The forces between spherical particles of cellulose (20-30 mu m) have been
measured in different solutions using an atomic force microscope, with a vi
ew to understanding the interactions in a model papermaking system. At low
ionic strength (0.1 mM KBr), the interaction profile is dominated by a long
range double layer force and shorter ranged electrosteric force. A qualiti
tatively similar profile is observed at high pH, but in this case both the
double layer force and electrosteric force increase as a consequence of cel
lulose charging. Conversely, the two force contributions both decrease in t
he presence of calcium ions. At high ionic strength (10 mM KBr) the electro
steric force is absent and the forces appear to be due solely to double lay
er forces. Overall, the results show that the surface is composed of looser
chains that extend out into the solution, the conformation of which is hig
hly sensitive to the solution conditions.