NMR Self-Diffusion Studies on PDMS Oil-in-Water Emulsion

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• 作者：Tatjana Garasanin ; Terence Cosgrove ; Leon Marteaux ; Axel Kretschmer ; Andy Goodwin ; and Klaus Zick
• 刊名：Langmuir
• 出版年：2002
• 出版时间：December 24, 2002
• 年：2002
• 卷：18
• 期：26
• 页码：10298 - 10304
• 全文大小：137K
• 年卷期：v.18,no.26(December 24, 2002)
• ISSN：1520-5827

文摘

In this paper, standard spin-echo pulsed field gradient (SE-PFG) and stimulated spin-echo pulsed fieldgradient (STE-PFG) ¹H NMR methods have been used to study the translational diffusion of polymeric-oil-in-water (O/W) emulsions, made with poly(dimethylsiloxane) PDMS fluids and two nonionic surfactantspolyoxethylene (4) lauryl ether (Brij-30) and polyoxethylene (23) lauryl ether (Brij-35p). A detailed analysisof the free (Gaussian) diffusion of the PDMS fluid, its restricted diffusion inside the emulsion droplets,and the Brownian diffusion of the droplets themselves are presented. A graphical representation, whichrelates the square root of the mean-squared displacement of the fluid and emulsion droplets with theexperimental diffusion times and the radius of the droplets, helps distinguish the different diffusion regimes.The Brownian diffusion of the emulsion particles becomes the dominant diffusion process with dilutionof the system and increase in the molecular weight (viscosity) of the PDMS. These different processeswhich contribute to diffusion in the system need to be considered if a correct size distribution of theemulsion droplets is to be determined. For a concentrated emulsion system, the condition for restricteddiffusion is reached by increasing the diffusion time. Under this condition, the Murday and Cotts modelfor diffusion inside a spherical droplet can be used to determine the size distribution of the emulsion. Invery dilute systems by increasing the diffusion time, the Brownian diffusion becomes the dominant processso that the Stokes-Einstein model can be applied to obtain the size distribution.