Polymeric Bicontinuous Microemulsions (original) (raw)
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Bicontinuous Polymeric Microemulsions from Polydisperse Diblock Copolymers†
2008
Polymeric bicontinuous microemulsions are thermodynamically stable structures typically formed by ternary blends of immiscible A and B homopolymers and a macromolecular surfactant such as an AB diblock copolymer. Investigations of these bicontinuous morphologies have largely focused on model systems in which all components have narrow molecular weight distributions. Here we probe the effects of AB diblock polydispersity in ternary blends of polystyrene (PS), polyisoprene (PI), and poly(styrene-b-isoprene) (PS-PI). Three series of blends were prepared using the same PS and PI homopolymers; two of them contain nearly monodisperse components while the third includes a polydisperse PS-PI diblock. The PS and PI homopolymers and two of the PS-PI diblocks were prepared by anionic polymerization using sec-butyllithium and have narrow molecular weight distributions. The polydisperse PS-PI diblock was prepared by anionic polymerization using the functional organolithium 3-tert-butyldimethylsilyloxy-1-propyllithium; this diblock has a polydisperse PS block (M w /M n) 1.57) and a nearly monodisperse PI block (M w /M n < 1.1). The phase behavior of the three series of blends was probed using a combination of dynamic mechanical spectroscopy, small-angle X-ray scattering, and cloud point measurements, and a bicontinuous microemulsion channel was identified in each system. These results prove that monodisperse components are not required to form bicontinuous microemulsions and highlight the utility of polydispersity as a tool to tune polymer blend phase behavior. The random-phase approximation, originally advanced by de Gennes, and self-consistent field theory are used to provide a theoretical supplement to the experimental work. These theories are able to predict the directions of the polydispersity-driven shifts in domain spacing, order-disorder transition temperatures, and the location of the microemulsion channel. Self-consistent field theory is also used in conjunction with the experimental data from a series of nearly monodisperse blends to probe the variations of with temperature. A single linear relation of the form) R/T + does not describe at all blend compositions. Rather, two separate relations describe as a function of temperature; one is obtained from data on the diblock-rich side of the bicontinuous microemulsion channel while the other is obtained from data on the homopolymer-rich side of the channel. The blend morphology, rather than the composition (homopolymer fraction), apparently dictates whether the system is in the "diblock " or "homopolymer " regime. These results reinforce the notion that a true understanding of still eludes the polymer science community.
Dynamics of bicontinuous microemulsion phases with and without amphiphilic block-copolymers
The Journal of Chemical Physics, 2001
Neutron Spin Echo and Dynamic Light Scattering techniques are used for an extensive investigation of the bicontinuous phase in water/decane microemulsions. The dynamical behavior of different surfactant systems, decyl polyglycol ether (C 10 E 4), C 10 E 4 mixed with polyethylenepropylene/ polyethyleneoxide amphiphilic block-copolymers-(PEP x /PEO y), and sodium-bisethylhexylsulfosuccinate ͑AOT͒ is investigated under comparable conditions. At scattering wave numbers q large compared to the inverse of the structure length scale, q 0 ϭ2/d, always stretched exponential relaxations ϰe Ϫ(⌫ q t)  with ⌫ q ϰq 3 are found, as predicted theoretically. The relaxation rate increases almost linearly as function of the bicontinuous structure correlation scale-Ӎd/2. The apparent bare bending modulus determined by fitting theoretical predictions to the experimental high-q data yields values of about 1.3k B T-as inferred from previous small angle neutron scattering ͑SANS͒ studies and from other methods. The effect of increasing rigidity of the surfactant layers by anchoring amphiphilic block-copolymers, predicted theoretically and revealed experimentally in structural investigations, could not be clearly resolved due to its small influence on the dynamics. At structural length scales, the relaxation rate in water-oil contrast shows a minimum corresponding to the maximum of the static structure factor. At length scales much larger than the typical structure length the relaxation is single-exponential with a q 2 dependent rate. In this regime we find indications of the additional membrane interaction due to the presence of block-copolymers.
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.
Confinement Effects in Block Copolymer Modified Bicontinuous Microemulsions
The Journal of Physical Chemistry B, 2013
It has been established that the addition of amphiphilic diblock copolymers has a boosting effect in bicontinuous microemulsions by decreasing the minimum amount of surfactant needed to solubilize equal volumes of oil and water. The strength of the polymer effect was found to be about twice larger than the theoretical prediction. This discrepancy is explained by confinement. Previous experimental studies always considered large oil and water domains of size d compared to the typical polymer end-to-end radius, R ee . The ratio of these two parameters R ee /d defines the confinement parameter. We investigated the sensitivity of the polymer influence extending the range of confinement. We combined macroscopic observations of the phase behavior with microscopic measurements of the structure by small-angle neutron scattering (SANS). Both results were compared with computer simulations on the basis of the theoretical concept of Helfrich. The simulations predict an enhanced sensitivity of the polymer at medium confinement and a reversed behavior at larger confinement. The higher sensitivity at medium confinement is only slightly visible experimentally, whereas the reversed behavior (antiboosting) is clearly present. Finally, a comparison with homopolymer addition showed a common high confinement behavior for diblock copolymers and for homopolymers.
Correlations and Structure Factor of Bicontinuous Microemulsions
Journal De Physique, 1988
2014 On calcule des fonctions de corrélation et le facteur de structure de microémulsions par une approche de thermodynamique statistique ; cette approche avait été utilisée auparavant pour obtenir les diagrammes d'équilibre des phases. Le facteur de structure S(q) a un pic pour un vecteur d'onde qmax ~ 03C0/03BE où 03BE est la taille des domaines d'huile et d'eau. L'origine physique de ce pic est liée aux corrélations introduites par l'énergie de courbure du film tensioactif ; la renormalisation du module de courbure par les fluctuations thermiques joue un rôle important dans la stabilité de ces fluctuations. En représentant ces corrélations dans l'espace réel, on montre qu'il y a plusieurs types de corrélations, de vecteurs q différents, qui contribuent de manière importante à S(q).
Journal of Rheology, 2002
We have investigated the effects of shear flow on a polymeric bicontinuous microemulsion using neutron scattering, light scattering, optical microscopy, and rheology. The microemulsion consists of a ternary blend of poly͑ethyl ethylene͒ ͑PEE͒, poly͑dimethyl siloxane͒ ͑PDMS͒, and a PEE-PDMS diblock copolymer. At equilibrium, the microemulsion contains two percolating microphases, one PEE rich and the other PDMS rich, separated by a copolymer-laden interface; the characteristic length scale of this structure is 80 nm. Low strain amplitude oscillatory shear measurements reveal behavior similar to that of block copolymer lamellar phases just above the order-disorder transition. Steady shear experiments expose four distinct regimes of response as a function of the shear rate. At low shear rates ͑regime I͒ Newtonian behavior is observed, whereas at intermediate shear rates ͑regime II͒ development of anisotropy in the morphology leads to shear thinning. When the shear rate is further increased, there is an abrupt breakdown of the bicontinuous structure, resulting in flow-induced phase separation ͑regime III͒. Rheological measurements indicate that the shear stress is almost independent of the shear rate in this regime. Light scattering reveals a streak-like pattern, and correspondingly a string-like morphology with micron dimensions is observed with video microscopy. Upon a further increase of the shear rate ͑regime IV͒, the sample resembles an immiscible binary polymer blend with the block copolymer playing no significant role; the stress increases strongly with the shear rate. In some respects these results resemble those from other weakly structured complex fluids ͑sponge phases, liquid crystals, worm-like micelles, a͒ Current address:
Block-copolymer-induced structure formation in microemulsions
The Journal of Physical Chemistry, 1991
Transient electric birefringence measurements were performed on water/AOT (sodium bis(2-ethylhexyl) sulfasuccinate)/istane microemulsions with various amounts of block-copoly(oxyethylene/isoprene/oxyethylene) added. We could show that addition of the copolymer leads to a formation of nancdroplet (ND)-copolymer-aggregates. The contributions of NDs and aggregates to the induced birefringence could easily be separated because the NDs exhibited a negative and the aggregates a positive induced birefringence and because the time scales corresponding to the two processes were different.
Journal de Physique Lettres
Résomé. 2014 On examine la transition de rugosité de l'interphase dans un mélange modèle constitué de copolymères diblocs amphiphiles de deux solvants non miscibles et d'un cosurfactant monomérique. L'équivalence entre ce modèle et celui du solide-sur-solide implique l'existence d'une composition critique XRAB du cosurfactant pour que la transformation d'une phase de micro-émulsion lamellaire ait lieu dans une structure désordonnée bicontinue. A une composition plus élevée 1-XRAB, une autre transition produit de nouveau une phase ordonnée. Abstract. 2014 The roughening transition of the interface in a model mixture of amphiphilic diblock copolymers, two immiscible solvents and a monomeric cosurfactant is examined. The equivalence of this model with the solid-on-solid Ising magnet implies the existence of a critical cosurfactant composition XRAB for the transformation of a lamellar microemulsion phase into a bicontinuous disordered structure. At a higher composition 1-XRAB another transition of the same nature produces again an ordered phase.
The Journal of Chemical Physics, 2004
We present an analysis of the structure of the fluctuation-induced microemulsion phase in a ternary blend of balanced AB diblock copolymers with equal amounts of A and B homopolymers. To this end, graphical analysis methods are employed to characterize two-dimensional configuration snapshots obtained with the recently introduced Field-Theoretic Monte Carlo (FTMC) method. We find that a microemulsion forms when the mean curvature diameter of the lamellar phase coincides roughly with the periodicity of the lamellar phase. Further, we provide evidence to the effect of a subclassification of the microemulsion into a genuine and a defect-driven region.