Stringimeter: an open source, cost-effective and versatile device for probing complex fluids in uniaxial extensional flow

It is increasingly common to use self-thinning of slender fluid filaments to infer the rheological properties of complex fluids under uniaxial extensional flow. These techniques require precise control over how filament thinning is triggered, as implemented in methods such as dripping-onto-substrate (DoS) and the commercial capillary-breakup extensional rheometer (CaBER), together with high-speed imaging to resolve rapid thinning dynamics. Here, we introduce the Stringimeter, a low-cost and modular capillary-driven thinning platform that integrates CaBER-like and DoS-like configurations within a single adaptable framework. The system combines moderate-speed imaging (up to 420 frames/s) with a temporal superposition strategy that increases the effective sampling rate and reduces reliance on expensive high-speed cameras. Validation with Newtonian fluids and polymer solutions demonstrates reliable extraction of elastocapillary timescales as low as τ EC ≈ 6 ms, corresponding to a polymer relaxation time of λ =τ EC /3≈ 2 ms within the Oldroyd–B model. The open-source architecture enables broad adaptability and, by maintaining a total system cost of approximately 1% of standard setups, provides accessible laboratory-scale extensional rheology measurements to a wide research community.