Modulated Phases: Review and Recent Results

Andelman, David; Rosensweig, Ronald E.

doi:10.1021/jp807770n

Cited by 78 publications

(73 citation statements)

References 83 publications

(154 reference statements)

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“…The uncharged micelles resulting from this competition has been called octopus micelles, due to the presence of the stretched legs and high density core (29). Interestingly, whereas the structures formed are similar to those found in modulated phases (31,32), in grafted chains the local segregation is not due to the competition between short and long range interactions but to the relatively short-range hydrophobic attractions and the lack of lateral mobility. Now we concentrate on the role of charge and charge regulation in modifying those structures.…”

Section: Resultsmentioning

confidence: 99%

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Tagliazucchi

Cruz

Szleifer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

165

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The competition between chemical equilibrium, for example protonation, and physical interactions determines the molecular organization and functionality of biological and synthetic systems. Charge regulation by displacement of acid-base equilibrium induced by changes in the local environment provides a feedback mechanism that controls the balance between electrostatic, van der Waals, steric interactions and molecular organization. Which strategies do responsive systems follow to globally optimize chemical equilibrium and physical interactions? We address this question by theoretically studying model layers of end-grafted polyacids. These layers spontaneously form self-assembled aggregates, presenting domains of controlled local pH and whose morphologies can be manipulated by the composition of the solution in contact with the film. Charge regulation stabilizes micellar domains over a wide range of pH by reducing the local charge in the aggregate at the cost of chemical free energy and gaining in hydrophobic interactions. This balance determines the boundaries between different aggregate morphologies. We show that a qualitatively new form of organization arises from the coupling between physical interactions and protonation equilibrium. This optimization strategy presents itself with polyelectrolytes coexisting in two different and well-defined protonation states. Our results underline the need of considering the coupling between chemical equilibrium and physical interactions due to their highly nonadditive behavior. The predictions provide guidelines for the creation of responsive polymer layers presenting self-organized patterns with functional properties and they give insights for the understanding of competing interactions in highly inhomogeneous and constrained environments such as those relevant in nanotechnology and those responsible for biological cells function.aggregates | charge regulation | local pH | responsive surfaces T he competition between physical interactions and chemical equilibrium is a challenging problem in physics, chemistry, and biology. A ubiquitous example of this competition in synthetic and life systems is the control of the charge state by protonation that regulates enzymatic activity (1), switches ionconductivity in biological (2) and synthetic channels (3), induces self-assembly (4-7), and determines the properties of technologically important polyelectrolyte layers (8, 9). These processes occur in confined inhomogeneous environments, where molecular organization is restricted and competition among interactions is augmented. The optimization of charge state by protonation depends not only on the solution pH but also on the local environment (10, 11). Therefore, it is imperative to understand whether the molecular organization is determined by the independent optimization of the acid-base equilibrium and the physical interactions, or if there are phenomena that arise exclusively from their coupling. This understanding is particularly relevant today given the large number of systems...

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Section: Resultsmentioning

confidence: 99%

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Tagliazucchi

Cruz

Szleifer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

165

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“…[23] The presence of competing attractions and repulsions leads to the possibility of either macrophase or microphase separation, and a Lifshitz point that defines the crossover from one inhomogeneous state of organization to the other. Block copolymer melts and solutions are perhaps the most studied member of this class of ''frustrated'' systems.…”

Section: Synthesis Of Janus Particlesmentioning

confidence: 99%

“…This is analogous to a liquid-vapor type demixing transition. However, beyond f ¼ 0.05 there is a crossover (Lifshitz point [23,27] ) to microphase separation corresponding to ordering on a finite length scale (nonzero k*). As the volume fraction further increases, the microphase separation temperature and ordering wavevector both increase.…”

Section: Theoretical Calculations Of the Phase Diagrammentioning

confidence: 99%

Janus Particle Synthesis and Assembly

et al. 2010

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Janus particles, colloid-sized particles with two regions of different surface chemical composition, possess energetic interactions that depend not only on their separation but also on their orientation. Research on Janus and colloidal particles that are chemically patchy in even more complicated fashion has opened a new chapter in the colloid research field. This article highlights recent progress in both experiment and theory regarding synthesis and self-assembly of Janus particles, and tentatively outlines some areas of future opportunity.

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“…Some of the most common morphologies are stripes and circular droplets in two dimensions (2d), as well as sheets, tubes and spherical droplets in three dimensions (3d). These systems are very diverse and include type I superconductor films, ferromagnetic films, block copolymers (BCP), and even lipid bio-membranes [1][2][3]. In each case the physical origin of the order parameter and the pattern characteristic differ with length scales or periodicity that vary from mesoscopic scales of tens of nanometers in biological membranes [4], to centimeters in ferrofluids [2,3].…”

Section: Introductionmentioning

confidence: 99%

Interfacial Phenomena of Solvent-Diluted Block Copolymers

Cohen

Andelman

2013

Macromolecules

Self Cite

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A phenomenological mean-field theory is used to investigate the properties of solvent-diluted diblock copolymers (BCP), in which the two BCP components (A and B) form a variety of phases that are diluted by a solvent (S). Using this approach, we model mixtures of di-block copolymers and a solvent and obtained the corresponding critical behavior. In the low solvent limit, we find how the critical point depends on the solvent density. Due to the non-linear nature of the coupling between the A/B and BCP/solvent concentrations, the A/B modulation induces modulations in the polymer-solvent relative concentration with a double wavenumber. The free boundary separating the polymer-rich phase from the solvent-rich one is studied in two situations. First, we show how the presence of a chemically patterned substrate leads to deformations of the BCP film/solvent interface, creation of terraces in lamellar BCP film and even formation of multi-domain droplets as induced by the patterned substrate. Our results are in agreement with previous self-consistent field theory calculations. Second, we compare the surface tension between parallel lamellae coexisting with a solvent phase with that of a perpendicular one, and show that the surface tension has a nonmonotonic dependence on temperature. The anisotropic surface tension can lead to deformation of spherical BCP droplets into lens-shaped ones, together with re-orientation of the lamellae inside the droplet during the polymer/solvent phase separation process in agreement with experiment.

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Modulated Phases: Review and Recent Results

Cited by 78 publications

References 83 publications

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

Janus Particle Synthesis and Assembly

Interfacial Phenomena of Solvent-Diluted Block Copolymers

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