Secondary mechanical relaxation effects in some cycloalkyl side groups containing polymers

Summary The dynamic mechanical properties at acoustic and low-ultrasonic frequencies (6–60 kHz) have been determined in polycyclopentylmethacrylate (PCPMA), polycyclohexylmethacrylate (PCHMA), polycyclohepthylmethacrylate (PCHpMA), polycyclooctylmethacrylate (PCOcMA), polycyclohexylacrylate (PCHA), polyvinylhexahydrobenzoate (PVHHBz), polyvinylcyclohexylether (PVCHE) and polyvinylcyclohexane (PVCH) Measurements were carried out by an electrostatic method (flexural vibrations) over the temperature range 60 °K to room temperature. All polymers, except for polyvinylcyclohexane, exhibit a γ-relaxation, connected with internal motion of the cycloalkyl ring, whose activation parameters depend exclusively on the nature of the ring. PVCHMA, PVCHA, PVHHBz, PVCHE and PVCH exhibit a further secondary relaxation effect (δ-process) at lower temperature, whose position on the temperature scale, strength (peak height) and activation parameters depend on the nature of the units to which the cyclohexyl ring is attached. The δ-process is attributed to some complex motion of the whole cyclohexyl ring, involving oscillatory rotation of the same around simple bonds which link it to the backbone chain. Contrarily to the δ-process of the phenyl side group containing polymers, the δ-process of the polymers here examined seems to be more sensibly dependent on intramolecuar effects.

---

Zusammenfassung Es wurden die dynamischen Eigenschaften im akustischen und im Bereich langsamer Ultraschallfrequenzen (6–60 kHz) untersucht für Polycyclopentylmethacrylat (PCPMA), Polycyclohexylmethacrylat (PCHMA), Polycycloheptylmethacrylat (PCHpMA), Polycyclooctylmethacrylat (PCOcMA), Polycyclohexylacrylat (PCHA), Polyvinylhexahydrobenzoat (PVHHBz) Polyvinylcyclohexyl?ther (PVCHE) und Polyvinylcyclohexan (PVCH). Die Untersuchungen wurden mit einer elektrostatischen Methode (Biegeschwingung) über den Temperaturbereich von 60 °K bis Raumtemperatur durchgeführt. Alle Polymeren, au?er Polyvinylcyclohexanen, zeigen eine γ-Relaxation verbunden mit internen Bewegungen des Cycloalkylrings, deren Aktivierungsparameter wesentlich von der Natur des Rings abh?ngen. PVCHMA, PVCHA, PVHHBz, PVCHE und PVCH zeigen einen weiteren sekund?ren Relaxationseffekt (δ-Proze?) bei tieferen Temperaturen, dessen Lage in der Temperaturskala, St?rke (Peakh?he) und Aktivierungsparameter von der Natur der Einheiten abh?ngen, an welchen der Cyclohexylring h?ngt. Der δ- Proze? wird irgendeiner komplexen Bewegung des ganzen Cyclohexylrings zugeschrieben, eingeschlossen oszillatorische Rotation desselben um die Einfachbindung, die ihn mit der Hauptkette verbindet. Anders als der δ-Proze? der Phenylseitengruppen enthaltenden Polymerenketten scheint der hier untersuchte δ-Proze? emfindlicher von intramolekularen Effekten abzuh?ngen.

     

Working without accumulation membrane in flow field-flow fractionation. Effect of sample loading on retention

Membraneless hyperlayer flow field-flow fractionation (Hyp FIFFF) has shown improved performance with respect to Hyp FIFFF with membrane. The conditions for high recovery and recovery independent of sample loading in membraneless Hyp FIFFF have been previously determined. The effect of sample loading should be also investigated in order to optimize the form of the peaks for real samples. The effect of sample loading on peak retention parameters is of prime importance in applications such as the conversion of peaks into particle size distributions. In this paper, a systematic experimental work is performed in order to study the effect of sample loading on retention parameters. A procedure to regenerate the frit operating as accumulation wall is described. High reproducibility is obtained with low system conditioning time.     

Analytic combinatory calculi and the elimination of transitivity

We introduce, in a general setting, an analytic version of standard equational calculi of combinatory logic. Analyticity lies on the one side in the fact that these calculi are characterized by the presence of combinatory introduction rules in place of combinatory axioms, and on the other side in that the transitivity rule proves to be eliminable. Apart from consistency, which follows immediately, we discuss other almost direct consequences of analyticity and the main transitivity elimination theorem; in particular the Church–Rosser and the leftmostreduction theorems for the associated notions of reduction. The last two sections deal with analytic combinatory calculi with the extensionality rule added. Here, as far as the elimination of transitivity is concerned, we have only partial results, which unfortunately do not cover, at present, full CL + Ext. Yet, they are sufficient to prove the decidability of weaker combinatory calculi with extensionality, including e.g. BCK + Ext.Mathematics Subject Classification (2000):03B40, 03F03, 03F07     

On the Surface Pressure for the Edwards-Anderson Model

For the Edwards-Anderson model we introduce an integral representation for the surface pressure (per unit surface) in terms of a quenched moment of the bond-overlap on the surface. We consider free , periodic and antiperiodic ^* boundary conditions (by symmetry ⁽⁾=^(*)), and prove the bounds We show moreover that at high temperatures ⁽⁾ is close to ^2/4 and ⁽⁾ is close to ^2/4 uniformly in the volume .     

An unexpected bispericyclic transition structure leading to 4+2 and 2+4 cycloadducts in the endo dimerization of cyclopentadiene

The stereospecific endo dimerization of cyclopentadiene takes place through an asynchronous and symmetrical bispericyclic transition structure, which shows a merging of the 4+2 and 2+4 cycloaddition paths. The shape of the transition structure testifies to the presence of attractive Salem/Houk secondary orbital interactions assisting the endo approach.     

Hybrid membranes based on sulfated titania nanoparticles as low-cost proton conductors

This work reports on a novel, hybrid solid-state membrane based on sulfated titania nanoparticles stabilized by a polyvinylidene fluoride–hexafluoropropylene copolymer. A fast solvent-casting technique was adopted as a valid alternative to a fully dry, hot-pressing preparation procedure. Self-standing, flexible membranes with high proton conductivity were obtained.     

Ordering effects in electric splay Freedericksz transitions

We analyze the interaction between a nematic liquid crystal and an electric field, in a cell in which splay Freedericksz geometry is enforced. Equilibrium configurations are explored both close to the Freedericksz threshold and in the limit of strong applied voltages. We frame within de Gennes’ order-tensor theory, which allows us to detect the effects of a variable degree of orientation on critical fields and bifurcation shapes. The applied voltage induces nontrivial effects on the degree of orientation as well. Up to the Freedericksz transition, the degree of orientation decreases, whereas ordering is recovered when the applied voltage drop increases. We also stress the role played by the dielectric anisotropy. In particular, the limit in which the dielectric anisotropy approaches the dielectric permittivities deserves attention, since the order-tensor theory regularizes some of the critical phenomena exhibited by classical Frank solutions.