Group 3 - Statistical Mechanics and Experimental Thermodynamics
Group Coordinator: António Palavra
After thirty years of existence the Group has developed an expertise in a wide spectrum of topics and techniques which comprise phase equilibria and supercritical extraction, transport and surface properties and molecular simulation.The work is carried out in collaboration with other Groups in the Centre and elsewhere, and ranges from fundamentals to applications, from molecular simulation to experiment, from solid to gas phase, from pure substances to multicomponent mixtures. During the 2002-2004 period, besides strengthening our fields of expertise, new lines of research will be opened. These involve the area of biomaterials and the application of new technologies to the solution of environmental problems. The description of the ongoing and planned work is organized into three sections:
Molecular Modelling of Fluids and Interfaces
Some of the most important developments within the Group result from the use of increasingly powerful computational methods, the performance of key experiments, and the access to new theoretical tools. This three-fold methodology was implemented through the combination of various facilities and techniques (available at the group or elsewhere):
- A locally-built computer cluster, where quantum/statistical mechanics algorithms are operational (Ab-initio, MD, MC);
- A wide range of complementary experimental techniques (VLE, surface tension/pressure studies), microscopy (AFM, BAM), spectroscopic analysis (NMR, GIXDS, PM-IRRAS);
- A set of theoretical tools (SAFT, Integral Equations, Isotope Effects Theories).
All on-going and future projects stress the link between the underlying molecular characteristics of a system and its macroscopic behaviour. The diversity of the studies (from the molecular point of view as well as the techniques used) can be exemplified by the following project list:
- Semifluorinated alkanes (mixed solutions and films of SFA, Langmuir/LB layers, colloidal solutions);
- Cyclic compounds (cycloalkanes in solution, cyclic surfactants in organized systems);
- Ionic liquids (modelling R-methylimidazolium salts, interfaces);
- Model molecular liquids (shape, mixtures of enanteomers);
- Molecular crystals ( metallocenes);
- Gas hydrates;
- Ternary diagrams (classification; building-up of model diagrams);
- Microphase separation (metastable water, gallium);
- Isotopic systems (aqueous argon and methane; integral equations);
- Near-critical or metastable systems (closed-loop immiscibility in aqueous methylpyridines; spinodal lines of mixtures).
Physical Chemistry of Surfaces
The stability and organization of mixed films of semifluorinated alkanes with different surfactants (hydrogenated and fluorinated fatty acids and alcohols, PS-PEO diblock copolymers) have been characterized using the Langmuir-Blodgett (LB) technique, Brewster angle microscopy (BAM), atomic force microscopy (AFM), GIXDS and PM-IRRAS. The solution behaviour and aggregation phenomena of some of these systems has been studied. The interfacial behaviour of ionic liquids with a fluorinated counterion was also addressed.
The main transition in natural phospholipids (with and without proteins) will be investigated by surface pressure and surface potential vs. area measurements, and BAM observation at the air-water interface. Phase diagrams of two-dimensional (monolayers at the air-water interface) and three-dimensional amphiphilic binary mixtures will be measured, and comparative studies will be applied to biomembrane models; it is hoped that this will contribute to the understanding of the functioning and behaviour of biomembranes through the study of the phase behaviour of model systems in different states of aggregation.
Biomembranes will be modelled by LB film deposition and will be further characterised by AFM and/or X-ray diffraction.
The aim is to understand the molecular mechanism of lung surfactants in biomembranes.
We will continue to collaborate with Group IV on the incorporation of proteins in dye/lipid mixed LB films.
The characterization of thin liquid films by interferometry and AFM is under development. The studied systems will include films of lipids and aqueous fluids on model surfaces of variable hydrophobicity. These studies will hopefully assist in the understanding of the role played by surface forces in the behaviour of wetting films. Film thickness and stability as well as disjoining pressure isotherms will be investigated.
The study of the interfacial properties of biomaterials in contact with biological model fluids will continue. The wettability studies performed in the Group laboratories will soon be complemented by Circular Dichroism (CD), SEM and AFM studies in collaboration with Group I and ICEMS (IST). The objective is the understanding of the influence of surface treatment, composition of the biological model fluid and conformation of the adsorbed proteins on the biomineralisation of model implant materials (such as titanium and hydroxyapatite).
Chemical Engineering and Materials Thermodynamics
The expertise in the design/construction of equipment for the measurement of thermophysical properties of fluids has naturally led to research in specific areas of industrial interest.
Concerning high viscosity liquids, the work aims at the establishment of New Viscosity Reference Fluids, mainly for industrial purposes. In particular, a new vibrating-wire sensor has been designed and constructed in order to measure high viscosity fluids. This project is being carried out within the framework of international collaborations, mainly under the International Association for Transport Properties. In addition, the measurement of viscosity and density of fluids covering wide ranges of temperature and pressure will proceed with novel vibrating-wire techniques. In particular, a programme aiming at the study of HFC’s, in collaboration with the Faculty of Sciences of the University of Lisbon, is being carried out.
Moreover, the research aiming at the design of clean separation processes using ionic liquids will continue to be addressed in collaboration with Centro de Processos Químicos of IST and with Group II of CQE.
The thermochemistry of synthetic apatites (hydroxy-, chloro- and bromo-) already under way, will be completed. The thermal characterization of materials (polyethylenes and polyethylene derivatives) will also be addressed. These two projects are conducted in collaboration with Group II.
Research will be carried out on the application of the Gas-Antisolvent (GAS) process to the production of encapsulated protein (and natural products such as lycopene, lutein, canthaxantine, and astaxanthine) microparticles, and theoretical analysis of the GAS process will be performed. Assessment through experiments and modelling of the role of process parameters (such as temperature, pressure, initial solute concentration, compressed gas addition rate) on process performance and product quality is also planned.
The encapsulated drugs produced by GAS will be used in release studies conducted in vitro and in vivo, in collaboration with the Faculty of Pharmacy, University of Lisbon. Other applications of supercritical fluid technology will be covered, namely studies on the minimization of the environmental impact of extraction and separation processes, on polymer surface modifications and on extraction of natural products.
The Group will produce new phase equilibria measurements, namely VLE data at high temperatures, and P-V-T data of binary gaseous mixtures. Also, we will continue studies of gas solubility on micellar aqueous solutions of a cationic surfactant at 1 atm.