Microfluidic Viscosity Measurement via Interface Positioning
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Solution Overview
Problem
Existing methods for measuring the viscosity of fluids as a function of shear rate are limited by high sample volume requirements, hydrodynamic instabilities, precision issues at low viscosities, and the need for manual adjustments, which are time-consuming and costly, especially when measuring high shear rates and low viscosities.
Innovation Solution
A method and device that allow for pre-selection of shear rates, control of fluid stream widths, and automated adjustment of flow rates using algorithms to calculate initial flow rates, enabling precise and reproducible viscosity measurements without user intervention, using a microfluidic junction with optical or electrical detection of fluid interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a rotational rheometer is used to measure viscosity, then a wide range of shear rates and viscosities can be covered, but large sample volume is required and hydrodynamic instabilities limit the maximum shear rate to around 1000 s⁻¹
Solution Approach 1:
The patent replaces the traditional rotational mechanical rheometer system with a microfluidic system that uses pressure-driven laminar flow. Instead of rotating geometries that create hydrodynamic instabilities, the invention uses controlled pressure gradients to drive fluid through microchannels, eliminating the mechanical rotation component and its associated limitations on shear rate and sample volume requirements
Solution Approach 2:
The patent transitions from the conventional rotational flow geometry to planar laminar flow in microchannels. This dimensional change from rotational to linear flow enables precise control of shear rates through pressure gradients while using minimal sample volumes, as the flow occurs in confined microchannel geometries rather than large rotational assemblies
2Measurement precision
If a rotational rheometer is used, then viscosity measurements can be obtained, but hydrodynamic instabilities and open geometry make it unsuitable for high shear rate applications and low viscosity measurements
Solution Approach 1:
The patent replaces the rotational mechanical system with pressure-driven microfluidic flow, eliminating hydrodynamic instabilities inherent in rotational geometries. The pressure-driven laminar flow in closed microchannels provides stable, reproducible flow conditions that enable reliable measurements at high shear rates without the instabilities that plague rotational rheometers
Solution Approach 2:
The patent employs closed microchannel geometries that confine the fluid flow, replacing the open geometry of rotational rheometers. This closed confinement prevents evaporation, contamination, and hydrodynamic instabilities, creating a controlled environment that enhances measurement reliability and stability across the full range of shear rates
3Measurement precision
If manual adjustment of flow rates is performed to obtain a centered interface, then measurement precision can be improved, but measurement time increases and sample volume consumption increases
Solution Approach 1:
The patent implements self-centering mechanisms through symmetric microchannel design and matched flow rate control. The system automatically positions the interface at the center of the channel through inherent geometric symmetry and balanced pressure gradients, eliminating the need for manual adjustment while maintaining high precision. The algorithm calculates optimal flow rates that naturally produce centered interfaces
Solution Approach 2:
The patent employs optical detection systems that monitor interface position and provide feedback to the flow rate control algorithm. The system continuously adjusts flow rates based on detected interface position, automatically maintaining optimal centering without manual intervention. This closed-loop feedback mechanism achieves high precision while reducing measurement time through automated real-time adjustments
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces measurement time and sample volume, improves precision and reproducibility, and allows for viscosity determination over a range of shear rates and temperatures with minimal manual intervention.
Implementation Method 1
The patent describes a co-flow of two fluids, including a reference fluid, in an observation channel. The method uses the co-flow of two fluids where viscosity is determined based on the position of the interface between the fluids.
Implementation Method 2
The patent mentions 'Comfortable visual measurement' as an advantage and describes optical observation methods for detecting the interface between co-flowing fluids in the microfluidic channel.
Implementation Method 3
The patent describes injecting fluids at controlled flow rates into a microfluidic junction and using pressure to drive the co-flow through the observation channel.
Data Source
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Figure 3
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AI summary
The invention relates to a measuring method for determining the viscosity of a fluid that is to be studied as a function of the shear rate applied to the fluid, using a device comprising a flow duct (10) at the end of which are two supply inlets (11, 12) connected to means (13, 14) for injecting a reference fluid and a fluid that is to be studied. The method comprises the following steps: calculating the initial flow rates of the reference fluid and the fluid that is to be studied for a given shear rate, starting the fluid injection means (13, 14), once the flow has stabilized, observing the visibility and the position of the interface between the two fluids, – iteratively changing the flow rate of the reference fluid as long as the interface is not detectable and positioned at a predetermined width, determining the viscosity of the fluid that is to be studied for the shear rate.