Extension rheology of liquid-crystalline solution/layered silicate hybrids

Abstract

The extension rheology of polymer/layered silicate composites based on liquid-crystalline (LC) solution of hydroxypropylcellulose (HPC) in oligomeric polyethyleneglycole (PEG) was studied. The HPC concentration was 60 wt%. Extension experiments have been carried out for materials in the different phase states. Compositions containing Na-montmorillonite (MMT) were prepared by a two-stage method. Final systems may be attributed to solutions of HPC in PEG, which intercalates into MMT galleries. The ordered domain structure of the LC matrix as well as hydrogen-bonded network between HPC and PEG molecules significantly reduce deformation at break and provide a strong nonlinear viscoelastic behavior at extension. Appearance of isotropic phase in solutions leads to a sharp drop of the elongation viscosity. The introduction of clay into LC solution only slightly affects the viscosity value but significantly suppresses the strain-hardening scale. In contrast, loading in biphasic state of HPC-PEG solution with even small amount (1 wt%) of MMT leads to the drastic viscosity increase that does not change in further growth of the filler concentration. Elastic properties of the systems under study demonstrate the similar behavior. This effect likely is caused by the interrelationship between deformability of the LC domain structure and the network strength formed by the clay particles. POLYM. ENG. SCI., 50:789-799, 2010.

Morphology and rheology of composites based on anisotropic polymer matrix and different clays

“…The character of viscous response changes drastically when the temperature of experiment was lowered and the matrix becomes biphasic (LC + isotropic). It has been established that HPC/PEG demonstrates unusual rheological behavior for nematic or cholesteric systems 14, 22. This behavior consists in the significant viscosity rise when phase separation takes place and a LC phase appears.…”

“…This behavior consists in the significant viscosity rise when phase separation takes place and a LC phase appears. In14 this behavior was explained as a result of reorganization of H‐bond network formed between terminal hydroxyl groups of PEG and the ones of hydroxypropyl groups in HPC macromolecules. In this case PEG molecules can act as both intradomain crosslinks and interdomain bridges.…”

“…On the one hand, a strong increasing of the strain‐hardening effect along with the increase of the clay content was observed in 12. On the other hand, it was reported13, 14 that clay particles suppress strain‐hardening and this suppression the stronger the higher filler content. In13 such kind of behavior was related to the intensive aggregation of clay particles at extension.…”

Comparative Study of Rheological Properties of Polyvinyl Alcohol and Polyethylene Glycol

“…The study of the viscoelastic behavior of PEG-poly(lactic acid) composites showed that these materials could have a higher magnitude of storage modulus than pure polymers [60]. Another study showed the increase of viscosity due to loading additives in the biphasic polymer solution, which did not change in further growth of the filler concentration [61]. The addition of clay to PEG could change its Newtonian flow behavior to thixotropic shear thinning when its structure broke down by mechanical shearing, and its viscosity decreased with time under conditions of constant shear rate [62].…”