the Ornstein-Zernike form the analysis of the scattered intensity profiles furnishes the dimension of such aggregates (∼ 2800 Å).
Solid State Communications 69(9):883-885. · 1.65 Impact Factor
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ABSTRACT: The porphyrin trans-bis(N-methylpyridinium-4-yl)diphenylporphyine (t-H2Pagg) is known to form in solution large assemblies and supramolecular structures in the presence of polyanions, such as nucleic acids, as a template support. We have studied the aggregation of the unbound porphyrin in 0.1 M NaCl aqueous solutions. The aggregation process was monitored by a time resolved small angle light scattering apparatus. The intensity profile of the scattered light as a function of the exchanged wavevector q, conforms to a scattered law for fractal aggregates in the range 0.2–31.4 μm−1. An analysis of the intensity data reveals a value of the fractal dimension df equal to 2.5.Additional dynamic light scattering measurements confirm the presence of almost monodispersed aggregates in the mesoscopic range.
Journal of Molecular Structure. 383:255-260.
