**Figure 6.**

*Advances in Microfluidics and Nanofluids*

**88**

**Figure 5.**

**Table 6.**

*Result of surface roughness by comparing same machining parameter.*

is higher than the center flow rate.

*Width of hydrodynamic focusing.*

focusing width of 67 μm and 89 μm can be produced. From the simulation results show that effective hydrodynamic focusing occurs only when the sheath flow rate

**Ratio Sheath flow rate Sample flow rate Width of hydrodynamic focusing**

 1000 μl/min 100 μl/min 89 μm 1000 μl/min 10 μl/min 67 μm 3000 μl/min 100 μl/min 60 μm 3000 μl/min 10 μl/min 39 μm

Furthermore, from the simulation results of nonlinear behavior will occur when too high a ratio is used. Increasing the ratio of sheath flow rate to large central

*Setup for hydrodynamic focusing experiment.*

flow will only have a small effect on hydrodynamic focusing and may even cause hydrodynamic focusing not to occur if too high a flow rate is used. As shown in **Figure 7**, the hydrodynamic focusing that occurs is in the state of laminate and fully developed. This experiment can also give the impression that the bonding technique between 2 PMMA wafers using ethanol material was successfully performed, since hydrodynamic focusing can be formed. However, it should be noted that the hydrodynamic focus that occurs is not only due to the inflow rate by the fluid only, but the microfluidic geometry constructed also has a significant impact on the characteristics of hydrodynamic focusing. Especially when taking into account the rectangular geometry is easier to do by a micro milling than a round design. The forces formed to control hydrodynamic focusing are more complex than hydrodynamic focusing calculated only on the flow rate ratio [24].

An important aspect of designing and operating for the purpose of hydrodynamic focusing is to identify the position of the focus flow formed. Both lateral flows should have the same flow rate to ensure that the focusing flow flows in the middle of the micro flow. If the asymmetric focusing flow, the focusing flow will be deducted from the flow axis. Based on **Figure 7**, it can be observed that the

**Figure 7.** *Hydrodynamic focusing.*

hydrodynamic focusing width will decrease if the ratio (sheath flow rate to the main flow rate) increases. It can also be observed from the experiment, it shows that the results of focusing will shrink if a larger ratio is used.
