Using the fractal analysis approach, the surface roughness and irregul
arities of nonporous carbon fibers (CF's) were estimated by analyzing
the nitrogen adsorption isotherms at 77 K. These fibers were prepared
from different precursors and subjected to different heat treatment te
mperatures. The fractal dimension, D, obtained by this method was corr
elated to the percent population, D', of (chemically reactive) carbon
active sites available at the external surface of the fibers. The high
er the value of D, the higher was D'. The fractal approach and the tec
hnique used to determine the population of carbon active sites are sho
wn to be highly informative and consistent methods for quantifying the
surface roughness of CF's. The extent of surface roughness as compute
d by D or D' is also in qualitative agreement with the images obtained
on CF's using scanning tunneling microscopy. The nitrogen isotherms o
n the CF's and on various carbon blacks yield a set of adsorption isot
herms ranging form pure van der Waals adsorption to pure capillary con
densation (and intermediate cases) on fractal surfaces. In one extreme
case (CF's), the surface exhibits fractal scaling over two decades of
length and induces capillary condensation from a monolayer upward.