Single molecule tracking studies of flow-aligned mesoporous silica monoliths: aging-time dependence of pore order.

Single molecule tracking (SMT) methods are employed to characterize the in-plane alignment and order of cylindrical mesopores in flow-aligned surfactant-templated silica monoliths prepared within glass microfluidic channels. The majority of dye molecules observed in wide-field fluorescence videos of these samples exhibit one-dimensional (1D) diffusive motions. Orthogonal regression analysis of these motions provides a measure of the mesopore orientation distribution function, which in turn is used to quantify the mesopore order via a two-dimensional orientational order parameter, ⟨P⟩. Mesopore organization is explored as a function of aging time between sol preparation and filling of the microfluidic channels. Channels filled well before gelation of the sol are shown to incorporate large monodomains having average pore alignment within a few degrees of the flow direction. These monodomains extend over several millimeters and yield aging-time-independent ⟨P⟩ values larger than ∼0.80. In contrast, channels ...