Swelling and shrinking behaviour of photoresponsive phosphonium-based ionogel microstructures

Abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. KeywordsStimuli responsive, photo-responsive, microstructures, photo-patterning, ionogel, ionic liquid. Page 2 of 38A c c e p t e d M a n u s c r i p t 2 AbstractPhotoresponsive N-isopropylacrylamide ionogel microstructures are presented in this study. These ionogels are synthesised using phosphonium based room temperature ionic liquids, together with the photochromic compound benzospiropyran. The microstructures can be actuated using light irradiation, facilitating non-contact and non-invasive operation. For the first time, the characterisation of the swelling and shrinking behaviour of several photopatterned ionogel microstructures is presented and the influence of surface-area-to-volume ratio on the swelling kinetics is evaluated. It was found that the swelling and shrinking behaviour of the ionogels is strongly dependent on the nature of the ionic liquid. In particular, the [P 6,6,6,14 ][NTf 2 ] ionogel exhibits the greatest degree of swelling, reaching up to 180 % of its initial size, and the fastest shrinkage rate (k sh = 29 ± 4 x 10 -2 s -1 ).

Porous self-protonating spiropyran-based NIPAAm gels with improved reswelling kinetics

“…In these systems a much smaller gel feature size is typically used, which means the effect will be faster than presented in this paper, making the structures overall more practical to use in a reversible manner, and rendering them more attractive for use as actuators/valves in microfluidic systems. [40] …”

Reusable ionogel-based photo-actuators in a lab-on-a-disc

“…It was found that the ionogel typically contracts by 40 ± 1 % (n = 3) of its initial swollen state after white light irradiation for about 5 min ( Figure 3B). A stronger white light is required for shrinking of the ionogel-based actuator compared to that reported by Czugala et al 22 (Aigo Digital Microscope GE-5) and…”

“…The rate constants of the shrinking process ksh (black line) were estimated using Eqn.3 and a value of 3.5 ± 0.6 10 -3 s -1 (n = 3). Czugala et al 22 reported the swelling and shrinking kinetics of 400 µm discs made of the same p(SPNIPAAm) ionogel. Faster swelling and shrinking constants, ksw of 4.5 ± 0.3 10 -2 s -1 and ksh 8.3 ± 0.9 10 -2 s -1 , respectively, were reported.…”

“…The switching mechanism, from MC-H+ to SP isomer, is reversible and triggers conformational rearrangements in the bulk p(NIPAAm) gel, changing it from a more hydrophilic to a hydrophobic nature, which in turn induces water loss and contraction of the gel. 22 Traditionally, organic solvents have been employed for the synthesis of p(SPNIPAAm) gels.…”

Phosphonium salts and P-ylides

“…It was found that the [P 66614 ][NTf 2 ] ionogel allowed the highest degree of swelling. 254,255 Deguchi, Kohno and Ohno designed polyelectrolytes derived from tributyl-n-alkylphosphonium 3-sulfopropylmethacrylate-type IL monomers. Based on these compounds, chemically cross-linked polyelectrolyte gels were prepared, showing LCST-type phase changes.…”