The effect of step-stretch parameters on capillary breakup extensional rheology (CaBER) measurements

• Published in: Rheologica acta Vol. 48; no. 6; pp. 625 - 639
• Main Authors: Miller, Erik, Clasen, Christian, Rothstein, Jonathan P.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.07.2009; Springer; Springer Nature B.V
• Subjects: Applied sciences; Breakup; Characterization and Evaluation of Materials; Chemistry and Materials Science; Complex Fluids and Microfluidics; Computational fluid dynamics; Computer simulation; Constitutive models; Cross-disciplinary physics: materials science; rheology; Deformation; Dependence; Exact sciences and technology; Fluid dynamics; Food Science; Fundamental areas of phenomenology (including applications); Instrumentation for fluid dynamics; Liquid bridges; Materials Science; Mechanical Engineering; Micelles; Miscibility; Morphology; Optimization; Organic polymers; Original Contribution; Parameters; Physicochemistry of polymers; Physics; Polymer blends; Polymer Sciences; Polymers; Preconditioning; Properties and characterization; Relaxation time; Rheological measurements; Rheological properties; Rheology; Rheology and viscoelasticity; Rheometry; Soft and Granular Matter; Surface tension; Techniques and apparatus; Viscoelastic fluids; Viscoelasticity; Viscosity; Polymer blend; Capillary rheometer; Wormlike micelles; Elongational flow; Polymer blends; Molten state; Theoretical study; Heterogeneous mixture; Polymer solutions; Investigation method; Micellar solution; Rheometer; Rheological properties
• DOI: 10.1007/s00397-009-0357-9
• ISSN: 0035-4511

Extensional rheometry has only recently been developed into a commercially available tool with the introduction of the capillary breakup extensional rheometer (CaBER). CaBER is currently being used to measure the transient extensional viscosity evolution of mid to low-viscosity viscoelastic fluids. The elegance of capillary breakup extensional experiments lies in the simplicity of the procedure. An initial step-stretch is applied to generate a fluid filament. What follows is a self-driven uniaxial extensional flow in which surface tension is balanced by the extensional stresses resulting from the capillary thinning of the liquid bridge. In this paper, we describe the results from a series of experiments in which the step-stretch parameters of final length, and the extension rate of the stretch were varied and their effects on the measured extensional viscosity and extensional relaxation time were recorded. To focus on the parameter effects, well-characterized surfactant wormlike micelle solutions, polymer solutions, and immiscible polymer blends were used to include a range of characteristic relaxation times and morphologies. Our experimental results demonstrate a strong dependence of extensional rheology on step-stretch conditions for both wormlike micelle solutions and immiscible polymer blends. Both the extensional viscosity and extensional relaxation time of the wormlike micelle solutions were found to decrease with increasing extension rate and strain of the step-stretch. For the case of the immiscible polymer blends, fast step-stretches were found to result in droplet deformation and an overshoot in the extensional viscosity which increased with increasing strain rates. Conversely, the polymer solutions tested were found to be insensitive to step-stretch parameters. In addition, numerical simulations were performed using the appropriate constitutive models to assist in both the interpretation of the CaBER results and the optimization of the experimental protocol. From our results, it is clear that any rheological results obtained using the CaBER technique must be properly considered in the context of the stretch parameters and the effects that preconditioning has on viscoelastic fluids.