Critical behavior of two interacting linear polymer chains in a good solvent

Abstract

A model of two interacting (chemically different) linear polymer chains is solved exactly using the real-space renormalization group transformation on a family of Sierpinski gasket type fractals and on a truncated 4-simplex lattice. The members of the family of the Sierpinski gasket-type fractals are characterized by an integer scale factorb which runs from 2 to ∞. The Hausdorff dimensiond F of these fractals tends to 2 from below as b → ∞. We calculate the contact exponent y for the transition from the State of segregation to a State in which the two chains are entangled for b = 2-5. Using arguments based on the finite-size scaling theory, we show that for b→∞, y = 2 - v(b) d_F, where v is the end-to end distance exponent of a chain. For a truncated 4-simplex lattice it is shown that the system of two chains either remains in a State in which these chains are intermingled in such a way that they cannot be told apart, in the sense that the chemical difference between the polymer chains completely drop out of the thermodynamics of the system, or in a State in which they are either zipped or entangled. We show the region of existence of these different phases separated by tricritical lines. The value of the contact exponenty is calculated at the tricritical points.