Anisotropic Self-Assembly of Spherical Nanoparticles in Polymer Nanocomposites

Columbia University, New York NY

Investigators

Abstract

Technical Summary: The PIs group has recently found that spherical nanoparticles, which are grafted with long polymer chains, assemble into highly anisotropic sheets when they are mixed with "matrix" chains of the same structure but which are longer than the brush. The samples have to be annealed for extended periods of time above the glass transition temperature of the polymer for these sheets to form and grow. Initial TEM tomography results suggest that these sheets are a few (2-5) particles thick, but that their lateral extent can be as large as tens of micrometers. These dimensions are akin to those of clay sheets, which have been extensively used in polymer nanocomposites to achieve unprecedented improvements in mechanical properties, gas permeation and flame retardancy. This proposal conjectures that the ability of spherical particles to assemble into sheet-like morphologies should allow for similar property improvements. At this point the factors which dictate this unusual assembly process are not understood. Thus, here, a highly integrated theoretical and experimental effort is proposed with the goal of controllably achieving morphologies between the limits of uniform particle dispersion (when the matrix chains are shorter than the brush) and highly anisotropic system spanning particle structures (when the brushes are shorter than the matrix). Specifically, the factors controlling the shapes that can be formed by self-assembling spherical particles, and if they are equilibrium or kinetically created will be focused on. The relationship between the resulting morphology and macroscopic properties will also be touched on so that nanocomposites with desired properties can be obtained. Non-Technical Summary: The ability to apparently create structures with controllable anisotropy is exciting in the context of potential applications since previous work has shown that unusual improvements in properties are achieved when highly anisotropic objects, such as carbon nanotubes or clay sheets, are added to polymers. The ability to spontaneously assemble nanoparticles into 'sheets" with, presumably, controllable lateral dimensions could allow for the creation of easily processable materials with tunable electrical, mechanical and transport properties. In addition to the investigation of an interesting physical situation, the Pt shall continue to mentor undergraduate and graduate students through a variety of forums. He will continue to develop REU programs which will target underrepresented minorities. An established collaboration with Prof. Ramakrishnan (Florida A&M University, a historically black school) will be leveraged to recruit undergraduate students with the goal of retaining them in the sciences. The P1 will also develop courses to teach graduate students the fundamentals of a new field, muttiscale modeling as applied to condensed phase systems. The P1 also teaches science to K-12 students in the New York city area, and is currently mentoring an 8th grade student on an science project.