Solvent Triggered Gels

Preparing Solvent (DMSO) Triggered Gels 

For some applications, solvent triggered low molecular weight gels may be used instead of pH triggered, or other, equivalents. Triggering gels in this manner carries the advantage of faster gelation and usually more straightforward sample preparation. Solvent triggered gels can be formed at different gelator concentrations, with different solvents and even solvent ratios, sometimes resulting in significant differences to the final gel properties.1 Gels produced via a solvent switch typically possess differing microstructure to those of the gelator networks within pH triggered gels.2 Usually DMSO is the organic solvent of choice for producing these gels in our group, but other organic solvents are viable. Typical solvent ratios of 10-30% DMSO:H2O are often used, but the specific ratio is dependent on the gelator used, as it has previously been shown that changes in network microstructure are incurred moving from high to low ratios of DMSO for some gelators.2  

To prepare solvent triggered gels: 

  1. Dissolve gelator in organic solvent so as to produce the final desired gelator concentration after subsequent dilutions. Often the gelator will dissolve readily with gentle swirling over a minute. A sonicator can be used to aid dissolution, if needed. 
  1. Pipette the desired amount of gelator DMSO stock solution into the vessel in which the gel is to be formed. Ensure even coverage, especially if using small volumes or low DMSO:H2O ratios. A 10 μL pipette tip can be used to aid spreading the solution, if necessary.  
  1. Trigger gelation by adding the water aliquot to the sample via pipette. This should be done as a single aliquot added rapidly. To ensure consistent samples, the water aliquot should be dispensed firmly via pipette from slightly above the DMSO gelator stock, to encourage effective mixing and thus a homogenous sample. 
  1. Some gels will go turbid upon triggering gelation, before slowly returning to transparent/translucent over the course of a few minutes, whereas others will stay transparent. Some gelators won’t gel at all through this method. 
  1. Gelation is typically complete after a few minutes, with different gelators leading to slightly longer or shorter gelation times. It is important not to disturb the samples during gelation. 

E.g. To prepare 2NapFF DMSO gels: 

Gels are typically formed with a final gelator concentration of 5 mg mL-1 in our group, so a gelator stock DMSO solution would be prepared at 25 mg mL-1, if using a 1 in 5 dilution to produce gels at 20% DMSO:H2O. For a 2 mL gel in a Sterilin vial formed at a solvent ratio of 20% DMSO:H2O, 0.4 mL of DMSO gelator stock would be pipetted into the vial, followed by 1.6 mL of deionised water.  

References

1 – Soft Matter, 2015, 11, 927-935 

2 – Soft Matter, 2011,7, 9721-9727