https://doi.org/10.1007/s100510050531
Collapse transitions of a periodic hydrophilic hydrophobic chain
Service de Physique Théorique,
CE-Saclay, 91191 Gif-sur-Yvette Cedex, France
Corresponding author: a enzo@spht.saclay.cea.fr
Received:
10
March
1998
Revised:
25
June
1998
Accepted:
1
July
1998
Published online: 15 November 1998
We study a single self avoiding hydrophilic hydrophobic polymer
chain, through Monte-Carlo lattice simulations. The affinity of
monomer i for water is characterized by a
(scalar) charge 
, and the monomer-water interaction
is short-ranged. Assuming incompressibility yields
an effective short ranged interaction between monomer pairs (i,j),
proportional to 
. In this article, we take
(resp. (
)) for hydrophilic
(resp. hydrophobic) monomers and consider a chain with (i) an equal
number of hydro-philic and -phobic monomers (ii) a periodic distribution of
the along the chain, with periodicity 2p. The
simulations are done for various chain lengths N, in d=2 (square
lattice) and d=3 (cubic lattice). There is a critical value 
of
the periodicity, which distinguishes between different low temperature
structures. For 
, the ground state corresponds to a
macroscopic phase separation between a dense hydrophobic core and
hydrophilic loops. For 
(but not too small), one gets a microscopic
(finite scale) phase separation, and the ground state corresponds to
a chain or network of hydrophobic droplets, coated by hydrophilic
monomers. We restrict our study to two extreme cases, 
and 
to illustrate the physics of the various phase
transitions. A tentative variational approach is also presented.
PACS: 61.41.+e – Polymers, elastomers, and plastics / 87.15.-v – Molecular biophysics / 64.70.-p – Specific phase transitions
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1998
