Colloids and Surfaces A: Physicochem. Eng. Aspects 242 (2004) 213–216 Communication Silica scale inhibition by polyaminoamide STARBURST ® dendrimers  Eleftheria Neofotistou, Konstantinos D. Demadis ∗ Department of Chemistry, University of Crete, Heraklion, Crete, GR-71409, Greece Received 1 December 2003; accepted 23 April 2004 Abstract This paper reports the inhibition efficiency of a family of polyaminoamide (PAMAM) STARBURST ® dendrimers in colloidal SiO 2 growth. PAMAMs of various generations (0.5, 1.5, 2.5 with –COOH termini, and 1, and 2 with –NH 2 termini) were tested and compared to control samples. Superiority of the dendrimer inhibitors with –NH 2 termini (maintaining ∼380 ppm soluble SiO 2 after 12 h) versus those with –COOH termini (maintaining ∼180 ppm soluble SiO 2 after 12 h) was discovered in solutions containing 500 ppm initial SiO 2 . These inhibitors present potential for water treatment applications. © 2004 Elsevier B.V. All rights reserved. Keywords: Polyaminoamide; Silica scale inhibition; STARBURST ® dendrimer; Water treatment; Deposit Dendrimers are well-defined globular macromolecules constructed around a core unit [1]. Tomalia pioneered the synthesis of polyaminoamide (PAMAM) dendrimers, known as “STARBURST ® polymers”, Fig. 1 [2]. Their main struc- tural feature is the growth of the dendrimer branches around a central core (in this case an ethylenediamine) via amide chemical linkages. The dendrimer generation number indi- cates its degree of growth and branching. More specifically, PAMAMs of generations 0.5, 1.5, 2.5 possess –COOH ter- mini, and those of generations 1 and 2 have –NH 2 termini. Fundamental studies, as well as a plethora of applications are at the epicenter of interest [3]. Our research efforts are currently focused on developing new chemistries for scale growth control, as it relates to chemical water treatment [4]. We have studied a novel application of STARBURST ® dendrimers as silica (SiO 2 ) scale growth inhibitors in process industrial waters, and we describe herein our findings. Silicate ion polymerizes via a condensation polymeriza- tion mechanism, at appropriate pH regions [5]. When it oc- curs in process waters used for cooling purposes, the result- ing silica precipitates form a hard and tenacious scale on  Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.colsurfa.2004.04.067. ∗ Corresponding author. Tel.: +30-2810-393651; fax: +30-2810-393601. E-mail address: demadis@chemistry.uoc.gr (K.D. Demadis). critical industrial equipment, such as heat exchangers, trans- fer pipes, etc. Silica removal by dissolution is a challenge [6] and the usual approaches to control it are avoiding supersatu- ration (leading to water wastage) or pre-treatment (with high equipment costs). Research on chemical inhibitors for SiO 2 is ongoing, but actual applications of inhibition chemistries in the field are rather limited. Various generations of STARBURST ® dendrimers were screened by a SiO 2 supersaturation test. 1 Test solutions of 500 ppm silicate (as SiO 2 ) were utilized in this study 2 1 Screening tests: Control. A 100 mL volume of 500 ppm SiO 2 stock solution in the form of Na 2 SiO 3 ·5H 2 O is placed in a polyethylene con- tainer charged with a teflon-covered magnetic stir bar. The pH of this solution is initially ∼11.8 and adjusted to 7.00 ± 0.1 by addition of HCl (the change in the resulting volume is negligible). The beaker is then covered and set aside without stirring. The solution is checked for solu- ble SiO 2 by the silicomolybdate spectrophotometric method every 2 h for the first 12 h or after 24, 48, 72 h time intervals after the pH reduction. Inhibitor test. The procedure above is followed except that before pH adjustment 400 L of inhibitor a 10,000 ppm stock solution is added to achieve a final inhibitor concentration of 40 ppm. Sampling and timing are the same as the control, except that samples are first filtered through a 0.45 micron syringe filter before testing for soluble SiO 2 . Most of the results were reproduced several times with excellent reproducibility, es- pecially those with PAMAM-1 and -2 as inhibitors. 2 These are considered to be “high stress” conditions with respect to SiO 2 supersaturation. Most untreated industrial cooling systems operate at <200 ppm SiO 2 . Use of these “high stress” conditions is necessary in order to differentiate between inhibitor efficiencies. 0927-7757/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2004.04.067