Archer group publishes on PNCs in Nature Communications
Rahul Mangal, a Ph.D. candidate in the Archer group, recently published a paper titled: “Phase stability and dynamics of entangled polymer–nanoparticle composites” in Nature Communications.
Particle fillers are routinely added to polymers to augment properties ranging from mechanical strength,gas permeability, thermal stability, and wear resistance. When the filler dimensions approach nanometer length scales, these particle-induced property enhancements are detected at volume fractions where continuum analysis suggests minimal effect of the particles. A recurrent theme in explaining this longstanding puzzle is that strong surface forces between particles drive phase separation of the particles to produce polymer swollen particle clusters able to span the entire material space.
Using polymer-tethered hairy nanoparticles as model systems, the Archer group has shown that it is possible to harness favorable enthalpic interactions between particle-tethered and high molecular weight host polymer chains to overcome surface forces that lead to particle-particle clustering. The further show that using this strategy it is possible to create model polymer-nanoparticle composites (PNCs) in which particles are distributed uniformly in a host polymer over large length scales. Investigation of the mechanical properties of these model PNCs reveal for the first time that nanoparticles influence their host polymer motions on all timescales, explaining their much greater than expected influence on physical properties of the host polymer. On short timescales, nanoparticles slow-down local motions of the host polymer segments and lower the glass transition temperature. On intermediate timescales, where polymer chain motion is typically constrained by entanglements with surrounding molecules, nanoparticles provide additional constraints, which lead to an early onset of entangled polymer dynamics. Finally, on long timescales, nanoparticles produce an apparent speeding up of relaxation of their polymer host, which leads to an apparent reduction in the viscosity of the host in violation of the classical Einstein-Batchelor hydrodynamic relation for particle suspensions.
Reference: Rahul Mangal, Samanvaya Srivastava and Lynden A. Archer. “Phase stability and dynamics of entangled polymer–nanoparticle composites” Nature Communications 6, 7198 doi:10.1038/ncomms8198