Nanophase separation on length scales of 1-5 nanometres has been reported previously for small-molecule liquids, metallic glasses and also for several semicrystalline, liquid-crystalline and amorphous polymers. Here we show that nanophase separation of incompatible main and side-chain parts is a general phenomenon in amorphous side-chain polymers with long alkyl groups. We conclude from X-ray scattering and relaxation spectroscopy data for higher poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) that alkyl groups of different monomeric units aggregate in the melt and form self-assembled alkyl nanodomains with a typical size of 0.5-2 nm. A comparison with data for other polymer series having alkyl groups reveals that important structural and dynamic aspects are main-chain independent. A polyethylene-like glass transition within the alkyl nanodomains is observed and discussed in the context of a hindered glass transition in self-assembled confinements. This is an interesting link between central questions in glass-transition research and structural aspects in nanophase-separated materials.

A differential AC-chip calorimeter capable of measuring the step in heat capacity at the glass transition in nanometer-thin films is described. Because of the differential setup, pJ/K sensitivity is achieved. Heat capacity can be measured for sample masses below 1 ng in broad temperature range as needed for the study of the glass transition in nanometer-thin polymeric films. Relative accuracy is sufficient to investigate the changes in heat capacity as the step at the glass transition of polystyrene. The step is about 25% of the total heat capacity of polystyrene. The calorimeter allows for the frequency dependent measurement of complex heat capacity in the frequency range from 1 Hz to 1 kHz. The glass transition in thin polystyrene films (50-4 nm) was determined at well-defined experimental time scales. No thickness dependency of the glass transition temperature was observed within the error limits (63 K)-neither at constant frequency (40 Hz) nor for the trace in the activation diagram (1 Hz-1 kHz).

Broadband dielectric spectroscopy (BDS), spectroscopic vis-ellipsometry (SE), X-ray reflectometry (XRR), and alternating current (ACC) as well as differential scanning calorimetry (DSC) are combined to study glassy dynamics and the glass transition in nanometric thin (≥5 nm) layers of polystyrene (PS) having widely varying molecular weights (27 500−8 090 000 g/mol). For the dielectric measurements two sample geometries are employed, the common technique using evaporated electrodes and a recently developed approach taking advantage of nanostructures as spacers. All applied methods deliver the concurring result that deviations from glassy dynamics and from the glass transition of the bulk do not exceed margins of ±3 K independent of the layer thickness and the molecular weight of the polymer under study. Our findings are discussed in the context of the highly controversial literature and prove that an appropriate sample preparation is of paramount importance.

Alternating current (AC) nanocalorimetry was used to measure the reversing heat capacity C p of low-energy indomethacin glasses as they isothermally transform into the supercooled liquid. As the film thickness increases from 75 to 600 nm, the transformation time increases by more than an order of magnitude, consistent with a surface-initiated transformation mechanism. Eventually, the transformation time becomes constant for films between 1.4 and 30 μm, indicating a distinct bulk transformation pathway. The observation of size-dependent transformation kinetics for glass samples approaching 1 μm is unprecedented. We interpret the crossover in thickness dependence at 1 μm to signify the average distance between transformation initiation sites in the bulk low-energy glass.

Broadband dielectric spectroscopy, heat capacity spectroscopy (3omega method), and viscosimetry have been used to study the dynamic glass transition of two glass-forming epoxy resins, poly [(phenyl glycidyl ether)-co-formaldehyde] and diglycidyl ether of bisphenol-A. In spite of their rather simple molecular structure, the dynamics of these systems is characterized by two well-separated crossover regions where the relaxation times of main transition and the two secondary relaxations beta and gamma approach each other. The main transition has three parts: The a process at high temperature, the a(') process between the two crossover regions, and the alpha process at low temperatures. Both the gamma-crossover region [around a temperature T-c(gamma)similar to(1.4-1.5)T-g and a relaxation time tau(c)(gamma)approximate to10(-10) s] and the beta-crossover region [around T-c(beta)similar to(1.1-1.2)T-g and tau(c)(beta)approximate to10(-6) s] could be studied within the experimentally accessible frequency-temperature window. Different typical crossover properties are observed in the two regions. The gamma-crossover region is characterized by onset of the (a',alpha) process, with a relaxation time about one decade greater than that of the quasicontinuous (a,gamma) trace. The beta-crossover region is characterized, besides splitting of main andbeta relaxation times, by a change in the temperature dependence of the main-relaxation time as reflected by a bend in the Stickel plot of the continuous (a('),alpha) trace, the separation of individual temperature dependences of different transport properties such as impurity-ions diffusion coefficient and viscosity, and a temperature-dependent main relaxation time that starts to be in accordance (at lower temperatures) with the Adam-Gibbs model. The cooperativity of the main process between the gamma and beta crossover seems to be small. Below the beta crossover, cooperativity increases up to values of order N(alpha)similar to100 near T-g, and configurational entropy seems to correlate with the main relaxation time. (C) 2002 American Institute of Physics