Amplification of Tension in Branched Macromolecules (2013)

Undergraduates: Alexandru Bacanu, James Brock Michael Rubinstein

Faculty Advisor: Michael Rubinstein
Department: Physics & Astronomy

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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.