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Original Articles

An Ellipsometric Study of the Adsorption of Gelatin on Silver Bromide

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Pages 279-285 | Received 01 Aug 1974, Published online: 23 Jul 2016
 

Abstract

Optically-polished surfaces of silver bromide were examined by ellipsometry to establish their optical properties. The adsorption of gelatin onto the surfaces from an aqueous solution at 40° C was then followed ellipsometrically. Measurements were carried out as a function of time and as a function of pH at pBr 3. From the measurements, it was possible to obtain the adsorption excess of the gelatin at the surface, the optical thickness of the adsorbed layer and the concentration of gelatin in the adsorbed layer. The optical thickness of the adsorbed layer was found to vary significantly with pH and to reach a maximum value of ca. 400 A at the isoelectric point of the gelatin.

Résumé

Les proprités optiques de surfaces de bromure d’argent polies optiquement ont été examinées par ellipsométrie. L´adsorption de la gélatine à 40° C à partir de solution aqueuse a été suivie par ellip sométrie. Les mesures ont envisagé l´influence du temps et du pH à PBr3. A partir de ces mesures, il a été possible d´évaluer l’excès de gélatine adsorbée à la surface, l´épaisseur optique de la couche adsorbée et la concentration de la gélatine dans cette couche.

L´épaisseur optique de la couche adsorbée varie significativement en fonction du pH et atteint une valeur maximale d´environ 400 A au Point isoélectrique de la gélatine,

Zusammenfassung

Optisch polierte Silberbromidoberflächen wurden ellipsometrisch untersucht und ihre optischen Eigenschaften Estimmt. Anschließend wurde die Adsorption von Gelatine aus wässriger Lösung bei 40° C an diesen Oberflächen ellipsometrisch verfolgt. e Messungen wurden in Abhängigkeit von der Zeit bei unterschiedlichen pH-Werten und konstantem pBr-Wert von 3 durchgeführt. Aus den Messungen konnte der Adsorptionsüberschuß der Gelatine an der Oberfläche, die Dicke der adsorbierten Gelatineschicht und die Konzen ration der Gelatine in der Adsorptionsschicht bestimmt werden.

Die Dicke der adsorbierten Gelatineschicht erwies sich als stark pH-abhängig und erreichte einen Maximalwert von ca. 400 A beim 80elektrischen Punkt der Gelatine.

Riassunto

Un cristallo di AgBr, le cui superfici sono state otticamente pulite, è stato esaminato mediante ellissometria per stabilirne le sue proprietà ottiche.

Lo stesso tipo di indagine è stato usato per seguire l´adsorbimento di gelatina, da soluzioni acquose a 40° C, sulle stesse superfici.

Le misure sono state fatte in base al tempo ed in base al pH a pBr di 3,00.

Da queste misure, è stato possibile stabilire non solo l’eccesso di adsorbimento di gelatina sulla superficie, ma anche lo spessore e la ooncentrazione in gelatina dello strato adsorbito.

Lo spessore ottico dello strato adsorbito varia significantemente col pH e raggiunge un massimo di circa 400 A, al punto isoelettrico della gelatina Stessa.

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