Shear rheology and scaling of semiflexible polymers: Effect of polymer‐solvent interactions in the semidilute regime

Abstract

Semiflexible polymers and their assemblies are important in biology as crosslinked networks of semiflexible polymers form a major structural component of tissue and living cells. This research used shear rheology to demonstrate the tuning from worm-like to rod-like conformation in semiflexible polymers by polymer-solvent interactions. The conformation was assessed by the persistence length l p , and its influence, in the semidilute regime, was assessed by the scaling of zero-shear viscosity η o with concentration c and molecular weight M. The polymers were poly n-butyl and poly n-octyl isocyanate (PBIC and POIC, respectively). PBIC exhibited the largest l p in chlorinated solvents, and the solutions obeyed the scaling law η o / c 3:0 M 6:6. However, when PBIC was dissolved in benzene the l p was greatly reduced and the scaling law now was η o / M 4:2 , consistent with a worm-like conformation. On the other hand, POIC dissolved in chlorinated and benzenic solvents exhibited a worm-like conformation and the scaling was η o / c 2:5 M 3:5. These results were contrasted with those of hydroxypropyl cellulose (HPC) aqueous solutions, which exhibit worm-like conformation, the solutions obeyed the scaling η o / c 2.5. Finally, the shear viscosity of the polyisocyanates and HPC obeyed the Saito scaling, valid for anisotropic particles in solution.

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

“…This study focused on the extensional flow of rigid‐rod polymer solutions of poly‐ n ‐butyl isocyanate (PBIC) and hydroxypropyl cellulose (HPC) in the isotropic, semidilute regime. A detailed study of shear flow behavior of these stiff‐chain polymers has been recently reported, where the influence of polymer concentration, molecular weight, temperature, and of the solvent was investigated 32 . The scaling of zero‐shear viscosity η o with concentration c and molecular weight M v was found quite sensitive to the macromolecular conformation and the findings confirmed theoretical predictions 33 .…”

“…The poly‐ n ‐butyl isocyanates (PBIC) studied were synthesized using anionic polymerization as described in detail by Romo‐Uribe 32 . Suffices to say that the commercially available monomers were obtained from Eastman Organic Chemicals (USA).…”

“…The polymerization reaction was terminated by pulling off the vacuum and adding methanol. The chemical structure of PBICs was confirmed by FTIR spectroscopy, and by nuclear magnetic resonance spectroscopy in deuterated chloroform, and the molecular weight was determined from intrinsic viscosity measurements [ η ], by gel permeation chromatography (GPC), and by static light scattering as described in detail by Romo‐Uribe 32 . The physical chemical properties of the PBIC s are listed in Table 1 and the chemical formula is shown in Scheme 1a.…”

“…PBIC and HPC were studied as these are well‐characterized stiff‐chain polymers. Romo‐Uribe characterized in detail the dimensions of PBIC and HPC in different solvents and as a function of molecular weight 32 . To the best of the authors' knowledge, this is the first report on the influence of molecular weight and conformation on the extensional flow of stiff‐chain polymers in isotropic semidilute solutions.…”

“…Shear rheology has shown that solutions of stiff‐chain polymers exhibit significant increase in shear viscosity with concentration and molecular weight. Hence, relatively low concentrations are needed to achieve a sufficiently viscous fluid 32,34–38 . To add the insight of stiff‐chain polymers under extensional flow, the flexible chain polymer, poly isobutylene (PI) was also studied.…”