## 3 Results
### Experimental Crystal Manipulation  
The optofluidic system is capable of crystal transport in the microchannel. Translation and rotation of a ZSM-5 crystal of dimensions of 15 \(\upmu\)m \(\times\) 15 \(\upmu\)m \(\times\) 75 \(\upmu\)m was achieved. The preferred orientation of zeolite crystals, as they are translated, is orthogonal to the flow direction, assuming the crystals are far (200 \(\upmu\)m for our 2-mm-wide channel) from lateral walls. Near these walls (less than 200 \(\upmu\)m), caused by the nonslip condition and parabolic shape of the velocity profile, the orientation of the crystal gradually tends to be parallel to the flow direction. According to simulations, we have found that the presence of a crystal disturbs the flow profile in the longitudinal and transversal channel axes (also in the vertical axis, but all of the observed crystals are close to the floor plane). In the transversal direction of the microchannel, a disturbance of the flow profile, 0.5 mm from both sides of the crystal, and 1 mm before and after the crystal position in the longitudinal direction were observed in simulations. This is important in the sense that crystals in the study should be far enough from each other that they have a good agreement between simulations (where only one crystal is studied) and experiments (multiple crystals in the microchannel). If crystals are very close, flow profile will be disturbed and consequently hydrodynamic forces will be altered. Entrance length for only one active input was found to be 3 mm which means that the flow is fully developed 3 mm after the input and 3 mm before the output. When two inputs of the same flow rate are used, this distance is greatly reduced, however only one input was used in the experimental results reported in this work. Crystal velocity and distance were estimated from the recorded video (30 FPS, \(640\times 512\)). The distance was estimated by extracting images from video of initial and end frames, with a scale factor of 0.428 \(\upmu\)m/pixel, when using the 10\(\times\) microscope objective. The crystal position was estimated from its centroid. Time reference was estimated from video frame rate. Flow rates (\(Q\)) of 40, 60, and 80 \(\upmu\)L/min were used to impart the hydrodynamic forces to start the crystal motion. Once the sample was prepared, the first experiment was carried out with \(Q\) = 40 \(\upmu\)L/min on 15 April 2021 19:55 and nine events were recorded. In the second experiment, \(Q\) = 60 \(\upmu\)L/min on 16 April 2021 13:52 and 10 events were recorded. The last experiment consisted of 10 events, recorded on 16 April 2021 14:48, with \(Q\) = 80 \(\upmu\)L/min. In Figure 8, an extract from the first video (\(Q\) = 40 \(\upmu\)L/min) is shown. Horizontal distances are not scaled because of overlapping between consecutive crystal orientation shifts. Figure 8: Experimental crystal translation/rotation for \(Q\) = 40 \(\upmu\)L/min. It is worth mentioning that for every flow rate, some of the events reported initiated with a stuck crystal, then a finger tap on one of the input hoses caused a sudden flow in the microchannel, which detached the crystal. After the finger tap, the crystal settled, then the microfluidic pump was activated with the programmed flow rate. For \(Q=40\)\(\mu\)L/min, in five out of nine events, the crystal was detached with a hose finger tap prior to the pump activation. For \(Q=60\)\(\mu\)L/min and \(80\)\(\mu\)L/min, the crystal was detached by finger taps, six times in a total of 10 events. In this work, we provide a method to estimate the opposing force experienced by a zeolite crystal near the bottom of a quartz microchannel, analyzing data from stationary and time-dependent simulations and the image velocimetry. Replacing the average translational velocity of the crystals in Equations (7)-(9), we calculate the aforementioned opposing force for the three flow rates.