Figure 1.

Long-arm centrifuge and contact angle measurement unit. (a) Photograph of the long-arm centrifuge and contact angle measurement unit. (b) Diagram of the long-arm centrifuge and contact angle measurement unit. (c) Diagram of centrifugation force. In a gravitational field, the acceleration of an object with the vector sum of the centrifugal and gravity forces at point A is $\sqrt{g^2+{\left({\omega }^2{r}_0\right)}^2}$, and at point B, it is $\sqrt{g^2+{\left[{\omega }^2\left(r_0+{\text{r}}_1\right)\right]}^2}$. Owing to L<<r₀, $\sqrt{g^2+{\left[{\omega }^2\left(r_0+{\text{r}}_1\right)\right]}^2}\approx \sqrt{g^2+{\left({\omega }^2{r}_0\right)}^2}$. The centrifugal acceleration gradient of the centrifuge is ~0.0028 G/mm.