Drying Affects the Fiber Network in Low Molecular Weight Hydrogels

Abstract

Low molecular weight gels are formed by the self-assembly of a suitable small molecule gelator into a three-dimensional network of fibrous structures. The gel properties are determined by the fiber structures, the number and type of cross-links and the distribution of the fibers and cross-links in space. Probing these structures and cross-links is difficult. Many reports rely on microscopy of dried gels (xerogels), where the solvent is removed prior to imaging. The assumption is made that this has little effect on the structures, but it is not clear that this assumption is always (or ever) valid. Here, we use small angle neutron scattering (SANS) to probe low molecular weight hydrogels formed by the self-assembly of dipeptides. We compare scattering data for wet and dried gels, as well as following the drying process. We show that the assumption that drying does not affect the network is not always correct.

How should multicomponent supramolecular gels be characterised?

“…It has also recently been shown that SANS can be used to follow the drying process if suitable contrast is achieved using deuterated dipeptide-based gelators. 24 The data showed that the scattering primarily probed the primary fibres, not aggregated fibres that were imaged using SEM.…”

“…For example, we have shown that drying a dipeptide-based LMWG leads to the fibres becoming much thicker than the primary structures which are observed using cryo-TEM. 24 Further issues can arise from the use of a stain for TEM, which can potentially lead to structural changes. It should also be stated that both SEM and TEM have such high magnifications that only a tiny fraction of a sample can be imaged in a realistic timeframe, meaning that there is always the question as to whether the images are representative.…”

The Power of Confocal Laser Scanning Microscopy in Supramolecular Chemistry: In situ Real‐time Imaging of Stimuli‐Responsive Multicomponent Supramolecular Hydrogels

“…Although microscopic techniques are powerful, there is a requirement for drying and/or freezing during the sample preparation, which may cause artifacts that change the self-assembled structure. [11] Furthermore, these techniques cannot discriminate chemical species in multicomponent systems. Recently, confocal laser scanning microscopy (CLSM) has emerged as a powerful tool for structural analysis of multicomponent supramolecular hydrogel systems ( Figure 1).…”

A Multi‐Component Reaction towards the Development of Highly Modular Hydrogelators

“…However, Mears et al. previously reported that due to the drying process required for sample preparation, SEM does not always show the primary network of fibers but instead depicts the aggregation of the fibers . The size of the fibers in the SEM images is therefore probably not representative of the size of the fibers in the gel state.…”

“…However,M ears et al previously reported that due to the drying process required for sample preparation,S EM does not always show the primary network of fibers but insteadd epicts the ag- www.chemeurj.org gregation of the fibers. [18] The size of the fibers in the SEM images is therefore probably not representative of the size of the fibers in the gel state. It can also be observed that fibers of gel 8 appear to be aligned parallelt oe ach other whereas fibers in gel 9 arranged aroundc enters in star-like patterns.…”