Mathematical Characterization of Thermo-reversible Phase Transitions of Agarose Gels

TL;DR

This study investigates the thermal phase transitions of agarose gels using UV-vis spectroscopy and models these transitions with a modified epidemic model to characterize gel points and transition temperatures.

Contribution

It introduces a mathematical framework modeling agarose gel phase transitions with a modified epidemic model, linking spectroscopic data to gelation behavior.

Findings

Transition temperatures slightly increase with agarose concentration.

Gel point location can be estimated by shifts in sigmoidal transition curves.

Differences between T0 and Tm vary with agarose content and transition direction.

Abstract

Thermal phase transition temperatures of high and low melting point agarose gels were investigated by using the UV-vis spectroscopy techniques. Transmitted light intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol-gel) processes. It was observed that the transition temperatures Tm, defined as the location of the maximum of the first derivative of the sigmoidal transition paths obtained from UV-vis technique, slightly increased with the agarose type and concentration. Here, we express the phase transitions of agar-water system, as a representative of reversible physical gels, in terms of a modified Susceptible-Infected-Susceptible epidemic model whose solutions are the well-known 5-point sigmoidal curves. The gel point is hard to determine experimentally and various computational techniques are used for its characterization. Based on previous work, we locate the gel point T0 of sol-gel and gel-sol transitions in terms of the horizontal shift in the sigmoidal transition curve. For the gel-sol transition (heating), T0 is greater than Tm, i.e. later in time, and the difference between T0 and Tm is reduced as agarose content increases. For the sol-gel transition (cooling), T0 is again greater than Tm, but it is earlier in time for all agarose contents and moves forward in time and gets closer to Tm as the agarose content increases.