ABSTRACT:The self diffusion coefficient D, of two labeled polystyrene (PS) samples in dibutyl phthalate (DBP) has been measured in the range of polymer concentration from 0.1 to 50 wt% using forced Rayleigh scattering (FRS) and fluorescence recovery after photo bleaching (FRAP). 2-Nitro-4-carboxy-4' -dimethylaminostilbene and 4-glycyl-7-nitrobenzofurazan have been used as photochromic dyes for FRS and FRAP measurements, respectively. Good agreement has been found between two sets of D, data in the range of D, from 10-8 to 10-12 cm 2 s -1 within experimental error. In the dilute region of c I wt%, mutual diffusion coefficient D of unlabeled but otherwise the same PSs in DBP has been measured by dynamic light scattering. The D, assymptotically approached D with decreasing polymer concentration.KEY WORDS Self Diffusion Coefficient / Forced Rayleigh Scattering / Fluorescence Recovery after Photobleaching / Polystyrene Solution / Photobleachable Dye / The self diffusion coefficient D. is a most useful quantity for the study of slow chain dynamics in condensed polymeric systems. 1 Among various techniques proposed for D. measurements, 2 -13 both forced Rayleigh scattering (FRS) and fluorescence recovery after photobleaching (FRAP) are methods which make use of photochromic dyes for labeling of polymers. The former method has been developed in the field of physical chemistry of synthetic· polymers, while the latter has been invented in the field of biophysics. 14 -17 Both methods have merits and demerits. The FRS method usually provides an accurate estimate of D. because of high diffracted intensity l. detected at the Bragg angle and of a definite value of 1. at time t-+oo, i.e., the base line value. However, the complicated photochemical process of a dye sometimes gives rise to an anomalous l. vs. t curve, which hinders unambiguous data analysis. 18 • 21 The FRAP method is free from the dye problem, but an indefinite value of 1. at t-+ oo makes it difficult to estimate D. accurately. 22 Furthermore it is troublesome in a strict sense that there is no standard material with a known D. value with which accuracy of the either measurement can be examined. On the other hand, it is reasonable to consider that the two techniques should give an identical D. value in principle, when applied to the same polymer-solvent system. Then good agreement for the absolute magnitude of D. may be obtained. In spite of the importance of the two techniques, such com-
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