Dilute solution properties,chain stiffness,and liquid crystalline properties of cellulose propionate

The solution properties of cellulose derivatives are of interest from both technological and purely scientific aspects. At high concentrations these solutions form liquid crystalline structures. In dilute solution cellulosic chains can be described as semiflexible or wormlike with properties intermediate between random coils and rigid rods. A series of fractions of cellulose propionate have been examined by dilute solution viscometry, static and dynamic light scattering, and polarizing microscopy. Power law exponents are considerably larger than those observed for flexible chains and analysis of the intrinsic viscosity and hydrodynamic radii has yielded chain diameters and Kuhn statistical segment lengths. Corresponding aspect ratios from the hydrodynamic measurements are in good agreement with those obtained from polarizing microscopy, as analyzed in light of Flory's theory. Some aggregation and specific solvent effects have been observed, however separation of these effects has proven to be difficult. Results of these studies are compared to previous work for other cellulose derivatives. ©1995 John Wiley & Sons, Inc.     

Steiner pentagon systems

A Steiner pentagon system is a pair (K_n, P) where K_n isthe complete undirected graph on n vertices. P is a collection of edge-disjoint pentagons which partition K_n, and such that every part of distinct vertices of K_n is joined by a path of length two in exactly one pentagon of the collection P. The number n is called the order of the system. This paper gives a somplete solution of the existence problem of Steiner pentagon systems. In particular it is shown that the spectrum for Steiner pentagon systems (=the set of all orders for which a Steiner pentagon system exists) is precisely the set of all n ≡ 1 or 5 (mod 10), except 15, for which no such system exists.     

Untersuchung von Fleisch und Fisch

Ohne Zusammenfassung     

FTIR-ATR-spectroscopic analysis of Bis-Crown ether based PVC-membranes

Summary To get more information on the phase boundary and bulk membrane processes, the short and long time behaviour of potassium selective solvent polymeric membranes was studied. In parallel with the measurement of the dynamic response of model membranes, in situ spectroscopic measurements applying the Attenuated Total Reflection (ATR) technique in the infrared region, were carried out in solutions containing anions of different lipophilicity (Cl^– and SCN^–). Thin membranes (thinner than the penetration depth of IR beam) coated on the germanium reflection element by the dipping technique show no time dependence of the SCN bands in contact with KSCN solution of different concentrations, while the diffusion process of species can be monitored in thick membranes as it was shown in a time resolved study. The extremely short response times of ionophore based solvent polymeric membranes (determined under appropriate experimental conditions in this work) imply that the fundamental potential determining step of the overall response of this type of electrodes is a phase boundary process. Thus the slow inner membrane diffusion process followed by IR spectroscopy on the molecular level may affect only the long-term membrane behaviour.

---

FTIR-ATR-spektroskopische Analyse von Bis-Kronenether-PVC-MembranenIII. Spektroskopische und elektrochemische in situ-Methoden zur Untersuchung von OberflÄchen- und Bulk-Membran-Prozessen

---

Part II: see [4]

---

Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday