The incidence of the structural features on the self-assembly of different poloxamines (the conventional sequential Tetronic 304, 901, 904, 908, 1107, 1301, and 1307; a reverse-sequential counterpart Tetronic 150R1; and a chemically modified derivative, N-methylated Tetronic 1107) was thoroughly studied in 10 mM HCl by means of pi-A isotherm, surface tension, and pyrene fluorescence measurements. The size and size distribution of the aggregates were investigated by dynamic and static light scattering, and the morphology was probed by transmission electron microscopy. The abilities of the different derivatives to solubilize the drug simvastatin were also evaluated. Poloxamines with both higher PO/EO ratio and molecular weight (T1301 and T150R1) led to micelles with larger and more hydrophobic cores, particularly adequate for hosting hydrophobic molecules and protecting the labile lactone form of simvastatin from hydrolysis. On the other hand, the hydroxy acid form of simvastatin interacted with the central ethylenediamine group under alkaline pH (T304) or when a permanent positive charge due to methylation was present. Micelles of long poloxamine molecules containing large PPO blocks (with 23-29 units, namely, T1301, T1307, and T150R1), particularly the one that also has long PEO blocks, were the most physically stable toward dilution.

A series of semifluorinated n-alkanes (SFAs) of the general formula F(CF 2 ) m (CH 2 ) n H, (in short FmHn) where m ) 10 and n ) 6-20, have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were obtained under a variety of experimental conditions such as spreading volume, subphase temperature, and compression speed. The Langmuir monolayer experiments have been complemented with Brewster angle microscopy results which enabled both direct visualization of the monolayers structure and estimation of the monolayer thickness at different stages of compression. Our results show that these "nonclassical" film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are capable of monolayer formation at the air/water interface. It has been observed that with the increase in the molecule's length, its stability at the free water surface increases. The negative sign of the measured surface potential, ∆V, proves that SFA molecules are oriented at the air/water interface with their perfluorinated parts directed toward the air. The effective dipole moments reach the value of -0.65 ( 0.1 D at the minimum for all stable SFAs. The analysis of the direction of the molecular dipole moment in respect to the main axis enabled us to estimate that the minimum effective dipole moment is achieved for a molecule oriented at the angle of about 35°to the surface normal. The relative intensity measurements allow one to conclude that film molecules are tilted in respect to the surface normal at the vicinity of collapse.