Nonionic latices in aqueous media

The rate of conversion of styrene into polystyrene by emulsion polymerisation has been investigated in the absence and in the presence of methoxy-polyethyleneglycol methacrylate, MeOPEGMA. The effect of adding MeOPEGMA at different stages of the polymerisation was also investigated. Additions at the beginning of the polymerisation and at the early stages gave a bimodal particle size distribution whereas late additions gave small particle size, monodisperse latices which were electrosterically stabilised. The latter materials were found to be colloidally stable to the addition of high concentrations of electrolyte and to freeze-thaw conditions.Part 3: Brit. Polymer J., 1987, 19:435     

Small angle neutron scattering studies on micellar systems part 2. Mixed systems of ammonium decanoate and ammonium perfluoro-octanoate

Mixtures of ammonium decanoate (AmDec) and ammonium perfluoro-octanoate (APFO), in ammonium chloride: ammonium hydroxide buffer at pH 8.8 and an ionic strength of 0.1, were examined by small angle neutron scattering with varying proportions of the two surface active agents. The results indicated that mixed micelles were formed and it is suggested from analysis of the data that these were cylindrical in shape at APFO: AmDec ratios of 21, 11 and 12. At 21 and 11 the micelles were found to contain more APFO than expected on the basis of ideal mixing of the surface active agents in the micelle. At a ratio of 19 the micelles were found to be spherical but larger than those formed from AmDec alone. A speculative model is proposed for the mixed micelle which still, however, allows for segregation between hydrocarbon and fluorocarbon chains within the micelle.     

A constraint on physical quantum states in cosmological space-times

The problem of constructing the Hilbert space of physical states for a free scalar quantum field propagating on a cosmological background is considered. The concept of energy-momentum for such a field is discussed and it is noted that, according to current renormalization theory, for a state ¦M to have finite energy density its associated anticommutator function must be of a particular form first discussed by Hadamard. This restriction is shown to lead to a constraint on the construction of the Hilbert space of physical states. This constraint is used to reject a recently proposed scheme for the construction of this space which was based on a principle of energy minimization.This essay received an honourable mention from the Gravity Research Foundation for the year 1984.-Ed.     

The influence of non-ionic surface active agents on the stability of polystyrene latex dispersions

Summary The influence ofn-dodecyl hexaoxyethylene glycol monoether on the stability of dispersions of polystyrene latices has been investigated by measuring the rates of flocculation, by lanthanum nitrate and hydrochloric acid, in the presence of various concentrations of the surface active agent. The adsorption isotherm for the non-ionic surface active agent on the latex surface showed that saturation adsorption was reached at about the critical micelle concentration to give a monolayer of vertically orientated molecules. A determination of the thickness of the adsorbed layer by an ultracentrifuge method confirmed the vertical orientation. In order to explain the results a theory has been developed based on the interaction between the adsorbed layers which includes a term to account for the interaction between the surface active molecule and the solvent.

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Zusammenfassung Der Einfluß vonn-Dodecyl-hexaoxyäthylen-glycolmonoäther auf die Stabilität von Dispersionen von Polystyrol-Latices wird durch Messung der Flockungsgeschwindigkeit durch Lanthannitrat und hydrochlorische Säure in Gegenwart von verschiedenen Konzentrationen überflächenaktiver Agentien untersucht. Die Adsorptionsisothermen von nichtionischen oberflächenaktiven Agentien an die Latexoberfläche zeigt, daß etwa bei der kritischen Micellkonzentration Sättigungsadsorption erreicht wird, die eine monomolekulare Schicht senkrecht orientierter Moleküle gibt.Die Bestimmung der Dicke der adsorbierten Schicht durch eine Ultrazentrifugenmethode stellt die senkrechte Orientierung sicher. Um die Ergebnisse zu erklären, wird eine Theorie entwickelt, die auf der Wechselwirkung zwischen den adsorbierten Schichten beruht, einschließend einen Term, um der Wechselwirkung zwischen den oberflächenaktiven Molekülen und dem Lösungsmittel Rechnung zu tragen.

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With 7 figures and 3 tables     

An electron microscope and X-ray examination of the influence of dodecylpyridinium iodide on the formation of silver iodide sols

Summary Examination of the influence of dodecylpyridinium iodide on the formation of silver iodide sols (conc. 5 × 10⁻⁴ M), by turbidimetric measurements, revealed the presence of four coagulation regions with intermediate regions in which stable sols were formed. The form of the sol particles and the structure of the coagula, formed under these conditions, has been investigated in detail using the electron microscope. Selected area microelectron-diffraction and X-ray diffraction examination of the various regions showed that the silver iodide particles generally had a hexagonal structure but under some conditionsγ-cubic silver iodide was also present. It was found that at low concentrations of surface active agent (10⁻⁶M) the rate of sol particle growth was enhanced but at higher concentrations (10⁻³M) it was greatly retarded. The phenomena observed were interpreted on the basis of the strong adsorption of dodecylpyridinium ions onto the negatively charged silver iodide surface.

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Zusammenfassung Prüfung des Einflusses von Dodecylpyridinium-Iodid auf die Bildung von Silberiodidsolen (Konzentration 5 · 10⁻⁴ M) durch Lichttrübungsmessung zeigt die Anwesenheit von vier Koagulationsgebieten mit Zwischengebieten, in denen stabile Sole gebildet werden. Die Form der Solteilchen und die Struktur der unter diesen Bedingungen gebildeten Koagulate wurden exakt mit dem Elektronenmikroskop untersucht. Elektronenbeugungs- und R?ntgenstrahlen-Interferenzuntersuchungen bestimmter Fl?chen der Abbildungen aus den verschiedenen Zustandsgebieten zeigen, da? die Silberiodidteilchen gew?hnlich hexagonale Struktur besitzen, da? jedoch unter gewissen Bedingungen auch gammakubisches Silber anwesend ist. Ferner wurde gefunden, da? bei niedrigen Konzentrationen von oberfl?chenaktiven Medien (10⁻⁶ M) die Geschwindigkeit des Solteilchenwachstums erh?ht wird, aber bei h?heren Konzentrationen (10⁻³ M) stark verz?gert wird. Die beobachteten Ph?nomene werden auf der Basis starker Adsorption von Dodecylpyridinium-Ionen auf der negativ geladenen Silberiodid-Oberfl?che gedeutet.

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On leave of absence from Faculty of Science, University of Zagreb (Yugoslavia).

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We wish to thank the Governing Body of Trinity Hall for a Consolidated Zinc Corporation grant to one o f us (E. M.).     

Studies on polytetrafluoroethylene latices Part 3. Electrophoretic mobility in univalent electrolytes

The electrophoretic mobilities of particles of polytetrafluoroethylene (PTFE), prepared by a dispersion polymerisation technique using a peroxyacid initiator, have been determined using a mass transport technique. Investigations were carried out as a function of sodium chloride concentration at pH 9 and as a function of pH in the presence of various salts, namely, sodium chloride, potassium nitrate and potassium thiocyanate. The particles were found to have a low surface charge density, consistent with the idea that sparsely distributed charged sites originated from initiator fragments leaving the major part of the surface in a hydrophobic condition. Below a pH of ca. 4.5 increases of mobility with decreasing pH were observed with chloride and thiocyanate as the anion. These were attributed to an anion adsorption process, dependent on thepKa of the surface groups, and a model for the process is described.