- Structure and Dynamics in Nanoconfined Self-Assembled Polymers

Involved researchers : A.C. Genix
(collaboration : J. Colmenero, A. Arbe, San Sebastian –SPAIN)

We are exploiting the selectivity of neutron scattering combined with isotopic substitution to study the structure and dynamics of poly(n-alkyl methacrylates). In these polymers, the alkyl side groups of different repeat-units seem to self-assemble forming nanodomains (called polyethylene (PE)-like). Moreover, the higher order PnMAs show two distinct glass-transitions which presumably correspond to the freezing of motions within the alkyl nanodomain and of the main-chain dynamics.
Our diffraction data nicely demonstrate the nanosegregation of main chains and side groups. Moreover, by Neutron Spin Echo (NSE) we have separately followed the structural relaxation of both subsystems. Contrary to the standard behaviour found at the main-chain level, the correlations involving long side groups within the alkyl nanodomains relax through an exotic logarithmic decay - probably a signature of nano-confinement of the side-groups by the more rigid main chains.

Figure. Center : diffraction patterns of PEMA (number of alkyl carbons n=2), PBMA (n=4) and PHMA (n=6). Left : Master curve built with the NSE data of PBMA at different temperatures obtained at the low-Q peak (confining matrix correlations) ; the times have been scaled with the mechanical temperature dependence. Solid line is a fit to a stretched exponential. Right : NSE results on PBMA at 1.3 Å^-1 (correlations within the alkyl nanodomains). Lines are fits to logarithmic decays. - © L2C

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Structure and Dynamics in Nanoconfined Self-Assembled Polymers