Mixed particle-surfactant layers at liquid interfaces. | Consiglio Nazionale delle Ricerche

Joint research project

Project leaders: Libero Liggieri, Shi-yow Lin
Agreement: TAIWAN - NSTC - National Science and Technology Council
Call: CNR/NSC 2014-2015
Department: Chemical sciences and materials technology
Thematic area: Chemical sciences and materials technology
Status of the project: New

Research proposal

The large availability of new nanomaterials and the increasing utilization of nanoparticles (NPs) in different products and technologies is raising the interest for their effects on the properties of liquid interfaces. In fact relevant chemico-physical effects of NPs have been already shown in relation to the mechanical stabilization of liquid interfaces, to droplet coalescence and to the basic properties such as surface/interfacial tension and dilational rheology (the response of surface tension to perturbations of the interfacial area). That opens interesting scenarios for the utilization of NPs as surface-active species [1-3], alternative to classical surfactants, in a vast number of products and technologies (foam and emulsion technologies, paints, inks, pharmaceuticals, cosmetics, foods, ....). NPs segregation at the liquid interface is driven by their hydrophilic/hydrophobic character.
Several medthods to modify such feature have been proposed, based on specific chemical or chemico-physical treatments of the NPs surface. However, these treatments are in general too complex and expensive for practical applications on an industrial scale. Surfactant adsorption onto the particle surface is an alternative way to obtain such modifications. In fact that can be simply obtained by adding surfactants to the NP suspensions. Tuning the surfactant concentration can bring in a simple way to achieve different degrees of hydrophobicity/hydrophilicity. In spite trivial from the operative point of view, using such strategy in practical applications requires a deep understanding of the complex physico-chemical interplay between particles and surfactants in the bulk phase and at the liquid interface.
Based on this idea, during the last years we have investigated the interfacial properties of aqueous dispersions of silica NPs after addition of common surfactants [4-8], such as Cetyl trimethylammonium bromide (CTAB), octadecylamine (ODA), or palmitic acid (PA). While a picture of the effects for aqueous-air surfaces is relatively clear, how these NP-surfactant mixtures behaves in water-oil systems is still to be explored in detail. The presence of oil soluble surfactants, such as ODA or PA opens, in fact, a variety of different scenarios, depending on the initial surfactant distribution among the two liquid phases [7-8].
Thus the present study is aimed at investigating in more and large detail these liquid-liquid systems containing NPs and surfactants, in order to clarify the role of the surfactant solubility and the way it impacts on the different phenomenological observations. The results are important to understand the basic behavior of these novel surface-active nanostructures and to find applications in emulsion technology (Pickering emulsions), as applied to oil industry, foods, liquid-liquid extraction processes and others.
Accordingly, aqueous dispersions of silica NPs of controlled sizes (10 to 200 nm), containing homologue series of surfactants mostly soluble (fat acids in the range C10 to C20) or insoluble (trimethylammonium bromides in the range C10-C16) in oil (hexane) will be investigated by a variety of techniques available at CNR-IENI and at NTUST, in order to characterize their surface properties, the adsorption of surfactant on the particles, the structure of the interfacial layers, the exchange of particles and surfactant between the liquid phases. These information will be utilized to build quantitative and qualitative models to describe the observations on the basis of the interactions in the system and the interplay of the different species. Finally the models will be applied to predict the ability of the studied particle-surfactant systems to generate foams and emulsions and improve their stability.
IENI and NTUST share a large expertise in the investigation of the chemico-physical properties of interfacial layers at liquid interfaces. In particular NTUST developed advanced methodologies based on the Drop Shape technique for the accurate measurement of dynamic and equilibrium surface/interfacial tensions.
CNR-IENI masters a spectrum of sophisticated techniques for the investigation of interfacial layers, such as dilational surface rheometers implemented in Drop Shape and Capillary Pressure tensiometers, a Langmuir trough equipped with Brewster Angle Microscopy and Ellipsometry to investigate the structure and phase behavior of these layers.
Both laboratories possess a large experience in the modeling of the thermodynamic features of adsorption layers and of the transport and kinetic processes involving surfactants in liquid-liquid systems.
The two laboratories have already collaborated recently within an international network on a similar subject, publishing a joint paper [5]

References:
1) P.B. Binks. Particles as surfactants-similarities and differences. Current Opinions in Colloids and Interface Science. 7 (2002) 21-41.
2) V. Dutschk, J. Chen, G. Petzold, R. Vogel, D. Clausse, F. Ravera, L. Liggieri. The role of emulsifier in stabilization of emulsions containing colloidal alumina particles. Colloids and Surfaces A-Physicochemical and Eng. Aspects 413 (2012) pp.239-247
3) D. Zabiegaj, E. Santini, E. Guzmán, M. Ferrari, L. Liggieri, et al., Nanoparticle-laden interfacial layers and application to foams and solid foams. Colloids and Surfaces A 2013. available on-line http://dx.doi.org/10.1016/j.colsurfa.2013.02.046
4) F. Ravera, E. Santini, G. Loglio, M. Ferrari , L. Liggieri. Effect of Nanoparticles on the Interfacial Properties of Liquid-Liquid and Liquid-Air Surface Layers. Journal of Physical Chemistry B, 110 (2006), pp. 19543.
5) P.A. Yazhgur, B.A. Noskov, L. Liggieri, S.-Y. Lin, G. Loglio, R. Miller, F. Ravera . Dynamic properties of mixed nanoparticle/surfactant adsorption layers. Soft Matter 9 (2013) pp. 3305-3314
6) L. Liggieri, E. Santini, E. Guzman, A. Maestro, F. Ravera. Wide-frequency dilational rheology investigation of mixed silica nanoparticle-CTAB interfacial layers. Soft Matter 7 (2011) pp. 7699-7709
7) E. Santini, E. Guzman, F. Ravera, M. Ferrari, L. Liggieri. Properties and structure of interfacial layers formed by hydrophilic silica dispersions and palmitic acid. Physical Chemistry Chemical Physics 14 (2012) pp. 607-615.
8).C.P. Whitby, D. Fornasiero, J. Ralston, L. Liggieri, F. Ravera. Properties of Fatty Amine-Silica Nanoparticle Interfacial Layers at the Hexane-Water Interface. J. Physical Chemistry C 116 (2012) pp. 3050-3058.

Research goals

The specific objectives of the proposed study are:
a) Investigation of the effects of particle size/area and of the surfactant solubility and concentration on:
- the transfer/partitioning properties of particle-surfactant complexes between immiscible liquids (aqueous and oily phases);
- the interfacial properties and interfacial rheology of the investigated aqueous-oily systems.
b) Increase the understanding of the different interactions and processes and develop quantitative models for the prediction of the observed behaviors.
c) Derive criteria for formulating emulsifier/foaming agents based on nanoparticle-surfactant associations. More generally these criteria could be used to address the formulation of de-emulsifier/de-foaming agents.

Besides the specific objectives, the project will allow establishing a synergy between two leading laboratories in the field of the dynamic physico-chemical processes at liquid-liquid interfacial layers, providing a unique opportunity to exchange the expertise on experimental methodologies and theoretical modeling and to complement measurements obtained with state-of-the-art instrumentation.

Last update: 08/06/2025