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Microfluidics application note

Published on 07 February 2025

High-Resolution Microfluidic Device for Precise Oil-in-Water Emulsion and Coalescence Analysis

Emulsion stability

         This application note describes oil-in-water droplet generation and coalescence analysis in petroleum samples, addressing challenges in emulsion stability studies. Utilizing Elveflow’s piezoelectric pump and advanced flow control technology, the custom microfluidic setup achieved precise droplet uniformity with size variations under 1%, critical for coalescence observations. Building on recent advances in 3D-printed microfluidic devices, the study integrates proprietary hydrophilic and solvent-resistant materials developed by Polaris. Developed in collaboration with the LC-GC research group at the Universidade Estadual de Campinas (Unicamp) and Petrobras, this approach combines high-resolution droplet generation and analytical techniques, offering a comprehensive solution to understand emulsion behavior, while showcasing Elveflow’s superior microfluidic flow control capabilities.

3D-printed-Microfluidic-device
Polaris Microfluidic Chip

Applications for analyzing emulsion stability

The developed microfluidic setup has broad applications in petroleum research, particularly in analyzing emulsion stability and coalescence phenomena. It can be utilized for studying oil recovery processes, optimizing demulsifier formulations, and investigating the impact of surfactants like naphthenic acids on emulsion behavior. Beyond petroleum, the system is versatile for assays in chemical engineering, environmental monitoring, and food sciences, where precise droplet generation and controlled flow conditions are critical. The integration of Elveflow’s advanced flow control and Polaris’ innovative materials further expands its potential in diverse research fields requiring high-resolution microfluidic analysis.

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Required materials

Microfluidic Device:

A custom-designed microfluidic device was fabricated using a novel polymer developed by Polaris. This material is hydrophilic, optically transparent, resistant to solvents such as toluene and xylene, and capable of achieving high-resolution channel geometries. The device incorporates a high-performance geometry tailored for passive coalescence of droplets without disrupting the laminar flow, enabling precise and efficient coalescence studies.

To replicate this microfluidic setup, the following instruments, consumables, and materials are required:

InstrumentsConsumables

Elveflow OB1 MK4+ microfluidic flow controller

Custom hydrophilic, solvent-resistant resin (developed by Polaris)

High-speed camera (e.g., Photron Fastcam S6)

Hexadecane (Sigma-Aldrich)

Inverted microscope (e.g., Nikon Ti-U Eclipse)

Ultrapure water (Millipore, 18.2 MΩ·cm)

External LED light source (e.g., HDF7010, Hayashi)

Technical mixture of naphthenic acids (Sigma-Aldrich)

3D printer (e.g., Phrozen Mini 4K)

Saline water samples with specified compositions

Anycubic Wash and Cure Plus machine

Demulsifier (20% w/w)

Flow sensor (e.g., MFS2, Elveflow)

HPLC-grade solvents (e.g., isopropanol, ethanol, dichloromethane, acetone, methanol)

Pressure sensors (e.g., MPS, Elveflow)

Sodium sulfate (anhydrous)

Rotary evaporator

 

Other Materials:

  • Nitrogen gas supply for drying
  • Glassware and vials for sample preparation
  • Laboratory consumables (pipettes, connectors, tubing)

This setup leverages the unique properties of the Polaris-developed polymer and advanced flow control systems, providing a robust platform for oil-in-water emulsion studies and coalescence analysis.

Figure-6-setup-device

Figure 1 : Microfluidic chip specifications. The device has three regions: A, B, and C. Region A corresponds to droplet generation, while regions B and C represent the first and second observation chambers, respectively. The histograms show the relative frequency of particles as a function of the equivalent diameter (µm) for these three regions. In histogram C, the coalescence of some droplets can be observed.

Oil-in-Water stability experiment setup

  • Microfluidic Chip:
    • Custom 3D-printed microfluidic device fabricated from a hydrophilic, solvent-resistant polymer developed by Polaris.
    • Features high-resolution channels optimized for passive droplet coalescence while maintaining laminar flow.
    • Provides robust and reproducible analysis of the coalescence process.
  • Flow Control System:
    • Integrated Elveflow OB1 MK4+ flow controller for precise regulation of pressure and flow in both continuous and segmented phases.
  • Imaging Setup:
    • Photron Fastcam S6 high-speed camera, mounted on a Nikon Ti-U Eclipse inverted microscope, captures high-frame-rate videos of droplet formation and coalescence.
    • An external LED light source ensures uniform illumination and enhances optical clarity for detailed observations.
  • Data Analysis:
    • High-speed videos are analyzed using custom software tailored for coalescence dynamics.
    • Extracts key parameters such as coalescence time, film rupture events, and droplet size variations.

The integration of advanced imaging and analysis tools ensures a deep understanding of the coalescence process and its relationship to surfactant properties in petroleum samples

Figure-3-A-experimental-system-
Figure-3-B-expreimental-setup

Figure 1 : Experimental setup with the Elveflow OB1 MK4+ system. The setup integrates the Elveflow OB1 MK4+ for precise flow control, a 3D-printed microfluidic device, a Photron Fastcam S6 high-speed camera, and an inverted microscope for real-time analysis of droplet generation and coalescence.

How to study Oil-in-Water coalescence?

The setup operates by precisely controlling the flow of fluids through a custom-designed 3D-printed microfluidic device using the Elveflow OB1 MK4+ system. A continuous phase (water) and a segmented phase (oil) are independently pressurized and delivered into the microfluidic device, where they intersect at a flow-focusing region to generate uniform oil-in-water droplets.

The high-resolution channels in the microfluidic device are optimized for passive coalescence, maintaining laminar flow conditions. Droplets move through serpentine channels and visualization chambers, where interactions and coalescence are observed. The system allows for real-time monitoring of droplet formation and coalescence using a Photron Fastcam S6 high-speed camera connected to an inverted microscope.

Captured videos are analyzed with custom software to extract key parameters such as droplet size distribution, coalescence time, and film rupture events. This approach ensures a detailed understanding of emulsion stability and the dynamics of coalescence (see video below).

Quick Start Guide: Setting Up the Microfluidic System

Step 1: Prepare the Microfluidic Device

  • Ensure the 3D-printed microfluidic device is clean and dry.
  • Flush the channels with isopropanol, ethanol, and ultrapure water using the Elveflow system at a flow rate of 200 µL/min.
  • Dry the device with nitrogen gas for 5 minutes.

Step 2: Assemble the System

  • Secure the microfluidic device using 3D-printed holders and adapters.
  • Connect the device inlets and outlets to the Elveflow OB1 MK4+ system using compatible tubing and connectors.
  • Mount the device on the stage of the inverted microscope.

Step 3: Set Up the Fluids

  • Prepare the continuous phase (e.g., ultrapure water or saline solution) and segmented phase (e.g., hexadecane with demulsifier).
  • Load each fluid into separate reservoirs connected to the Elveflow system.
  • Calibrate the pressure for both phases (e.g., 80 mbar for the continuous phase, 5 mbar for the segmented phase).

Step 4: Adjust the Observation System

  • Align the microscope and high-speed camera (Photron Fastcam S6) with the flow-focusing region of the device.
  • Set the camera to record at 1000 fps for real-time droplet monitoring.
  • Ensure uniform illumination using the external LED light source.

Step 5: Start Droplet Generation

  • Gradually increase the pressure on the Elveflow system to initiate fluid flow.
  • Observe droplet formation at the flow-focusing region. Adjust pressures as needed for uniform droplet sizes.

Step 6: Record and Analyze

  • Record high-speed videos of the droplets as they move through the device.
  • Use custom software to analyze droplet size, coalescence time, and film rupture dynamics.

Step 7: Troubleshooting

  • Check for blockages or leaks in the device or tubing.
  • Adjust pressures to maintain laminar flow and consistent droplet generation.
  • Recalibrate the camera and microscope alignment if necessary.
  •  
Figure-5-Droplet-analysis-SI
Figure-4-Coalescence-phenomenon

Figure 2 : (Left) Droplet analysis software interface, Displays droplet size, coalescence time, and film rupture dynamics with real-time visualization and data extraction tools. (Right) Coalescence phenomenon observed in the microfluidic device. Sequence showing droplet coalescence with film rupture occurring within 0.9 ms, highlighting the system’s ability to capture rapid dynamics.

Key results for OIL-IN-Water droplet Coalescence study

This research showcased how a custom microfluidic setup enables high-precision analysis of oil-in-water emulsions and coalescence phenomena. Key findings from the study include:

  1. High-Precision Droplet Generation:
    • The microfluidic device achieved droplet size variation below 1%, critical for observing coalescence dynamics.
    • Uniform droplets were generated at flow-focusing regions without disrupting laminar flow, highlighting the effectiveness of the device geometry.
  2. Influence of Naphthenic Acids (NAs):
    • NAs were shown to inhibit coalescence by reducing interfacial tension, stabilizing emulsions at concentrations up to 1000 ppm.
    • Optimal NA concentrations for stabilization were identified, providing insights into their role in emulsion behavior.
  3. Advanced Coalescence Analysis:
    • Coalescence events were captured within 0.9 ms using a high-speed camera, enabling the analysis of film rupture dynamics and droplet interactions.
    • Custom analysis software extracted quantitative data, including droplet size distribution, coalescence times, and stability metrics.
  4. Versatile and Robust Setup:
    • Integration of Elveflow’s flow control and the custom 3D-printed device allowed for real-time manipulation and analysis of complex fluid systems.
    • Solvent-resistant, hydrophilic polymer ensured durability and compatibility with petroleum samples.

Conclusion

Microfluidics offers significant potential for improving the understanding of emulsion stability and coalescence phenomena in complex fluid systems. In this study, a custom 3D-printed microfluidic device—fabricated from a proprietary hydrophilic and solvent-resistant polymer—was combined with Elveflow’s precise flow control system to generate highly uniform droplets with size variations below 1%. This level of precision allowed for detailed observations of coalescence dynamics, including film rupture within 0.9 ms, shedding light on the influence of surfactants like naphthenic acids in emulsion behavior.

Key advantages to remember:

  1. High resolution and flexibility of the 3D-printed device, allowing for tailored geometries and robust performance under demanding conditions.
  2. Precise control of flow parameters, enabling reproducible results and detailed studies of droplet interactions.
  3. Versatility for applications beyond petroleum research, such as in chemical engineering, environmental science, and food technology.

The results can guide the optimization of emulsion stabilization strategies, development of demulsifiers, and enhancement of oil recovery processes. The integration of advanced microfluidics and analytical techniques paves the way for innovations in emulsion-based systems across diverse industries.

Acknowledgements

We gratefully acknowledge the financial support provided by Petróleo Brasileiro S.A. (Petrobras), whose resources were instrumental in the success of this research. Petrobras, through its research and development center (CENPES), has been at the forefront of advancing knowledge and technologies in the petroleum industry. For more information, visit Petrobras R&D. 

We also extend our thanks to the LC-GC Group at the Universidade Estadual de Campinas (Unicamp) for their collaborative efforts and technical expertise. This group specializes in advanced chromatographic and spectrometric techniques applied to complex mixtures, fostering innovations in analytical chemistry. Learn more about their work at Unicamp LC-GC Group.

Additionally, Polaris Microsystems & Nanotechnology extends heartfelt thanks to Elveflow for their exceptional support and partnership throughout this research. Their advanced flow control systems were instrumental in achieving the precision and reliability required for our experiments. Over the years, this collaboration has grown into a valued friendship, and we deeply appreciate their unwavering commitment to innovation and excellence.

Written and reviewed by Dr. Reverson Fernandes Quero and Louise Fournier, PhD. For more content about microfluidics, you can have a look here.

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References
  1. Bresciani, A.E., Alves, R.M.B., Nascimento, C.A.O. (2010). Coalescence of water droplets in crude oil emulsions: analytical solution. Chemical Engineering & Technology, 33(2), 237–243.
  2. Dudek, M.; Bertheussen, A.; Dumaire, T.; Øye, G. Microfluidic Tools for Studying Coalescence of Crude Oil Droplets in Produced Water. Chemical Engineering Science, 2018, 192, 1011–1021. 
  3. Facanali, R.; Porto, N. de A.; Crucello, J.; Carvalho, R. M.; Vaz, B. G.; Hantao, L. W. Naphthenic Acids: Formation, Role in Emulsion Stability, and Recent Advances in Mass Spectrometry-Based Analytical Methods. J Anal Methods Chem 2021, 2021, 1–15.
  4. Tadros, T. F. Emulsion Formation, Stability, and Rheology. In Emulsion Formation and Stability; Wiley, 2013; pp 1–75.
  5. Quero, R. F.; de Jesus, D. P.; da Silva, J. A. F. Simple Modification to Allow High-Efficiency and High-Resolution Multi-Material 3D-Printing Fabrication of Microfluidic Devices. Lab on a Chip, 2023, 23(16), 3694–3703. 
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