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The size control of gold nanoparticles synthesized insurfactantfree water with a continuous flow mode was elucidated and used toproduce higher concentration (3 mM) of stabilized gold nanoparticles.The originality of the synthesis was to finely modulate the initialpH of the reducing agent instead of the gold precursor to modify thekinetic of the reaction. The acceleration of the kinetic (∼1s) prevents the modification of the gold precursors ensuring the controlof the final size (from 3 to 25 nm) of the nanoparticles with a lowpolydispersity for aqueous surfactant free solution. The accuratemeasure of the size distribution by small angle X-ray scattering wascombined to the use of a model based on the coupling of nucleationand growth equations together with a progressive injection of monomers.The results on the final state show that the size of the nanoparticlesis indeed controlled by the kinetic of reduction of gold atoms. Amillifluidic setup equipped with a homemade mixer offers a robustway of rapid mixing to obtain a reproducible production of large amountsof nanoparticles. [ABSTRACT FROM AUTHOR]

A comprehensive study of the mechanism of gold nanoparticle formation has been conducted using third-generation synchrotrons. The particles were obained by reduction of AuCl3by BH4−in toluene. Gold oxidation state was monitored by X-ray absorption near edge spectroscopy (XANES), while the size and concentration of the nanoparticles were assessed by small-angle X-ray scattering (SAXS). A time-resolution of 100 ms has been achieved for a total formation time of a few seconds. The change with time of the total amount of Au(0) present in the solution is obtained by XANES. The change of the amount of Au(0) inside the nanoparticles is obtained from the SAXS signal. The comparison between these two quantities shows that a measurable amount of Au(0) exists transiently as monomers (or very small entities) in solution and this quantity is linked to an observed burst of nucleation of nanoparticles. The reduction kinetics is strongly influenced by the presence of ligands and a change in temperature. A model coupling the observed reduction kinetics and nucleation and growth laws is able to recover the final size and number densities of the explored experimental conditions. [ABSTRACT FROM AUTHOR]

We show in this paper that three ways of characterizing “spontaneous” lateral packing of amphiphiles are equivalent: the spontaneous curvature, the molecular packing parameter, and the refined hydrophilic−lipophilic balance known as HLD (hydrophilic−lipophilic deviation). Recognition of this equivalence, with its underlying hypothesis of incompressible fluid with lowest surface energy, reinforces the single parameter bending energy expression implicit in the classical papers by Ninham and Israelachvili, as well as all the predictive models of solubilization developed as yet. [ABSTRACT FROM AUTHOR]

A complex between cetyltrimethylammonium bromide (CTAB) surfactant and silver bromide (CTASB) is recognized by NMR and X-ray photoelectron spectroscopy (XPS) to be the entity at the surface of gold nanorods, resulting from an in situformation in the classical scheme of synthesis. It can thus be introduced directly along with the initial reactants in place of silver(I) salt to produce a new effective synthesis of these objects. Complementary XPS and quartz crystal microbalance (QCM) measurements on macroscopic gold surfaces confirm a strong adsorption of CTASB that is higher than that of CTAB and any other CTAX surfactants. The role of CTASB as a rod inducing agent by surface complexation is stressed. [ABSTRACT FROM AUTHOR]

By means of small-angle neutron scattering and conductivity measurements, we study the microstructure of octylammoniumoctanoate/octane/water catanionic reverse microemulsions with an excess of anionic or cationic surfactant. Increasing the surface charge makes the microemulsion able to incorporate much more water than in the neutral case, up to 10 water molecules per surfactant. Even with charges in the surfactant film, wormlike micelles are present in the microemulsion domain. Along water dilution lines, the classical rod-to-sphere transition due to the minimization of the curvature energy of the rigid surfactant film is observed. When temperature is decreased, a re-entrant phase transition associated with the liquid−gas equilibrium of attractive cylinders is observed. Using the framework of the Tlusty−Safran theory, attraction could originate from junctions between wormlike reverse micelles. In any case, the spontaneous curvature of the catanionic surfactant film depends on both the temperature and the net charge, whatever the sign of the latter. [ABSTRACT FROM AUTHOR]