Rheological studies of the interactions in cellulose/ethylene diamine/salt systems

Degree of polymerization (DP) of cellulose was measured to confirm that aging time and salt concentration did not cause cellulose degradation. Dynamic rheological studies of cellulose solutions were carried out to probe the evolving interactions between cellulose and ethylene diamine (EDA)/salt solvent system. Potassium thiocyanate (KSCN) was used as the salt in these studies. Steady shear studies indicated that all solutions exhibited shear‐thinning behavior. The empirical Cox‐Merz rule did not hold true for the cellulose system with weak gel microstructure. The shear viscosities at the shear rates explored decreased with aging time. The zero‐shear viscosity, however, increased with increasing salt concentration. Oscillatory shear studies were investigated and the time temperature superposition (TTS) method was used to extend the experimental frequency range of the instrument. The results showed that the average relaxation time of the cellulose system decreased as the sample aged and increased with increasing salt concentration, indicative of dynamic interactions between cellulose and the solvent system in solution. The conformations of cellulose chains were constantly changing over time. The system gelled when the salt concentration was increased to a critical point. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2326–2334, 2008     

Inelastic neutron scattering study of the dynamics of the AlNiCo decagonal phase

The dynamics of the decagonal AlNiCo phase has been investigated on a single-grain quasicrystalline sample using inelastic neutron scattering. The decagonal structure can be viewed as a periodic stacking of quasiperiodic planes. The anisotropy between the modes propagating in the periodic and quasiperiodic directions is found to be much weaker than theoretically predicted. A strong resonance splitting is observed at an energy transfer of 15 meV for transverse modes polarized in the quasiperiodic plane. Received: 18 November 1998 / Accepted: 27 November 1998     

Organic–inorganic hybrid networks by the sol–gel process and subsequent photopolymerization

Organic–inorganic hybrid materials were prepared by a convenient two‐step curing procedure based on sol–gel condensation and subsequent photopolymerization. Novel bismethacrylate‐based hybrid monomers with pendant, condensable alkoxysilane groups were prepared by Michael addition and possessed number‐average molecular weights between 580 and 1600 g/mol. The formation of inorganic networks by sol–gel condensation of the alkoxysilane groups in the presence of aqueous methacrylic acid was monitored with rheological measurements. The condensation conversion was monitored with solid‐state ²⁹Si cross‐polarization/magic‐angle spinning NMR spectroscopy. Subsequent photopolymerization led to organic–inorganic hybrid networks and low volume shrinkage, ranging from 4.2 to 8.3%, depending on the molecular weight of the hybrid monomer applied. Highly filled composite materials with glass filler fractions greater than 75% showed attractive mechanical properties with Young's moduli of 2700–6200 MPa. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4274–4282, 2001     

Oxidative Hydroxylation of Benzene and Toluene by Nitrous Oxide Over Fe-Containing ZSM-5 Zeolites

The gas-phase partial oxidation of benzene and toluene to phenol and to cresols over Fe-containing ZSM-5 zeolites prepared by various methods was studied using N₂O as oxidant. Over FeZSM-5 synthesized by either isomorphous substitution or ion exchange the phenol selectivity reached nearly 100% at 573 K, however, only 25-30% cresol (mainly p-cresol) selectivity was observed in the oxidation of toluene because of the formation of benzaldehyde and benzoic acid in the fast oxidation of the methyl group.     

Designing Multivalent Ligands to Control Biological Interactions: From Vaccines and Cellular Effectors to Targeted Drug Delivery

Multivalent interactions in which multiple ligands on one object bind to multiple receptors on another are commonly found in natural biological systems. In addition, these interactions can lead to increased strength and selectivity when compared to the corresponding monovalent interaction. These attributes have also guided the design of synthetic multivalent ligands to control biological interactions. This review will highlight the recent literature describing the use of multivalent ligand display in the design of vaccines, immunomodulators, cell signaling effectors, and vehicles for targeted drug delivery.