Soft Report - Dipartimento di Fisica - Sapienza

Scientific Report – Non Equilibrium Dynamics and ComplexityReferences[1] M. Plazanet, C. Floare, M.R. Johnson, R.Schweins, H.P. Trommsdorff, J. Chem. Phys. 121,5031 (2004).[2] M.Plazanet, M.Dean, M.Merlini, A.Hüller,H.Emerich, C. Meneghini, M.R. Johnson andH.P.Trommsdorff, “Heat induced crystallization andcomplex phase behavior of α-cyclodextrin solutions”,JACS, submitted.AuthorsM.Plazanet (a,b), P.Bartolini (a,b), A.Taschin (a,b)and R. Torre (a,b,c).(a) INFM-CRS-Soft (CNR), Univ.la Sapienza.(b) LENS , Univ. di Firenze. (c) Dip. di Fisica, Univ. diFirenze.Aqueous micellar solutionsA new Dielectric Spectroscopy technique wasdeveloped in the frequency range 30 MHz - 3 GHz.The complex permittivity of liquids is measured intransmission lines by a Vector Network Analyzer bydifferential methods. Two coaxial line cells weredone, differing for the length, and measured emptyand filled by the sample.This method gives "absolute measurements". Nocalibration by standard liquids is required. The cellshave to be machined with precision of 0.05 mm.Aqueous micellar solutions have been studied atconstant temperature and pressure. The sodiumdodecyl sulphate micellar solutions in the range 30mM - 520 mM were studied by three models, SingleDebye, Cole-Cole and Double Debye. The Cole-Coleand Double Debye models lead to know therelaxation time and the dielectric constant stepamplitude of the relaxation processes of the system.Two processes related to the micelle and to theinterfacial water have been shown with stepamplitudes from 10 to 30 vs. concentration andrelaxation times from 800 ps to 500 ps for themicelles, and step amplitudes from 1 to 12 vs.concentration and relaxation times practicallyconstant 110 ps for the interfacial water. The resultshave been tested by the Grosse's model for thedielectric constant and by the Kallay's model for theconductivity, taking into account the parametersobtained by small-angle neutron scattering, SANS,radius of the micelle, interfacial layer, fractionalionization and aggregation number.We are working on new fluorinated compounds bySolexis-Solvay that lead to ionic micellar solutions inwater. SANS measurements have been performed todefine the microstructure of the system as a functionof the surfactant counterion. Shape and dimension ofthe micelles as well as the parameters of theinteraction potential between micelles have beenevaluated for the ammonium, potassium, lithium,cesium and diethanol ammonium, having differentvolumes.The micelles interaction is due to hard sphere plusrepulsive Coulomb screened potential: Debye'slength and contact potential. As a function ofconcentration, temperature and counterion, themicelles can be spherical or ellipsoidal.Increasing the surfactant concentration, the micellegrow changes vs the volume increase, i.e. themicelle ionization degree decreases and the axialratio increase from 1.6 to 4.2 whereas the interfacialFig.7. The real and imaginary parts of the complexdielectric constant for water and sodium dodecylsulphate aqueous micellar solutions at differentsurfactant concentrations.layer is constant 0.4 nm. The detailed structure isknown for the micelles, included the area per polarhead. These results are very important for manyapplications. Since 2004, the study of a portion of agiant multidomain protein from vertebrate muscles insolution, the β-connectin, is performed by DynamicLight Scattering (DLS). We are comparing AtomicForce Measurements on single molecule performedby a CNR - ISC group with DLS resultsReferencesLeandro Lanzi, M.Carla', C.M.C.Gambi and LeonardoLanzi, J. of Non – Cryst. Solids 351, 2864 (2005).C.M.C. Gambi, R. Giordano, A. Chittofrati, R. Pieri, P.Baglioni; and Teixeira J.J. Phys.Chem. B 109, 8592(2005).AuthorsL.Lanzi (a,b), S.Marchetti (a,b) and C.M.C.Gambi(a,b).(a) INFM-CRS-Soft Matter (CNR), Univ. la Sapienza.(b) Dip. di Fisica, Univ. di Firenze.SOFT Scientific Report 2004-0684