A re-investigation of the Mark-Houwink-Sakurada parameters for cellulose in Cuen: a study based on size-exclusion chromatography combined with multi-angle light scattering and viscometry.

The MHS parameters for cellulose in Cuen (0.5 M) were calculated by determining the weight (DP(w)), number (DP(n)), and the viscosity average (DP(v)) of partially hydrolysed celluloses using SEC-MALLS in DMAc containing 0.5% LiCl, combined with intrinsic viscosity measurements in Cuen. The modified MHS equation is: η=2.45DP(v)(0.70)=0.070 M(v)(0.70). Application of the equation provides the true viscosity average DP (DP(v)) for any type of distribution. In contrast, the apparent 'DP(v)' referred to in standard methods (ASTM, SCAN) is an undefined type of average DP which depends on the chain length distribution, and may differ considerably from both DP(v) and DP(w). The DP values obtained by SEC-MALLS depend on the quality of the data, in particular the specific refractive index increment at constant chemical potential (dn/dc)(μ), which was found to be 0.117 ml/g (at λ(0)=633 nm). Further analysis of the SEC-MALLS and viscometry data in terms of the wormlike chain model provided estimates of the persistence length, obtaining 4.7 nm in Cuen and 8.2 nm in 0.5% DMAc/LiCl, illustrating the more expanded structure in the latter solvent.