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The gamma distribution model for pulsed-field gradient NMR studies of molecular-weight distributions of polymers

Magnus Röding (Institutionen för matematiska vetenskaper, matematisk statistik) ; Diana Bernin (Institutionen för kemi- och bioteknik, Teknisk ytkemi) ; Jenny Jonasson (Institutionen för matematiska vetenskaper) ; Aila Särkkä (Institutionen för matematiska vetenskaper) ; D. Topgaard ; Mats Rudemo (Institutionen för matematiska vetenskaper, matematisk statistik) ; Magnus Nydén (Institutionen för kemi- och bioteknik, Teknisk ytkemi)
Journal of Magnetic Resonance (1090-7807). Vol. 222 (2012), p. 105-111.
[Artikel, refereegranskad vetenskaplig]

Self-diffusion in polymer solutions studied with pulsed-field gradient nuclear magnetic resonance (PFG NMR) is typically based either on a single self-diffusion coefficient, or a log-normal distribution of self-diffusion coefficients, or in some cases mixtures of these. Experimental data on polyethylene glycol (PEG) solutions and simulations were used to compare a model based on a gamma distribution of self-diffusion coefficients to more established models such as the single exponential, the stretched exponential, and the log-normal distribution model with regard to performance and consistency. Even though the gamma distribution is very similar to the log-normal distribution, its NMR signal attenuation can be written in a closed form and therefore opens up for increased computational speed. Estimates of the mean self-diffusion coefficient, the spread, and the polydispersity index that were obtained using the gamma model were in excellent agreement with estimates obtained using the log-normal model. Furthermore, we demonstrate that the gamma distribution is by far superior to the log-normal, and comparable to the two other models, in terms of computational speed. This effect is particularly striking for multi-component signal attenuation. Additionally, the gamma distribution as well as the log-normal distribution incorporates explicitly a physically plausible model for polydispersity and spread, in contrast to the single exponential and the stretched exponential. Therefore, the gamma distribution model should be preferred in many experimental situations.

Nyckelord: Pulsed-field gradient NMR, Self-diffusion, PEG, Polymer, Gamma distribution, Log-normal distribution, nuclear-magnetic-resonance, self-diffusion, integral-equations, spin-echo, water, polydispersity, cellulose



Denna post skapades 2012-10-10. Senast ändrad 2012-10-11.
CPL Pubid: 164550

 

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Institutioner (Chalmers)

Institutionen för matematiska vetenskaper, matematisk statistikInstitutionen för matematiska vetenskaper, matematisk statistik (GU)
Institutionen för kemi- och bioteknik, Teknisk ytkemi
Institutionen för matematiska vetenskaperInstitutionen för matematiska vetenskaper (GU)

Ämnesområden

Biokemi