In this work two different examples of water absorbtion in polymers are studied by Monte
Carlo simulations. Both of them are of large technical and commercial impotance. The first
example is the water absorption in polyethylene cables where the water absorption plays a
crucial role in the degradation of the cable insulation and thus should be as low as possible.
The second example is bio-based superabsorbents made from denatured protein where water
absorption capability is the prime desired property.
Gibbs Ensemble Monte Carlo simulations  were used to study the hydration of polymers.
All simulations are performed with two boxes, one of which is filled with water at the start of
the simulation, whereas the other contains polymer molecules and possible ions. The polymer
molecules are not allowed to swap boxes whereas the water molecules are allowed to do so
thus constituting an osmotic Gibbs ensemble . For the polyethylene a connectivity-altering
algorithm was used whereas the protein molecules were simulated using a side-chain
regrowth model in addition to traditional Monte Carlo moves. For the polyethylene, the
TraPPE  force field was used and the protein molecules, the Amber force field  was
used. Water was modelled using simple point charge models . Electrostatic interactions are
treated using Ewald summation methods. The protein molecules were of different amino acid
compositions and in different conformations, e.g., β-turns and random coils obtained using
the amorphous cell method. Studies were made with different degrees of charging on, e.g.,
lysine side chains mimicking different ionization states.
The studies of polyethylene revealed the importance of ions left from the polymerisation
catalyst for the absorbtion of water and the concomitant degradation of polyethylene cable
insulation. Also the absorption properties of the protein molecules is strongly related to the
presence of charged groups and fully charged protein molecules absorb large amounts of
water. However, neither native nor denatured protein molecules show superabsorbing
properties (i.e. absorbing hundreds of times their own mass) as they show in experimental
studies and the reasons for this discrepancy will be discussed.
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