Aggregate Structure and Dynamic Percolation in Microemulsions

Abstract

This contribution deals with a special class of soft matter systems called microemulsions. They are mixtures of oil and water stabilized with a surfactant. The stabilisation is achieved through the reduction of interfacial tension by the amphiphilic surfactant. They thus consist of oil and water phases separated by a surfactant layer. The nanoscopic structure of these phases, in particular that of spherical nano droplets, is analysed in this chapter. The impact of temperature and mixing ratio of the constituents is shown. The fascinating phenomenon of dynamic droplet percolation and aggregation near a temperature induced phase separation are discussed. Microemulsions provide an excellent model system for the investigation of confinement effects on molecules. Conversely these guest molecules modify structural and dynamical properties of the microemulsion. This may even lead to the formation of transient networks with short time gel-like and long time self-diffusion dynamics of droplets.

In Situand Real-Time Monitoring of Nanoparticle Formation in Microemulsion by Means of Dielectric Spectroscopy

“…Because droplets in a water-in-oil ME can carry instantaneous excess charge due to spontaneous fluctuations in the numbers of surfactant molecule and counterion, they behave as large “ions” and give rise to an effective charge transport and a finite conductivity. , The DC conductivity of the ME below percolation is thus determined by where η is the viscosity of the oil phase, and ρ, r , and ⟨ z 2 ⟩ are the number density, the radius, and the mean-square charge of the droplet, respectively. As discussed above, the relaxation time of interfacial polarization is mainly functions of λ D and D .…”

“…Because droplets in a water-in-oil ME can carry instantaneous excess charge due to spontaneous fluctuations in the numbers of surfactant molecule and counterion, they behave as large "ions" and give rise to an effective charge transport and a finite conductivity. 52,53 The DC conductivity of the ME below percolation is thus determined by…”

Enhancement in Elastic Bending Rigidity of Polymer Loaded Reverse Microemulsions

“…The behavior of the conductivity curve remains qualitatively same for all the three cases, while the percolation temperature shifts to higher values upon introducing PEG ( Δ T P = +1.6 °C) and further increases for PVP-loaded reverse microemulsions ( Δ T P = +3.9 °C). PEG-loaded reverse microemulsions are known to show an increase in T P which is explained by taking into account the stiffening of AOT surfactant shell by the adsorption of PEG polymer chains at the water–AOT interface. ,, Attractive electrostatic interactions between added PEG and AOT facilitate the adsorption of polymers onto the surfactant monolayer and was first discussed by de Gennes . A recent report on PEG-loaded reverse microemulsions provides direct evidence for the adsorption of a PEG polymer chain onto the AOT surfactant interface in water–AOT– n -decane reverse microemulsions from small-angle scattering measurements .…”

“…The manifestation of nanodomains leads to different phases of microemulsion known as lamellar, bicontinuous and droplet, where in droplet phase, domains can be spherical water droplets dispersed in an oil matrix (w/o) or vice versa (o/w). In particular, the investigation of the droplet phase of microemulsions is not only interesting from a fundamental science point-of-view but also has attracted considerable attention for its manifold technological applications . Incorporation of different guest molecules like polymers, glass forming liquids, and proteins into the microemulsion core ,, is found to have significant effects on properties of microemulsions and also on the dynamics of the guest molecules confined by the fluctuating soft surfactant shell (soft-confinement) .…”

“…In particular, the investigation of the droplet phase of microemulsions is not only interesting from a fundamental science point-of-view but also has attracted considerable attention for its manifold technological applications . Incorporation of different guest molecules like polymers, glass forming liquids, and proteins into the microemulsion core ,, is found to have significant effects on properties of microemulsions and also on the dynamics of the guest molecules confined by the fluctuating soft surfactant shell (soft-confinement) . Especially, reverse microemulsions loaded with polymers are widely investigated, because addition of polymers allows one to tailor and/or control the macroscopic properties and phase behavior of MEs.…”