Abstract
Agarose gels are viscoelastic soft solids that display a porous microstructure filled with water at 90% w/w or more. Despite an extensive use in food industry and microbiology, little is known about the drying kinetics of such squishy solids, which suffers from a lack of time-resolved local measurements. Moreover, only scattered empirical observations are available on the role of the gel composition on the drying kinetics. Here we study by in-situ interferometry the drying of agarose gels of various compositions cast in Petri dishes. The gel thinning is associated with the displacement of interference fringes that are analyzed using an efficient spatiotemporal filtering method, which allows us to assess local thinning rates as low as 10 nm/s with high accuracy. The gel thinning rate measured at the center of the dish appears as a robust observable to quantify the role of additives on the gel drying kinetics and compare the drying speed of agarose gels loaded with various non-gelling saccharides of increasing molecular weights. Our work shows that saccharides systematically decrease the agarose gel thinning rate up to a factor two, and exemplifies interferometry as a powerful tool to quantify the impact of additives on the drying kinetics of polymer gels.
Highlights
In previous work recently reviewed in ref. 34, the addition of relatively large amount of sucrose to agarose gels is reported to increase the elastic modulus G′and reduce the water loss, which is quantified by measuring the amount of water released after an arbitrary duration from a gel submitted to an external constant load
In ref. 32, the authors explore a large range of concentrations in sucrose, always larger than 20% w/w, and show a negative correlation between the value of the elastic modulus and the extent of the water loss, which they interpret as a change in the gel microstructure for increasing sucrose content
Our study shows that the addition of non-gelling mono- or poly-saccharides, even in minute amounts, is enough to decrease the thinning rate of the gel without any significant change in the gel elastic modulus
Summary
Water-holding capacity of the gel and potentially impact the gel drying kinetics. Understanding the drying kinetics of agarose gels and the influence of minute amounts of additives upon the gel thinning rate is of key practical importance. We show that the thinning rate of agarose gels is systematically reduced by addition of minute amounts (
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