Biaxial transitions

Soft-drink bottles made from poly(ethylene terephthalate) (PET) are usuady made by stretch-blow mol ding in a two-step process. Eirst, a test-tube-shaped preform is molded, which is then reheated to just above its glass-transition temperature, stretched, and blown. Stretching the PET produces biaxial orientation, which improves transparency, strength, and toughness of the botde (54,56). A one-step process is used for many custom containers that are injection stretch-blow molded. 

The electrodeposited precursor films, annealed in air at 870 °C in the presence of a TBSBCCO pellet, produce a biaxial textured Tl-1223 phase, as confirmed by an XRD pole-figure measurement. The omega and phi scans indicate full-width at half-maximum (FWHM) values of only 0.92° and 0.6°, respectively, which indicates a very high-quality film. The superconductive transition temperature of the Tl-1223 film, determined resistively, was about 110 K. Figure 7.11... 

Note 2 At a transition to a uniaxial vanishes. The relative biaxiality, rj, is... 

Stretching denotes a monoaxial or biaxial mechanical stress of a molded article close to the glass transition temperature. This leads to a controlled orientation of the molecular chains in the direction of stretching and thus to a substantial change in some physical properties. Fibers and foils made of synthetic polymers gain their optimal properties only by this mechanical post-treatment. Stability, stiffness, and dimensional stability of fibers, for example, increase nearly proportionally with the stretch ratio, whereas stretchability decreases. In practice, the stretch ratio is between 1 2 and 1 6, depending on the polymer material and the desired properties. 

The PET studied was Mylar C film (DuPont) of 12 to 25 micron thickness. Such films are biaxially oriented and are about 50% crystalline. The glass transition and melting temperatures are about 70° and 250°C., respectively. The polymer contains several parts per thousand of inorganic materials, moisture, and 1 to 2% cyclic oligomers (mostly trimer) (8). The number-average molecular weight of the polymer molecules is... 

Lin PC, Yang S (2007) Spontaneous formation of one-dimensional ripples in transit to highly ordered two-dimensional herringbone structures through sequential and unequal biaxial mechanical stretching. Appl Phys Lett 90 241903... 

An elongational or extensional viscosity (%) develops as a result of a conformational transition when disperse systems are forced through constrictions, or compressed or stretched (Kulicke and Haas, 1984 Rinaudo, 1988 Barnes et al., 1989 Odell et al., 1989 Clark, 1992). The intuitive logic is that the random coils resist the initial distortion. % is believed to elicit the human sensation of stringiness (Clark, 1995). If shear viscosity is denoted iq, rheologists define a Trouton ratio as %/ti, wherein % > T) by a factor approximating 3 for uniaxial extension and 6 for biaxial extension. Alternatively stated, the Newtonian ly calculates to one-third to one-sixth % (Steffe, 1992). 

The phase transition temperature of the Step 7 product was also examined using a polarizing microscope. When the temperature was initially elevated, the crystal phase reverted to isotropic liquid phase in the vicinity of 80°C. Gradually lowering the temperature from 90°C resulted in an N phase at approximately 60°C. When the temperature was finally lowered to ambient temperature, the formation of a crystal phase was observed. As a result this agent was judged to be a biaxial liquid crystal. 

Danch et al. studied the effect of thermal history on the assignment of the glass transition event associated with the biaxial orientation of the smectic... 

The properties of SAN and rubber-modified SAN copolymers have also been evaluated for oriented films. Biaxial orientation can increase the glass transition temperature by up to 15 °C and decrease the water vapor transmission rate by 30% [105]. 

The phenomenon of polymorphism was noted by Martin Heinrich Klaproth °i in 1798, when he proposed that the minerals calcite and aragonite must have the same chemical composition, CaCOa. Calcite forms a rhombohedral uniaxial crystal and is the stable form under normal conditions, with a density of 2.71 g/ml. Its metastable polymorph, aragonite, is an orthorhombic biaxial crystal with a density of 2.94 g/ml. This work was continued by Louis Jacques Thernard, Jean Baptiste Biot, and Eilhard Mitscherlich. Mitscherlich, for example, reported on it in his studies of phosphates and arsenates. The transition from calcite to aragonite has been studied at different pressures. ... 

Legrand et al. [100] reported F wideline NMR measurements on a 70/30 mol% VDF-TrFE random copolymer, made in order to study molecular motion both below and above the ferroelectric transition temperature, Tc. The samples consisted of semicrystalline copolymer films of 0.51 mm thickness, with biaxial orientation of the crystalline axis. The samples were rolled (without poling) at 70°C, with a draw ratio of 300%. The F resonance was chosen, rather than the proton resonance, because the abundance ratio of F to nuclei is 1.4. In addition, the F free-induction decay (FID) lasts longer than that of the proton, which decreases the influence of spectrometer deadtime. FID analyses were made assuming a simple superposition of two... 

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