Adsorption Kinetics of Poly(benzyl acrylate) Chains onto Alumina Interface during the Flow-Driven Translocation...

In this work, the adsorption kinetics of the PBA/AAO system under flushing condition has been investigated, where PBA and AAO represent poly(benzyl acrylate) and anodic alumina oxide (AAO, average pore radius R₀ ≈ 10 nm) nanochannel, respectively. Our specially designed double-pump flushing system is proved to eliminate the overshoot phenomenon and in situ monitor transmembrane pressure (ΔP) as a function of flushing time (t) and flow rate (Q), which gives the effective pore radius (R), cross-sectional coverage factor (χ = [1 - (R/R₀)²]), and characteristic ratio (r_c) of the increments of χ during each adsorption/desorption cycle at a given bulk solution concentration (C_bulk). Our findings include: (1) by gradient increasing C_bulk from 10 to 200 mg/L at Q = 10 mL/h, the shortest PBA₄₀ displays a saturation adsorption behavior when C_bulk ≥ 80 mg/L and t ≥ 2000 s, which agrees well with the prediction of blob model, whereas for the longer PBA chains, the chain length (N) and concentration-dependent adsorption tendency get stronger as N increases from 40 to 620 at t ≥ 2000 s, in particular, R/R₀ ∼ N^-0.20 is observed at C_bulk = 140 mg/L; (2) by focusing on the platform χ in the saturation adsorption regime (χ_sat), the longer PBA displays a stronger adsorption trend with partially reversible feature at Q = 5.0 mL/h, namely, as N increases from 40 to 620, χ_sat increases from 0.15 to 0.83 at C_bulk = 100 mg/L, where r_c changes from 0.25 ± 0.10 to 0.80 ± 0.10 as the adsorption/desorption flushing cycle increases from 1 to 8 at C_bulk = 100 mg/L; (3) by further assuming a solvent nonpenetrating and nondraining adsorption layer, χ_sat determined in the case of curved surface can be comparable to the physical meaning of adsorption thickness (Δ_ad) in the case of flat-surface adsorption, and the fitting result indicates χ_sat ∼ Δ_ad ∼ N^0.58, falling between Δ_ad ∼ N^1/2 and Δ_ad ∼ N^1.0 predicted by the mean-field and scaling theories for real multichain adsorption, respectively. Overall, the present work not only clarifies some controversies but also provides unambiguous evidence supporting the existence of tightly adsorbed internal and loosely adsorbed external layers.