Fig. 1: Structure of metallo-supramolecular polymer formed by complexing a bifunctional ligand E5 with Zn(II) Metallo-supramolecular polymers, formed via complexation of a metal ion with a bifunctional ligand (Fig.1), combine the properties of the metal ion (e.g. catalysis, photonics, bioactivity) with the mechanical properties of a polymer. In collaboration with my colleague Stuart J. Rowan, we have discovered that a class of such polymers, E5:Zn (Fig. 1), forms stimuli-responsive, mechanically-reversible gels by self-organizing into semi-crystalline colloidal particles (Fig. 2) under poor solvent conditions. We can tune the optical transparency and mechanical strength using a mixed good solvent/poor solvent system, e.g. DMSO/water (Figs. 3 and 4). Optical transparency is accompanied by a structural transformation in which the crystalline organization of the colloidal particles in the poor solvent is replaced by a new solvent-swollen structure with a lamellar small-angle x-ray scattering (SAXS) pattern, which evidently exhibits refractive-index matching characteristics (Fig. 5). Fig. 2: Optical microscopy of air-cooled E5:Zn(II) gels in acetonitrile: (a) Differential interference contrast (DIC) images; (b) Polarized images Fig.3: Gelation of E5:Zn in DMSO/water at Vol% DMSO values of 60%, 70%, 80%, and 82.5%, from left to right; Fig.4: Storage modulus of E5:Zn gels as a function of DMSO/water ratio Fig.5: SAXS of E5:Zn gels in DMSO/water (a) (b) Fig. 1: Structure of metallo-supramolecular polymer formed by complexing a bifunctional ligand E5 with Zn(II) Tuning the Optical And Rheological Properties of a Class of Stimuli-Responsive Metallo-Supramolecular Polymers which Exhibit a Novel Gel-Forming Mechanism Alexander M. Jamieson, Case Western Reserve University, DMR

Training and Development Three graduate students have been supported on this grant: (a) Wengui Weng (PhD January, 2007), now research scientist at Tremco Corporation, Beachwood, Ohio): Wengui was departmental teaching assistant in the size exclusion chromatography lab. In addition, he provided research assistance to several extramural research projects, including (i) rheology of hydrogels from self-assembling nucleopeptides for tissue engineering (for Dr. Matthew Simmons of Cleveland Clinic), and (ii) particle sizes using dynamic light scattering (DLS) of pluronic block copolymers as vehicles for drug delivery applications (for Dr. Agata Exner of Cleveland University Hospitals). Wengui also mentored, as a summer REU student, a freshman undergraduate, Steven Vesole, who is currently a senior, majoring in polymer science. (b) Tejas Upasani (MS, January, 2007), now Process Engineer at Freudenberg-NOK, Gloucester, Massachusetts. (c) Zheng Li (current PhD student). Zheng is teaching assistant in the departmental rheology lab, and has provided research assistance to several extramural research projects, including (i) rheology of greases used as a model system for in flow and fracture of metallic glasses (for Prof. J. Lewandowski of the CWRU Materials Science Department) and (ii) particle sizes using DLS of quantum dots for biomedical applications (for Prof. Clemens Burda of the CWRU Chemistry Department). In addition, he has mentored two undergraduate students, John Root and Robert Russo, in freshman research projects involving polymer gel rheology. International Collaboration As part of a collaboration on the properties of electro-responsive composites, based on conducting polymers, with Professors Anuvat Sirivat and Ratana Rujiravanit of the Petroleum and Petrochemical College of Chulalongkorn University in Bangkok, Thailand, three PhD students each spent spent three months in my laboratory carrying out rheological studies under the mentorship of my graduate students, which contributed to their thesis research, using instrumentation not available in their home institution: (a) Piyanut Hiamtup (PhD Summer, 2007) now Sr. Engineer, Western Digital Co., Thailand), (b) Siriluck Suksamranchit (PhD Summer, 2007), now Sr. Process Engineer, Fabrinet Co. Thailand), (c) Tuspon Thanpitcha (PhD Summer 2009), now Postdoctoral Associate, Faculty of Chemistry, Materials, and Bioengineering, Kansai University, Osaka, Japan. This collaboration has resulted to date in six publications in refereed journals, which acknowledge nonstipendiary support through DMR