Tunable Permeability of Cross-Linked Microcapsules from pH-Responsive Amphiphilic Diblock Copolymers: A Dissipative Particle Dynamics Study

Abstract

Using dissipative particle dynamics simulation, we probe the tunable permeability of cross-linked microcapsules made from pH-sensitive diblock copolymers poly(ethylene oxide)-b-poly(N,N-diethylamino-2-ethyl methacrylate) (PEO-b-PDEAEMA). We first examine the self-assembly of non-cross-linked microcapsules and their pH-responsive collapse and then explore the effects of cross-linking and block interaction on the swelling or deswelling of cross-linked microcapsules. Our results reveal a preferential loading of hydrophobic dicyclopentadiene (DCPD) molecules in PEO-b-PDEAEMA copolymers. Upon reduction of pH, non-cross-linked microcapsules fully decompose into small wormlike clusters as a result of large self-repulsions of protonated copolymers. With increasing degree of cross-linking, the morphology of the microcapsule becomes more stable to pH change. The highly cross-linked microcapsule shell undergoes significant local polymer rearrangement in acidic solution, which eliminates the amphiphilicility and therefore enlarges the permeability of the shell. The responsive cross-linked shell experiences a disperse-to-buckle configurational transition upon reduction of pH, which is effective for the steady or pulsatile regulation of shell permeability. The swelling rate of the cross-linked shell is dependent on both electrostatic and nonelectrostatic interactions between the pH-sensitive groups as well as the other groups. Our study highlights the combination of cross-linking structure and block interactions in stabilizing microcapsules and tuning their selective permeability.

Controllable Multigeometry Nanoparticles via Cooperative Assembly of Amphiphilic Diblock Copolymer Blends with Asymmetric Architectures

“…As a coarse-grained method, DPD has been used to investigate physical phenomena of soft materials, where repeat units or cluster of molecules are grouped together and represented by a single bead, for larger time and length scales than typical molecular dynamics (MD). [39][40][41] The time evolution is governed by Newton's equation of motion m dv i /dt = f i , where v i and f i indicate the velocity and force on the ith bead with mass m at time t. The velocity-Verlet algorithm has been used for the integration of the equation of motion. 38 In the simulations, the force on a bead i at position r i surrounded by beads j ≠ i at r j (distance vector r ij = r i -r j and unit vector e ij = r ij /r ij with r ij = |r ij |) is a sum of the components of the conservative force F C , the dissipative force F D , the random force F R , as well as the bond stretching force F S , f i = (F C ij + F D ij + F R ij + F S ij ), where the sum runs over all beads j within a cutoff radius r c .…”

Directed Self‐Assembly of Patchy Microgels into Anisotropic Nanostructures

“…Based on the DPD theory proposed by Groot and Warren, the repulsive parameter a ii between the neutral same species was chosen to be 25, such as the interaction of core–core ( a 11 ) and water–water ( a 33 ). If the repulsive interaction existed in the same components, for example, the repulsive interaction between microgel shell ( a 22 ), the a ii was usually adjusted to >25 …”

Micellar polymerization: Computer simulations by dissipative particle dynamics

“…During one reaction step all active centers (in average) are checked. Of course, it is not the only one way to realize polymerization, for example, it is possible to connect two randomly chosen beads via additional bead using variable nearest‐neighbor bonding principle …”