Drying Affects the Fiber Network in Low Molecular Weight Hydrogels.

Laura L E Mears,Emily R Draper,Zhuola Zhuola,Bart Dietrich,Dave J Adams,Honggang Cui,Ana M Castilla,Hao Su,Riaz Akhtar,Sarah Rogers,Michael C Nolan,James Doutch,Gregory N Smith

doi:10.1021/acs.biomac.7b00823

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.

Highlights

Low molecular weight gels (LMWG) are receiving a lot of attention.[1−9] Unlike covalently cross-linked polymer gels, LMWG are formed when small molecules self-assemble into one-dimensional structures such as fibrils, fibers, or tubes
The in situ hydrated primary self-assembled structures of LMWG that lead to the gel can be probed using small angle neutron scattering (SANS) across a wide length scale from a few nanometers to a couple of hundred nanometres.[25,26]
SANS is suited to aqueous systems such as those described here, as the water component is replaced by D2O to provide scattering length density (ρ) contrast; we refer to this as a H-gel in D2O since the gelator is fully hydrogenous (Figure 2)

Summary

Introduction

Low molecular weight gels (LMWG) are receiving a lot of attention.[1−9] Unlike covalently cross-linked polymer gels, LMWG are formed when small molecules self-assemble into one-dimensional structures such as fibrils, fibers, or tubes. At a sufficiently high concentration (the so-called minimum gelation concentration (mgc)), these structures entangle and branch to a sufficient degree that a sample spanning network is formed. This immobilizes the solvent, resulting in a gel. Such gels are reversible, for example reverting to a solution on heating.[7] For peptide-based

Methods

Results

Conclusion