Relaxation of normal stresses in flowing polymer systems

The authors discuss the relaxation of the first difference of the normal stresses σ(t) after cessation of steady shear flow in viscoelastic polymer systems in the linear region of their mechanical behavior. They show that this phenomenon is associated with a group of relaxation characteristics of the material. they discuss a method of calculating the relaxation spectrum from σ(t); the validity of this suggested method is verified experimentally.     

Viscoelastic properties of butadiene-styrene block copolymers

Summary The viscous properties of SBS block copolymers (of Cariflex TR-1102 in this work) have been determined with the rate of shear being varied by 10⁸ times. It has been shown that in the region of low shear rates the polymer behaves as a structured highly concentrated disperse system which exhibits sharply pronounced thixotropy. In the region of high shear rates, the viscous properties of the polybutadiene matrix are of decisive importance. At low values of shear stress the compliance of the SBS block copolymer exceeds that of the polybutadiene matrix almost by a decimal order.At high shear stresses, just as in the case of viscous properties, the elastic behaviour of the SBS block copolymer approaches that of the polybutadiene matrix. Measurements of the dynamic characteristics at frequencies, which vary by a million times, most spectacularly point to the specificity of the viscoelastic properties over a wide temperature range. Under conditions of low temperatures the SBS block copolymer behaves as a rubber, while at temperatures above the glass transition temperature of polystyrene, at low loading intensities (low amplitudes and small deformations) the block copolymer shows low fluidity. This is most clearly seen from the frequency dependence of the loss modulus, especially in comparison with the relation typical of polybutadiene.

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Zusammenfassung Die viskosen Eigenschaften von SBS-Block-Copolymeren (hier Cariflex TR-1102) werden in einem Bereich von acht Zehnerpotenzen der Schergeschwindigkeit untersucht. Es wird gezeigt, daß im Bereich niedriger Schergeschwindigkeiten das Polymer sich wie ein strukturiertes hochkonzentriertes disperses System verhält, das eine ausgeprägte Thixotropie besitzt. Im Bereich hoher Schergeschwindigkeiten sind dagegen die viskosen Eigenschaften der Polybutadien-Matrix von entscheidender Bedeutung. Bei niedrigen Schubspannungswerten übersteigt die Komplianz des SBS-Block-Copolymeren diejenige der Polybutadien-Matrix höchstens um etwa 10%.Bei hohen Schubspannungen nähert sich das elastische Verhalten analog wie bei den viskosen Eigenschaften demjenigen der Polybutadien-Matrix an. Die Messung der dynamischen Charakteristiken über einem Frequenzbereich von sechs Zehnerpotenzen lassen die spezifischen viskoelastischen Eigenschaften in einem weiten Temperaturbereich sehr deutlich erkennen. Bei tiefen Temperaturen verhält sich das Polymer wie ein Gummi, während bei Temperaturen oberhalb der Glasübergangstemperatur des Polystyrols unter geringer Belastung (d.h. kleinen Amplituden bzw. Deformationen) das Polymer eine geringe Fluidität zeigt. Dies erkennt man am deutlichsten an der Frequenzabhängigkeit des Verlustmoduls, insbesondere durch Vergleich mit derjenigen bei Polybutadien.

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With 6 figures     

Suppression of superluminous precursors in high-power backward Raman amplifiers

The very promising scheme for producing ultrapowerful laser pulses through Raman backscattering of pump lasers in plasmas can be jeopardized by superluminous precursors. Growing from the leading part of the Raman pumped seed pulse, these precursors can disturb the plasma and the pump ahead of the pumped pulse. These ruinous effects, however, might be averted by a detuning, large enough to suppress the precursors, yet small enough to allow the desired backscatter effect.     

High-elasticity of polyisobutylene and polystyrene solutions

Summary A study is made of the high-elastic properties of solutions of polyisobutylene and polystyrene in a range of solvents of different quality with respect to these polymers. Measurements were carried out at room temperature in the concentration range 20–100% for polyisobutylene and 20–67% for polystyrene.It is shown that in contrast to the known effect of the nature of solvent on the viscous properties of polystyrene, the modulus of high elasticity of polystyrene solutions, as well as those of the flexible-chain polymer (polyisobutylene), measured in the linear range of mechanical behaviour of the system, depends only on the content of polymer in the solution and is practically independent of the nature of solvent.In the region of fairly high molecular weights the modulus of high elasticity is independent of the molecular weight of monodisperse polymers, but decreases with broadening MWD. The predominating role is not that of the high-molecular-weight fractions, but of the width of MWD.At high shear rates in the case of solutions of polymers in good solvents the variations of the modulus with shear rate is of an external nature, so that with shear rate is of an external nature, so that with a very high viscosity anomaly the modulus can decrease.

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Zusammenfassung Es werden die hochelastischen Eigenschaften von Polyisobutylen-bzw. Polystyrol-Lösungen untersucht, wobei verschiedene Lösungsmittel eingesetzt werden. Die Messungen wurden bei Raumtemperatur im Konzentrationsbereich von 20–100% bei Polyisobutylen und von 20–67% bei Polystyrol durchgeführt.Es zeigt sich, daß sowohl der Hochelastizitätsmodul von Styrol-Lösungen als auch der Modul von Polyisobutylen im linearen mechanischen Bereich nur vom polymeren Gehalt der Lösung und nicht vom Lösungsmittel abhängt. Dieses Verhalten weicht von den Viskositätseigenschaften ab, die bekanntlich durch das Lösungsmittel mitbestimmt werden.Im Bereich recht hoher Molekulargewichte wird der Modul der Hochelastizität unabhängig vom Molekulargewicht monodisperser Systeme, hingegen sinkt er mit breiter werdender Molekulargewichtsverteilung ab. Die beherrschende Rolle spielt nicht der Antcil des hohen Molekulargewichts, sondern die Molekulargewichtsverteilung.Bei hohen Schergeschwindigkeiten ist in guten Lösungsmitteln die Modulabhängigkeit von dieser Geschwindigkeit durch äußere Umstände bedingt, so daß bei sehr großer Viskositätsanomalie der Modul sinken kann.

     

Correlation of p16(INK4A) expression and HPV copy number with cellular FTIR spectroscopic signatures of cervical cancer cells

Cervical cancer, a potentially preventable disease, has its main aetiology in infection by high risk human papillomavirus (HR-HPV). Approaches to improving cervical cancer screening and diagnostic methodologies include molecular biological analysis, targeting of biomarker proteins, but also exploration and implementation of new techniques such as vibrational spectroscopy. This study correlates the biomarker protein p16(INK4A) expression levels dependent on HPV copy number with the infrared absorption spectral signatures of the cervical cancer cell lines, HPV negative C33A, HPV-16 positive SiHa and CaSki and HPV-18 positive HeLa. Confocal fluorescence microscopy demonstrated that p16(INK4A) is expressed in all investigated cell lines in both nuclear and cytoplasmic regions, although predominantly in the cytoplasm. Flow cytometry was used to quantify the p16(INK4A) expression levels and demonstrated a correlation, albeit nonlinear, between the reported number of integrated HPV copies and p16(INK4A) expression levels. CaSki cells were found to have the highest level of expression, HeLa intermediate levels, and SiHa and C33A the lowest levels. FTIR spectra revealed differences in nucleic acid, lipid and protein signatures between the cell lines with varying HPV copy number. Peak intensities exhibited increasing tendency in nucleic acid levels and decreasing tendency in lipid levels with increasing HPV copy number, and although they were found to be nonlinearly correlated with the HPV copy number, their dependence on p16(INK4A) levels was found to be close to linear. Principal Component Analysis (PCA) of the infrared absorption spectra revealed differences between nuclear and cytoplasmic spectroscopic signatures for all cell lines, and furthermore clearly differentiated the groups of spectra representing each cell line. Finally, Partial Least Squares (PLS) analysis was employed to construct a model which can predict the p16(INK4A) expression level based on a spectral fingerprint of a cell line, demonstrating the diagnostic potential of spectroscopic techniques.     

Zur Stabilitätsfrage Rotierender Elastischer Stäbe

Ohne ZusammenfassungDie nachstehende Arbeit bildet eine namentlich nach der variationstheoretischen Seite hin orientierte Weiterentwickelung einer von der philosophischen Fakultät der Friedrich-Wilhelm-Universität Berlin genehmigten Doktor-Dissertation (Referenten: Prof. Dr. R. v. Mises, Geheimrat Prof. Dr. M. Planck.)     

Non-linearity in rheology —an essay of classification

Different non-linear phenomena (such as non-Newtonian flow, large elastic deformations, instabilities of different types and many others) are the heart of rheology. Therefore many attempts were carried out to find quantitative, or at least qualitative, models of non-linear behavior. The general or perhaps most attractive way of developing rheological constitutive equations consists in the search for the most general method to describe everything in the framework of a single approach. Naturally, this leads to very complicated and ambiguous equations. Meanwhile, it is reasonable to try another way based on separating observed phenomena into different types depending on observed phenomena into different types depending on their physical origin. An attempt to propose such their physical origin. An attempt to propose such classification of nonlinear rheological effects is made.According to the assumed scheme three levels of non-linearity are distinguished. There is a group of phenomena which originate as a consequence of finite elastic deformations. This is weak non-linearity related to equilibrium properties of a matter. The second level can be characterized as strong non-linearity. It is related to reversible structure changes, developing in time and connected with changes in relaxation properties of a matter. This group of effects can be treated as kinetic phenomena. Lastly, the third level of non-linearity is connected with breaking or phase transitions induced by deformations. This leads to the most severe consequences and can be treated as effects of thermodynamic nature. It is shown that some well known rheological effects can be explained if we consider them as a superposition of non-linearity of different types.Presented as keynote lecture at the European Rheology Meeting, September 4–9, 1994, Sevilla, Spain     

Temperature-frequency reduction of the dynamic functions of black-filled rubbers in the nonlinear region

The possibility of using temperature-frequency reduction of the dynamic functions of black-filled rubbers in the nonlinear region is demonstrated and an additional applicability criterion — similar slopes of the isotherms of the amplitude dependences of the dynamic functions — is formulated. In the case of heavily filled rubbers it may be necessary to determine the constants of the Williams-Landel-Ferry equation and the reference temperature T_S from the experimental data — they may not coincide with the universal values. Master curves of the dynamic functions are obtained for a series of shock-absorbing rubbers at a shear strain amplitude =0.01.A. V. Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Scientific-Research Institute of the Rubber Industry, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 751–754, July–August, 1973.     

The dual photochemical reactivity of 1,2-dihydroquinolines

Conclusions The lack of electrocyclic ring opening in 1,2-dihydroquinolines not containing a substituent at the nitrogen atom is related to the possibility of efficient homolytic dissociation in the excited state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 768–772, April, 1985.