8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P4.32Fri 911:10-14:00Orientation mobility of dendrimer segments in dilutesolutions: comparison of analytical calculations,computer simulation and NMR relaxation experimentsVladimir Matveev, 1 Denis Markelov, 1 Petri Ingman, 2 and Erkki Lahderanta 31 Saint-Petersburg State University, Ulianovskaya 1, 198504, Saint Petersburg,Russian Federation2 University of Turku, Turku, Finland3 Lappeenranta University of Technology, Lappeenranta, FinlandThe main goal of the work was to check some theoretical predictions for an orientation mobilityof dendrimer segments using NMR relaxation measurements in so-cold ”dispersion domain”, i.e.near ω 0 τ c 1 condition. Recent Brownian dynamics simulation [1] has shown that the characteristictime τ c in this domain is determined only by local reorientation of an individual segment in thedendrimer under study and larger-scale processes - such as the rotation of the dendrimer branch(pulsation) or the dendrimer rotation as a whole - do not influence the τ c value. As a result NMRrelaxation rate measurements lead to the direct evaluation of the minimal characteristic time of adendrimer relaxation spectrum. In addition both analytical calculations and computer simulationshave predicted an independency of a characteristic time of the interior dendrimer reorientationon the dendrimer size (number of generations). In order to test the predictions above we havemeasured a temperature dependence of 1 H NMR relaxation rates, in dilute CDCl3 solutions of anumber of carbosilane dendrimers 1 to 5 generations in the temperature range 320 K - 225 K [2,3]. For the first time, the maximum of 1/T 1 value was achieved for majority of the dendrimerfunctional groups, and the values of both the τ c and the activation energies were obtained. Wehave found a practical independency of the position of the NMR relaxation rate maximum on bothdendrimer size and segment position hence, we have obtained direct experimental confirmation ofboth our predictions. [1] D. A. Markelov, S. V. Lyulin, Yu. Ya. Gotlib et al. , J. Chem. Phys. 130,044907 (2009) [2] D. A. Markelov, V. V. Matveev, P. Ingman et al. , J. Phys. Chem. B 114, 4159(2010). [3] D. A. Markelov, V. V. Matveev, P. Ingman et al. , J. Chem. Phys. , submitted.32