# Relationship between viscosity and film Thickness

Regarding "Relationship between the pull-up speed and film thickness"、film thickness is proportional to the kinematic viscosity η to the $\frac{1}{2}$ or $\frac{2}{3}$.

Viscosity is also called viscosity coefficient, and its units are Pas (pascal second) in the SI unit system and P (poise) in the CGS unit system.

One poise is the viscosity at which a stress of 1 dyne (dyn)/cm2 occurs in the direction of the velocity gradient in a plane perpendicular to the direction of the velocity gradient when there is a velocity gradient of 1 cm per centimeter per second (cm/s) in the fluid.

The relationship between Pascal seconds and Poise is

1Pa・s＝10P

1mPa・s＝1cP

In practice, centipoise and millipoise were used.

1P＝100cPcentipoise

1P＝1000mPmillipoise

In dip coating, the reality is that adjustment by viscosity is limited.

Simulation of production volume and pull-up speed is necessary.

In addition, viscosity varies greatly with temperature, so controlling the liquid temperature is also important in dip coating.

Examples of viscosity

 Mayonnaise 8000 HumiSeal 230 Kerosene（20℃） 10 IPA（30℃） 1.77 Water（20℃） 1 Ethyl acetate（20℃） 0.449 MEK（20℃） 0.4

Unit（cP）

※ HumiSeal is a trademark of Chase Corp., HumiSeal Division.

A rheometer is recommended for viscosity control.

In cases where the dip coating operation lasts for several hours, the viscosity of the coating liquid may change due to volatilization of solvent components or changes in liquid temperature. Even if the dip coating equipment itself operates with high reproducibility, changes in the physical property of the liquid can lead to poor reproducibility.

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