Modeling the formation of layered, amphiphilic gels

• Modeled formation of two-layered incompatible, stackable gel using DPD simulations.
• Examined all possible combinations using ATRP and FRP to form stacked gel.
• Active radicals in lower ATRP gel help form interconnected gel layers.
• Lack of active radicals in lower FRP gel leads to weakly connected stackable gel.

The efficient formulation of layered gels that encompass both hydrophilic and hydrophobic domains could lead to novel materials with a range of vital functionalities. To facilitate the fabrication of these materials, we perform dissipative particle dynamics (DPD) simulations to model the formation of two-layered stackable gels where the gels are incompatible and their respective solvents are immiscible. The bottom layer of the gel is created first and then a solution of new initiators, monomers and cross-linkers is introduced on top of this first layer. These components then undergo living copolymerization to form the second gel layer. We investigate all possible combinations using free radical polymerization (FRP) and controlled/living atom transfer radical polymerization (ATRP) to form the two-layered material. When the lower gel is formed via ATRP, the system forms connected, stacked gel layers. If, however, the lower gel is formed via FRP, the gels do not form interconnected layers. The presence of active radical chain ends in the lower gel grown by ATRP enables the formation of covalent bonds with the upper gel layer. On the other hand, the lack of active radicals in the lower FRP gel leads to a sharp interfacial region, with negligible inter-gel bonds connecting the two layers. Our simulations provide insight into the nanoscale nature of the interface between the gel layers and yield guidelines for forming mechanically robust, “stackable” amphiphilic gels.

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