Viscoelasticity of phospholipid layers at different fluid interfaces

The interfacial relaxation behaviour of the phospholipid L-alpha-dipalmitoy l phosphatidyl choline (DPPC) as soluble adsorption layer at the water/chlo roform interface and as spread insoluble monolayer at the water/air interfa ce has been investigated. Transient changes of the area of a pendent drop g enerated by definite drop volume increments induce interfacial relaxations of the phospholipid adsorption layer at the liquid/liquid interface. The dy namic interfacial tension response to small disturbances of the equilibrium state were determined using the axisymmetric drop shape analysis (ADSA) te chnique. From the response function information on the exchange of surfacta nts and the interfacial dilational elasticity of the phospholipid layer are obtained. A Langmuir trough equipped with an oscillating barrier was used to investigate the relaxation behaviour of a spread insoluble phospholipid monolayer. Harmonic area perturbations initiate relaxation processes in the monolayer and provide information on the dilational elasticity and viscosi ty of the DPPC monolayer. The elasticity behaviour for soluble and insolubl e phospholipid layers at different fluid interfaces is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.