Soft Report - Dipartimento di Fisica - Sapienza

Scientific Report – Non Equilibrium Dynamics and ComplexityA porous glass (PG) is a usual silicate glass where ispresent a random network of empty pores. There aredifferent techniques to produce such porous glassesand the most common is based on sol-gel method.With this techniques it is possible to generate PGcharacterized by different porous shape anddimension distribution (see figure fig1). PG arecommercially available and they are known as VycorCCl 4, that it has been very well studied in its bulkphase. Our first investigation analyses two transportphenomena of the filled PG, in particular the acousticpropagation and the thermal diffusion, and comparethem with the same processes in bulk matter.Indeed the filled PG must be considered as twostrongly interacting materials, here the liquid andglass matrix, so that the transport phenomena coulddiffer substantially from the bulk one.References[1] A.Taschin, R.Cucini, P.Bartolini and R.Torre.“Acoustic propagation in liquid filled porous glasses,a test of Biot model”. In preparation (2006).AuthorsA.Taschin (a,c), R.Cucini (c), P.Bartolini (a,c) andR.Torre(a,b,c).(a) INFM-CRS-Soft (CNR), Univ. la Sapienza. (b) Dip.di Fisica, Univ. di Firenze. (c) LENS, Univ. di Firenze.Fig.2. In the figure we show a 3D computer modelof the porous glass structure. The empty pores andcavities have typical dimension of severalnanometers.Micro-emulsion: Water in OilMicro-emulsion is a colloidal suspension composed ofdrops of water stabilized by surfactant molecules in aoily solvent. Typically they have diameters of fewnano-meters and represent a soft dynamic nanostructure.In this soft matter example there are threecomponents, a solute (water) a solvent (oil) and astructuring agent (surfactant), that play a role indefining the local structure present in the materialand, furthermore, the long range disorder is dynamic.Thus in micro-emulsion the correlation between microand macro proprieties is more articulated than in thePG glasses, where only two interacting componentsare present and the disorder is static. We areperforming a series of time-resolved and frequencyspectroscopic experiments on a very well studiedFig.3. Here we report two experimental resultswith the relative fitting functions. The sample is aporous glass filled with a molecular liquid (CCl 4 inVycor 7030) and the data are obtained by means oftime resolved transient grating.(a trade mark from Corning Glass company): this PGshow a very narrow distribution of porous diametersaround 40 nm. PG can be easily filled with liquid ofdifferent nature and it represents a very useful solidmatrix to produce a static and rigid nano-structuringof the liquid. The porous glass filled with a liquid isindeed an interesting nano-structured disorderedmaterial, not only as a remarkable model for thebasic research on interaction at the nano scale butalso as effective example of many material presentin nature and in technological creation. We startfilling the Vycor glass with a simple molecular liquid,Fig. 4. A computer simulation of a inverse micellecharacterizing the AOT microemulsion. Only thesurfactant and water molecules are shown.micro-emulsion: the AOT-water-decane microemulsion,being AOT the surfactant and decane theoil. We focus on the investigation of acousticpropagation in this system as a function oftemperature, in order to measure and characterizethe interplay between the colloidal phase/structuremodifications and sound propagation. In particular weinvestigated the effect of the “percolation line”present in the phase diagram of this microemulsion(i.e. a supposed transition between two differentstates of dynamic aggregation), on the soundvelocity. Our preliminary results shown a weak effecton the elastic modulus of the dispersed phase (AOT-Water).SOFT Scientific Report 2004-0682