Microfluidic mixing cells

 

Microfluidic cells provide a unique way of investigating chemical reactions, mixing/separation and flow dynamics in situ. This is possible because of their small size which allows them to be used in combination with microscopic remote-probe experimental techniques. As constrained mixing environments they offer an opportunity to mimic the microscopic dimensions of many biological systems. In addition, the mixing and flow dynamics can be tailored by altering channel geometry during fabrication. As microfludic cells only require very small liquid volumes, they are particularly useful for studying substances which cannot be obtained in bulk quantities.

On-chip microfluidic cells typically incorporate channel diameters of 100 µm or more, orders of magnitude bigger than a typical ID13 X-ray beam diameter. For this reason, the X-ray beams offered by ID13 are ideally suited to the non-invasive probing of microfludic channel contents. ID13 uses currently microfluidic cells in glass technology, which provide a particularly low background for SAXS experiments. The adaptation of other cell types to the beamline is possible and could provide advantages in cell transmission and geometry. However, these issues should be discussed directly with beamline staff prior to making a formal beamtime application.

 

Microfluidic cell and syringe assembly (left) and microscope image of mixing channels within cell (right)

The syringe-pump injection system can provide a continuous flow from 1.3 pL/min to 439.4 µL/min through one or more syringes.

 

Microdroplet hydration/mixing

 

The ID13 microdroplet generation system is a research-grade commercial device, capable of delivering targetted <100 picolitre droplets at tuneable frequencies and at a range of temperatures. The system is based upon piezo technology, allowing microsecond delivery periods and giving direct control over the droplet's exit velocity. Meanwhile, droplet volume can be chosen by the selection of different microdrop heads. The ID13 microdrop system is ideal for remote operation, which is necessary for use on the beamline. Dedicated software gives full control over timing whilst visualisation is possible using stroboscopic illumination coupled to the triggering frequency.

Using a single microdroplet generator it is possible to study local hydration or the chemical modification of surfaces. Using coupled microdroplet generators in-flight droplet mixing can be performed. This allows chemical reactions to be investigated with millisecond time resolution. ID13 is particularly well-suited to the use of microdroplets due to its small beam sizes and routine use of microscopic samples.

 

 

 

 

 

 

 

 

 

 
 

Microdroplet generator at sample position (left) and the local hydration of a single fibre (right)

 

Image series showing the in-flight mixing of 50 µm diameter droplets at 2 m/s velocity.