Abstract:A Monte Carlo simulation for the micellization of ABA-and BAB-type triblock copolymers in a selective solvent. II.Multimolecular micelles in polar solvents formed by polystyrene-block-poly͑methacrylic acid͒ ͑PS-PMA͒, hydrophobically modified by a naphthalene tag between blocks and an anthracene tag at the end of PMA block, are studied by a lattice Monte Carlo method. The model is parametrized according to available experimental data and several structural characteristics of the PMA shell together with the fluo… Show more
“…This, we believe, (i) provides a proof that the used SCF method yields a reasonable description of the system behavior and (ii) helps to interpret the true physical meaning of the H strip as a spherical layer containing small and compact hydrophobic domains distributed on average uniformly in all directions. 4 Snapshot of E1−H−E2 shell, pH 7, I = 0.01 mol/L and for n E1 = 30 (a) and n E1 = 90 (b) obtained by Monte Carlo simulations developed in refs and with parameters optimized in ref to mimic the studied system. The gray circles represent polyelectrolyte units (both dissociated and nondissociated) and the black circles represent hydrophobic units.…”
Section: Resultsmentioning
confidence: 99%
“…Snapshot of E1−H−E2 shell, pH 7, I = 0.01 mol/L and for n E1 = 30 (a) and n E1 = 90 (b) obtained by Monte Carlo simulations developed in refs and with parameters optimized in ref to mimic the studied system. The gray circles represent polyelectrolyte units (both dissociated and nondissociated) and the black circles represent hydrophobic units.…”
The behavior of amphiphilic polyelectrolyte shells of micelles with kinetically frozen hydrophobic cores in aqueous solutions was studied by self-consistent field calculations. The calculations emulate the behavior of annealed (weak) shell-forming polyelectrolyte chains, e.g., poly(methacrylic acid), PMA, containing a relatively low fraction of strongly hydrophobic units, e.g., polystyrene, PS. The hydrophobic units are arranged either in sequences, or are distributed uniformly in the shell-forming chains. The analysis of concentration profiles of individual species reveals strong segregation and important self-organization of hydrophobic units in the shell. Hydrophobic units either adsorb at the core, or form small hydrophobic domains relatively far from the core. The transition from one type of conformations to the other, which depends on the position of hydrophobic sequence in the polyelectrolyte chain, can be provoked by changes in pH and ionic strength. The behavior of shell-forming chains composed of a long inner polyelectrolyte sequence (grafted to the micellar core), a short middle hydrophobic sequence and a peripheral polyelectrolyte sequence is of interest. The calculations yield a bimodal distribution of hydrophobic units as a function of the radial distance from the core/shell interface. It means that two types of chains (fairly stretched and loop-forming ones) coexist in the shell.
“…This, we believe, (i) provides a proof that the used SCF method yields a reasonable description of the system behavior and (ii) helps to interpret the true physical meaning of the H strip as a spherical layer containing small and compact hydrophobic domains distributed on average uniformly in all directions. 4 Snapshot of E1−H−E2 shell, pH 7, I = 0.01 mol/L and for n E1 = 30 (a) and n E1 = 90 (b) obtained by Monte Carlo simulations developed in refs and with parameters optimized in ref to mimic the studied system. The gray circles represent polyelectrolyte units (both dissociated and nondissociated) and the black circles represent hydrophobic units.…”
Section: Resultsmentioning
confidence: 99%
“…Snapshot of E1−H−E2 shell, pH 7, I = 0.01 mol/L and for n E1 = 30 (a) and n E1 = 90 (b) obtained by Monte Carlo simulations developed in refs and with parameters optimized in ref to mimic the studied system. The gray circles represent polyelectrolyte units (both dissociated and nondissociated) and the black circles represent hydrophobic units.…”
The behavior of amphiphilic polyelectrolyte shells of micelles with kinetically frozen hydrophobic cores in aqueous solutions was studied by self-consistent field calculations. The calculations emulate the behavior of annealed (weak) shell-forming polyelectrolyte chains, e.g., poly(methacrylic acid), PMA, containing a relatively low fraction of strongly hydrophobic units, e.g., polystyrene, PS. The hydrophobic units are arranged either in sequences, or are distributed uniformly in the shell-forming chains. The analysis of concentration profiles of individual species reveals strong segregation and important self-organization of hydrophobic units in the shell. Hydrophobic units either adsorb at the core, or form small hydrophobic domains relatively far from the core. The transition from one type of conformations to the other, which depends on the position of hydrophobic sequence in the polyelectrolyte chain, can be provoked by changes in pH and ionic strength. The behavior of shell-forming chains composed of a long inner polyelectrolyte sequence (grafted to the micellar core), a short middle hydrophobic sequence and a peripheral polyelectrolyte sequence is of interest. The calculations yield a bimodal distribution of hydrophobic units as a function of the radial distance from the core/shell interface. It means that two types of chains (fairly stretched and loop-forming ones) coexist in the shell.
“…The study and characterization of polymer and polyelectrolyte spherical brushes have received considerable attention including experimental works, 41,42 theoretical 33,43,44 and selfconsistent field ͑SCF͒ developments, [44][45][46][47][48][49][50][51] as well as numerical simulations. 17,32,42,[52][53][54][55][56][57][58] The determination of the pairwise interaction [59][60][61][62][63][64] and the study of solutions of spherical brushes [65][66][67][68] have also been studied extensively. Nonetheless, despite the large insight obtained from these works, the behavior of spherical brushes in constrained geometries is still poorly understood and has only been addressed in few works: the behavior of spherical brushes and star polymers within slit geometries has been recently addressed by Romiszowski-Sikorski, 69 while the behavior of concave spherical brushes and three layer onion type micelles has been studied by Prochazka and co-workers.…”
We present an extensive numerical study on the behavior of spherical brushes confined into a spherical cavity. Self-consistent field (SCF) and off-lattice Monte Carlo (MC) techniques are used in order to determine the monomer and end-chain density profiles and the cavity pressure as a function of the brush properties. A comparison of the results obtained via SCF, MC, and the Flory theory for polymer solutions reveals SCF calculations to be a valuable alternative to MC simulations in the case of free and softly compressed brushes, while the Flory's theory accounts remarkably well for the pressure in the strongly compressed regime. In the range of high compressions, we have found the cavity pressure P to follow a scale relationship with the monomer volume fraction v, P approximately v(alpha). SCF calculations give alpha=2.15+/-0.05, whereas MC simulations lead to alpha=2.73+/-0.04. The underestimation of alpha by the SCF method is explained in terms of the inappropriate account of the monomer density correlations when a mean field approach is used.
“…Reversible association of the studied sample is a favorable condition for the study, but the PE block bears the C12 group from the chain transfer agent at its free end, which modifies and complicates the association behavior. We studied the behavior of hydrophobically modified chains in micellar shells some time ago 66,[73][74][75][76][77][78][79][80][81] and found that a fraction of the modified shell-forming chains recoil back towards the core, but the other PE chains remain highly stretched with hydrophobic groups localized in the outermost part of the shell. At finite polymer concentrations, when the micelles are relatively close to each other, C12 groups behave as stickers and form bridges which temporarily interconnect several core/shell micelles.…”
The paper describes successful preparation of onion micelles by sequential combination of self-assembly of amphiphilic polyelectrolytes (PE) in aqueous media and electrostatic coassembly of core/shell micelles formed in the first step with the oppositely charged doublehydrophilic copolymer. Experimental study and computer modeling (dissipative particle dynamics with explicit electrostatics) aimed at important features and trends of the assembly process were motivated by the controversy between the easiness of the process deduced from thermodynamic considerations and the low number of successful literature reports. The results show that onion micelles can be prepared if the studied system fulfils certain thermodynamic criteria and avoids kinetic obstacles. Nevertheless, the formation of well-developed onion micelles requires some hydrophobicity of PE backbones and their incompatibility with the soluble block. Otherwise, irregular low-density gel-like associates are formed. The increase in PE hydrophobicity and incompatibility promotes the assembly and improves the uniformity and spherical shape of onion micelles.
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