Otilia Cinteza

The aqueous liquid/liquid interphases formed by chitosan-anionic surfactant complexes

The solubility behavior of cationic chitosan complexes with two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium bis(2-ethylhexyl)sulfosuccinate (AOT), as well as the formation of gel-like membranes capable of separating two aqueous polymer and surfactant solutions has been investigated. The chitosan—surfactant complexes can exist either as homogenous clear solutions or precipitates or as membranes, depending on the molar ratio between the polymer structural units and the surfactant and the degree of protonation of the polymer. The transitions between the phases were determined and correlated with structural and compositional parameters. The conditions for the formation of new stable chitosan AOT microcapsules were observed and were compared with those of chitosan-SDS. The two surfactants with different structures behave very differently. SDS forms gel-like membrane with chitosan at a much lower concentrations than AOT, even though the former has a higher critical micellar concentration. It was postulated that in forming a gellike membrane from chitosan—surfactant complexes a certain role is played by the existence of micelles and their size and shape. The smaller, spherical, more abundant micelles in SDS solutions lead to the formation of mechanically resistant membranes at a lower concentration than AOT. The difference in behavior is more evident in the concentration domain where AOT forms lamellar self-assemblies. The added ethyl alcohol affects both the solubility curves and the membrane formation.

Influence of hydrophobic characteristic of organo-modified precursor on wettability of silica film

The objective of this study is to design new hybrid silica materials as templates with hydrophobic properties, prepared at room temperature by a base catalyzed sol–gel process. As silica sources, organoalkoxysilanes functionalized with short hydrophobic chains were used: tetraethylorthosilicate (TEOS), methyltriethoxysilane (MTES), vinyltriethoxysilane (VTES), octyltriethoxysilane (OTES) and isobutyltriethoxysilane (iTES). It was shown that hydrophobicity of the functionalized silica nanoparticles increased as a function of length of the aliphatic chains (MTES < iTES < OTES) or when, instead of a hydrophobic alkyl chains (substituting group of silica precursors), a monounsaturated group was used (VTES). It was observed that the samples responded in a specific way to each type (hydrophilic or hydrophobic) of the dropped liquid. Even though the experiments were limited to short hydrocarbon chains, they showed that there is a threshold to reach high hydrophobicity of the hybrid surface.

Researches on the Embedding of Decorporators in Microemulsions

In this research, microemulsions of various types (Winsor II, III and IV) and structures (droplets or bicontinuous) were prepared and the effect of the embedded EDTA-Na and DTPA-Zn chelators on the phase behaviour and stability of the microemulsions was investigated. For all types of microemulsions, the presence of decorporators at therapeutical concentration modifies the whole equilibrium of the system.