*Microfluidics for Time-Resolved Small-Angle X-Ray Scattering DOI: http://dx.doi.org/10.5772/intechopen.95059*

flow, with no bubbles or leaks, and should have similar chemical compatibility to that of the microfluidic device [25]. We favour modular syringe pump systems, which have the ability to adapt the amount of dosing units to the number of channels. Other options include flow regulated gear pumps, positive air pressure systems or even on-chip fluid reservoirs. In any case, fluid flows should be accurately calibrated immediately prior to use, to ensure the correct dosage, flowrates and thereby the correct flow profile. A further consideration in fluid handling is minimising dead volumes (in particular by using appropriate fluidic connections and minimising tubing lengths), to prevent wastage of sample. Further, it is ideal, particularly for time resolved SAXS experiments where access to the system is restricted, if the fluid handling system can be controlled and triggered remotely, as this allows for accurate initiation of the reaction and data acquisition. The usability of all devices should be tested before each experiment to avoid leakage and proper function of the channels, especially with regard to flow focusing. Tubing and device

In general, homogeneous temperature control of the reaction solution has to be achieved. It is possible to submerge the whole microfluidic device and tubing in a water / oil bath. However, for *in situ* investigation, there needs to be unimpeded access to the channel, and this approach is thus not viable. In this case, custom designed heating elements, e.g. heated enclosures, are employed to regulate temperature. Temperature control is only limited by the geometric constraints of the measurement, and the heat transmission of the device material. For example, we have implemented copper heating tubes for surrounding the glass capillary of hybrid microfluidic chips, incorporating a window for the X-ray beam that provided excellent thermal control of the measurement [26, 27]. A key to good thermal stability is to also incorporate heating elements for the fluidics systems, to keep the reaction solutions at appropriate temperatures and ease the thermal load on heating

After the microfluidic devices are designed, fabricated, tested and fluid control is established, final considerations involve the implementation of the complete setup in an X-ray beam, either in a SAXS lab instrument or at a synchrotron beamline. Depending on SAXS instrument design a number of adjustments and considerations are required to achieve good integration for the measurement. As every synchrotron has slightly different parameters and sample environments, it is recommended to contact the beamline staff if considering a microfluidic-based

SAXS measurements are dependent on the volume and composition of all objects in the X-ray beam. Consideration should therefore be given to not only the material's resistance to radiation damage, but also the relative volumes of device material and sample that are going to be presented over the measurement channel. For example, 2–3 mm of any device-polymer either side of a sample channel of 50

failure are common frustrations in obtaining good data.

**3.1 Incorporating microfluidic experiments into SAXS**

time-resolved SAXS experiment for specific advice.

*2.3.2 Temperature control*

*Advances in Microfluidics and Nanofluids*

elements in the device.

*3.1.1 Device modifications*

**24**

**3. Microfluidics and SAXS**

micron means that the scattering from the sample in the channel will be entirely masked by the scattering of the polymer device, even if the polymer scattering is low. Further, the more material that is in the beam pathlength the more attenuation of the X-ray beam will occur. This means that less photons will hit the sample, get scattered, and escape the device to be detected. Calculations based on composition and thickness of the material should be done in advance to determine the expected transmission of the device. In many cases, this requires a redesign of the device itself to thin down the supporting material around the channels, incorporate X-ray transparent windows, or change the device material.
