Fine Structure of the Main Transition in Amorphous Polymers:  Entanglement Spacing and Characteristic Length of the Glass Transition. Discussion of Examples

Abstract

The main transition of amorphous polymers is analyzed with respect to a fine structure by means of new experimental dynamic shear, dielectric, and heat capacity data for the following polymers: poly(n-alkyl methacrylate)s with alkyl = methyl, ethyl, propyl, butyl, and hexyl, polystyrene, poly(vinyl acetate), a series of weakly vulcanized natural rubbers, a series of butyl rubbers with different carbon black content, polyisobutylene, and bromobutyl rubber. The components of the fine structure are assumed to be a proper glass transition at short times, followed by a confined flow zone, and, at large times, a hindering zone caused by entanglements at large times. Two lengths are assumed to correspond to the first and third components, respectively, the characteristic length to the proper glass transition and the entanglement spacing to the hindering zone. The confined flow will be described by a dispersion law (general scaling) across the main transition. The characteristic length of the glass transition for the poly(n-alkyl methacrylate)sonly of order 1 nm as determined by calorimetryis confirmed by backscaling from the entanglement spacing by means of a Rouse dispersion law for shear. The fate of the Rouse modes below the αβ splitting of the glass transition is discussed for the other amorphous polymers. Finally, a speculative molecular picture of the different modes in the main transition is described. The new element is a low-viscosity longitudinal motion of individual chain parts in the confined flow zone. A simple rheological model for the confined flow is also presented.

Segmental dynamics and the correlation length in nanoconfined PMMA

“…A non-spherical cooperative region seems to be at odds with the compact shape envisioned in the RFOT model [28]. Note that it has been shown recently by MD of polymer thin films [24] that independently of the interactions at the interfaces, the correlation between the polymer dynamics and x remains unchanged, consistent with our results (Fig. 3).…”

“…This is smaller than the value estimated from the dielectric measurements (eq. (4)), very similar to the differences between the two methods when applied to bulk PMMA [1,24]. Dalle-Ferrier et al [25] have pointed out that the precision in the measurement of correlation volumes is highest for dielectric spectroscopy; thus, the larger N c herein are more reliable.…”

Temperature and Pressure Dependence of the Free Volume in Polyisobutylene from Positron Lifetime and Pressure‐Volume‐Temperature Experiments

“…[1][2][3][4][5][6][7][8] and the references given therein). As an example, PIB seems to be the least fragile polymer and exhibits a relatively large stretching exponent of the structural relaxation function.…”

Comment on “Heat capacity, enthalpy fluctuations, and configurational entropy in broken ergodic systems” [J. Chem. Phys. 133, 164503 (2010)]

“…18 It does not indicate loss of configurational degrees of freedom on the time scale of the stimulus. Specific heat relaxation spectra show variation of the real and imaginary (out of phase) components, C p and C p , of C p * = C p − iC p , with temperature-oscillation frequency ν (Hz), and they result from the phase lag between heat oscillation and temperature oscillation, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] not from the loss of S conf over the time-duration of observation, t obs = (1/ν). As ν is increased, C p decreases in an inverted sigmoid-shape manner and C p shows a peak.…”