Microemulsion Efficiency Boosting and the Complementary Effect. 1. Structural Properties (original) (raw)
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SANS studies of polymer efficiency boosting in microemulsions—diblock copolymers versus homopolymers
Physica B: Condensed Matter, 2004
Amphiphilic diblock copolymers proved to dramatically increase the efficiency of surfactants in bicontinuous microemulsions. Now we investigated corresponding homopolymers as possible additives for microemulsions in order to tune the viscosity. Experiments showed that the efficiency is decreased, which qualitatively agrees with a theory of Eisenriegler. Simultaneous addition of diblock copolymers and homopolymers showed the possible superposition of the two opposite effects, and allowed to keep the efficiency constant with increased polymer content. r
Applied Physics A: Materials Science & Processing, 2002
The effect of amphiphilic block copolymers on ternary microemulsions (water, oil and non-ionic surfactant) is investigated. Small amounts of PEP-PEO block copolymer lead to a dramatic expansion of the one-phase region where water and oil can be solubilized by the mediation of surfactant molecules. Small-angle neutron-scattering experiments employing a high-precision two-dimensional contrast-variation technique demonstrate that the polymer is distributed uniformly on the surfactant membrane, where it modifies the membrane curvature elasticity. Furthermore, a new approach to determine the bending rigidity of an amphiphilic membrane is proposed, which is precise enough to measure the logarithmic scale dependence of the bending rigidity and its universal prefactor in bicontinuous microemulsions. PACS: 61.12.Ex; 68.05.Gh; 61.25.Hq Membrane systems represented by surfactant monolayers in microemulsions or by lipid bilayers have received much interest recently. Experimentally the interaction between polymers and membranes, which is very common in all kinds of biological membranes, has been studied intensively. A good example is "stealth liposomes" effective drug carrier systems where polymers anchored to phospholipid bilayers protect artificial vesicles against the body's immune response . Theoretically the concept of the curvature elasticity [2] has been found to be very useful in understanding many phenomena in these systems, which are the shapes, fluctuations, phase behavior and more. For a detailed comparison of theory and experiment, it is necessary to measure the parameters of this model, which are the spontaneous curvature c 0 , the bending rigidity κ, and the saddle-splay modulusκ.
Efficiency boosting and optional viscosity tuning in microemulsions studied by SANS
Physica B-Condensed Matter, 2004
It was shown that amphiphilic diblock copolymers increased the efficiency of surfactants dramatically in bicontinuous microemulsions. In the present study we investigate a possible transfer of the polymer boosting effect on droplet microemulsions. Furthermore the corresponding homopolymers are investigated as possible additives for bicontinuous microemulsions in order to tune viscosity. r
SANS studies of confined diblock copolymers in microemulsions
Physica B: Condensed Matter, 2006
Using small angle neutron scattering (SANS) polymers were studied as additives in microemulsions. Usually, one assumes no or small confinement, which is expressed by the ratio of the polymer size R g and the domain size d. For amphiphilic diblock copolymers, an increased surfactant efficiency and a more rigid surfactant membrane were observed. The sensitivity of the diblock copolymer effect on polymer concentration agreed with theoretical predictions. The current study is focused on medium and higher confinement of diblock copolymers. A computer simulation predicted elevated sensitivities for medium confinement and a reversed behaviour for high confinement. Experimentally, we found evidence for the reversal between medium and high confinement. The correlation length, which is proportional to the membrane rigidity, increased or decreased depending on the level of confinement. This result supports the interpretation that at high confinement the anchored diblock copolymer and the free homopolymer cannot be distinguished anymore. r
Colloid and Polymer Science, 2006
The effect of some amphipilic diblock-copolymers and comb-polymers on a balanced Winsor III microemulsion system is investigated with the quaternary system n-octyl-β-d-glucoside/1-octanol/n-octane/D2O as basis system. The diblock-copolymers are polyethyleneoxide-co-polydodecenoxide (PEOx PEDODOy ) and polyethyleneoxide-co-polybutyleneoxide (PEOx PEBUy ), constituted of a straight chain hydrophilic part and a bulky hydrophobic part. Addition of the diblock-copolymer leads to an enhancement of the swelling of the middle phase by uptake of water and oil; a maximum boosting factor of 6 was obtained for PEO111PEDODO25. Nuclear magnetic resonance diffusometry yields the self-diffusion coefficients of all the components in the system. The diffusion experiments provide information on how the microstructure of the bicontinuous microemulsion changes upon addition of the polymers. The reduced self-diffusion coefficients of water and oil are sensitive to the type of polymer that is incorporated in the film. For the diblock-copolymers, as mainly used here, the reduced self-diffusion coefficient of oil and water will respond to how the polymer bends the film. When the film bends away from water, the reduced self-diffusion of the water will increase, whereas the oil diffusion will decrease due to the film acting as a barrier, hindering free diffusion. The self-diffusion coefficient of the polymer and surfactant are similar in magnitude and both decrease slightly with increasing polymer concentration.
Surfactants for microemulsions
Current Opinion in Colloid & Interface Science, 1997
Research effort in past years has focused on the •development of microemulsions with specific properties, namely, high solubilizing power and temperature insensitivity. Phase behavior studies have provided the foundations for this development. On the basis of mass balance analysis and the geometry of three-phase tie triangles, the composition of the surfactant films separating micro-water and oil domains in bicontinuous type microemulsions has been determined. This information allows a beller comparison of the solubilizing power .of surfactants. In addition, decisive progress has been made in the development of surfactant systems for the preparation of biocompatible microemulsions.
The Phase Behavior and Microstructure of Efficient Cationic–Nonionic Microemulsions
Journal of Colloid and Interface Science, 2001
A surfactant mixture of didodecyldimethylammonium bromide (DDAB) and n-alkyl polyglycol ethers (C i E j ) can make efficient microemulsions of decane and water. Increases in surfactant efficiency by up to a factor of four are realized as 2% C 8 E 3 is replaced with DDAB. As little as 6% of an appropriate surfactant mixture can microemulsify equal masses of oil and water. The increase in DDAB concentration causes the spacing of the bicontinuous domains of oil and water to decrease and the correlation length of the surfactant monolayers to increase. These changes in structural parameters, as detected by small-angle neutron scattering, are in quantitative accord with theoretical calculations of changes in structure as a result of electrostatic stiffening of elastic membranes. Although the reported changes in microstructure are consistent with predictions, they alone cannot explain the observed large increases in overall surfactant efficiency. C 2001 Academic Press
Membrane decoration by amphiphilic block copolymers in bicontinuous microemulsions
Physical Review Letters, 2000
The effect of various amphiphilic block copolymers of different molar masses on the structure and phase behavior of ternary amphiphilic systems (water, oil, and nonionic surfactant) is investigated. Small amounts of PEP-PEO block copolymer lead to a dramatic increase in the volumes of oil and water, which can be solubilized in a bicontinuous microemulsion. High-precision neutron scattering experiments with a sophisticated contrast variation technique demonstrate that the polymers form uniformly distributed mushroom conformations on the surfactant membrane. Based on these observations, we propose a universal mechanism for the swelling behavior, which is due to the variation of the membrane curvature elasticity.