| Περίληψη: | The present Ph.D. Thesis has received funding from the European Union’s Horizon 2020 Program
(Marie Skłodowska-Curie project titled: “Training in Bio-Inspired Design of Smart Adhesive
Materials, BioSmartTrainee”, Grant agreement No. 642861) for carrying out computational work
that can aid the rational design and development of new, bio-inspired materials capable of bonding
and de-bonding according to the micro-environmental conditions on wet, rough, and fouled
surfaces. This project falls under the BioSmartTrainee ETN program (for more information please
refer to the following link: http://biosmarttrainee.eu/) and established a network of 10 full partners
from academia and industry (BASF, AkzoNobel, and URGO) for developing new links between
polymer science, adhesion technology, and biomechanics. In the framework of the
BioSmartTrainee ETN program, different material strategies have been suggested for the design
of switchable adhesives capable of bonding and de-bonding on demand under wet conditions,
including among others: a) polymer brushes, b) micro-patterned surfaces, and c) polyelectrolyte
gels (complex coacervates).
The objective of the present Ph.D. Thesis was to develop and implement computational
algorithms capable of providing quantitative predictions of the microstructure, state of hydration,
and dynamics (segmental and terminal) of bulk aqueous solutions of weak polyelectrolytes, and
investigate their response to relevant physicochemical parameters (such as pH, total polymer
concentration, and chain length) starting from the molecular level. Additional work was carried
out for determining the phase boundary of aqueous solutions containing symmetrical (in terms of
charge density and molecular length), oppositely charged polyelectrolytes undergoing complex
coacervation (that leads to liquid-liquid phase association) by computing the salt-polymer binodal
phase diagram.
Suitable modelling methodologies at different levels, such as Quantum Mechanics (QM) and
Molecular Dynamics (MD), were employed to gain improved insight into the connection between
detailed molecular structure and macroscopic properties of aqueous solutions of the following
weak polyelectrolytes:
• poly(acrylic acid) (PAA)
• poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), and
• poly(ethylene imine) (PEI) The global and local conformation as well as the dynamics of PAA chains in infinitely dilute
solutions were first examined as a function of pH (equivalent to acid, neutral, and basic pH
conditions) and chain degree of polymerization N (= 20, 23, 46, 70 and 110). Our predictions were
compared to previous experiments and already established scaling theories for flexible
polyelectrolytes.
The effect of the total polymer concentration on the state of hydration, structure, and dynamics
of PDMAEMA aqueous solutions was investigated next. In collaboration with one of our
BIOSMART partners (Wageningen University), we also carried out rheological measurements of
PDMAEMA solutions as a function of concentration.
Aqueous solutions containing PEI of either a linear or a short chain branched architecture were
also considered in the present Ph.D. Thesis in order to study the effect of pH and molecular weight
on local rigidity, global conformation, and diffusive behaviour of PEI. These systems were
simulated in infinitely dilute solution at ambient conditions. A detailed comparison to established
theories and previous studies was reported.
In the final stages of the Thesis, we computed (using fully atomistic models and free energy
calculations) the phase boundary of an aqueous solution of two oppositely and fully charged weak
polyelectrolytes, poly(acrylic acid) (PAA) and poly(N,N-dimethylaminoethyl methacrylate)
(PDMAEMA). Such a system, under certain conditions (temperature, salt concentration, and
molecular length) undergoes a particular type of liquid-liquid phase separation (LLPS) that leads
to the formation of two distinct phases co-existing in thermodynamic equilibrium: a dense polymer
phase (the coacervate) showing up in the form of liquid droplets and a dilute or polymer-deficient
phase (the supernatant). The salt-partitioning in the two phases was also studied, followed by a
detailed analysis of the specific interactions between certain pairs of atoms or groups of atoms in
the two polyelectrolytes driving complexation and eventually phase separation.
|
|---|
