Energy needed in breaking a drop of radius R into n drops of radius r, is

Energy needed = work done In splitting, the volume remains unchanged
$\therefore \frac{4}{3}\pi R^3=\frac{4}{3}\pi r^3\times n$
or $r=\mathrm{R}/(\mathrm{n}{)}^{1/3}$ 
Energy needed = W = surface tension x change in area 
$=\mathrm{T}\left[4{\mathrm{\pi r}}^2\mathrm{n}-4{\mathrm{\pi R}}^2\right]$