Phospholipid Langmuir Film as Template for in Situ Silica Nanoparticle Formation at the Air/Water Interface

This study describes for the first time the in situ formation of small-sized silica nanoparticles after the polycondensation of tetraethylorthosilicate (TEOS) at the air/water interface. Mixtures of TEOS and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) are prepared with different molar ratios (TEOS/DPPC 15:1, 50:1, 500:1, and 5000:1) and dissolved in chloroform. Spreading TEOS/DPPC 15:1 and 50:1 on the water surface of a Langmuir trough leads to an initial increase of the surface pressure (∼26−29 mN/m) after allowing chloroform to evaporate. Within the reaction time of 21 h, only a slight decrease of the surface pressure by ∼2 mN/m occurs. Films of silica/DPPC mixtures are transferred from the air/water interface to silicon wafers by dip-coating. The morphologies of the silica nanoparticles and agglomerates together with DPPC are observed using tapping mode atomic force microscopy (AFM). An ordered array of silica nanoparticles can be observed after 21 h reaction of the precursor solution of TEOS/DPPC 500:1 and transfer onto hydrophilic silicon substrate. A mixture with a molar ratio of TEOS/DPPC of 5000:1 is also placed onto the water surface. DPPC forms a uniform film observed by AFM after film transfer. Silica rich domains can be observed with mesoporous morphology.