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Krafft Points and Cloud Points of Polyoxyethylated Nonionic Surfactants

Part 2 Quantitative Cloud Point Relations

Krafft- und Trübungspunkte von polyoxyethylierten nichtionischen Tensiden
Teil 2 Quantitative Trübungspunktrelationen
H. Schott

Abstract

Polyoxyethylated nonionic surfactants (POSs) are more soluble in cold than in hot water. On heating, they precipitate reversibly from aqueous solution at and above characteristic temperatures, which are called cloud points (CPs) because the solutions turn cloudy/opaque. The CPs of normally distributed POSs are correlated with the average number p of oxyethylene units per molecule by the linear equation (p – p0)/CP=A+B(p – p0). In a homologous series of POSs, the smallest value of p conducive to solubility in ice-cold water, p0, belongs to the surfactant with CP=0°. Its hydrophile-lipophile balance, HLB0, is a quantitative measure of the hydrophobicity of the parent fatty alcohols, CmH2m+1OH, fatty acids and alkylphenols. New CPs, especially of POSs with p approaching p0, are combined with published CPs in this study. The order of increasing HLB0 and hydrophobicity of the parent compounds, accompanied by decreasing CPs of their ethoxylates, is: saturated linear primary alcohols [m=18 (lowest HLB0=8.2), 16, 14.6, 13.3, 12.7, 12.0]<oleyl alcohol<saturated primary alcohols with multiple methyl branches (m=10, 13)<Guerbet alcohols (2-hexyldecanol, 2-butyloctanol)<p-nonyl (i.e., triisopropyl)phenol<p-octyl (i.e., diisobutyl)phenol<esterified saturated linear acids [m=18, 12 (highest HLB0=11.4)]. Interpolation by means of the equation above with the appropriate values of p0, A and B supplies the CP for any homologous POS belonging to one of the 14 groups investigated, based on its degree of ethoxylation p.

Kurzfassung

Polyoxyethylierte nichtionische Tenside (POSs) sind in kaltem Wasser mehr löslicher als in heißem. Beim Erhitzen in wässriger Lösung, bei und über einer charakteristischen Temperatur, fallen sie als reversibler Niederschlag aus, dem sogenannten Trübungspunkt (CP), da die Lösung nach trüb/opak wechselt. Die CPs normal verteilter POSs korrelieren mit der Durchschnittszahl p der Oxyethylengruppen pro Molekül nach der linearen Gleichung (p – p0)/CP=A+B(p – p0). In einer homologen Reihe von POSs trägt der kleinste Wert von p zur Löslichkeit in Eiswasser bei, p0, der zu dem Tensid mit CP=0° gehört. Seine Hydrophil-Lipophil-Balance, HLB0, ist ein quantitatives Maß für die Hydrophobie der Stamm-Fettalkohole CmH2m+1OH, Fettsäuren und Alkylphenole. In dieser Arbeit wurden neue CPs, speziell von POSs mit p annähernd zu p0, mit publizierten CPs kombiniert. Die Reihenfolge der Erhöhung der HLB0 und Hydrophobie der Muttersubstanzen wird begleitet durch eine Erniedrigung der CPs ihrer Ethoxylate und lautet: Gesättigte, lineare, primäre Alkohole [m=18 (niedrigster HLB0=8.2), 16, 14.6, 13.3, 12.7, 12.0]<Oleylalkohol<gesättigte, lineare, primäre Alkohole mit mehrfachen Methylgruppen (m=10, 13)<Guerbet-Alkohole (2-Hexyldecanol, 2-Butyloctanol)<p-Nonyl (d.h., Triisopropyl)phenol<p-Octyl (d.h., Diisobutyl)phenol<veresterte, gesättigte, lineare Säuren [m=18, 12 (höchster HLB0=11.4)]. Die Interpolation der entsprechenden Werte von p0, A und B anhand der oben aufgeführten Gleichung liefert den CP für jedes homologe POS, das zu einer der 14 untersuchten Gruppen gehört und auf dem Ethoxylierungsgrad p basiert.


Hans Schott, 801 W. Beaver Hill Apts., 100 West Avenue., Jenkintown, PA 19046, U.S.A.

Prof. Dr. Hans Schott obtained an M.S. in colloid chemistry from the University of Southern California and a Ph.D. in physical chemistry from the University of Delaware. After performing and directing research at the Du Pont, Olin, and Lever Brotherss companies, he joined the School of Pharmacy of Temple University. He is presently Professor Emeritus of Pharmaceutics and Colloid Chemistry. His research deals with the application of colloid, polymer, and physical chemistry to pharmaceutical, cosmetic, and industrial systems based on nonionic surfactants, gelatin, suspensions of hydrous oxides, clays, drugs, and bacteria, and to detergency.


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Received: 2006-10-09
Accepted: 2006-10-25
Published Online: 2013-03-31
Published in Print: 2006-12-01

© 2006, Carl Hanser Publisher, Munich