Interaction of Carbon Black Particles and Dipalmitoylphosphatidylcholine at the Water/Air Interface: Thermodynamics and Rheology

The interaction of carbon black particles (CB) with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) at the water/air interface has been investigated by means of a pool of surface sensitive techniques, in order to analyze the thermodynamic and rheological aspects of these mixed systems. The incorporation of carbonaceous particles to the lipid monolayers induces changes on the surface pressure-area isotherm, as revealed by the shifting to higher surface area of the maximum packing degree of the monolayer, and the decrease of the collapse pressure. These changes are strongly dependent on the DPPC:CB weight ratio at the interface and can be explained by the disruption of the monolayer structure due to the particle incorporation that provokes the modification of the cohesive interactions along the monolayer. Measurements of dilational viscoelasticity against frequency, at different degrees of monolayer compression, have been performed by means of the Oscillatory Barrier method. The rheological response of the monolayer is only slightly affected by the presence of CB, even if a modification of the quasi-equilibrium dilational elasticity, as well as of the frequency dependence of the viscoelastic modulus, is appreciable increasing the particle concentration. Being DPPC the major component of many systems with biological interest (cell membranes, lung surfactant), the results obtained here are expected to contribute to the understanding of the carbon particle interaction with biological relevant systems.