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In this we are going to discuss about the apparatus and methods of mixing of two micro fluids. This devices and methods are applicable for the steady and dynamic state mixing flow. We are going to see the effective mixing of the confluent streams. This is done with electro kinetic flow and to lesser degree with pressure driven flow. Again the same apparatus can be used for separation of micro fluid. This devices and methods of fluids separation can be an equal or unequal concentration of reactant. In the electro kinetic flow the surfaces of the walls are coated. They are coated in order to achieve high mixing efficiency. This invention decreases the channel length using wells in the channel for the mixing purpose.
In our day to day to life we come across many micro fluidic devices. The application of this micro fluid device can be seen in many chemical or biological fields. There has been a rapid growth in last few decades in the field of micro fluids. There have been many highly successful applications of these devices. Though many useful application there lie's other limitations exist, notably reagent mixing. This present invention enhances the mixing reagent in electro kinetic flow and pressure driven flow. The degree of mixing is lesser in the case of the pressure driven flow. This invention significantly reduces the length of the channel. It uses set of wells for the mixing or to split the fluid. The present invention are specifically pertains to mixers and splitters of micro fluidic flow. The electro osmotic flow may enhance the performance of the present invention. Electro osmotic flow is a surface driven mechanism.
Mixing of fluids:
In the low flow rate condition the mixing depends of diffusive mixing. The natural laminar flow and reagent's inherent diffusion coefficient causes the reagent to mix. Hence the mixing channel is extended in order to mix the micro fluids completely.
If the flow rate is high then we need excessively long mixing channel. This is because of the system which is restricted to the laminar flow regime and also due to the feature size. The limitation of long channel has been overcome by the lack of turbulence. This helped us to design many devices. This device utilizes the multi laminate or flow splitting technique for mixing in the channel. In the mixing technique, the streams are divided into several streams. This is done in order to reduce the mixing equilibrium time. After the mixing these narrower channel are brought together to the main channel. There are other techniques for mixing like stirring paddles etc. They rely on active mechanical mixing technique. In the case of small fluidic flow, devices are fragile and difficult to develop.
Invention of mixing device:
In order to provide the maximum advantage of the device and method of mixing two confluent micro fluidic laminar flows that did not excessively long channel to effectively mix the flows.  Hence we develop this invention to overcome the disadvantages and limitations of mixing. In this mixing technique we use two confluent laminar reagents to flow through very short stream length. This can be done by passing this flow over a series of narrow wells that are angled across the width of the channel. 
The mixer of laminar micro fluid streams is propelled by using electro kinetic flow. In the device we can see the two inlets through which the fluids flows. Then a mixing channel is provided with wells, so that the fluids mix well. These wells are oriented substantially across the width of the mixing channel. In the device the length of the channel is 0.8cm. The other dimensions are 72µm wide at top, 28µm wide at bottom and 31µm deep. The wells are laser etched. The wells have a depth of 85µm. The first four wells are parallel to each other and are inclined at an angle 45. The other well can orient diagonally. These wells are perpendicular to each other.
Figure 1: Embodiment of present invention of a micro fluid mixer
In the device the two inlet stream are mixed in the mixing region. The flow may be electro kinetic, electro osmotic or pressure driven flow. The electro osmotic flow is a wall driven phenomenon. This flow has the surface charge of micro channel wall and local electric field. The electro kinetic flow is a combination of electro osmotic and electro phoretic. In the case of pressure driven flow it is not a wall driven. In this the fluid is not force to enter the well like electro osmotic flow. The pressure driven flow is not as effective as electro kinetic flow with wells.
The reading is taken for the electro osmotic fluids. The sample's fluid taken is confluent of Rhodamine B in carbonate buffer and carbonate buffer. We take two flow rates for our experiment. One at 0.06 cm/s and the other flow rate at 0.81 cm/s. From the graph we can see the degree of perfect mixing at both the flow rate are same. But in the case of no mixer the rate of mixing is quite high for 0.81cm/s flow rate. This means with higher rate flow the degree of mixing of fluid also increases. Then we can see the degree of mixing with the wells for both flow rates.
The degree of mixing can be measure by using the intensity and position. We can see that in the below.
Graph1 : Degree of mixing of fluid in Embodiment with Electro osmotic flow.
Now we take the reading for the pressure driven flow for the fluids. We use the same fluid with the same capillary tube. Here also we consider two pressures driven flow. One at 0.21 cm/s and the other driven flow at 1.25 cm/s. The pressure driven flow are not wall driven flow. Hence they are not forced enter the wall. The graph drawn below is with the wells.
Graph 2: The experiment setup with pressure driven flow.
Considering both electro osmotic flow and pressure driven flow. We can see that pressure driven flow is not as effective as electro osmotic flow.
Sample with length around 130µm:
This experiment helps to know the degree of mixing at small length. Here also we use the same sample with 4 wells or 3 wells and 2 inlets. The other dimensions remain the same as previous. The wells are parallel to each other. In this we consider the electro osmotic flow at 0.06cm/s and 0.81cm/s. We notice that as the number of wells increases the mixing rate also increases.
Figure 2: Embodiment of the invention with length of 130µm.
Graph 3: Degree of mixing of fluid in Embodiment with Electro osmotic flow of 0.06 & 0.81 cm/s.
Splitting of the fluids:
The present invention used to split the fluids into equal or unequal concentration. The application of this invention can be used in lab-on-a-chip or µ-TAS system. This invention can be used in series, such as separate and spilt, then separate and spilt. This helps to get different dilutions of the original stream. This kind of system is known as serial dilution.
In the graph 5 we can see two distinct humps; this indicates that the fluid can be split into two equal fluids. This device consists of 2 inlets and 2 outlets with 3 wells. These wells are parallel to each other and are at an angle of 45. The length of the embodiment consider for the measurement is around 618µm.
Figure 3: Embodiment of the stream splitter
The fluid is passed through the two inlets. The fluid is passed over the wells. The fluid gets split's due to the presence of slanted wells.
Study of capillary tube:
Consider a capillary tube with two inlet and 4 wells. These 4 wells are at an angle of Î¸ with centre line axis of the mixer. The dimensions are same as the previous tube. In order to study the capillary tube we consider 4 cross sections in the capillary tube. Cross section A illustrates the incoming streams prior to mixing. Cross section B will illustrate the mixing of stream in the well. Cross section C & D illustrates the mixing stream at 5 and 420 µm.
At 45 angles and at different µm depths:
The wells at 45 and 10 µm depth shows very little mixing of the fluids.
At 50µm we can see substantial portion of mixing.
At 85µm depth the substantial portion of mixing is occurring at wells.
But here we notice that with limited depth the degree of mixing is low. The degree of mixing is even low with higher depth. These can be seen n below figures. These take us two conclusions, that as the degree of mixing doesn't depends on depth and the wells affect the mixing.
Figure 4: Embodiment of four well mixers anal sized for the computation of fluid dynamics.
At various angles with finite depth of 50 µm:
We measure the degree of mixing of fluid at the wells angles at 60, 30 and 15.
The result indicates as the angle decreased the degree of mixing increases. This is because of the increase in the lateral transport.
In case of perpendicular wells there is no lateral transport across the width of the well. Hence the degree of mixing decreased.
The folding acting is an important mechanism for the efficient mixing.
The various effect of change in the angle and electro osmotic mobility can be seen in the following figure drawn below.
Figure 5: illustration of the computational analysis of flow at various depths.
Manufacturing and equipment used for the invention:
The micro channels were made from polycarbonate (PC) sheet. Poly ethylene terephthalate glycol (PETG) was used to cover and seal the micro channel sheet. PC is used as substrate because of its high absorption cross section. PETG is used to seal the micro channel because of its low glass transition temperature than PC. Hence the thermal sealing performed doesn't cause any distortion to the PC channel due to temperature.
The whole manufacturing process is shown in the figure below:
Figure6: illustrate computational analysis of flow at various angle.
Before the hot imprinting method the PC substrate was blown clean with ionized air. The channels were hot imprinted in the substrate material by silicon stamp with T-shaped. Then the Pc was placed over the silicon stamp. It undergoes some process like aluminium heating and hydraulic press. Then the imprinted substrate is removed from template and allows cooling down. Then it undergoes Laser Ablation method. In this the 248nm excimer laser is used to ablate the microstructure within the micro channel. We can see that in the figure above.
Methods of measuring well depths and profile:
The depth of the micro channel is measured by cutting the micro channel. We can do that in two ways. Cutting it parallel to the slanted well or cutting it perpendicular to the axis of the outlet channel. Then the wells are imaged and measured using white light microscopy. Then again after the measuring the micro channel is sealed with PETG.
The image of the flowing fluid (rhodamine dye) was taken using a fluorescence microscopy. The digital images were acquiring using scion image software and scion LG-3 frame grabber. These images were taken in less than a second (around 1/60th of second).
Advantages of the present invention:
The flow may combined and mix with shorter length.
Invention like this can be used to split the fluid in equal and unequal portion of reagents.
These conventional devices can adjust their wells in order to mix the fluid.
The performance of the present invention can be change by using various electro osmotic mobility coating, orientation, depths.
Electro osmotic flow is much effective than the pressure driven flow. The present invention mixes the two fluids with conventional length. This invention splits the fluid into equal and unequal concentration. The degree of mixing of fluid does not depend on the depth of well. As the number of wells increases the degree of mixing of the fluid also increases. As the wells angle decreases the rate of mixing increases. This invention reduces the length of the tube for mixing. The device and the methods are applicable for the steady state and dynamic mixing.