Influence of Amphiphilic Block Copolymers on Lyotropic Liquid Crystals in Water−Oil−Surfactant Systems

Abstract

In ternary water-oil-nonionic alkyl polyglycol ether (CiEj) microemulsions, an increase in efficiency is always accompanied by the formation of a lamellar (LR) phase. The addition of an amphiphilic block copolymer to the ternary base system increases the efficiency of the microemulsion drastically while suppressingsat least partlysthe formation of the L R phase. However, amphiphilic block copolymers can be used not only to suppress the formation of lyotropic liquid crystals but also for the opposite effect, namely, to induce their formation. To understand to what extent the increase in efficiency is accompanied by the formation of lyotropic liquid crystals, we studied phase diagrams of water-n-alkane-n-alkyl polyglycol ethers (C iEj)-PEPX-PEOY at a constant volume fraction of oil in the water/oil mixture. Using polymers of the poly(ethylene propylene)-copoly(ethylene oxide) type, with MPEP ) X kg mol -1 and MPEO ) Y kg mol -1 , we determined phase diagrams as a function of the polymer concentration, size, and symmetry. Moreover, the influence of a particular polymer mixture was studied, which turned out to be the best system if both a high efficiency and a low tendency to form an L R phase are needed.

Purification, Surface Tensions, and Miscibility Gaps of Alkyldimethyl and Alkyldiethylphosphine Oxides

“…For example, phosphine oxide surfactants can be designed such that they can be used for the formation of highly efficient microemulsions. It is well-known from ternary water-oil-nonionic alkyl polyglycolether (C i E j ) microemulsion studies that an increase in efficiency is always accompanied by the unwanted formation of a lamellar (L a ) phase [3,4,25,26]. It is also well known that branches in the lipophilic side chains of surfactants suppress the (mostly undesired) formation of lyotropic liquid crystalline phases.…”

Coexisting lamellar phases in water–oil–surfactant systems induced by the addition of an amphiphilic block copolymer

“…3 of [17]. It is concluded in [17] that under certain circumstances the polymer induces a phase separation into a surfactant-poor and a surfactant-rich L α phase, the former serving as a host for the polymer.…”

“…Moreover, mixtures of polymers offer a wide variety of parameters to play with. Only recently, an extensive study was published in which the influence of the polymer structure on the one hand, and of polymer mixtures on the other, were studied in detail [17]. The most important results of this study can be summarized as follows.…”

“…Influence of polymer size An increase of the polymer size at constant polymer mass fraction had only a minor effect on the efficiency boosting (see [17] for details). However, the polymer size has a significant effect on the formation of the L α phase.…”

“…The larger the polymer the more favorable the formation of a bicontinuous microemulsion and the less favorable the formation of an L α phase. This observation was attributed to the smaller domain size ξ of the L α phase compared to the bicontinuous microemulsion, namely ξ μE = 1.5ξ L α [17]. The smaller the domain size the larger the loss of entropy for a polymer that is confined in the respective domain.…”