how Animate change ColumnDefinition width in wpf?

I need to change the width of a column by click on a button, and this change should be slow and animated.

  <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" x:Name="Col1"/>
            <ColumnDefinition Width="2*" />
        </Grid.ColumnDefinitions>

        <Button >change Width Col1</Button>
  </Grid>