Percolation Diffusion into Self-Assembled Mesoporous Silica Microfibres.

John Canning,Dongqi Shi,Alison Beavis,Andrew Mcdonagh,Miles Ma,Kevin Cook,George Huyang,David Bishop,Gang-Ding Peng,Maxwell Crossley

doi:10.3390/nano4010157

John Canning, Dongqi Shi + Show 8 more

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Percolation diffusion into long (11.5 cm) self-assembled, ordered mesoporous microfibres is studied using optical transmission and laser ablation inductive coupled mass spectrometry (LA-ICP-MS). Optical transmission based diffusion studies reveal rapid penetration (<5 s, D > 80 μm2∙s−1) of Rhodamine B with very little percolation of larger molecules such as zinc tetraphenylporphyrin (ZnTPP) observed under similar loading conditions. The failure of ZnTPP to enter the microfibre was confirmed, in higher resolution, using LA-ICP-MS. In the latter case, LA-ICP-MS was used to determine the diffusion of zinc acetate dihydrate, D~3 × 10−4 nm2∙s−1. The large differences between the molecules are accounted for by proposing ordered solvent and structure assisted accelerated diffusion of the Rhodamine B based on its hydrophilicity relative to the zinc compounds. The broader implications and applications for filtration, molecular sieves and a range of devices and uses are described.

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The recent cold fabrication of optical microfibre waveguides from silica nanoparticles using a combination of self-assembly and controlled fracturing [1,2,3] offers a route to a range of applications exploiting new components and waveguides, single photon sources for quantum communications, potential interconnect applications, specialty sensors, molecular sieves and filters and so on
The overall fcc and hcp packing at the surface is verified by atomic force microscopy (AFM) on the current fibres, shown in Figure 3e— there is no observable difference in outcome using gravity assisted directional evaporative self-assembly (GADESA), indicating laminar flow within the drops
The question about the validity of extending the uniformity of structure at the surface to that of the volume and everywhere else along the microfibre given that both Scanning electron microscopy (SEM) and AFM are highly localized techniques was qualitatively addressed in other work using gas adsorption studies [3] where pore size distribution of (2–6) nm agrees with calculations

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The recent cold fabrication of optical microfibre waveguides from silica nanoparticles using a combination of self-assembly and controlled fracturing [1,2,3] offers a route to a range of applications exploiting new components and waveguides, single photon sources for quantum communications, potential interconnect applications, specialty sensors, molecular sieves and filters and so on. Convective, microfluidic flow within a pinned drop during evaporation along with attractive intermolecular forces first leads to ordered, “spontaneous” self-assembly or packing of the nanoparticles into a 2-D film on an amorphous substrate. Self-organisation occurs despite being on a hydrophilic, amorphous borosilicate surface with inhomogeneous chemical and surface topology, suggesting that the role of template driven self-assembly is not significant. The driver is a tendency towards the densest possible state, or lowest free energy [9] configuration, which for classical hard spheres are hcp and fcc lattices [10]

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