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A frequency-dependent electrical monitoring technique was developed for characterizing emulsion polymerization online. High resolution electrical impedance spectroscopy (EIS) was conducted to study emulsion polymerization of styrene in terms of the key process parameters. Relationships between EIS data and process and product attributes such as monomer conversion and particle size were investigated. Electrical impedance values were measured at frequencies ranging from 1 Hz to 100 kHz. EIS parameters revealed changes in emulsion properties with time for both aqueous and organic phases during polymerization. At relatively higher frequencies (≥1 kHz) EIS data were found to be dominated by events in the continuous phase showing transitions in polymerization rates and intervals, while changes in monomer droplet and polymer particle sizes were dominant at lower frequencies (1 Hz). The EIS data were found to correlate well with polymerization rate, monomer conversion and particle size profiles at the appropriate frequencies in real time.

Colloidal behavior of a widely used non-ionic emulsifier, sorbitan monooleate (Span80), was investigated in non-polar solvents (cyclohexane and xylene) using electrical impedance spectroscopy (EIS). The electrical characteristics of the colloidal mixtures were measured with frequency scans ranging from 1 Hz to 200 kHz. The conductances at low frequencies were found to increase with an increase in Span80 concentration. The source of conductivity for non-polar solvents using non-ionic emulsifiers is usually attributed to ionic impurities either in the Span80 or in the non-polar solvents. The measured electrical characteristics for pure Span80 and pure non-polar solvents revealed that the source of ionic conduction is impurities in Span80. It was confirmed that the ionic impurities in the non-polar solvents are in form of aggregate of ions, ion-pairs, and triple ions which is unaffected with the emulsifier concentration. Analyses using equivalent electrical circuits confirmed that the critical MaxwellWagner frequency is 0.6-1.8 Hz for the mixtures. The conductance-concentration profiles for the mixtures at 1 Hz showed transitions from a square root to a linear concentration dependence at the CMC. This indicated that the dissociation model holds below the CMC, while the fluctuation model applies above the CMC. The conductance profiles enabled estimates of the relative hydrophilic core radius and the fraction of charged micelles in both non-polar solvents.

Electrical impedance spectroscopy was employed for on‐line monitoring of monomer conversion and particle interfacial area during inverse emulsion polymerization.