GOALI: Large-Scale Structures in Colloids with Moderate-Range Attractions

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0853551BhatiaColloidal particles with attractive interparticle potentials are important from both a fundamental and applications standpoint. Much of the research to date has focused on colloids with short-range attractions, which may form either attractive colloidal glasses or networked gels. However, recent studies have shown that a new phase containing stable dense clusters of particles may be formed in systems with moderate-range attractions. These exciting results underscore the importance of the range of attraction as an additional parameter to explore in determining the phase behavior of attractive colloids. In this GOALI project, we will develop a fundamental understanding of how the range of attractive interactions impacts large-scale structure in colloidal dispersions, including aggregation and formation of finite sized clusters, and apply this knowledge to develop improved toner formulations. We confine ourselves to systems in which the attractions arise from bridging chains and in which the particle polymer size ratio is O(1). Our study distinguishes itself from previous work in that we will both quantify the interparticle potential using small angle scattering and explore structure using scattering and imaging techniques. The main objectives of the proposal are to: 1. Develop a model system where the range of attraction can be tuned, and characterize the interparticle potential using small angle neutron scattering; 2. Probe large scale structure and aggregation in systems at rest using ultra-small angle neutron scattering (USANS), dynamic light scattering, confocal microscopy, and TEM; 3. Investigate the effect of shear on cluster morphology and rheology; and 4. Test the extensibility of our findings to industrially relevant systems, through graduate student internships and industrial interactions provided by researchers at Xerox Corporation. Xerox Corporation is interested in applications of colloidal aggregation to toner production and will serve as the industrial partner for this GOALI. Inclusion of Xerox as a partner will add value by facilitating transfer of the research results into an industrially relevant technology and by broadening the training experiences of graduate and undergraduate students involved in the project. Xerox personnel will actively participate by providing comments and suggestions at regular research team meetings, by arranging student internships to evaluate the applicability of the research to toner production, by providing funds in support of portions of the work, and by participating in an industrial short course.