The mechanical properties of polyacrylic acid is investigated on the molecular scale by using of an atomic force microscopy. Polyacrylic acid was adsorbed onto the glass substrate

then picked up at one point of the chain with an AFM tip and stretched. The elongation of individual molecules was recorded as a function of the applied load.In the force curves of PAA

the monotonically rising forces with the elongation of the polymer chain is observed.After normalization according to their contour lengths

all of the force curves can be found

indicating that the mechanical properties of polyacrylic acid scale linearly with their lengths.The force-extension curve can be modeled by a modified Langevin Function.It is found that all of the poly (acrylic acid) chains have the same Kuhn length (0.64±0.05nm) and same segment elasticiy(13000±2000 pN/nm).Both the experimental results and fit results cleaely indicate that single polyacrylic acid chain is stretchen and nanomechanical properties of single poly(acrylic acid)chain is measured.