How is the colored toothpaste designed? Why can't colors mix together?

How is the colored toothpaste designed? Why can't colors mix together?

There is a kind of toothpaste with colored stripes. No matter how you squeeze it, it won't mix together. Why? Is there any black technology inside toothpaste?

As early as the 1960s, colored toothpaste appeared. At first, people put white bars with high viscosity at the back of the pipe, and red bars with low viscosity near the exit. When we squeeze them out hard, the two kinds of toothpaste will mix together. This mode of production has been eliminated at present. At present, the whole process of toothpaste production has been mechanized. The machine will put colored strips of different colors into a tube with a partition, and then the filling machine will pump all the colored strips into the toothpaste tube and cut the toothpaste. We will find that there is no partition in the tube, and the toothpaste is not mixed because of the colorant.

In the production of toothpaste color strips, water-insoluble and oil-insoluble colorants were added, and chemically stable polyethylene materials were used to prevent the pigment package from seepage. Moreover, the characteristic of toothpaste is that it can't flow like a solid when it is not stressed, and it can only start to flow when it is squeezed, so when the toothpaste is placed there, the color bar will remain stable all the time. When you squeeze toothpaste, the paste will flow like a liquid, and its flow conforms to a hydrodynamic law-Reynolds number. The greater the viscosity of a fluid, the smaller its Reynolds number. On the contrary, the smaller the viscosity of a fluid, the greater its Reynolds number, which determines the flow mode of the liquid. When Reynolds number is less than 2300, liquids will flow in parallel and will not mix with each other. This flow is called laminar flow. If the Reynolds number is greater than 4000, the liquid will mix and flow, which is called turbulence.

The viscosity of toothpaste is very high, Reynolds number is much lower than 2300, and its flow means that the laminar colored strips and white strips will flow out in parallel together, and the extruded toothpaste is bright in color. In fact, in addition to squeezing toothpaste, laminar flow will also occur when running water. 20 18 12 15, an Italian photographer visited the Alps and found the tap water in the tap as still as icicles. At this time, some people have doubts. I feel that water is not viscous and Reynolds number should be very high. Why is there laminar flow?

Looking at the calculation formula of Reynolds number again, we can know that Reynolds number is related not only to liquid viscosity, but also to flow rate. Laminar flow will occur when the flow velocity is slow. When the ratio of the average velocity to the maximum velocity of the fluid in the water pipe is equal to 0.5, each water molecule can accurately follow the trajectory of the previous water molecule. Moreover, according to the comparison table of water viscosity and temperature, it can be found that when the water temperature is 20 degrees Celsius, its viscosity is thin, and with the decrease of temperature, the viscosity of water will increase continuously. Therefore, when the water temperature is relatively low, plus the inside of the water pipe is smooth and the friction with water is small, the running water will be in a laminar state.