# Colloid¶ The colloid node allows to define a particle distribution. This node is only used in the Mie node.

Colloid are described with a dielectric function (Absorbance or Complex), the volumic density (or the percentage of volume occupied by particles) and the size density distribution.

The size density distribution is defined as $N(r)$ and correspond as the « Particle number density distribution », the size’s unit is micrometers and the value is just a number. Be careful of the type on your size distribution :

• $$r^3 N(r)$$ : Volume frequency $$\left [\mu m^{-1}\right]$$

• $$N(r)$$ : Particle Number density distribution $$\left [\mu m^{-3}.\mu m^{-1}\right]$$

• $$N(r) \text{d}r$$ : Number density $$\left [\mu m^{-3}\right]$$

Such as the volumic concentration is :

$\nu = \frac{4 \pi}{3} \int^{r_{max}}_{r_{min}} r^3 N(r) \text{d}r$

The Lorenz-Mie theory used with colloids is well-defined for sperical particles and size-distribution can be ajusted for other shapes. Usually, the particle size is within a few nanometers and less than one millimeter.

Be careful, the pre-calculation time can be significant for a large particle size, a large number of colloids or an over-sampled size distribution.

## Children Nodes¶

 The dielectric function of the particle

## Parameters¶

name

type

description

density

real

Volumic density of particle, no unit

size distribution

table

The tabulated distribution of particle size. The first column is the apparent-radius of the particle in micrometers and should be ordered. The second column is the particle number density and does not need to be normalized.

## Ocean XML 6.1 example¶

<colloid name="Gold" density="5.18e-005">
<param name="sizedistribution" type="list">
<row size="0.0935" value="10.202"/>
<row size="0.0985" value="24.4251"/>
<row size="0.1035" value="35.6239"/>
<row size="0.1085" value="21.3833"/>
<row size="0.1135" value="8.13718"/>
</param>