Scanning tunneling microscopy investigation of the aggregation phases of amphiphile molecules

In the present paper various aggregation phases of the binary system of an amphiphile, P507 and water have been studied by means of scanning tunneling microscopy (STM), local-barrier-height(φ) images and the tip height as a function of bias voltage. The sample was prepared by spreading a thin layer of P507 water solution on the graphite substrate and left in air for natural drying. Three different lyotropic mesomorphic phases (lamellar, hexagonal and cubic phases) along with the spherical, disk-like and rod-like micelles were imaged on the sample surface. The geometric shape and dimension of these phases match nicely what speculated in previous papers. Combining information from the STM and φ images we are able to tell if the hydrophilic part of the molecules of a phase is inward or outward. Besides, the mechanical characteristics of the aggregation phases, which might be responsible for many important functions of biological membranes, have also been studied.