What is a Janus Fluid?
The recent development of new sophisticated synthesis laboratory techniques in the field of colloidal particles allowed the realization of the Janus fluid in the laboratory and his characterization. In parallel, recent Monte Carlo simulations on the Kern
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What is a Janus Fluid?
Unus mundus sum
Abstract The recent development of new sophisticated synthesis laboratory techniques in the field of colloidal particles allowed the realization of the Janus fluid in the laboratory and his characterization. In parallel, recent Monte Carlo simulations on the Kern and Frenkel model of the Janus fluid have revealed that in the vapor phase, below the critical point, there is the formation of preferred inert clusters made up of a well defined number of particles: the micelles and the vesicles. This is responsible for a re-entrant gas branch of the gas-liquid coexistence curve of the phase diagram. Detailed account of these new developments and new findings are given in the chapter where the Janus fluid is introduced at a statistical physics theoretical level outlining the progresses made in the use of the most common statistical physics instruments to study such a complex fluid, like the numerical simulations, the integral equation approach, and the thermodynamic perturbation approach. Keywords Janus fluid · Janus particles · Kern-Frenkel model · Monte Carlo simulation · Integral equation theory · Thermodynamic perturbation theory · Radial distribution function · Structure factor · Phase diagram · Micelle · Vesicle · Lamella.
1.1 Introduction A Janus fluid is one made of Janus particles immersed in a solvent. A Janus particle like the Roman God Janus, depicted in Fig. 1.1, is one that has two faces with two different functionalities. Originally, the term Janus particle was coined by Casagrande et al. in 1988 [4] to describe spherical glass particles with one of the hemispheres hydrophilic and the other hydrophobic. In that work, the amphiphilic beads were synthesized by protecting one hemisphere with varnish and chemically treating the
R. Fantoni, The Janus Fluid, SpringerBriefs in Physics, DOI: 10.1007/978-3-319-00407-5_1, © The Author(s) 2013
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1 What is a Janus Fluid?
Fig. 1.1 A statue representing Janus Bifrons in the Vatican Museums
other hemisphere with a silane reagent. This method resulted in a particle with equal hydrophilic and hydrophobic areas [5]. The Janus particles are commonly found amongst the soft matter colloidal particles [6]. Today an unprecedented development in particle synthesis is generating a whole new set of colloidal particles, characterized by different sizes, shapes, patterns, particle patchiness, and functionalities [7]. The concept of “Janus particles” was first raised by de Gennes 20 years ago in his Nobel Prize lecture [8]. What de Gennes had in mind was that these amphiphilic Janus particles might behave like surfactant molecules to adsorb at the water-air interface, forming a mono-layer that de Gennes described as a “skin that can breathe” since small molecules would still be able to diffuse through the interstices between the Janus particles in the mono-layer. Janus particles are the analogue to the surfactant molecule, which has a hydrophilic head group and hydrophobic tail(s). When we think about Janus particles, we usually consid
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