34 research outputs found
The inter and intra-molecular dynamics of polymethylphenylsiloxane under 1-D and 2-D confinement
The inter and intra-molecular dynamics of polymethylphenylsiloxane under 1-D and 2-D confinement
The dielectric
The question of whether the glass transition temperature in thin polymer films depends on the film thickness or not has given rise to heated debate for almost two decades now. One of the most puzzling findings is the seemingly universal thickness independence of the dielectric α-relaxation observed for supported films. It is puzzling not only in view of the fact that other techniques or other geometries sometimes showed a significant shift of as a function of film thickness, but more so, because computer simulations for all types of polymer film models revealed changes in the structure and dynamics close to a hard surface or a free surface. Our results suggest to explain this apparent contradiction by the fact that only within 1â2 nm from the wall the density changes are sufficiently large to alter the dynamics. Additionally, the wall desorption kinetics, which introduces a new energy scale (at least for simple van der Waals attraction), is enslaved to the α-relaxation at low temperatures
The inter and intra-molecular dynamics of polymethylphenylsiloxane under 1-D and 2-D confinement
Legislative Documents
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Confinement for More Space:A Larger Free Volume and Enhanced Glassy Dynamics of 2-Ethyl-1-hexanol in Nanopores
Environmental enteric dysfunction and systemic inflammation predict reduced weight but not length gain in rural Bangladeshi children
Structure and Dynamics of Asymmetric Poly(styreneâ<i>b</i>â1,4-isoprene) Diblock Copolymer under 1D and 2D Nanoconfinement
The
impact of 1- and 2-dimensional (2D) confinement on the structure and
dynamics of polyÂ(styrene-<i>b</i>-1,4-isoprene) PÂ(S-<i>b</i>-I) diblock copolymer is investigated by a combination
of Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM),
Grazing-Incidence Small-Angle X-ray Scattering (GISAXS), and Broadband
Dielectric Spectroscopy (BDS). 1D confinement is achieved by spin
coating the PÂ(S-<i>b</i>-I) to form nanometric thin films
on silicon substrates, while in the 2D confinement, the copolymer
is infiltrated into cylindrical anodized aluminum oxide (AAO) nanopores.
After dissolving the AAO matrix having mean pore diameter of 150 nm,
the SEM images of the exposed PÂ(S-<i>b</i>-I) show straight
nanorods. For the thin films, GISAXS and AFM reveal hexagonally packed
cylinders of PS in a PI matrix. Three dielectrically active relaxation
modes assigned to the two segmental modes of the styrene and isoprene
blocks and the normal mode of the latter are studied selectively by
BDS. The dynamic glass transition, related to the segmental modes
of the styrene and isoprene blocks, is independent of the dimensionality
and the finite sizes (down to 18 nm) of confinement, but the normal
mode is influenced by both factors with 2D geometrical constraints
exerting greater impact. This reflects the considerable difference
in the length scales on which the two kinds of fluctuations take place