A possible mechanism for stabilizing elongational flow in certain polymeric liquids at constant temperature and composition

Summary A new calculation of the stability of elongational flow of a liquid filament is based on an idealized treatment of the effects of non-uniformity of filament diameter. Two uniform cylindrical filaments of different initial cross-sectional areas are connected by a fictitious deformable clamp which transmits tensile force without interfering with the assumed homogeneous elongational flow of each filament. A uniform tensile force is suddenly applied and kept constant. For a Newtonian liquid, the area ratio rapidly tends to infinity. For a rubberlike liquid, the area ratio at first increases but then becomes constant; this suggests that finite deformation of a Gaussian molecular network may provide a possible mechanism for spinnability at constant temperature and composition.

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Zusammenfassung Eine neuartige Berechnung der Stabilität des Dehnungs-Fließverhaltens wird auf einer idealisierten Behandlung des Einflusses der Ungleichförmigkeit des Fadendurchmessers aufgebaut. Das Modell besteht aus zwei gleichförmigen zylindrischen Fäden von verschiedenem Ausgangsquerschnitt mit einer fiktiven Verbindung, die Zugkräfte überträgt ohne die angenommenen homogenen Dehnungs-Fließzustände der beiden Fäden zu beeinträchtigen. Eine konstante Zugkraft wird gleichförmig und sprungartig aufgebracht. Für eine Newtonsche-Flüssigkeit geht das Verhältnis der Fadenquerschnitte sehr schnell gegen unendlich. Für eine gummiartige Flüssigkeit nimmt das Verhältnis zuerst zu, bleibt dann aber konstant. Das erlaubt den Schluß, daß endliche Deformation eines Gauss schen molekularen Netzwerks einen möglichen Mechanismus für die Spinnbarkeit bei konstanter Temperatur und Zusammensetzung zu liefern vermag.

     

Thermodynamic characteristics of poly(cyclohexylethylene‐b‐ethylene‐co‐ethylethylene) block copolymers

A series of poly(cyclohexylethylene‐b‐ethylene‐co‐ethylethylene) (C‐E/E_E) diblock copolymers containing approximately 50% by volume glassy C blocks and varying fraction (x) of E_E repeat units, 0.07 ≤ x ≤ 0.90, was synthesized by anionic polymerization and catalytic hydrogenation. The effects of ethyl branch content on the melt state segment–segment (χ) interaction parameter and soft (E/E_E) block crystallinity were studied. The percent crystallinity ranged from approximately 30% at x = 0.07 to 0% at about x ≥ 0.30, while the melting temperature changed from 101 °C at x = 0.07 to 44 °C at x = 0.28. Dynamic mechanical spectroscopy was employed to determine the order–disorder transition (ODT) temperatures, from which χ was calculated assuming the mean‐field prediction (χN_n)_ODT = 10.5. Previously published results for the temperature dependent binary interaction parameters for C‐E (x = 0.07), C‐E_E (x = 0.90), and E‐E_E (x = 0.07 and x = 0.90) fail to account for the quantitative x dependence of χ, based on a simple binary interaction model. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 566–574, 2010     

Temperature-dependent micellar structures in poly(styrene-b-isoprene) diblock copolymer solutions near the critical micelle temperature

The temperature dependence of the micelle structures formed by poly(styrene-b-isoprene) (SI) diblock copolymers in the selective solvents diethyl phthalate (DEP) and tetradecane (C14), which are selective for the PS and PI blocks, respectively, have been investigated by small angle neutron scattering (SANS). Two nearly symmetric SI diblock copolymers, one with a perdeuterated PS block and the other with a perdeuterated PI block, were examined in both DEP and C14. The SANS scattering length density of the solvent was matched closely to either the core or the corona block. The resulting core and corona contrast data were fitted with a detailed model developed by Pedersen and co-workers. The fits provide quantitative information on micellar characteristics such as aggregation number, core size, overall size, solvent fraction in the core, and corona thickness. As temperature increases, the solvent selectivity decreases, leading to substantial solvent swelling of the core and a decrease in the aggregation number and core size. Both core and corona chains are able to relax their conformations near the critical micelle temperature due to a decrease in the interfacial tension, even though the corona chains are always under good solvent conditions.     

An instrument for measuring the oscillatory electric birefringence properties of polymer solutions

An instrument for measuring the oscillatory electric birefringence properties of synthetic polymer dissolved in organic solvents has been designed and constructed. Novel features of the design include an in situ variable inter-electrode spacing Kerr cell and a double-beam optical train. The accessible frequency range extends from below 1 Hz to at least 100 kHz, with electric fields variable up to approximately 6000 V cm^?1 (peak-to-peak). Measurements are made with a powerful computerized data acquisition and processing system, based on an approach previously used for viscoelastic and oscillatory flow birefringence experiments. Preliminary results on a viscous liquid, Aroclor-1248, indicate that time-temperature superposition holds to reduced frequencies of at least 100 MHz. Comparison with theoretical predictions for rigid rod suspensions suggests that this liquid exhibits relaxation behavior with a time constants of ca. 6 ns at 25.00°C.     

Synthesis and self‐assembly of fluorinated block copolymers

Fluorinated block copolymers combine the unique properties of fluoropolymers and the intriguing self‐assembly of hybrid macromolecules. The preparation of the title molecules by selective fluorination procedures and the effect of fluorine incorporation on the material thermodynamics are presented. We highlight two fluorination schemes developed in our laboratory, difluorocarbene and perfluoroalkyliodide additions to polydienes, that allow for the selective and tunable incorporation of different fluorinated groups into model block copolymers. The fluorination changes the physical properties of the parent materials and leads to interesting changes in the component incompatibilities. The role of fluorination in determining block copolymer thermodynamics in both the solid state and in solution and in ultimately exploiting fluorination to produce novel, higher order structures is central to our research efforts. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 1–8, 2002     

On the comparison of the predictions of lifshitz theory with experiment: Van der Wads forces between mica plates

The behavior of the experimental force-separation curve for two crossed cylinders of mica is compared to theoretical force-separation curves for two flat parallel plates. The theoretical force is computed using a dielectric function for mica, which contains different ir and uv frequencies from that employed previously by Richmond and Ninham. A theoretical method is described for determining the variation in the force-power law with distance of separation.