High electric permittivity of polymer-modified cement due to the capacitance of the interface between polymer and cement

The electric permittivity is a material property that relates to the dielectric and electromagnetic behaviors. This work reports the effect of polymer admixtures on the permittivity (2 kHz) of cement paste. The permittivity is increased significantly by the addition of either methylcellulose (dissolved) or latex (styrene–butadiene, not dissolved), due to the capacitance of the interface between polymer and cement. The permittivity is effectively modeled by a material-level equivalent circuit model that comprises cement, polymer and cement/polymer interface in parallel. The series model is not effective. For both methylcellulose and latex, the cement and cement/polymer interface dominate the contributions to the permittivity, while the polymer contributes little. The contributions of polymer and cement/polymer interface increase monotonically with increasing polymer/cement ratio, while the contribution of cement decreases monotonically. Methylcellulose at the highest proportion of 1.4% by mass of cement gives permittivity 52, whereas latex at the highest solid latex proportion of 14% by mass of cement gives permittivity 43. For the same polymer/cement ratio, the permittivity is much higher for methylcellulose than latex. The difference between methylcellulose and latex is due to the much greater contribution of the cement/polymer interface to the permittivity for methylcellulose than latex, as caused by the nanoscale morphology of the methylcellulose and the consequent large cement/polymer interface area. At the same polymer/cement ratio, the fractional contribution from the cement/polymer interface is greater for methylcellulose than latex, though those from the polymer and cement are greater for latex than methylcellulose.