Shear-Induced Isotropic–Nematic Transition in Poly(ether ether ketone) Melts

Parisi, Daniele; Seo, Jiho; Nazari, Behzad; Schaake, Richard P.; Rhoades, Alicyn M.; Colby, Ralph H.

doi:10.1021/acsmacrolett.0c00404

Cited by 12 publications

(17 citation statements)

References 64 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…With W > 50 MPa, strong viscosity (or shear stress) fluctuations are monitored presumably due to dynamic motions of polydomain PEEK nematic directors. 32 For low shear rates of γ̇< 5 s −1 at T s = 328 °C, the strong viscosity fluctuations cannot be observed since the onset of crystal growth occurs before reaching W ∼ 50 MPa.…”

Section: Resultsmentioning

confidence: 98%

“…Parisi et al 32 have recently observed a nematic phase of PEEK in shear flow by monitoring the birefringence and instability of shear flow using an optical rheometer. With rheology, the existence of a flow-induced nematic phase was verified from uncorrelated fluctuations of shear flow that are attributed to the diverse dynamic motions of polydomain nematic directors, such as tumbling, wagging, log-rolling, or kayaking.…”

Section: Resultsmentioning

confidence: 99%

“…The tumbling and wagging are movements as oriented in the velocity direction, while log-rolling and kayaking are dynamic motions as oriented in vorticity direction. 32 The nematic phase, which is composed of aligned and/or stretched chains, may represent the early stage of the shear-induced structure formation due to the structural similarity. Following the reported method, the startup of shear for PEEK 450G is performed at various shear rates (0.3 < γ̇< 300 s −1 ) at T s = 328 °C to detect flow-induced structures, as shown in Figure 7.…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Flow-Induced Crystallization of Poly(ether ether ketone): Universal Aspects of Specific Work Revealed by Corroborative Rheology and X-ray Scattering Studies

et al. 2020

Self Cite

View full text Add to dashboard Cite

When a semicrystalline polymer melt is processed in intense flow, the nucleation rate can be accelerated and the resultant morphology is transformed to anisotropic structures. These cumulative changes to the crystallization process are referred to as flow-induced crystallization (FIC). In this study, shear flow-induced crystal formations of poly(ether ether ketone) (PEEK) are investigated after applying a short-term shear (γ̇ = 20 s–1 and t s < 230 s) via rheology and ex situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). Using rheology, three types of dynamic response are monitored during FIC: no flow effect, nucleation acceleration, and instant crystal growth without crystallization induction time. Ex situ SAXS is employed with sheared PEEK disks to evaluate the flow-induced lamellar structure and orientation. The short-term shear changes the fraction and degree of lamellar stack orientation, whereas the lamellar structure is barely affected by shear, in terms of the long spacing (L* = 14.6 nm), linear crystallinity (χc = 0.34), and crystalline and amorphous layer thicknesses (Lc = 5.0 nm and La = 9.6 nm). Ex situ WAXS patterns indicate that PEEK chains (c-axis) are aligned in the shear direction within crystalline domains.

show abstract

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Flow-Induced Crystallization of Poly(ether ether ketone): Universal Aspects of Specific Work Revealed by Corroborative Rheology and X-ray Scattering Studies

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…Further extensional flow studies on the poly-alkyl isocyanates and other stiff-chain polymers are currently underway where the influence of solvent, temperature and solution concentration is being investigated, especially at higher concentrations as it is suggested that extensional flow would induce an isotropic-to-liquid crystal transition reported in shear flow in relatively rigid polymer chains 42,43 and may explain the spider silk web processing. 44,45 4 | CONCLUSIONS This investigation showed that the transient extensional response of stiff-chain polymers is rather complex, suggesting multiple macromolecular orientation changes.…”

Section: Resultsmentioning

confidence: 99%

Extensional flow of stiff‐chain polymer solutions in the semidilute regime

Romo-Uribe

2021

J of Applied Polymer Sci

View full text Add to dashboard Cite

Stiff-chain polymers are preponderant in biology as structural components of tissue and living cells. Hence, understanding their solution behavior under different flow histories is fundamental. Here, the extensional flow under capillary breakup of isotropic semidilute solutions of stiff-chain poly-n-butyl isocyanate (PBIC) and hydroxypropyl cellulose (HPC) has been studied. PBIC-chloroform and HPC-water were studied as the polymer-solvent interaction tunes the molecular conformation (Romo-Uribe, J. Appl. Polym. Sci. 2021, 138, e49712).PBIC in chloroform exhibits a rod-like conformation, and capillary breakup at constant concentration and temperature initially showed an exponential decay of filament diameter D(t) followed by a sudden decrease of D, and finally slow filament thinning. Increasing the molecular weight by threefold increased the breakup time τ b by twofold. HPC in water adopts a semiflexible conformation and the filament thinning also exhibited three stages, however the breakup time was shorter than PBIC. Hence, the extensional viscosity as a function of strain of PBIC and HPC solutions exhibited three regimes, where initial constant extensional viscosity η E was followed by strain hardening and finally a sudden decrease of extensional viscosity as strain increased. It was found that the filament breakup time τ b is a function of the radius of gyration R g .

show abstract

“…Semiflexible LCPs enabled the fundamental understanding of shear‐induced isotropic‐to‐nematic transition where highly aligned structures appeared as precursors of the nematic order 14 . Recently, the detection of a shear‐induced isotropic‐to‐nematic transition in the flexible chain poly(ether ether ketone) (PEEK) was reported, thus suggesting that the nematic phase may represent the early stage of the formation of shear‐induced crystallization precursors 15 …”

Section: Introductionmentioning

confidence: 99%

Shear‐induced textures and viscoelasticity in the nematic and isotropic phase of semiflexible thermotropic polymers. A rheo‐optical study

Romo-Uribe

2020

Polymers for Advanced Techs

View full text Add to dashboard Cite

The striking similarities in response to shear flow of nematic semi‐flexible thermotropic liquid crystalline polymers (LCPs) is reported. Insights into their complex flow was gained by in‐situ polarized optical microscopy (POM) whereas spatial correlations below optical resolution were characterized by small‐angle light scattering (SALS). The LCPs contained mesogenic units separated by ten (10) alkyl spacers, the polyether TPB10 of = 17 kDa and the polyester PSHQ10 of = 53 kDa. The quiescent nematic phase consisted of microdomains randomly oriented, that is, polydomain texture. Shear stretched and aligned the μm‐sized domains. After cessation of shear the texture sprang back and relaxed, PSHQ10 produced banded texture, whereas TPB10 only produced a disordered texture. Strikingly, high shear rate induced monodomains. Upon shear cessation the monodomain in PSHQ10 slowly relaxed to a polydomain, whereas TPB10 maintained a defect free texture. Shear reversal induced crisscross structure in both LCPs and SALS showed asymmetric “butterfly” patterns revealing a tilted microstructure. Shear rheometry in the nematic phase revealed that: (i) PSHQ10 displayed a terminal and rubbery regime, indicating the existence of entanglements; (ii) TPB10 exhibited only a liquid‐like behavior where G″ ≫ G′. The rubbery modulus Ge of PSHQ10 was ca. five times higher in the isotropic than in the nematic phase indicating that a change of conformation is involved in the nematic‐to‐isotropic transition. This study has resulted in correlations between rheological properties and shear‐induced microstructure thus developing new insights into their underlying deformation mechanisms.

show abstract

Shear-Induced Isotropic–Nematic Transition in Poly(ether ether ketone) Melts

Abstract: In a previous work on a poly(ether ether ketone) (PEEK) melt, above

Cited by 12 publications

References 64 publications

Flow-Induced Crystallization of Poly(ether ether ketone): Universal Aspects of Specific Work Revealed by Corroborative Rheology and X-ray Scattering Studies

Flow-Induced Crystallization of Poly(ether ether ketone): Universal Aspects of Specific Work Revealed by Corroborative Rheology and X-ray Scattering Studies

Extensional flow of stiff‐chain polymer solutions in the semidilute regime

Shear‐induced textures and viscoelasticity in the nematic and isotropic phase of semiflexible thermotropic polymers. A rheo‐optical study

Contact Info

Product

Resources

About