Localisation of anchored polymers in lamellar liquid–crystalline dispersions by confocal microscopy

Abstract The localisation of an anchored polymer in a lamellar liquid–crystalline dispersion has been investigated by confocal microscopy. For that purpose, the polymer is tagged with a fluorescent label and the microscopic technique used is fluorescent confocal scanning light microscopy. The continuous phase of the lamellar dispersion, a model liquid detergent system, is a concentrated electrolyte solution. The polymer, a copolymer of sodium acrylate (NaA) and laurylmethacrylate (LM), also known as decoupling polymer, can be labelled successfully with fluorescein, although this labelling is not restricted to the NaA/LM molecules exclusively. Also, a fraction of this pure polymer, sodium polyacrylate homo polymer molecules, is labelled and shows up in the microscopic images as continuous background. Localisation studies of fluorescently labelled NaA/LM polymers result in positive evidence that the polymer is present in highly increased concentration at the interface between the lamellar droplet and the continuous electrolyte phase. Inside the lamellar droplets a faint fluorescence signal and, often, an intense fluorescent small “nucleus” in the centre of the dispersed droplets has been observed. A special fraction of the decoupling polymer is suggested to be responsible for these fluorescent signals. This fraction, also known as the “scum” in pure decoupling polymer solution/dispersions, has a low NaA/LM ratio, is poorly solvable in the lamellar dispersion and therefore remains present as a separate, dispersed polymer-rich liquid phase, located inside the lamellar droplets or as separate entities in the continuous phase. Confocal scanning light microscopy has demonstrated, by direct visualisation, the localisation of NaA/LM-type decoupling polymers in the very outer region of the lamellar droplets. Due to restrictions in the resolution of the light microscope, measurement of the thickness of this outer region is not possible.