92
T. A. Deaton et al.
to study the properties of polyelectrolyte triblock as a function of volume fraction, length of polyelectrolyte and salt concentration (Fig. 3b). They found that
the fraction of bridges between hydrophobic domains (crosslinks) relates to the gel
elastic modulus, where the scaling exponent depends on polyelectrolyte length and
salt concentration. The morphological predictions were corraborated by cryo-TEM
experiments on DNA hydrogels (Fig. 3b). The computational predictions of polyelectrolyte micelles and gels qualitatively agree with theory and experimental results,
which demonstrates that the model can successfully predict the morphology and salt
responsiveness of ionic BCPs. Generally, the ISIS-DPD method enables the incorporation of ionic contributions to predict mesoscale assemblies of diblock copolymers.
The elimination of explicit calculations of electrostatic interactions sacrifices local
resolution, but dramatically reduces the computational power needed to simulate
large systems.
Another method of incorporating ions and ionic BCPs in DPD is by adding
coarse-grained ion beads to the solution and incorporating the electrostatic interactions in the conservative force a ij parameter [146]. Rodriguez-Hidalgo et al. examined micelles formed from poly(N-(morpholino)-ethyl methacrylate)-b-poly(4-(2sulfoethyl)-1-(4-vinylbenzyl) pyridinium betaine) (PMEMA-b-PSVBP) in aqueous
solutions with varying concentrations of two inorganic salts, Na 2 SO 4 and NaBr. This
diblock copolymer, originally synthesized by Wang et al. [147], has unique properties in that a PMEMA homopolymer will become insoluble at increased levels
of Na 2 SO 4 (>0.6 M) while a PSVBP homopolymer will dissolve with the addition
of NaBr (>0.2 M). Exploiting a combination of the two homopolymers forming a
diblock provides the opportunity to create a micelle under desired conditions, and
then invert the corona and core by adjusting the two salt concentrations in the solvent.
Rodriguez-Hidalgo et al. used the Fan et al. [148] method of mixing binary systems
to estimate the monomer–monomer, monomer-water, and monomer-inorganic salt
interactions by determining the Flory–Huggins interaction parameter based on the
Gibbs energy, pairwise coordination number, and differential energy pairwise interaction. Using this method allows for all of the desired molecular characteristics to be
encompassed in the interaction parameter, implicitly including the electrostatic and
van der Waals interactions.
Employing the resolved interaction parameters, Rodriguez-Hidalgo et al. investigated a system that included a PSVBP-core micelle with NaBr added to the solution
(Fig. 3c–a, top). At a NaBr volume fraction of 0.25, the micelle dissociated due to
the change in the solubility of the PSVBP segments as NaBr was added to the solvent
(Fig. 3c–b, top). The solubility of PMEMA was unaffected by NaBr which agreed
with experiments (Fig. 3c–c, top). They also modeled a system with Na 2 SO 4 added
to a solution of free chains, water and NaBr (Fig. 3c–a, bottom). At a Na 2 SO 4 volume
fraction of 0.29 (Fig. 3c–b, bottom), a micelle with inverted core-corona (namely,
PMEMA-core and PSVBP-corona) was formed (Fig. 3c–c, bottom). This led to
the inversion mechanism being characterized in three steps: 1-micelle dissociates
when NaBr is added, 2-free chains in solution, and 3-assembly of inverted micelle
upon addition of Na 2 SO 4 . Rodriguez-Hidalgo et al. have since used this method
T. A. Deaton et al.
to study the properties of polyelectrolyte triblock as a function of volume fraction, length of polyelectrolyte and salt concentration (Fig. 3b). They found that
the fraction of bridges between hydrophobic domains (crosslinks) relates to the gel
elastic modulus, where the scaling exponent depends on polyelectrolyte length and
salt concentration. The morphological predictions were corraborated by cryo-TEM
experiments on DNA hydrogels (Fig. 3b). The computational predictions of polyelectrolyte micelles and gels qualitatively agree with theory and experimental results,
which demonstrates that the model can successfully predict the morphology and salt
responsiveness of ionic BCPs. Generally, the ISIS-DPD method enables the incorporation of ionic contributions to predict mesoscale assemblies of diblock copolymers.
The elimination of explicit calculations of electrostatic interactions sacrifices local
resolution, but dramatically reduces the computational power needed to simulate
large systems.
Another method of incorporating ions and ionic BCPs in DPD is by adding
coarse-grained ion beads to the solution and incorporating the electrostatic interactions in the conservative force a ij parameter [146]. Rodriguez-Hidalgo et al. examined micelles formed from poly(N-(morpholino)-ethyl methacrylate)-b-poly(4-(2sulfoethyl)-1-(4-vinylbenzyl) pyridinium betaine) (PMEMA-b-PSVBP) in aqueous
solutions with varying concentrations of two inorganic salts, Na 2 SO 4 and NaBr. This
diblock copolymer, originally synthesized by Wang et al. [147], has unique properties in that a PMEMA homopolymer will become insoluble at increased levels
of Na 2 SO 4 (>0.6 M) while a PSVBP homopolymer will dissolve with the addition
of NaBr (>0.2 M). Exploiting a combination of the two homopolymers forming a
diblock provides the opportunity to create a micelle under desired conditions, and
then invert the corona and core by adjusting the two salt concentrations in the solvent.
Rodriguez-Hidalgo et al. used the Fan et al. [148] method of mixing binary systems
to estimate the monomer–monomer, monomer-water, and monomer-inorganic salt
interactions by determining the Flory–Huggins interaction parameter based on the
Gibbs energy, pairwise coordination number, and differential energy pairwise interaction. Using this method allows for all of the desired molecular characteristics to be
encompassed in the interaction parameter, implicitly including the electrostatic and
van der Waals interactions.
Employing the resolved interaction parameters, Rodriguez-Hidalgo et al. investigated a system that included a PSVBP-core micelle with NaBr added to the solution
(Fig. 3c–a, top). At a NaBr volume fraction of 0.25, the micelle dissociated due to
the change in the solubility of the PSVBP segments as NaBr was added to the solvent
(Fig. 3c–b, top). The solubility of PMEMA was unaffected by NaBr which agreed
with experiments (Fig. 3c–c, top). They also modeled a system with Na 2 SO 4 added
to a solution of free chains, water and NaBr (Fig. 3c–a, bottom). At a Na 2 SO 4 volume
fraction of 0.29 (Fig. 3c–b, bottom), a micelle with inverted core-corona (namely,
PMEMA-core and PSVBP-corona) was formed (Fig. 3c–c, bottom). This led to
the inversion mechanism being characterized in three steps: 1-micelle dissociates
when NaBr is added, 2-free chains in solution, and 3-assembly of inverted micelle
upon addition of Na 2 SO 4 . Rodriguez-Hidalgo et al. have since used this method