Abstract:

Micro- and macrostructural behaviors of three different lyotropic liq. crystals (LLCs) loaded with a dendrimer, namely second generation poly(propylene imine) (PPI-G2), were studied by rheol. and ESR (EPR). The three mesophases were L$\alpha$, Q224, and HII composed of glycerol monooleate (GMO) and water-PPI-G2 soln. (and d-$\alpha$-tocopherol (vitamin E) in the case of HII). We characterized the impact of PPI-G2 interactions with the components of the host mesophases on their structural characteristics on different length scales. The incorporation of PPI-G2 within the L$\alpha$ and HII systems induced the formation of more elastic hexagonal systems with a solid-like behavior, while in the Q224 system a different trend with a liq.-like behavior was obsd. As a result, the dendrimer induced a remarkable change in both the structural and viscoelastic properties of the systems. Hence, the microenvironment in the interface region within the systems was monitored by computer-aided EPR using 5-doxylstearic acid (5-DSA) as a pH-dependent probe. The microviscosity ($\tau$) and order (S) of systems were sensitive to the PPI-G2 presence: when PPI-G2 concn. increased, $\tau$ and S increased in both the L$\alpha$ and Q224 systems. In the HII systems two trends were obsd., reflecting a decrease in $\tau$ and S up to 10 wt.% PPI-G2 and subsequently their increase at higher dendrimer concns. PPI-G2 interacted strongly with the GMO hydroxyl groups in the L$\alpha$ phase, with the water mols. in the Q224 systems. In the HII mesophase strong interactions with both the water and GMO hydroxyl mols. were detected. [on SciFinder(R)]