Amplification of Tension in Branched Macromolecules (2013)
Undergraduates: Alexandru Bacanu, James Brock Michael Rubinstein
Faculty Advisor: Michael Rubinstein
Department: Physics & Astronomy
The pom-pom molecule consists of two star polymers whose
cores are joined together by a linear spacer, and through steric
repulsion, the bond tension in the spacer is amplified compared to
the tension in the arms of each star. In the regular dendrimer core
of each star, the bond tension undergoes an exponential increase
from the star arms to the spacer F(g) = Fmin(f - 1)^(kg), where g
is the generation number, f is the branching functionality, Fmin
is the tension in the outermost core bond, and k is a constant
that depends upon the average branching angle. Results from
molecular dynamics simulations show that as the length, l, of
the arms is increased, the spacer bond tension increases first as
l^(0.71), and then as l^(0.11). As the number of arms, z,
is increased, spacer tension undergoes two regions of tension
amplification. In the first regime, average bond tension in the
spacer, Fsp, is proportional to Fsp = z^(0.58), where z is
the number of arms. The spacer tension in the second regime
increases proportionally to Fsp = z^(1.83)/ m^(1.19). The theoretical
values are Fsp = z^0.75/m^(0.5) and Fsp = z^(1.5)/m^(1) , respectively.