Glass transition andα-relaxation dynamics of thin films of labeled polystyrene

Abstract

The glass transition temperature and relaxation dynamics of the segmental motions of thin films of polystyrene labeled with a dye, 4-[N-ethyl-N-(hydroxyethyl)]amino-4-nitraozobenzene (Disperse Red 1, DR1) are investigated using dielectric measurements. The dielectric relaxation strength of the DR1-labeled polystyrene is approximately 65 times larger than that of the unlabeled polystyrene above the glass transition, while there is almost no difference between them below the glass transition. The glass transition temperature of the DR1-labeled polystyrene can be determined as a crossover temperature at which the temperature coefficient of the electric capacitance changes from the value of the glassy state to that of the liquid state. The glass transition temperature of the DR1-labeled polystyrene decreases with decreasing film thickness in a reasonably similar manner to that of the unlabeled polystyrene thin films. The dielectric relaxation spectrum of the DR1-labeled polystyrene is also investigated. As thickness decreases, the α-relaxation time becomes smaller and the distribution of the α-relaxation times becomes broader. These results show that thin films of DR1-labeled polystyrene are a suitable system for investigating confinement effects of the glass transition dynamics using dielectric relaxation spectroscopy.

Segmental dynamics and the correlation length in nanoconfined PMMA

“…These multilayer films were prepared by melt co-extrusion, using a forced assembly technique developed by Baer and coworkers [13e15]. Unlike conventional thin films [16,17], the macroscopic size of these multilayer films makes possible modulated scanning calorimetry (MDSC) to determine the complex heat capacity, supplementing the dielectric measurements. The ability to measure both dynamic and thermodynamic properties allows two independent determinations of the dynamic correlation length.…”

Segmental Mobility and Glass Transition Temperature of Freely Suspended Ultrathin Polymer Membranes

“…Atactic polystyrene of three different molecular weights (M w ) 932, 1200, and 3000 kg/mol, PDI < 1.3) was used as received from Polymer Source Inc. Because of the low value of the intrinsic dipole moment of PS, the polymer was doped with a small fraction (0.5 wt %) of 4,4′-(N,N-dibutylamino)-(E)-nitrostilbene, (DBANS), an organic molecule with a high dipole moment acting as "dielectric probe". The feasibility of this approach has been already tested successfully in bulk and confined polymer layers by means of both dielectric 20,21 and fluorescent probes. 6,[22][23][24] Here, the addition of DBANS solely increases the sensitivity of our measurements and does not alter the segmental mobility.…”

Structural relaxation of stacked ultrathin polystyrene films

“…For example, both supported and unsupported (free standing) polystyrene ultrathin films show a noticeable T g depression relative to that of the bulk state. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] For polystyrene, the magnitude of depression can be as great as 70 C in freely standing ultrathin films. 6 In addition, Ellison and Torkelson's work 9 on labeled layers in supported polystyrene films shows that there is a gradient in the T g depression with a greater depression at the surface and only a small depression at the polystyrene/glass substrate interface.…”

“…However, the effects of the nanoconfinement on physical aging have not been well studied, and some of the results are seemingly contradictory. 21,22,[27][28][29] Both acceleration and retardation of structural relaxation during physical aging were reported for different types of nanoconfinement and materials. Acceleration is observed for small molecules confined in nanopores because the equilibrium state below T g differs under this type of nanoconfinement due to isochoric vitrification resulting in smaller relaxation times at temperatures a given distance below T g .…”