Report No xxxx - Instytut Fizyki JÄ drowej PAN

T 1 DISPERSION AND SELF-DIFFUSION NMR STUDY
OF WATER MOLECULES IN POLY(ACRYLIC ACID) HYDROGELS
Grzegorz Nowaczyk, Marek Kempka, Stefan Jurga
Institute of Physics, Adam Mickiewicz University, Umultowska 85,PL-61614 Poznań, Poland
A detailed understanding of the structure of hydrogels and the dynamics of molecular
motions of water in gels is very important for biomedical drug delivery processes that use
hydrogels as carriers (1).
One of the most extensively used and studied hydrogels is poly(acrylic acid) gel. Here
we report studies of water molecules in poly(acrylic acid) microgels (carbopol ® 971) by means
of Fast Field Cycling Realaxometry and NMR diffusion methods.
Carbopol ® 971 was provided by Noveon, Inc. The polymer powder was dispersed in
distillated water with or without surfactants. The polymer content of gels was 0,5 and 1%.
10% NaOH was added to neutralize the sample to pH 3.
T 1 dispersion of water was measured in the frequency range from 10 kHz to 9 MHz at
293 and 281K, whereas the self-diffusion measurements were performed using homemade
spin-echo NMR spectrometer operating at 16,5 MHz at temperature range from 297 to 323K.
Proton NMR data shows decreasing of T 1 spin-lattice relaxation time with the decrease
of Larmor frequency down to 1,5 Mhz. The slopes, determined for this dependence, are equal
υ~0,51 (293K) and υ~0,22 (281K) (Fig. 1.). Below 1 MHz T 1 is frequency independent.
The diffusion coefficients for systems containing 1% of carbopol are very similar to
unrestricted water (2). It was found that an addition of surfactants to gels leads to a slowing
down of the diffusion of water molecules (Fig. 2.).
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T 1
(s)
293K
281K
ν∼0.51
10 0 ν∼0.22
10k 100k 1M 10M
Larmor frequency (Hz)
Fig. 1. 1 H spin-lattice relaxation times versus Larmor
frequency for Carbopol (0,5%) at 281 and 293K.
D(10 -5 cm 2 /s)
4
3
Carbopol 1%
Carbopol 1%+surfactant (Brij 58) 1%
E a
=4,1 (kcal/mol)
E a
=3,9 (kcal/mol)
2
3,05 3,10 3,15 3,20 3,25 3,30 3,35 3,40
1000/T
Fig. 2. Water diffusion in Carbopol hydrogels.
[1] M. Dittgen, M. Durrani, K. Lehmann, Acrylic polymers. A review of pharmaceutical applications,
Stp Pharma Sci. 7 (1997) 403-437
[2] B. Peneke, S. Kinsey, S. J. Gibbs, T. S. Moerland, B. R. Locke, Proton diffusion and T 1 relaxation
in polyacrylamide gels: A unified approach using volume averaging, J Magn Reson 132 (1998) 240-254
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