Adsorption on Ordered and Disordered Duplex Layers of Porous Anodic Alumina

Abstract

We have carried out systematic experiments and numerical simulations of the adsorption on porous anodic aluminum oxide (AAO) duplex layers presenting either an ordered or a disordered interconnecting interface between the large (cavity) and small (constriction) sections of the structured pores. Selective blocking of the pore openings resulted in three different pore topologies: open structured pores, funnel pores, and ink-bottle pores. In the case of the structured pores having an ordered interface, the adsorption isotherms present a rich phenomenology characterized by the presence of two steps in the condensation branch and the opening of one (two) hysteresis loops during evaporation for the ink-bottle (open and funnel) pores. The isotherms can be obtained by summing the isotherms measured on uniform pores having the dimensions of the constrictions or of the cavities. The numerical analysis of the three different pore topologies indicates that the shape of the junction between the two pore sections is only important for the adsorption branch. In particular, a conic junction which resembles that of the AAO pores represents the experimental isotherms for the open and funnel pores better, but the shape of the junction in the ink bottle pores does not matter. The isotherms for the duplex layers with a disordered interface display the same general features found for the ordered duplex layers. In both cases, the adsorption branches coincide and have two steps which are shifted to lower relative pressures compared to those for the ordered duplex. Furthermore, the desorption branches comprise hysteresis loops much wider than those of the ordered duplex layers. Overall, this study highlights the important role played by morphologies where there are interconnections between large and small pores.

Intrusion and extrusion of a liquid on nanostructured surfaces

“…This theory predicts that hysteresis should vanish if the pore dimension is of the order of 2 nm; at this scale, however, the macroscopic theory may become unsuitable for describing the system. Similar hysteretic behaviors are common in the neighboring field of porous materials [20,21] in which, for example, the intrusion/extrusion curves of mercury are used as a means to characterize the pore structure [22]. At the origin of these experimental evidences of hysteresis in the intrusion of a liquid in nanostructured or porous surfaces is the presence of strong metastabilities; however, the microscopic aspects and the dependence on the surface geometry are not clearly understood and call for additional investigations.…”

“…The chemistry of the solid also plays an important role in determining the characteristics of the intrusion/extrusion cycle, compare, e.g., the present results with the experiments on hydrophilic Alumina [21]. To address this issue we have computed the free energy profiles at various ∆P of an hydrophilic surface with θ Y ≈ 55 • [39] (Fig.…”

Nanoporous anodic alumina-based iontronics: fundamentals and applications

“…At the completion of the fabrication process, they opened the BOL of these nanostructures to obtain through-hole NAA with open-ended pores. 78 Li et al presented a facile nanofabrication method comprising of a single HA step followed by multistep MA and etching to obtain a range of self-ordered three-dimensional alumina taper-nanopores with different architecture such as linear and whorl-embedded cone, funnel, pencil, parabola, and trumpet (Fig. 4d).…”

“…4a), [70][71][72] funnel-like (Fig. 4b), [73][74][75][76][77][78] and multi-layered (Fig. 4c) [79][80][81][82][83] is the use of multistage fabrication based on several anodization steps at different anodizing parameters and pore widening treatment.…”

Duplex nanoporous alumina and polyelectrolyte adsorption: more insights from a combined neutron reflectivity and electron microscopy study

“…Such organization induces a geometrical constriction, i.e. a reduction of pore diameter along the pore channel, that plays an important role for instance in gas adsorption and condensation [9][10][11] . Duplex nAAO systems require original and suitable experimental strategies to characterize at the nanometer scale the different layers and also to investigate the behavior of incorporated nano-objects such as liquid crystals 12 , liquid mixtures 13 , polymer melts 14 or polyelectrolytes 15 (PEs).…”