In a study of colloidal systems based on diethylene glycol, we found that the miscibility of this liquid with chlorinated hydrocarbon solvents o-dichlorobenzene and dichloromethane is different.  We found that diethylene glycol (DEG) is miscible with dichloromethane (DCM) in all proportions, but its miscibility with o-dichlorobenzene (DCB) is limited.  Dielectric constants of all three fluids, 32 for DEG, 8.9 for DCM and 10.1 for DCB, suggest similar behavior in both binary mixtures, or even opposite, because DCB is slightly more polar than DCM.  We looked closer at the DEG/DCB system and determined that it has two zones where homogeneous mixtures can be obtained, the DEG-based (100-47 wt.%), and the DCB-based (100-91.7 wt.%).  In order to determine if both, homogeneous by appearance, compositions are true solutions or emulsions with small-size particles, we studied these systems by use of Dynamic Light Scattering (DLS).  Four mixtures of DEG with DCB were prepared, two of them on each side of the composition range, namely saturated and diluted with the major component.  All mixtures looked transparent with no noticeable turbidity.  The refraction index, density, and viscosity of each were measured at room temperature and used as dispersion medium parameters for the Malvern Zetasizer Nano ZS instrument software.   Obtained results showed that all four compositions were emulsions with small particle size, which decreased from 2.9 nm to 1.1 nm upon dilution in the DEG side of the scale, but increased from 3.3 to 4.4 nm upon dilution in the DCB side of the scale.  The count rate went down upon dilution in both colloids, which is what one would expect. Dichloromethane formed true solutions with diethylene glycol.  This difference in behavior of the two chlorinated solvents presumably evidences the stronger molecular association in o-dichlorobenzene than in dichloromethane, which is possibly due to the ?-? interaction.

Surfactant-free dispersion systems involving diethylene glycol and o-dichlorobenzene

243rd National Meeting (2012)

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