Dendritic polyamine architectures with lipophilic shells as nanocompartments for polar guest molecules: A comparative study of their transport behavior

Dendritic core-shell architectures were synthesized by simple melt reactions of polyethylenimine (PEI) with different fatty acids. These systems were investigated towards their ability to encapsulate various guest molecules. Parameters, such as the length of the attached alkyl chain, size of the polymer core, concentration of the core-shell architecture in solution, pH, and nature of the guest molecule were investigated and compared. Guest molecules that bear anionic groups, such as carboxylate, phosphate, sulfonate, or acidic OH groups, as present in phenol units, are readily encapsulated and transferred from the aqueous phase to the organic phase because of multiple anionic–cationic interactions. Hyperbranched polymer architectures exhibit enhanced encapsulation properties when compared with their linear counterparts. In case of the hyperbranched system PEI₂₅C16 amide higher transport capacities were observed at lower concentrations of the polymer, for example, 26 guest molecules at 10⁻⁵ mol L⁻¹ versus 143 at 10⁻⁶ mol L⁻¹, suggesting formation of larger aggregates. The aggregation behavior of these polar nanocompartments were investigated at different concentrations by AFM showing particle aggregates of typically 250 nm at a concentration of 10⁻⁵ M. The individual particle sizes in these aggregates are similar to the particle size at 10⁻⁶ M concentration, typically 4.0–5.5 nm (AFM height). This indicates that aggregate formation takes place at concentrations higher than 10⁻⁸ M and transport might be mediated by small aggregates rather than unimolecular particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2287–2303, 2007     

Critical petermann K factor for intensity noise squeezing

We investigate the impact of the Petermann-excess-noise factor K>/=1 on the possibility of intensity noise squeezing of laser light below the standard quantum limit. Using an N-mode model, we show that squeezing is limited to a floor level of 2(K-1) times the shot noise limit. Thus, even a modest Petermann factor significantly impedes squeezing, which becomes impossible when K>/=1.5. This appears as a serious limitation for obtaining sub-shot-noise light from practical semiconductor lasers. We present experimental evidence for our theory.     

Search for isovector giant monopole resonances via the Pb(3He,tp) reaction

The (nat)Pb(3He,tp) reaction at E(3He) = 177 MeV was studied to identify 2Planck's over 2piomega isovector monopole strength in Bi isotopes. Monopole strength was found in the region -45相似文献