Structural change accompanying volume change in amorphous polystyrene as studied by small and intermediate angle x-ray scattering

• Published in: Macromolecules Vol. 20; no. 11; pp. 2723 - 2732
• Main Authors: Song, Hyun Hoon, Roe, Ryong Joon
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.11.1987
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis; Modification; Influence; Styrene polymer; Mass volume; X ray scattering; Structure
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma00177a016

X-ray intensities scattered at small and intermediate angles from amorphous polystyrene were measured to study the change in the structure of the material as its volume was altered by five different methods. The volume changes were effected by (i) temperature change above T sub g , (ii) temperature change below T sub g , (iii) densification by application of pressure above T sub g and subsequent release of the pressure at room temperature, (iv) spontaneous volume expansion of the pressure-densified material, and (v) spontaneous volume contraction on isothermal annealing below T sub g (physical aging). The intensity data were examined either directly or after transformation into the density fluctuation function, the latter evaluated as a function of the size of the region of interest. The results show that the large scale density fluctuation correlates fairly well with the change of specific volume, irrespective of the different methods used to induce it. On the other hand, the small scale density fluctuation, indicating the degrees of local ordering, depends very sensitively on the method of volume change employed. In particular, (a) the volume contraction by temperature change above T sub g and by physical aging gives rise to enhanced short-range ordering, (b) the volume contraction by temperature change below T sub g and the spontaneous volume expansion of pressure-densified sample are accompanied with little change in local structural ordering, and (c) the pressure-densified samples, despite their much higher density, exhibit greatly reduced local ordering. The results suggest that the properties of glassy materials, such as the mechanical relaxation rate, are determined not only by the free volume content but also by the state of local packing of segments. The results also show that an approximate measure of the local structural order can be obtained, in practice, by measuring the height of the amorphous peak intensity. 39 ref.--AA