TOURNAL
-I
O F T H E AMERICAN CHEMICAL S O C I E T I Registered in L'. S . Patent O&ce.
a
Copyright, 1963, b y the A m e r i c a n Chemical Society
NOVEMBER 5 , 1963
VOLUME€5,NUMBER21
P H Y S I C A L A N D IIiTORGANIC CHEMISTRY [CONTRIBUTION FROM THE
DEPARTMENT OF CHEMISTRY,
PRINCETON UNIVERSITY, PRISCETON,
N. J . ]
Coagulation of Colloidal Gold BY B. V. ENUSTUNAND
JOHN
TURKEVICH
RECEIVED MAY31, 1963 Kinetics of coagulation with NaCIOl of 200 A. colloidal gold which was stabilized by citrate ions was investigated by electron microscopy. The results were compared with the Derjaguin-Verwey-Overbeek theory and a n agreement was obtained only in the very early stage of coagulation a t low electrolyte concentration. The discrepancies observed otherwise were explained on the basis of variation of the stabilizing potential due to adsorption of cation and anion of t h e electrolyte introduced. T h e Hamaker constant A was calculated as erg. T h e morphology of t h e aggregates formed under various conditions was also explained on 2.3 X the basis of t h e behavior of t h e electrical double layer.
1. Introduction
The subject of coagulation of lyophobic colloids has been studied extensively since the early days of colloid chemistry. The aim of these investigations was to establish the mechanism of coagulation and thus to understand the very existence of the colloidal state. Certain qualitative observations, such as coagulation OY electrolytes, the dependence of the coagulation rate on tile electrolyte concentration, the existence of a fairly well defined critical concentration as a border line between slow and fast coagulation, and certain empirical rules, such as that of Schultze-Hardy correlating the critical concentration to the valency of the electrolyte had been accumulated when Von Smoluchowski2 put forward his well-known theory of kinetics of coagulation. He treated coagulation as a diffusion process and arrived a t a series of equations which give not only the rate of rapid coagulation, but also the relationship between the number of clusters formed containing various numbers of primary particles. T o describe the kinetics of slow coagulation, Smoluchowski merely introduced a rate-reducing factor in his equations without going further to consider how this factor depended on the nature of the colloid and on the type and concentration of the electrolyte. Smoluchowski's rapid coagulation theory has been verified satisfactorily by a number of experimental works. R - - l ? The methods used were ultramicroscopy, colorimetry, and Tyndallometry. Therefore, the veri(1) H Schultze, J . pvakl. C h r w , 27, 320 (18831, Roy. Soc (London), 6 6 , 110 (1900)
U' B Hardy, Proc.
(2) >I V. a n Smoluchowski, P h y s i k 2 , 17, 5.57, 585 (1916); Z. p h y s i k . C h e m . . 92, 129 (1917). ( 3 ) I < . Z s i g m o n d y , i b i d . , 92, 600 (1917). (4) A LVestgren and J Reitstotter, i b i d , 92, 750 (19171, J . P h y s . Chem , 26, 337 (192'21, A Westgren, A r k i v K e m i M i n e r a l , 7, S o . 1, 1 (1918) ( 5 ) H I
