# The Effect of Solutes on the Temperature of Miscibility Transitions in Multi-component Membranes

## TL;DR

This paper models how small-chain alcohols affect the miscibility transition temperature in multi-component membranes, explaining experimental observations through Flory-Huggins theory and entropic effects.

## Contribution

It introduces a theoretical model using Flory-Huggins theory to explain how solutes influence membrane phase transition temperatures based on entropic considerations.

## Key findings

- Alcohols can either raise or lower transition temperatures depending on their interactions.
- The model accounts for non-monotonic dependence on alcohol chain length.
- Experimental behaviors are explained by competition between dilution effects and solute preferences.

## Abstract

We address questions posed by experiments which show that most small-chain alcohols reduce the miscibility transition temperature when added to giant plasma membrane vesicles, but increase that temperature when added to giant unilamellar vesicles. In both systems the change in temperature depends non-monotonically on the length of the alcohol chain. To emphasize the roles played by the internal entropies of the components, we model them as linear polymers. We show that, within Flory-Huggins theory, the addition of alcohol causes an increase or decrease of the transition temperature depending upon the competition of two effects. One is the dilution of the solvent interactions caused by the introduction of solute, which tends to lower the temperature. The other is the preference of the solute for one phase or the other, which tends to raise the temperature. The magnitude of this term depends on the entropies of all components. Lastly we provide a reasonable explanation for the behavior of the transition temperature with alcohol chain length observed in experiment.