V. Arcoleo

AFM investigation of gold nanoparticles synthesized in water/AOT/n-heptane microemulsions

Abstract Gold nanoparticles, synthesized within AOT reversed micelles, have been imaged by an atomic force microscope (AFM) operating in the contact mode in air at room temperature. The AFM images show an attractive interaction among gold nanoparticles leading to the formation of well distinct aggregates where, however, each nanoparticle retains its individuality. Moreover, the AFM images show that the mean size of gold nanoparticles is a function of the size of the AOT reverse micelles and offer evidence of a stabilization mechanism of the nanoparticles due, most probably, to the formation of an adsorbed layer of surfactant molecules at the nanoparticle surface. This stabilization mechanism results in being active even at high nanoparticle concentration.

Study of AOT-stabilized microemulsions of formamide and n-methylformamide dispersed in n-heptane

Abstract A wide investigation of some physicochemical properties (density, viscosity, conductance, IR spectra, permittivity) of AOT-stabilized dispersions of formamide and n -methylformamide in n -heptane has been performed. The experimental data are consistent with the hypothesis that these highly hydrophilic substances are encapsulated within AOT reversed micelles and that this structure is maintained for both systems well above the volume fraction of the dispersed phase where a percolative transition occurs. In addition, the observed properties of these microemulsions reveal the pivotal role of intermicellar attractive interactions in driving the percolative transition. A marked modification of the structural and dynamical properties of formamide and n -methylformamide accompanying their solubilization within AOT reversed micelles has also been observed.

Calorimetric investigation of the formation of ZnS nanoparticles in w/o microemulsions

The enthalpies of precipitation of ZnS nanoparticles within water containing reversed micelles of sodium bis(2-ethylhexyl) solfosuccinate, L-α phosphatidylcholine, tetraethyleneglycol-mono-n-dodecyl ether and didodecyldimethylammonium bromide as a function of the molar concentration ratioR (R=[water]/[surfactant]) were measured by calorimetric technique. The results indicate that the energetic state of ZnS nanoparticles confined in the aqueous core of the reversed micelles is different from that in bulk water. Effects due to nanoparticle size, adsorption of HS− ions on the nanoparticle surface and interactions between nanoparticles and water/surfactant interfaces are discussed.

Electrical conductivity and permittivity of water-AOT-n-heptane microemulsions

Measurements of the electrical conductivity and of the complex permittivity of water-sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-n-heptane microemulsions are reported. The experimental results are rationalized in terms of a hopping mechanism of AOT anions within clusters of reversed micelles. The dependence of the hopping rate and of the cluster dimensions upon the ratio [water]/[AOT] and temperature is discussed.

Physico-chemical characterization of Pd nanoparticles synthesized in w/o microemulsions

Abstract The long time stability of surfactant-coated Pd nanoparticles in w/o microemulsions has been investigated. It has been proven that in suitable conditions, the use of the functionalized surfactant Pd(AOT)2 allows to obtain very stable nanosized Pd particles and to finely control their average size.

Structural and dynamical investigation of gelation containing water-in-oil microemulsions

The gelatin (Bloom 300)/water/AOT/n-heptane system has been investigated at fixed water/AOT molar ratioR (R=31.1) as a function of the gelatin content. Several experimental techniques (densitometry, refractometry, conductometry, rheology, dielectrometry, ultrasonics, hypersonics) have been used to investigate the role played by the gelatin molecule in the observed sol-gel transition above a critical gelatin content. The results appear consistent with the hypothesis of a rigid network of gelatin-water rods coated by surfactant molecules coexisting with gelatin-free AOT reversed micelles at the gelation point.

Precipitation of calcium carbonate and calcium fluoride in microemulsions. Calorimetric investigation

Abstract The enthalpies of precipitation of calcium carbonate and calcium fluoride in water/sodium bis-2-ethylhexyl sulfosuccinate/ n -heptane, water/didodecyldimethylammonium bromide/ n -heptane and water/tetraethyleneglycol-mono- n -dodecyl ether/isooctane microemulsions were measured by a calorimetric technique. The results indicate that the energetic state of CaCO 3 and CaF 2 nanocrystals encapsulated in the aqueous microregions of these microemulsions is strongly different from that in bulk water. Effects due to the smallness of the nanocrystals, interactions between nanocrystals and water/surfactant interfaces and changes of the thermodynamic parameters in nanoscopic water environments are discussed.

Calorimetric investigation of water/lecithin/cyclohexane microemulsions

The enthalpies of dilution of water/lecithin/cyclohexane microemulsion-gels at variousR values (R=[water]/[lecithin]) and molar enthalpies of solution of water in lecithin/cyclohexane at a fixed lecithin concentration were determined calorimetrically at 25°C. Through a description of the process of dilution of water/lecithin/cyclohexane microemulsion-gels as one involving mainly the scission of lecithin reversed micelles in to smaller ones, the concentration dependence of the enthalpy was rationalized. Surprisingly, in order to account for the dilution enthalpies, it was not necessary to hypothesize a thermal effect arising from the breakage of the micellar network present in the micremulsion-gels. This result indicates that the building-up of the micellar network mainly arises from topological entanglements and steric hindrances among the lecithin reversed micelles. Attribution of the molar enthalpy of solution of water essentially to the thermal effect arising from the intermicellar aggregation process induced by the water addition allowed a rough estimation of the scission energy (the energy necessary to break an Avogadros number of micelles) and of the micellar aggregation number.

Calorimetric investigation of the interaction between a macromolecular prodrug of diflunisal and human platelets

The thermal effect due to the interaction between human platelets and α,β poly(N-hydroxy-ethyl)-DL-aspartamide (PHEA) or the PHEA-Diflunisal conjugate was measured by the calorimetric technique at 25°C. The experimental data confirm that PHEA is a biocompatible macromolecule and that its conjugate influences the physiological activity of human platelets.ZusammenfassungMittels einer kalorimetrischen Methode wurde der thermische Effekt im Zusammenhang mit der Wechselwirkung zwischen Thrombozyten des Menschen und α,β-Poly(N-hydroxyethyl)-DL-Aspartamid PHED-Diflunisal-Konjugat gemessen. Die experimentellen Daten zeigen, daß PHEA ein biokompatibles Makromolekül ist und daß sein Konjugat die physiologische Aktivität der Thrombozyten beeinflußt.