Shape Transitions in Soft-Matter-Based Charged Nanoparticles Regulated by Surface Tension

Shape-reconfigurable nanoparticles (NPs) have important applications as self-assembling building blocks for the design of novel materials and as drug-delivery carriers that change shape in response to external cues. Experiments and simulations show that tunable short-range and long-range interactions can be used to deform soft-matter-based (soft) NPs. The shape and size of soft NPs is a function of surface composition and environment. In this work, molecular dynamics is used to explore the role of surface tension in deforming the shape of uniformly charged, soft NPs subject to a volume constraint. Results show that surface tension modulates the relative favorability of oblate disk to prolate rod morphologies. Disk-to-rod transitions are facilitated by increasing surface tension (1 - 20 dynes/cm). NPs with different bending rigidities (10 - 30 k_BT), radii (10 - 30 nm), and surface charge (100 - 900 e) under variable solution ionic strengths (1 mM - 0.5 M) are investigated. Global free-energy changes and energy patterns on the NP surface are evaluated and correlated with the shape transitions. New pathways for the design of dynamic NP-based building blocks for hierarchical self-assembly are proposed.