Abstract Number: 491 Working Group: Health Related Aerosols
Abstract It is very difficult to suspend nanomaterial powder whose surface are coated with strongly hydrophobic. Therefore, surfactants are generally added to water to suspend hydrophobic nanomaterials. We propose a new method for making water-suspension of hydrophobic nanomaterial powder without adding any surfactants. The method implements water-based growth tube collector (GTC) manufactured by Aerosol Dynamics, Inc. First, nanomaterial powder is aerosolized using a dry dispersion technique. The aerosolized nanomaterial forms agglomerates whose aerodynamic diameter is in a few micrometer range. These aerosol particles are sampled by a GTC whose sampling flowrate is set at 3.1 L/min. Supersaturated water-vapor condense onto nanomaterial powder, and condensation-grown particles are collected onto a substrate using inertial impaction technique. During the collection process the substrate is kept wet to keep the condensed water on the nanomaterial surface. Immediately after the collection process the collected material is dispersed in ultrapure water placed in an ultrasonic bath. Two types of titanium dioxide (TiO2) nanomaterial powder were used in our experiments. First type was Aeroxide P25 whose surfaces are naturally hydrophilic. Second type was Tayca JMT-150IB whose surfaces were presumably coated with isobutyl-functional group. Mass based collection efficiencies of the GTC were evaluated. The values were about 80% and 30% for P25 and JMT-150IB, respectively, indicating that the probability of activating condensation is lower for hydrophobic material. Collected JMT-150IB in water were periodically re-suspended by applying ultrasonic waves, and the particle number concentration in the suspension was monitored qualitatively by light scattering technique up to two weeks. It was concluded that initial state of the dispersion can be easily reproduced.