(716a) Assembling Self-Repairing Ultra-Flexible Magnetic Chains and Networks By Nanocapillary Binding

Authors: 
Bharti, B., North Carolina State University
Fameau, A. L., National Institut of French Agricultural Research
Rubinstein, M., University of North Carolina at Chapel Hill
Velev, O. D., North Carolina State University

Colloidal assemblies in the form of one-dimensional arrays, chains and gels of particles are of special interest as the core of functional materials with applications in biomedicine, electronics and sensors. One rapid and efficient technique for linear assembly of colloidal particles is the use of external electrical or magnetic field. The attractive dipolar and multipolar interactions induced in the particles under the action of external field determine the interparticle arrangement. However, the resulting ordered structures are temporary and last only as long as external field is present. We report a novel method for permanently assembling superparamagnetic nanoparticles covered by lipid shell into magnetically responsive ultraflexible chains. Initial burst of magnetic field aligns the particles into bundles and after switching off the field the particles retain their linear arrangement by a soft attractive potential induced by the lipid junctions. These soft lipid junctions play the role of nanocapillary bridges and we highlight that the phase of the surface wetting lipid governs the bridge and hence the chain formation. The role of surface wettability and formation of liquid menisci was related to the thermodynamic phase of the surface adsorbed lipid. No nanocapillary bridging was observed until the temperature was less than the gel-fluid phase transition temperature of the corresponding lipid. The presence of nanocapillary bridges provides high flexibility to the resulting chains by allowing for particle rolling and sliding. We evaluate persistence length of the chains by finding the decay in bond correlations along the chain contour. We demonstrate that despite of high linear density, persistence length still remains comparable to persistence length of bio-molecules proving the ultrahigh flexible nature and reconfigurability of the assembled chains. The square-well like "snapping" induced by the lipid shells can be used in making self-closed ring-like objects and self-repairing networks. This assembly mechanism opens new pathways for making multifunctional structures and materials, which can be dynamically reconfigured and programmed, including reassembling micrograbbers and microbots, and self-repairing gels with unusual magnetic and rheological responses.