Characterizing organic monolithic columns using capillary flow porometry and scanning electron microscopy

Polyethylene glycol diacrylate monoliths prepared using different amounts of monomer, porogen ratio, and capillary dimensions were characterized using capillary flow porometry (CFP) and scanning electron microscopy (SEM). Our results reveal good agreement between SEM and CFP measurements for through-pore size distribution. The CFP measurements for monoliths prepared by the same procedure in capillaries with different diameters (i.e., 75, 150, and 250 μm) clearly confirmed a change in through-pore size distribution with capillary diameter, thus, certifying the need for in-column measurement techniques over bulk measurements (e.g., mercury intrusion porosimetry). The mean through-pore size varied from 3.52 to 1.50 μm with a change in capillary diameter from 75 to 250 μm. Consistent mean through-pore size distribution for capillary columns with the same internal diameter but with different lengths (1.5, 2, and 3 cm) confirms the high interconnectivity of the pores and independence of CFP measurements with respect to capillary length. CFP and SEM measurements not only allow pore structure analysis but also prediction of relative column performance. Monoliths with narrow through-pore size distribution (0.8-1.2 μm), small mean through-pore size, and thin skeletal size (0.55 μm) gave the best performance in terms of efficiency for polyethylene glycol diacrylate monoliths.