ABSTRACT
Phospholipids, which belong to a group of lipids, besides the principal role they play in biological membranes, are also biosurfactants [l], especially those with shorter hydrocarbon chain(s). They can stabilize or destabilize dispersed systems, such as emulsions or suspensions. Lecithin of natural origin is commonly used in food processing, pharmaceutical products, cosmetics, and others. The stability of the dispersed systems is generally determined by electrostatic repulsive forces (zeta potential) and attractive London dispersion forces. In the case of long-chain surfactants, steric stabilization can also take place. However, the principal role they play is that of constituents of the living cell membrane, where they form bilayers. Therefore, the model biological membranes, which are monolayers, bilayers, and multilayers of lipids and phospholipids, have been extensively investigated for several decades, not only with respect to the membrane properties but also with respect to many practical applications. In this chapter, we will briey discuss the historical background
3.1 Introduction .......................................................................................................................... 121 3.1.1 Historical Background .............................................................................................. 122
3.1.1.1 The Langmuir Films .................................................................................. 122 3.1.1.2 The Langmuir-Blodgett Films .................................................................. 123 3.1.1.3 The Structure of Biological Membrane ..................................................... 123
3.1.2 Fabrication of Solid-Supported Lipid Layers ........................................................... 125 3.1.3 Current and Prospective Advanced Techniques for the Investigation of Solid-
Supported Lipid Layers ............................................................................................ 126 3.2 Studies of Wettability of Lipid Layers .................................................................................. 127
3.2.1 Surface Free Energy ................................................................................................. 127 3.2.2 Contact Angles on Solid-Supported Lipid Layers .................................................... 128
3.2.2.1 Contact Angles on DPPC Layers Formed by Aqueous Solution Spreading ...128 3.2.2.2 Contact Angles on DPPC and DOPC Layers Formed by Chloroform
Solution Spreading ..................................................................................... 130 3.2.2.3 Contact Angles on DPPC Layers on Various Supports Formed by
Spin-Coating .............................................................................................. 133 3.2.2.4 Contact Angles on Phospholipid Layers Deposited Using the LB/LS
Techniques ................................................................................................. 135 3.2.3 The Effect of Enzymes on Changes in the Wettability of Phospholipid Layers ...... 139 3.2.4 Perspectives .............................................................................................................. 142
3.3 Conclusions ........................................................................................................................... 142 Acknowledgments .......................................................................................................................... 143 References ...................................................................................................................................... 143
of these investigations, the preparation methods for the solid-supported phospholipid layers, and the methods for their investigations, with special emphasis on the advanced techniques applied nowadays. Finally, studies on the wettability of such layers that we have recently carried out will be described. Some of the results will also be compared with the atomic force microscopy (AFM) images of the investigated layers. Some future research we are planning to carry out will also be mentioned.
