From Heterocoagulation to Biorecognition: Preparation of Surfaces for Direct Measurement of Their Interactions in a Surface Force Apparatus Patrick Kékicheff Summary: Due to the atomic resolution in surface separation accessible the Surface Force Apparatus technique provides an avenue for investigating the interactions in real systems, provided the model surfaces chosen for study have both equivalent intricate surface chemistry and structural properties. To overcome the difficulty of surface-altering treatments when preparing suitable surfaces for the SFA and to realize interfaces fully representative of real systems immersed in solvents we have developed different experimental procedures. In particular, adsorption of nanoparticles from bulk colloidal dispersions, controlled solvent flow for coating substrates with polyelectrolytes multilayers, Langmuir Blodgett deposition of phospholipids membranes inserting ligands/receptors, all illustrate how one can get insights into subtle phenomena revealed by the force-distance profiles when the true colloidal state is maintained, biomaterials are built and molecular recognition is involved. Keywords: biomaterials; coatings; colloids; molecular recognition; polyelectrolytes Introduction Surface forces play a crucial role in the stabilisation of colloidal suspensions, aggre- gation, phase behaviour in surfactant sys- tems, membrane behaviour, recognition between protein and biological species, adhesion, lubrication, coating, and many other applied and commercially important areas (detergency, food industry, cosmetics, drug delivery, enhanced oil recovery, biocompatibility, etc.). [1] Both repulsive and attractive forces can occur between surfaces, and they can extend in range from only a few molecular diameters to micro- meters. The materials constituting the bodies may be crystalline, amorphous, metallic, and the interfaces may be solid or liquid, while the space between the bodies may consist of pure liquids or solutions, gases or vapors, or even vacuum in certain industrial processes. The surface properties of the bodies are usually modified by the adsorption of various molecular species, e.g. vapor, liquid conden- sates (as bridges of capillary-condensed liquid), ions, surface active agents and macromolecules. Nature and industrial pro- cesses take advantage of these surface properties modifications as the effects on the surface forces allow similar and dissimilar materials to arrange themselves into intricate structures and to form complex composite architectures, as found in many fields spanning from the phenomena of hetero- coagulation in colloid science to biorecogni- tion between ligands and receptors attached to surfaces. Therefore the subtle interplay between all the interactions acting between two bodies must be understood not only between like materials, but also between unlike materials; its control will allow the scientists and engineers to develop new advanced materials. Surface forces have been inferred from different techniques, which can be classified into two complementary categories. [2] Ei- ther the interaction profile is measured at Institut Charles Sadron, C.N.R.S., Université de Strasbourg, 23, rue du Loess, B.P. 84047, 67034- Strasbourg cedex 2, France E-mail: patrick.kekicheff@ics-cnrs.unistra.fr Macromol. Symp. 2014, 335, 24–42 DOI: 10.1002/masy.201200119 24 | ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com