1. Low Field Nuclear Magnetic Resonance High Field (Resolution) NMR: 7.5 T < B < 37 T Study of chemical structures, reactions (only solution) Low Field (Resolution) NMR: 0.37 T < B < 2.43 T Study of physical structures (solid, liquid, gel, solution, suspension, emulsion) Hydrogen H  i (permanent magnetic momentum) H H H H H H H H H H B 0 = 0 H 6.1

2. B 0 ≠ 0 0 =  B 0 0 = Larmor frequency (Hz)  = hydrogen giromagnetic ratio (2.67*10 8 rad/Ts) H H H H H H H H H H HH H H H H H H H H H H H

3. B 0 ≠ 0 H t = t 0 - - - > B 1 >> B 0 H B0B0 B1B1 Z X Y

4. t = t 1 > t 0 - - - > B 1 = 0 H B0B0 Z Y X M z /M 0 M xy /M 0 Relaxation (T 1 ) Relaxation (T 2 )

5. Determination of T 2i Continuous spectrum a(T2)a(T2) B CD A4A4 A3A3 A2A2 A1A1 Discontinuous spectrum A4A4 A3A3 A2A2 A1A1

6. EXTERNAL WATER HOMOGENEOUS HYDROGEL  PORES CONFINED WATER WATER MOLECULE =  “Free” water molecules: LONG RELAXATION TIME (T 2 ) T 2 ~ 2200 ms (25°C) “ Bound” water molecules: SHORT RELAXATION TIME (T 2 ) T 2 ≤ 300 ms Effect of environment on T 2 It can be demonstrated 1 that T 2 f(  )

7. TWO FRACTION – FAST EXCHANGE MODEL 2 Water molecule T 2b T 2s  1) Diffusion between bulk and surface much faster than relaxation 2) If f b ≈ 1 and f s ≈ 0(  > 10 nm) 3) T 2 << T 2b (≈ 2200 ms T = 25°C, B = 0.47 tesla)

8. T 2b = 2200 ms

9. k determination Mesh size distribution

10. determination: gradient test B0B0 B1()B1()B 1 (  /2) t(ms) B0B0 B 1 (  /2)B1()B1()  Signal intensity (A 0 )  t(ms) B0B0 B 1 (  /2)B1()B1()    gradient Signal intensity (A)

11. It can be demonstrated that the following relation holds 2 : Ln(A/A 0 ) = -  2 D  2 (  -  /3) G 2 A = signal intensity with gradients A 0 = signal intensity without gradients D = water molecules self diffusion coefficient  = hydrogen giromagnetic ratio D can be determined as a function of the diffusion time t d =  -  /3  = gradient duration  = intergradient separation G = gradient intensity (T/m) B0B0 B1()B1() B 1 (X) 0 =  B(x) phase shift phase shift zeroed NO H DIFFUSION B0B0 B1()B1() B 1 (X) 0 =  B(x) phase shift phase shift still present H DIFFUSION

12. It can be demonstrated that the for small t d, the following relation holds 3 : t d = diffusion time (=  -  /3) D(t d ) = water self diffusion coefficient inside the hydrogel at t d D 0 = water self diffusion coefficient

13. Latour 4 proposed the following expression holding for every t d  = characteristic time  = network tortuosity

17. Water diffusion coefficient (D H2O ) dependence on temperature (T) 5

18. REFERENCES 1)Brownstein K.R., et al. Physical Review A, 1979 19, 2446. 2)Brownstein K.R., et al., J. Magnetic Resonance, 1977, 26, 17 3)Mitra P.P., et al. Physical review B, 1993, 47(14), 8565. 4)Latour L.L. et al., J. Magnetic Resonance A, 1993, 101, 342. 5)Holz M. et al., Phys. Chem. Chem. Phys., 2000, 2, 4740.