Elastic behavior of 4-branched star polymer chain with different chain length N adsorbed on attractive surface is investigated using steered molecular dynamics (SMD) simulation method based on the united-atom (UA) model for branched alkanes. The simulation is realized by pulling up the chain via a linear spring with a constant velocity v = 0.005 nm/ps. At the beginning

the chain lies extensionally on adsorbed surface and suffers continuous deformations during the tensile process. Statistical parameters as mean-square radii of gyration S2xy

S2z

shape factor δ

describing the conformational changes

sectional density den which gives the states of the chain

and average surface attractive energy Ua

average total energy U

average force f probed by the spring

which characterize the thermodynamic properties

are calculated in the stimulant process. Remarkably

distinguishing from the case in linear chains that there only exists one long plateau in the curve of f

the force plateau in our study for star chains is multiple

denoting different steps of desorption

and this agrees well with the experimental results in essence. We find during the tensile process

there are three characteristic distances Zc

Zt and Z0 from the attractive surface

and these values vary with N. When Z = Zc

the chain is stripped from the surface

but due to the form of wall-monomer interaction

the surface retains weak influence on the chain till Z = Zc. From Z = Zt

parameters Ua

U and f respectively reach a stable value

while the shape and the size of the chain still need adjustments after Zt till Z0 to reach their equilibrium states. Specifically

for short chain of N = 41

Zt and Z0 are incorporated. These results may help us to deepen the knowledge about the elastic behavior of adsorbed star polymer chains.