Applied Colloids Surfactants

Poster at 17th International Symposium on Surfactants in Solution on August 17-22, 2008 Berlin

Easing formulation of suspensions by bottom focused back scattering

Selection of efficient dispersants, their optimum concentration and processing conditions is a demanding and time consuming process. In almost all cases a high sedimentation stability is required. Evaluation of sedimentation stability can be eased when focusing on the changes in particle concentration right at the bottom part of the suspensions.

A new multisample approach using light backscattering signals is presented. It allows for fast measurement of stability and/or demixing phenomena and separation kinetics of up to 8 different samples simultaneously. The concentration change is measured in a very small region of interest at the bottom of sample cell by light back scattering. The method was applied to trace the optimum dispersant concentrations for mineral suspensions stabilized by nonionic or anionic surfactant. Further the influence of processing conditions and pH was evaluated.

Poster at 17th International Symposium on Surfactants in Solution on August 17-22, 2008 Berlin

Easing formulation of emulsions by bottom focused back scattering

Selection of efficient emulsifiers, their optimum concentration and processing conditions is a demanding and time consuming process. In almost all cases a high creaming stability is required. Evaluation of creaming stability can be eased when focusing on the changes in droplet concentration right at the bottom part of the emulsion samples.
A new multisample approach using light backscattering signals is presented. It allows for fast measurement of stability and/or demixing phenomena and separation kinetics of up to 8 different samples simultaneously, by monitoring the concentration change in a very small region of interest at the bottom of sample cell.
The method was applied to trace the optimum emulsifier concentrations for silicone oil emulsions stabilized by nonionic or anionic surfactant. Further the influence of processing time and intensity was evaluated for a high speed rotor stator mixer.

Poster at 17th International Symposium on Surfactants in Solution on August 17-22, 2008 Berlin

Sedimentation and consolidation behaviour of mineral suspensions flocculated by adsorbing and nonadsorbing polymers

In many industrial applications stability and rheological behaviour of dispersions is adjusted using polymeric additives. Nonadsorbing polymers used as thickeners to stabilise formulations not only increase fluid viscosity but can also induce depletion flocculation. On the other hand adsorbing polymers are used mainly to flocculate suspensions for enhanced separation. Both types of flocculation are concentration dependent, high polymer concentration can lead to restabilization.

In this paper the sedimentation and consolidation behaviour of flocculated polydisperse quartz dispersions were investigated as function of polymer concentration. Depletion flocculation was induced by adding anionic polyacrylamide, electrostatic flocculation by adding a high charge density cationic polymer (PolyDADMAC).
Sedimentation and consolidation behaviour was measured as function of excess pressure applied using a multisample analytical centrifuge. This results in information about dispersion stability, packing density, dewaterability and rheological properties (compressive yield stress, elasticity).
The packing density as function of polymer concentration and centrifugal pressure applied was separately determined by X-ray adsorption. In addition to the average packing density obtained by analytical centrifugation this method allows to determine the local distribution of particle concentration.

Presentation at 17th International Symposium on Surfactants in Solution on August 17-22, 2008 Berlin

A New Method Based on Light Backscattering Signals to Trace Sedimentation and Creaming

A considerable percentage of industrial products are dispersions (emulsions, suspensions, suspoemulsions). In addition to microbiological and chemical stability, physical stabilities manifested in creaming and/or sedimentation processes are also of great importance, both for the R&D and production process. The increasingly complex demands placed on new formulations require fast, reliable and cost-efficient means for analysing equipments.
A new multisample approach using light backscattering signals is presented. It allows for fast measurement of destabilisation and/or demixing phenomena and separation kinetics of up to 8 different samples simultaneously, by monitoring the concentration change in a very small region of interest at the bottom of sample cell.
The paper deals with the measuring principle and the analysis of the measuring signals. The whole time course can be described by a three parametric function. We represent applications regarding classification of dispersions with different stabilities due to different surfactants or emulsifiers as well as checking of destabilisation procedures.

This study was supported by a grant from the Federal Ministry of Economics and Technology (grant number KA0248303FK6).

Presentation at 17th International Symposium on Surfactants in Solution on August 17-22, 2008 Berlin

Rapid emulsifier selection and evaluation of emulsion stability for reformulation

Selection of emulsifiers and evaluation of emulsion stability is a frequent task. This relates to practical issues like formulation of emulsions, optimization of preparation conditions, quality control, shelf life estimation and breaking of emulsions. Due to European legislation (REACH) many companies are facing the problem to replace proven components in their formulations (low volume speciality compounds or problematic chemicals). This also applies to emulsifiers and emulsion based products.
A multisample technique based on analytical centrifugation is presented which allows for an accelerated study of creaming, sedimentation and of separation of oil and water phases. Not only information on the extent of phase separation is provided but also the kinetics are measured directly in-situ. The latter is of great practical importance for estimation of shelf life and in relation to the engineering of separation processes.
The method was applied to check for alternatives to nonyl phenol based surfactants as emulsifiers for silicone oil emulsions. Due to the multisample approach one centrifugal run with 12 different samples was sufficient to identify more environmentally benign emulsifiers with identical or better performance. In a second run the efficiency of emulsifier combinations was tested. In addition to these investigations the applicability of the method for selection of the most efficient emulsification conditions was demonstrated.

Artikel in Welt der Farben Ausgabe Juli/August 2008

Farben & Lacke: Schnelle Bewertung von Entmischung und Segregation

Titus Sobisch, Dietmar Lerche, Arnold Uhl, L.U.M. GmbH, Rudower Chaussee 29, 12489 Berlin

Problemstellung

Zur Gewährleistung der Kundenzufriedenheit sind folgende Stabilitätsprobleme von Farben und Anstrichstoffen zu vermeiden oder zu minimieren:

· Synerese – an der Oberfläche scheidet sich das Dispersionsmedium ab

· Pigmentsegregation – Änderung der Farbzusammensetzung innerhalb des Behälters

· Partikelsegregation – Änderung der Partikelgrößenzusammensetzung innerhalb des Behälters.

Diese Aufgaben stellen sich sowohl bei der Entwicklung neuer Produkte als auch regelmäßig bei der Qualitätssicherung in der Produktion. Zur Lösung dieses Problems läßt sich die Analytische Zentrifugation mit Mehrprobenrotor einsetzen, wodurch eine bis zu 2300-fach beschleunigte Bewertung der Entmischungsstabilität von Produkten der Farb- und Lackindustrie ermöglicht wird. Durch Einsatz der Zentrifugation werden Entmischungsprozesse und somit die Bewertung der Produkte beschleunigt.

see also
Paint products: Accelerated stability and quality testing
Part I: Direct measurement of separation and segregation by multisample analytical centrifugation

Scope

To assure continued consumer satisfaction the following stability issues of paint products have to be minimized or avoided:

· Syneresis – separation of the liquid dispersion media

· Pigment segregation – change of colour composition inside a container

· Particle segregation – change of particle size distribution inside a container

These stability issues have to be addressed not only during development of new paint products but also for quality assurance during production on a regular basis. This application note demonstrates that multisample analytical centrifugation can be used as an efficient tool for the accelerated evaluation of separation stability of paint products.

In addition this technique provides for high resolution data of particle size distributions of pigments or emulsions.