Surface Chemistry

Institut Laue-Langevin

Adsorption from solution

The adsorption of molecules from liquids and solutions to solid surfaces is central to many areas of academic and industrial importance such as colloidal stability, lubrication, and making ice cream. Although of enormous importance almost nothing is known about these adsorbed layers. We have recently developed a combination of experimental methods that can provide details of the state, absolute composition and crystallographic structure of the adsorbed layers. Currently projects are available to investigate formation of crystalline layers for a number of interesting materials and also to probe their surface mixing behaviour [Messé et al.(2005), Duim and Clarke(2006), Inaba et al.(2002), Arnold et al.(2002)]. Amongst the techniques we use to study surface adsorbtion are Differential Scanning Calorimetery (DSC) at the BP Institute, neutron diffraction at ILL Grenoble, and X-ray diffraction at various facilities across Europe.

A Special Relationship

Phase behaviour of amine and carboxylic acid mixtures in the bulk and in two-dimensional layers

Odd-n carboxylic acids aligned on a graphite substrate Amines (RNH2) and carboxylic acids (RCO2H) can exchange a proton to give an ionic salt RNH3+ RCO2-. Hence the interaction between the two species is much stronger than expected. Interestingly, amines and acids have a rather special relationship, as it appears that several other complexes between them can also form eg. A3B containing three acid molecules and one amine [Cheah et al.(2004)]. Although important in the bulk, this effect is particularly interesting in 2D adsorbed monolayers. Such strong interactions may be expected to produce particularly stable monolayers with a range of applications from detergency to lubrication. We are presently using calorimetry and Scanning Tunneling Microscopy (STM) to map the phase behaviour of particular combinations of acids and amines when adsorbed as two-dimensional layers and to image the adsorbed molecules at molecular resolution, in collaboration with groups in Spain and Belgium.

Some of the Black stuff

Adsorption of heterocyclics from solution at the solid-liquid interface

This is part of an ongoing project to identify and characterize molecular monolayers physisorbed from liquid mixtures and solutions to solid surfaces. These layers are central to many areas of academic and industrial interest including colloidal stability, photovoltaics, detergency, lubrication and oil recovery. We aim to investigate the behaviour of asphaltenes devivatives (large poly-heterocyclic species that form a thick black residue in crude oils) adsorbing to a solid surface from a liquid solution. The adsorption of these species is considered to be very important in oil recovery because their adsorption seems to change the wetting characteristics of the oil-bearing rock. The rock is changed from water loving to oil loving, making the oil, which we would like to recover, stick more strongly and making it harder to recover.

Messé, L., Clarke, S.M., Inaba, A., Perdigón, A., Castro, M.A. and Arnold, T. (2005) Alkane-alcohol mixed monolayers at the solid/liquid interface. Langmuir 21, 5085-5093.
◾Duim, W.C. and Clarke, S.M. (2006) Adsorption and mixing behavior of ethers and alkanes at the solid/liquid interface. J. Phys. Chem. B 110, 23853-23859.
◾ Inaba, A., Clarke, S.M., Arnold, T. and Thomas, R.K. (2002) Mixing behaviour in 2D layers of linear alkanes adsorbed on graphite. Chemical Physics Letters 352, 57-62.
◾Arnold, T., Thomas, R.K., Castro, M., Clarke, S.M., Messé, L. and Inaba, A. (2002) The crystalline structures of the even alkanes hexane, octane, decane, dodecane and tetradecane monolayers adsorbed on graphite at submonolayer coverages and from the liquid. Physical Chemistry: Chemical Physics 4, 345-351.
◾Cheah, N.P., Messé, L. and Clarke, S.M. (2004) The formation of solid monolayers of linear amines adsorbed on graphite from the liquid. J. Phys. Chem. B108, 4466-4469.