A Positron-Annihilation-Lifetime Study of Polymer Blends
- PDF / 360,982 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 67 Downloads / 208 Views
J. LIU, AND Y. C. JEAN Department of Chemistry, Kansas City, MO 64110 H. YANG Eastman Chemical Co.
STUDY OF POLYMER BLENDS
University of Missouri-Kansas City
Kingsport, TN 37662-5001
ABSTRACT Positron-annihilation-lifetime (PAL) spectroscopy has been utilized to investigate the free-volume properties of two types of polymer blends, a miscible blend of bisphenol-A polycarbonate (PC) and tetramethyl bisphenol-A polycarbonate (TMPC), and an immiscible blend of PC and polystyrene (PS). In the miscible blend, the freevolume hole size and its fraction follow a linear relationship with respect to the weight fraction while in the immiscible blend, the relationship is not linearly additive. The free-volume hole distributions in the immiscible blend are found to be significantly broader than those in the pure polymers. The difference is thought to be a result of the free volume formed and associated with the conformation and interchain packing between the dissimilar chains in incompatible polymers. INTRODUCTION In the last few decades, it has been realized that many physical and mechanical properties of polymers can be significantly improved by a process of blending. [1] The miscibility and the phase separation
phenomena
of polymer blends have
received significant
attention in polymer applications. [2] In order to predict and enhance the materials properties of blends, it is important to understand the nature and the underlying reasons of blending at a molecular level. One of rational approaches in this line of research is to investigate the free-volume properties on blending.[3] There exist many physical probes for characterizing the structures and properties of polymer blends.[l,4] However, only a limited number of probes are available for characterizing the freevolume properties because of the vdry small size and the dynamic nature of the free volume.[4] In recent years, positronannihilation-spectroscopy (PAS) has emerged as a unique probe for characterizing the free-volume properties in polymers.[5] In PAS, one employs the anti-particle of electrons, the positron, as a nuclear probe. Because of its positively charged nature, the positron is repelled by the ion cores and preferentially localized in atomic-size free-volume holes of a polymeric material. Therefore, the positron and positronium (a bound atom which consists of a positron and an electron) annihilation signals are found to be contributed mainly from the free-volume holes in a polymer. 47 Mat. Res. Soc. Symp. Proc. Vol. 321. ©1994 Materials Research Society
Currently, PAS has been mainly developed in monitoring the ortho-positronium (o-Ps) annihilation lifetimes (PAL) for polymeric applications. The results for o-Ps lifetime and its probability are related to the free-volume hole size, fraction and distribution. Free-volume hole sizes, fractions, and distributions in a variety of polymers have been reported using PAL methods. In polymer blends, some PAL results have been reported.[ 6,7] In this paper, we report a PAL study for two well-known polymer bl
Data Loading...
