Glassy PS Research Articles

Dielectric Spectroscopy of Binary Polystyrene/Poly[styrene-b-(ethylene oxide)] Blends and Ternary Composites of Polystyrene/Poly[styrene-b-(ethylene oxide)] Swollen with Homopoly(ethylene oxide)

The effect of incorporating poly[styrene-b-(ethylene oxide)], PS-b-PEO into PS/PEO composites has been examined microscopically and dielectrically. The addition of block copolymer stabilizes the dispersion of PEO in PS and can produce composites of PEO in PS in which the PEO domain size ranges from the size of the micelle core in binary PS/PS-b-PEO composites to larger PEO-swollen micelles to micron-sized phases of PEO stabilized by small amounts of PS-b-PEO. Dielectric spectra have been obtained as a function of frequency and temperature for binary composites of PS/PS-b-PEO and ternary composites of PS/PS-b-PEO/PEO, wherein the total content of PEO residues is held constant at 4.7% by weight. The dispersion of PEO in PS enables the observation of the full dielectric spectrum of the PEO phase. The dielectric spectrum of binary composites of PS/PS-b-PEO shows a predominant peak for the β‘ relaxation of PEO chain segments covalently tethered to the glassy PS continuum. Ternary PS/PS-b-PEO/PEO composites sho...

Study of diffusion and trapping of a fluorinated hydrocarbon in ion beam irradiated poly(styrene) by nuclear resonance reaction analysis

The swelling of a poly(styrene) (PS) glass by sorption of a fluorinated hydrocarbon, 3,5-bis (trifluoromethyl) aniline (TFMA) is considered in a regime characterized by so called case II diffusion. Attention is focused on diffusion and trapping of vapor into ion beam irradiated glassy PS by using nuclear resonance reaction analysis. The diffusion coefficient for the TFMA is dramatically decreased on irradiation with a 30 keV H+ with 5×1013–1×1014 atoms/cm2 at 22.5 °C. These ion beam irradiation effects are similar to temperature effects on diffusion. As an application of the observed effect, trapping the TFMA was carried out between two different ion beam irradiation regions into PS at room temperature. This feature may allow development of new kinds of devices for applications.

Diffusion and solution of methanol vapor in poly(2-vinylpyridine)- block- polyisoprene and poly(2-vinylpyridine)-block-polystyrene

Diffusion and solution behavior of methanol vapor in two diblock copolymers, poly(2-vinylpyridine)—block—polyisoprene [P(2VPbI)] and poly(2-vinylpyridine)—block—polystyrene [P(2VPbS)], was studied by the weighing method at 25°C. The domain structure of films of both copolymers showed an alternating lamellar arrangement. Methanol is a good solvent for P2VP, but a nonsolvent for PI and PS. Methanol dissolved exclusively in the P2VP phase of the copolymers. For both copolymer systems, absorption and desorption processes of non-Fickian type were observed as characterized by a thickness anomaly. However, the magnitude of the deviations from purely Fickian behavior was small, and the integral diffusion coefficient, D̄, was obtainable with reasonable accuracy. At low and medium concentrations, D̄ for P(2VPbI) was greater, by about one order of magnitude, than that for P2VP, while D̄ for P(2VPbS) was lower than that for P2VP. A similar trend was observed in plots of the permeability coefficient against the vapor pressure of methanol. The results indicate that the rubbery PI phase may facilitate the transport of penetrant molecules in the P(2VPbI) film. On the other hand, the glassy PS phase in the P(2VPbS) film merely interferes with the transport of methanol molecules.

Relation between intramolecular mobility in glassy polystyrene and the effect of liquid media on mechanical properties

A study was made of the effect of physically active liquid media — dilute solutions of normal aliphatic alcohols—on mechanical properties of amorphous glassy PS at temperatures higher and lower than temperatures of the relaxation transition related to the motion of small sections of a macromolecule (smaller than the segment). It was shown that below the temperature of this relaxation transition the medium has an adsorption effect and is due to a reduction in interphase surface energy on the polymer-medium boundary. Above this temperature local plasticization becomes significant in the thin layer of the polymer against the apex of growing silvery cracks which is due to accelerated diffusion of liquid molecules in the material under stress.

A molecular theory of the fracture toughness of low molecular weight polymers

Recent experiments by Robertson show that the fracture toughness GIC of glassy polystyrene PS does not decrease to the ideal brittle value 2γ (where γ is the surface energy for PS) at molecular weights Mw below Mc the entanglement molecular weight. Instead GIC is more than an order of magnitude above 2γ at Mc and decreases slowly below Mc. It is postulated that a small craze exists at the crack tip in such low molecular weight glassy polymers. However, since entanglements do not occur single molecules must span this craze; if they do not the craze becomes unstable and the crack advances. Under these conditions a critical craze surface displacement exists and GC can be computed to be GIC=Sc(λ−1) 〈R2〉1/2, where λ and Sc are the craze fibril extension ratio and craze surface drawing stress observed in high molecular weight crazes (both quantities should be only weak functions of Mw) and 〈R2〉1/2 is the root mean square end-to-end distance of the PS molecule in the glass from neutron scattering measurements. The fracture toughness is predicted to decrease as Mw1/2; this prediction and the absolute magnitude of GIC are in excellent agreement with experiment.