Concentration Dependence of the Extensional Relaxation Time and Finite Extensibility in Dilute and Semidilute Polymer Solutions Using a Microfluidic Rheometer

Abstract

We investigated the composition dependence of the finite extensible nonlinear elastic (FENE) constant of poly(ethylene oxide) (PEO) solutions by the Tikhonov regularization method with the measured normal stress in microfluidic channels. We measured the normal stress of the PEO solutions in response to the extensional flows in microfluidic channels. Additionally, we extracted the extensional relaxation time distributions and the FENE constants of the PEO solutions from the measured normal stress by inverse calculations. The linear average value of the extensional relaxation times was consistent with that measured using a capillary breakup extensional rheometer. The shortest extensional relaxation time was close to the mean value of the Zimm relaxation time distribution. The FENE constant evaluated in the semidilute regime was 10.3 times higher than that in the dilute regime. The proposed method is promising for the determination of the Zimm time, FENE constant, as well as the extensional relaxation times of low-viscosity solutions.

The Role of Concentration on Drop Formation and Breakup of Collagen, Fibrinogen, and Thrombin Solutions during Inkjet Bioprinting

“…Hence, the corresponding local Weissenberg number Wi = λ e ε̇ = 2/3 at the pinch-off region is the same for all polymer solutions, which follow eq . However, the effective relaxation time λ e depends on polymer molecular weight and concentration. , In general, when 0.5 < Wi < L E , the tensile elastic stress at the pinch-off region grows unrestrictedly because of the coil-stretch transition. , The parameter L E is the polymer chain finite extensibility, which is the ratio of contour length of a polymer chain to its unstretched end-to-end distance (therefore, L E > 1). , At some time point beyond the critical pinch-off time t c , when the Weissenberg number Wi > L E , the polymer chains are completely stretched and the elastic resistance to the capillary thinning saturates . As a result, the ligament diameter decreases linearly with time and eventually, a droplet pinches off.…”

“…42,44 The parameter L E is the polymer chain finite extensibility, which is the ratio of contour length of a polymer chain to its unstretched end-toend distance (therefore, L E > 1). 48,50 At some time point beyond the critical pinch-off time t c , when the Weissenberg number Wi > L E , the polymer chains are completely stretched and the elastic resistance to the capillary thinning saturates. 47 As a result, the ligament diameter decreases linearly with time and eventually, a droplet pinches off.…”

Plasticizer for controlling single‐walled carbon nanotube fibers and zincophilic sites of microfiber supercapacitor

“…The PTFE tubes were used to measure the steady shear viscosity of the SWCNTs/super acid solutions. The steady shear viscosities were measured using a tube with different lengths employing standard capillary rheometry, at a shear rate of 52 s −1 19,20 . The shear rate was controlled using a syringe pump (NE‐1600, New Era), and the pressure in the tubes was measured using a load cell (LC302‐50, Omega Engineering).…”

“…Another approach is wet-spinning, which can achieve a highly aligned and packed SWCNT fiber structure 6,7 and also can be used for mass production. Since welldispersed SWCNT dope is required, solvents, 14,15 polymers, 16 surfactants, 17,18 and functionalizations [19][20][21] are often involved. While there may be some improvements at mechanical properties, they work as insulators in the materials.…”

A Review of Microfluidic Devices for Rheological Characterisation

“…This device was called differential pressure extensional rheometer, and it was based on the comparison of the pressure difference between the converging channel and the reference straight channel (Figure 5d). The authors employed this device to first characterise the extensional viscosity [35] and then the longest relaxation time [99] of several PEO solutions in diluted and semidiluted conditions. [92].…”