Organic Crystal Growth on Flexible Templates

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Guangzhao Mao, Wayne State University"Organic Crystal Growth on Flexible Templates"This project will to explore the possibility of morphological control and confinement of organic crystals using polymeric templates. The nucleation and crystallization of model organic dyes will be studied on two-dimensional (2-D) polyelectrolyte templates, and in three-dimensional (3-D) polyelectrolyte shells by atomic force microscopy and other in situ methods. The proposed research aims at (1) understanding the effect of polyelectrolytes on organic crystallization; and (2) encapsulating organic crystals in polyelectrolyte shells.This research explores the rich interplay between the surface structure of polyelectrolytes and the habit of nascent crystals. Polyelectrolytes exert templating effect via preconcentration of lattice ions, geometric and stereochemical match, specific interactions, and adsorption-induced stabilization. Polymeric substrates differ from inorganic templates in that they do not show the order and rigidity implicit in the epitaxial mechanisms. However natural polymers are known to induce crystals of a uniform habit that is different from those grown without the polymers. Research in biomineralization has shown that the templating effect of polyelectrolytes does not require the same degree of geometric match as the inorganic counterparts. Polyelectrolytes may display rich stereochemical control because of their many surface conformations. There may exist several geometric matches for a given crystal face. Segments protruding into solution may stabilize side faces of the nascent crystal. Based on the above notions, an approach consisting primarily of experiments, but also utilizing the Cerius2 program, will be used to study the interfacial structure between the polyelectrolyte template and the nascent dye crystal. Initial experiments will focus on the crystallization of dyes on 2-D thin films so that the kinetics and crystal habit modification can be probed at the molecular scale. The kinetic parameters include critical supersaturation, pH, induction time, and rate of crystallization. The crystal habit variables include size, shape orientation, and correlation to the template structure. In the second stage, the study will focus on the dye crystallization inside the polyelectrolyte shell. The shell will consist of polyelectrolyte multilayers permeable to small polar molecules but not their crystals. In addition to the polyelectrolytes, supported phospholipid bilayers will be used as templates because they provide intermediate order and flexibility. This project is intended as a proof-of-concept study. Future work can go beyond the generic polyelectrolytes using polymers with higher architectural definitions such as amphiphilic polymers, ionomers, and biopolymers.This research may have broader impact in terms of its relationship to the concept of nano-science and technology especially in areas such as materials processing, color displays, information storage, nanocomposites, drug encapsulation, and sensors. For example, the encapsulated colloids can be used as tips for micropipettes, as chemical sensors to detect pollutants, and as heterogeneous catalysts.Also, the support will allow the P.I. to continue exploring the molecular mechanisms in the templated growth of organic with potential applications in encapsulation, coatings, and materials processing. It will also help the P.L to establish long-term collaboration and exchanges with a foreign research institution: the Max-Planck-Institute of Colloids and Interfaces. Some experiments will be conducted at the Institute with a number of characterization methods not present at the P.I.'s home institution. The planned educational and outreach activities include incorporation of research topics into materials engineering curricula, global education associated with the World Bridge program, mentoring of Detroit high school students in the Science Summer Camp program, and training science teachers from local community colleges.