*2.3.1 Fluid handling*

A key practical consideration for the use of microfluidics is the method for introducing fluid into the device. For the most part, each interface channel should have its own fluid handling system, which should be capable of smooth, pulse free

**Polymer**

**22**

**PDMS**

 **NOA 81 THV815 GZ THV610 AZ THV500 GZ THV221**

 **ET 6235 HTE-1705Z**

 **PS PMMA**

 **TOPAS 8007/6013**

 **Bendlay**

 **SIFEL SU8 50**

*Advances in Microfluidics and Nanofluids*

**Solvent**

THF

Toluene

Chloroform

Dioxane

Acetone

Octadecene

*x: dissolution or swelling of the material, o: no change observed,*

**Table 1***.* *Stability test of various polymers and the* 

*corresponding*

 *solvents.*

 o

 o

 x

o

*: not tested. Results in () showed insignificant*

o

o

 o

 o

 *swelling, the device could be continued to be used [23].*

o o

 x

 o

 o

 x

x

o

x

 o

 o

x x

 o

 (x)

 x

 x

o

o

o

 o

 o

x x

 o

 x

 x

 x

o

o

o

 o

 o

x x

 x

 x

 (x)

 x

o

o

o

 o

 o

x o

 x

 x

 x

 x

o

o

x

 o

 (x)

 x x

 x

x

x

x

x

x

o

—

 —

 o

—

 o

 o

 o

 o

 o

 o

 o

 o 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 failure are common frustrations in obtaining good data.

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

It should be expected that the device will be required to be perpendicular to the beam. Further consideration should also be given to the orientation of the channels, with respect to the beam dimensions. Generally, it is optimal to orient the channels so that as much of the beam is going through the channel as possible, and as little as possible is hitting the device body. This minimises background, and optimises the signal that can be achieved. In the best case scenario, the beamline will have the capability to generate micro beams of a few micron in any dimension. This allows for optimal exposure for the sample, and greatly increased time resolution in time-

It is best if the device has a chip-holder to mount the device in, which in most cases is specific to the setup and design. This holder must allow for any necessary connections of inlet and outlet tubing while holding the microfluidic device steady and without tension on any connections to pumps or vials. Ideally, this holder would be placed on a motor-controlled, adjustable stage to facilitate precise alignment in the X-ray beam and movement of the device to scan along outlet channels

In many cases, beamlines and lab instruments will maintain a vacuum along the complete X-ray flight path, and may include a vacuum sample environment. As Xrays interact with all matter, it is a requirement that there not be air in the majority of the SAXS instrument. Vacuum sample environments take this further by removing all air in the system to reduce and minimise background scattering. If a vacuum sample environment is in use, the microfluidic device must be designed to withstand the vacuum levels, and to minimise outgassing and other deleterious effects.

A fundamental principle in nature and technology is self-assembly – the formation of ordered structures of components of a system out of chaotic arrangements without external forces. These processes can be induced by a multitude of parameters, e.g. change of solvent, pH, temperature, pressure or by introduction of additional reactants. SAXS, being sensitive to length scales of 1–100 nm is an ideal technique for studying nanoparticle size and structure from nucleation to the final particle. *In situ* SAXS measurements of nanoparticle synthesis is typically used

**Metal nanocrystals.** Metal nanoparticle syntheses is particularly amenable to SAXS analysis, as their high electron density contrast allows measurements in dilute suspensions even at the very early stages of particle nucleation. This has been employed for investigating silver (Ag) and gold (Au) nanoparticle formation and structure [28–31]. The first steps towards microfluidic setups were stopped flow measurements, for example the kinetics of gold nanoparticle formation, and the

to monitor the kinetics of this process [7], and increasingly incorporates

transparent windows, or change the device material.

*Microfluidics for Time-Resolved Small-Angle X-Ray Scattering*

*DOI: http://dx.doi.org/10.5772/intechopen.95059*

*3.1.2 Device mounting in beamline/SAXS instrument*

for different points in time of reaction kinetics.

**3.2 Nanoparticle nucleation and growth**

resolved samples.

microfluidics.

**25**
