Electrokinetic and rheological properties of sepiolite suspensions in the presence of hexadecyltrimethylammonium bromide

The effect of cationic surfactant, hexadecyltrimethylammonium bromide (HDTMABr), on the electrokinetic and rheological properties of sepiolite suspensions was investigated. The zeta potential measurements indicate that the addition of HDTMABr into the sepiolite suspensions causes the change of surface charge of clay particles from negative to positive. The concentration of sepiolite in the suspension affects differently the flow behavior of sepiolite–water suspensions. The sepiolite–water suspensions containing less than 2.0 wt.% of sepiolite show a thixotropic behavior and a hysteresis loop, whereas the suspensions containing more than 2.0 wt.% of sepiolite exhibit a rheopexic behavior and a hysteresis loop. The addition of 5.0 × 10−4 M cationic surfactant into the clay suspensions containing 3.0 wt.% of sepiolite leads to a transition from rheopexic suspension to thixotropic suspension. The sepiolite–water and sepiolite–HDTMABr suspensions exhibit a Bingham type flow behavior. The plastic viscosity (ηpl) values of suspensions decrease with the increase of temperature from 25 °C to 45 °C. The ηpl values of sepiolite suspensions are affected differently depending on the surfactant concentration. It can be concluded from the rheological measurements that the flow behaviors and the ηpl values of sepiolite suspensions can be controlled with the sepiolite and HDTMABr concentrations. The interactions between sepiolite and HDTMABr were also investigated by FTIR spectrometer.