Phosphatidylcholine is a lipid that can be found in egg yolk. When phosphatidylcholine is mixed with water it will form micelles – spherical particles. Molecular weight (Mw) for the particles is 97*000 g/mole Density for the particles is 1.018 g/cm3 The temperature is 25°C a) What is the radius for the particles? Assume that the particles are not hydrated. The viscosity of water (eta) at the given temperature is 0,9 mPa·s (milliPascal second) Boltzmann constant: 1,38 ´ 10-23 J/K (Pa=kg/ms2 and J=kgm2/s2) b) What is the diffusion coefficient (D) for the particles in water? a) One particle has the mass m = (97 000 g/mol)/6.02E23 = 1.61E-19 g. This gives V = 1.58E-25 m3, and since the volume of a sphere is given by (4/3)*pi*r^3, the radius for the particles is 3.35 nm. b) Stokes-Einstein: What's wrong here?
That looks about right. I have the following table of diffusion coefficients for uncharged spheres in water at 20°C (after Shaw) Radius........Diffusion Coeff 1nm............2.1E-10 10nm...........2.1E-11 100nm..........2.1E-12 1μm..............2.1E-13 Best I can do at midnight here, I'm off to bed. g'nite