Wettability and topography of phospholipid DPPC multilayers deposited by spin-coating on glass, silicon, and mica slides.

The surface free energy of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) layers deposited on glass, silicon, or mica by the spin-coating method was estimated. For this purpose, the advancing and receding contact angles of water, formamide, and diiodomethane were measured, and then two concepts of the interfacial interactions were applied. In the contact angle hysteresis approach, the apparent total surface free energy is calculated from the advancing and receding contact angles of the probe liquids, and in the Lifshitz-van der Waals/acid-base approach, the total surface free energy is calculated from previously determined components of the energy, that is, the apolar Lifshitz-van der Waals and the polar electron-donor and electron-acceptor, which are calculated from the advancing contact angles of the probe liquids alone. Comparison of the results obtained using these two approaches provided more information about changes in the hydrophobic/hydrophilic character of the DPPC layers and, simultaneously, a verification of the approaches. Moreover, the roughness and topography of the investigated layers were also examined by atomic force microscopy measurements. The hydrophilic character of the DPPC layers decreased if up to 0.5 mg of DPPC/mL was used to deposit on the substrates by the spin-coating method. Then it increased and leveled off if up to 2-2.5 mg of DPPC/mL was used. The changes in the energy were correlated with the changes in topography of the surfaces.