Formation and structure of the microemulsion phase in two-dimensional ternary AB+A+B polymeric emulsions (original) (raw)
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Fluctuation Effects in Ternary AB + A + B Polymeric Emulsions
Macromolecules, 2003
We present a Monte Carlo approach to incorporating the effect of thermal fluctuations in field theories of polymeric fluids. This method is applied to a field-theoretic model of a ternary blend of AB diblock copolymers with A and B homopolymers. We find a shift in the line of order-disorder transitions from their mean-field values, as well as strong signatures of the existence of a bicontinuous microemulsion phase in the vicinity of the mean-field Lifshitz critical point. This is in qualitative agreement with a recent series of experiments conducted with various three-dimensional realizations of this model system. Further, we also compare our results and the performance of the presently proposed simulation method to that of an alternative method involving the integration of complex Langevin dynamical equations.
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.
Polymeric Bicontinuous Microemulsions
Physical Review Letters, 1997
High molecular weight block copolymers can be viewed as macromolecular surfactants when blended with thermodynamically incompatible homopolymers. This Letter describes the formation of polymeric bicontinuous microemulsions in mixtures containing a model diblock copolymer and two homopolymers. Although we attribute development of this equilibrium morphology to the effects of fluctuations, mean-field theory provides a quantitative strategy for preparing the bicontinuous state at blend compositions near an isotropic Lifshitz point. [S0031-9007(97)
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.
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.
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).
Structure of Microemulsion−ABA Triblock Copolymer Networks
Langmuir, 2008
Structural equilibrium properties of transient networks formed by microemulsion droplets and ABA triblock copolymers in solution have been studied by Monte Carlo simulation. The droplets were represented by soft spheres, and the polymers were represented by junctions connected by harmonic bonds with an angular potential regulating the intrinsic chain stiffness. The interaction parameters were selected such that the end A-blocks were localized inside the droplets and the middle B-block in the continuous phase. The influence of (i) the polymer concentration, (ii) the polymer stiffness, and (iii) the contour length of the middle B-block on the formation and the structure of the microemulsion-polymer network were investigated using polymer end-to-end separation probability distribution functions, droplet radial distribution functions, droplet-droplet nearest-neighbor probability distribution functions, and network connectivity indicators. An increase of the polymer-droplet number ratio had a strong impact on the network formation. Under typical conditions and at an intermediate polymer-droplet number ratio, (i) the fraction of polymers forming bridges between droplets increased from essentially zero to unity and (ii) the fraction of polymers that were forming loops decreased as the ratio of the polymer end-to-end separation and the surface-to-surface separation between neighboring droplets for a hypothetical homogeneous droplet distribution was increased from 0.5 to 2. For long and flexible polymers, a mesoscopic segregation triggered by a depletion attraction between droplets appeared, and, furthermore, for sufficiently stiff chains, only bridge conformations occurred. The percolation probability could be represented as a function of the average droplet cluster size only, across all systems.
Macromolecules, 1997
The morphological similarity between a phase-separated polymer blend and a one-phase bicontinuous microemulsion is discussed in detail by comparing their respective light and X-ray scattering intensity distributions with structure factors computed according to the random wave model (RWM). In the RWM, a three-parameter spectral function introduced by Lee and Chen is used in conjunction with Berk's theory and Cahn's clipping scheme to calculate the Debye correlation function for the scattering intensity. The agreement between experiment and theory is excellent. The three parameters determined by fitting the scattering intensities are then used to calculate the average Gaussian curvature of the interfaces between the two isometric phases for the first time. The RWM can also be used to generate the 3D morphologies of both the bicontinuous phase-separated polymer blend and the one-phase microemulsion. There is a striking resemblance between the morphologies of these two unrelated systems, in spite of a difference in length scales characterizing the structures of a factor of about 250.
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.