| 학회 | 한국고분자학회 |
| 학술대회 | 2005년 봄 (04/14 ~ 04/15, 전경련회관) |
| 권호 | 30권 1호, p.19 |
| 발표분야 | 나노구조형 고분자 분광분석 |
| 제목 | Positron Annihilation Lifetime Spectroscopic (PALS) Evidence to Demonstrate the Flux-Enhancement Mechanism in Morphology-Controlled Thin-Film-Composite (TFC) Membrane |
| 초록 | Positron annihilation lifetime spectroscopy (PALS) is a unique and valuable technique which characterizes the molecular-level free-volume hole properties in the solid polymeric systems based on the detection of annihilation of ortho-positronium (o-Ps) in samples. The o-Ps of parallel spin state has an intrinsic lifetime of 142 ns in vacuum, while in electron dense samples such as polymers, the lifetime is shorten to a few ns. The measured lifetime has been proven to be highly correlated with the average size (radius, R of ~ Å) and distribution of hole spaces present in the solid polymers; the longer the lifetime, the larger the R, and vice versa1. where τo-Ps is o-Ps lifetime (ns), R is radius (Å) of free hole space, and R0 is R+ΔR where the fitted empirical electron layer thickness ΔR is 1.66 Å. In this study, PALS is applied to explain the flux-enhancement mechanism in thin-film-composite (TFC) membranes prepared by using the dimethyl sulfoxide (DMSO) as an additive in the interfacial polymerization. The TFC membranes show a large increase in water flux, up to 5-fold compared to nonadditive membrane. Atomic force microscopy (AFM) shows that surface roughness and surface area increase when DMSO in the aqueous phase solution phase works to increase miscibility of the aqueous and the organic phase by reducing the solubility difference of two immiscible solutions. X-ray photoelectron spectroscopy (XPS) reveals the variation of the chemical compositions to the extent that there is a considerable increase in the crosslinked amide linkages of the flux-enhanced TFC membranes. The effects of these structural changes on the molecular-size free volume properties are evaluated based on PALS studies. The PALS results exhibit two types of o-Ps lifetimes, i.e. τ3 and τ4 for short and longer components, which indicate that the thin film polymer of crosslinked aromatic polyamide RO membrane are composed two types of pore structure having radii of range of about 2.1~2.4 Å and 3.5~4.5 Å for τ3 and τ4 ,respectively. These observation agrees with the theoretical model proposed by Sourirajan et al2, where he named the small and large pores as network and aggregate pores, respectively. According to him, water permeation of TFC membrane takes place both in two types of pores, while salt can permeate only in the larger aggregate pore. The PALS analysis shows that the size and the number of network pores increase with the more addition of DMSO. Furthermore, the size of large pores permeable to salts increases, although the evitable decrease in the number of the aggregate pore. From the combined consideration, the flux-enhancement of the TFC membrane can be explained as follows. First, the increase in the size and number of network pores by means of DMSO addition during interfacial polymerization enhance the water flux notably. Next, the size increase of aggregate pores may contribute to enhance water flux. The PALS shows a valuable evidence to demonstrate the flux-enhancement of highly-crosslinked TFC membrane and is expected to be used as a powerful tools to characterize the molecular-level free volume structure of polymer samples. 참고문헌 1) H. Nakanishi, Y. C. Jean, Positron and Positronium Chemistry, Elsevier Science: Amsterdam, 1988; p. 159-192. 2) T. D. Nguyen, K. Chan, T. Matsuura, S. Sourirajan, Ind. Eng. Chem. Prod. Res. Dev., 24, 655 (1985). |
| 저자 | 김성호, 곽승엽 |
| 소속 | 서울대 |
| 키워드 | thin-film-composite membrane; positron annihilation lifetime spectroscopy; flux-enhancement |
