Surfactant Addition Can Lead to Phase Separation of DNA

A common phenomenon observed for mixed solutions of a pair of oppositely charged colloids, surfactant-surfactant, surfactant-polymer, polymer-polymer, is associative phase separation, namely, the two oppositely charged colloids concentrate in one phase in equilibrium with a very dilute solution [30]. 

Such behavior has been extensively studied for polyelectrolyte-oppositely charged surfactant systems. The extent of the phase separation increases with increasing alkyl chain length of the surfactant and with the polyelectrolyte charge density and molecular weight [31-33]. The nature of the concentrated phase varies with polymer and surfactant and with conditions it can be a concentrated solution or gel, a liquid crystalline phase (lamellar, hexagonal, cubic) or a solid crystalline phase. 

3 Suifactant Addition Can Lead to Phase Separation cfDNA 1185 

However, contrary to other polyelectrolyte-surfactant systems [39-42], the precipitate does not redissolve with an excess of surfactant, at least in the examined, very broad, interval of concentrations. The difficulty of the redissolution of complexes composed of very highly charged polymers has also been observed in some other studies [41, 43, 44]. 

Further information drawn from the phase map is that the precipitate is formed at very low amounts of DNA and low surfactant concentrations, far below the surfactant cmc. This is a logical observation, since, as mentioned above, the polyelectrolyte-op-positely charged surfactant systems have a cac lower than the cmc of free surfactants, often by orders of magnitude. 

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