Stoichiometric polyelectrolyte complexes of ionic block copolymers and oppositely charged polyions

Micellization in dilute solutions of diblock copolymers with a polyelectrolyte and a hydrophilic nonionic blocks and oppositely charged polyions is studied using mean-field theory. In aqueous solutions the micelle core consists of the polyelectrolyte complex (PEC) while the corona is formed by hydrophilic blocks of the block copolymers. Describing PEC as a globule in the framework of the Lifshitz [Zh. Eksp. Teor. Fiz. 55, 2408 (1968)] globule theory we calculate the surface tension of the micellar core/solvent interface as a function of the polyion degree of ionization, solvent quality, and concentration of low-molecular-mass salt. The equilibrium aggregation number of starlike micelles formed by block copolymers and homopolymers of opposite charge at stoichiometric mixture compositions is found as a function of the system parameters. It is shown that micelles disintegrate upon addition of salt.     

Polyion complex nanomaterials from block polyelectrolyte micelles and linear polyelectrolytes of opposite charge: 1. Solution behavior

The present study investigates whether block polyelectrolyte micelles can form soluble complexes upon interaction with oppositely charged linear polyelectrolytes. The phase behavior and molecular characteristics of the complexes were examined by turbidimetry, phase analysis, dynamic light scattering, and sedimentation velocity techniques. At an excess of polyelectrolyte micelles, soluble complexes were formed either independently on the route of preparation or, for select linear polyelectrolytes, through routes that avoided macrophase separation. Such soluble complexes are in a thermodynamic equilibrium state for all polyion pairs. The hydrodynamic sizes and sedimentation coefficients did not depend on the chemical nature of the linear polyelectrolyte, but were determined by the charge ratios and the hydrodynamic properties of the initial micelles. At an excess of linear polyelectrolyte, complex solubility and molecular characteristics depended on the chemical nature of the linear polyelectrolyte. In this region, linear polyelectrolytes formed soluble complexes with micelles if soluble complexes could be formed with the corresponding linear analogues of the block polyelectrolyte.     

PBMA-b-PSt磺化嵌段离聚体在DMF溶液中的聚集行为

采用激基缔合物荧光光谱法研究了轻度磺化聚甲基丙烯酸丁酯－b－聚苯乙烯（PBMA-b－PSt）嵌段离聚体在极性溶剂N，N－二甲基甲酰胺（DMF）溶液中的聚集行为；发现嵌段离聚体的磺化度和浓度强烈影响溶液中聚合物链的聚集态结构，不同的磺化度样品具有不同的临界聚集浓度；随磺化度增加，聚合物链缠绕密集，形成具有多苯环的聚集体，而且当磺化度为摩尔分数x＝3．59％时，荧光发射光谱最大发射峰波长出现最大红移，临界聚集浓度最低，说明最容易形成多苯环聚集体，该磺化点可以认为是磺化聚甲基丙烯酸丁酯－b－聚苯乙烯体现离聚体行为和聚电解质行为的临界磺化度。     

Ionic micelles in solutions of polyelectrolytes and block copolymers with oppositely charged blocks: Computer simulation

Complexation in solutions of strongly charged polyelectrolytes and diblock copolymers composed of oppositely charged and neutral blocks were studied via the molecular dynamics method. Stoichiometric micellar complexes formed in a dilute solution represent cylindrical brushes whose conformation is determined by the linear charge density on the polyelectrolyte and by temperature. As the concentration of macromolecules increases, the orientational ordering of anisotropic ionic micelles takes place. The complexation can induce the stiffening of the polyelectrolyte chain.     

Molecular bottle brushes in a solution of semiflexible polyelectrolytes and block copolymers with an oppositely charged block: a molecular dynamics simulation

Using a coarse-grained model, we performed molecular dynamics simulations of the electrostatically driven self-assembly of strongly charged polyelectrolytes and diblock copolymers composed of oppositely charged and neutral blocks. Stoichiometric micelle-like complexes formed in a dilute solution represent cylindrical brushes whose conformation is determined by the linear charge density on the polyelectrolyte and by temperature. The core-shell morphology of the cylindrical brushes is proven. The core of these anisotropic micelles consists of an insoluble complex coacervate formed by the ionic chains and a shell made up of the neutral solvophilic blocks. As the concentration of macromolecules increases, the orientational ordering of ionic micelles takes place. The complexation can induce effective steric stiffening of the polyelectrolyte chains.     

Effective intramolecular interactions in weakly charged polyelectrolytes: Relation to structural behavior of solution

A self-consistent integral equation theory in the form of a hybrid Monte Carlo/PRISM computation scheme was used to study a polyelectrolyte solution. The static conformational and structural properties of polyions of different rigidities in a good solvent were studied with explicit allowance for counterions over a wide concentration range. An analysis of the calculated effective potentials and correlation functions confirms the presence of effective attraction between units of the charged polymer in semidilute and concentrated solutions; this attraction leads to the collapse of polyions under certain conditions. It was shown that the cause of effective attraction is the dipole-dipole interaction of ion pairs. For the region of polyelectrolyte transition from the semidilute to the concentrated state of solution, the results qualitatively agree with experimental data and theoretical predictions. Visualized images of conformations in the test range of parameters are given.     

Mixed micelles of oppositely charged poly(N‐isopropylacrylamide) diblock copolymers

Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N‐isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two‐dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D ¹H NMR NOESY), dynamic light scattering, and small angle X‐ray scattering measurements. Well‐defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D ¹H NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1457–1469     

Cylindrical cell model for the electrostatic free energy of polyelectrolyte complexes

Associative phase separation (complex coacervation) in a mixture of oppositely charged polyelectrolytes can lead to different types of (inter-)polyelectrolyte complexes (soluble micelles, macroscopic precipitation). In a previous report [Langmuir 2004, 20, 2785-2791], we presented a model for the electrostatic free energy change when (weakly charged) polyelectrolyte forms a homogeneous complex phase. The influence of ionization of the polymer on the electrostatic free energy of the complex was incorporated but the influence of complex density neglected. In the present effort, cylindrical cells are assumed around each polyelectrolyte chain in the complex, and on the basis of the Poisson-Boltzmann equation, the electrostatic free energy is calculated as a function of the complex density. After combination with Flory-Huggins mixing free energy terms and minimization of the total free energy, the equilibrium complex density is obtained, for a given ratio of polycations to polyanions in the complex. The analysis is used in an example calculation ofpolyelectrolyte film formation by alternatingly applying a polycation and a polyanion solution. The calculation suggests that the often observed exponential growth of a polyelectrolyte film when the polymer is weakly charged has a thermodynamic origin: the polyelectrolyte complex shifts repeatedly between two equilibrium states of different densities and compositions. However, when the polyelectrolytes are strongly charged the difference in the compositions between the two equilibrium states is very small, and exponential growth by an absorption mechanism is no longer possible.     

Surfactant polymer interactions between strongly interacting cationic surfactants and anionic polyelectrolytes from conductivity and turbidity measurements

The interactions between oppositely charged surfactant/polymer mixtures have been studied using conductivity and turbidity measurements. The dependence of aggregation phenomenon on the chain length and head group modifications of conventional cationic surfactants, i.e., hexadecyl- (HTAB), tetradecyl- (TTAB), and dodecyltrimethylammonium bromides (DTAB) and dimeric cationic surfactants, i.e., decyl- (DeDGB) and dodecyldimethylgemini bromides (DDGB), is investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolytes at critical aggregation concentration (cac). The cac values are considerably lower than the critical micelle concentration (cmc) values for the same surfactant. After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in aqueous polyelectrolyte than in pure water. Among the conventional and dimeric cationic surfactants, DTAB and DeDGB, respectively, have been found to have least interactions with oppositely charged polyelectrolytes.     

Micellization through complexation of oppositely charged diblock copolymers: Effects of composition,polymer architecture,salt of different valency,and thermoresponsive block

The structural and electrical characteristics of polyelectrolyte complex micelles (PCMs) formed by mixing of oppositely charged double hydrophilic copolymers are studied by means of molecular dynamics simulations. In mixtures of linear diblock copolymers we found that the preferential aggregation number N_p of PCMs is a universal function of the ratio γ_± of the total positive to total negative charges of the mixture. The addition of divalent salts ions induces a secondary micellization. In mixtures of copolymers bearing a common neutral thermoresponsive block, micelles with contracted corona consisting of thermoresponsive blocks and complex polyelectrolyte core are formed at low salt concentration and temperature far away the biphasic regime. At high salt concentration and temperature in the biphasic regime, reversed micelles are obtained. In equimolar mixtures of linear copolymers with miktoarm stars we found that N_p of PCMs decreases as the number of charged branches of miktoarm copolymer increases. The shape of micelles progressively changes from spherical to worm-like with the increase of number of branches of miktoarm copolymers. Our findings are in full agreement with existing experimental and theoretical predictions and provides new and additional insights.     

Comparison of complex coacervate core micelles from two diblock copolymers or a single diblock copolymer with a polyelectrolyte

With light scattering titrations, we show that complex coacervate core micelles (C3Ms) form from a diblock copolymer with a polyelectrolyte block and either an oppositely charged polyelectrolyte, a diblock copolymer with an oppositely charged polyelectrolyte or a mixture of the two. The effect of added salt and pH on both types of C3Ms is investigated. The hydrodynamic radius of mixed C3Ms can be controlled by varying the percentage of oppositely charged polyelectrolyte or diblock copolymer. A simple core-shell model is used to interpret the results from light scattering, giving the same trends as the experiments for both the hydrodynamic radii and the relative scattering intensities. Temperature has only a small effect on the C3Ms. Isothermal titration calorimetry shows that the complexation is mainly driven by Coulombic attraction and by the entropy gain due to counterion release.     

Directed motion of a polyelectrolyte micelle along tethered chains of oppositely charged polyelectrolyte brush

The complexation of different single polyelectrolyte (PE) micelles formed by linear diblock copolymers with oppositely charged brushes with varying grafting densities and charge content was studied by means of molecular dynamics simulations using the primitive model. We found that all micelles perform a directed motion along the vertical z axis on the grafted surface where they trapped while on the other axes the motion is restricted in a circle in which the diameter decreases with the increase of the hydrophilic length of the linear diblock copolymer. The motion of micelles is characterized as super diffusion inside brushes with low densities and low charge content. At high grafting densities and charge content the diffusion becomes Fickian or slightly subdiffusive. The number of the absorbed brush chains on the micelle corona increases almost monotonically with the increase of brush grafting density or with the decrease of charge content. The distance from the surface in which the micelle is trapped can be controlled by the charge density along the grafted PE chain. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 621–631     

Physicochemical properties of pH-controlled polyion complex (PIC) micelles of poly(acrylic acid)-based double hydrophilic block copolymers and various polyamines

The physicochemical properties of polyion complex (PIC) micelles were investigated in order to characterize the cores constituted of electrostatic complexes of two oppositely charged polyelectrolytes. The pH-sensitive micelles were obtained with double hydrophilic block copolymers containing a poly(acrylic acid) block linked to a modified poly(ethylene oxide) block and various polyamines (polylysine, linear and branched polyethyleneimine, polyvinylpyridine, and polyallylamine). The pH range of micellization in which both components are ionized was determined for each polyamine. The resulting PIC micelles were characterized using dynamic light scattering and small-angle X-ray scattering experiments (SAXS). The PIC micelles presented a core–corona nanostructure with variable polymer density contrasts between the core and the corona, as revealed by the analysis of the SAXS curves. It was shown that PIC micelle cores constituted by polyacrylate chains and polyamines were more or less dense depending on the nature of the polyamine. It was also determined that the density of the cores of the PIC micelles depended strongly on the nature of the polyamine. These homogeneous cores were surrounded by a large hairy corona of hydrated polyethylene oxide block chains. Auramine O (AO) was successfully entrapped in the PIC micelles, and its fluorescence properties were used to get more insight on the core properties. Fluorescence data confirmed that the cores of such micelles are quite compact and that their microviscosity depended on the nature of the polyamine. The results obtained on these core–shell micelles allow contemplating a wide range of applications in which the AO probe would be replaced by various cationic drugs or other similarly charged species to form drug nanocarriers or new functional nanodevices.     

The combination of ionic surfactants with polyelectrolytes-a new material for membranes?

The combination of two oppositely charged polyelectrolytes results in polyelectrolyte complexes. The simultaneous interfacial reaction between the different polyions leads to formation of polyelectrolyte complex membranes. Some of these have a very good performance in the membrane process pervaporation, especially for dehydration of organic liquids. The combination of a polyelectrolyte with an ionic surfactant of opposite charge results like-wise membranes but with other separation properties. The differences between the two types of membranes, formed from cellulosesulfate in combination with cationic polyelectrolytes or cationic surfactants, will be discussed.     

Electrostatic self-assembly of neutral and polyelectrolyte block copolymers and oppositely charged surfactant

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.     

Structure and phase equilibria of mixtures of the complex salt hexadecyltrimethylammonium polymethacrylate, water and different oils

This work reports on phase diagrams for mixtures of a complex salt formed by a cationic surfactant and an oppositely charged polyelectrolyte, hexadecyltrimethylammonium polymethacrylate, in binary mixtures with water and in ternary mixtures containing water and organic solvents of different polarity ('oils'): decanol, octanol, p-xylene and cyclohexane. The liquid crystalline structures formed were identified by small angle X-ray scattering measurements, which also provided information about changes in the size of the aggregates as a function of the system composition. These results are analysed in comparison with others previously reported [Bernardes et al., J. Phys. Chem. B 110 (2006) 10332-10340] for the analog complex formed with polyacrylate and, in general, reveal that the presence of an extra methylene group in the polymer chain does not produce significant changes in the complex phase diagrams nor in the structure of the liquid crystalline phases formed. Additionally, the obtained results confirm once more the approach used to analyze these kinds of systems formed by polymer and oppositely charged surfactant.     

Preparation and characterization of polyion complex micelles with a novel thermosensitive poly(2-isopropyl-2-oxazoline) shell via the complexation of oppositely charged block ionomers

Novel thermosensitive polyion complex (PIC) micelles were prepared in an aqueous medium based on the complexation of a pair of oppositely charged block ionomers, poly(2-isopropyl-2-oxazoline)-b-poly(amino acid)s (PiPrOx-b-PAA), containing thermosensitive PiPrOx segments. The controlled synthesis of PiPrOx-b-PAA was achieved via the ring-opening anionic polymerization of N-carboxyanhydrides (NCA) of either eta-benzyloxycarbonyl-l-lysine (Lys(Z)-NCA) or beta-benzyl-l-aspartate (BLA-NCA) with omega-amino-functionalized PiPrOx macroinitiators and the subsequent deprotection reaction under acidic or basic conditions. Gel permeation chromatography (GPC) and 1H NMR spectroscopy revealed that the syntheses of two block ionomers, poly(2-isopropyl-2-oxazoline)-b-poly(l-lysine) [PiPrOx-P(Lys)] and poly(2-isopropyl-2-oxazoline)-b-poly(aspartic acid) [PiPrOx-P(Asp)], proceeded almost quantitatively to give samples with a narrow molecular weight distribution (Mw/Mn 相似文献   

The interaction between sodium alkyl sulfate surfactants and the oppositely charged polyelectrolyte, polyDMDAAC, at the air-water interface: the role of alkyl chain length and electrolyte and comparison with theoretical predictions

The effect of alkyl chain length and electrolyte on the adsorption of sodium alkyl sulfate surfactants and the oppositely charged polyelectrolyte, polyDMDAAC, at the air-water interface has been investigated by surface tension and neutron reflectivity. The variations in the patterns of adsorption and surface tension behavior with alkyl chain length and electrolyte are discussed in the context of the competition between the formation of surface active surfactant/polyelectrolyte complexes and polyelectrolyte/surfactant micelle complexes in solution. A theoretical approach based on the law of mass action has been used to predict the surface effects arising from the competition between the formation of polyelectrolyte/surfactant surface and solution complexes and the formation of free surfactant micelles. This relatively straightforward model is shown to reproduce the principal features of the experimental results.     

Absorption of ionic amphiphils by oppositely charged polyelectrolyte gels

Slightly cross-linked polyelectrolytes absorb oppositely charged surfactants in aqueous media. Transfer of amphiphilic ions from solution into the swollen network proceeds as a frontal heterogeneous cooperative reaction causing a collapse of the original polyelectrolyte gel. Small and wide angle X-ray diffraction data show that electrostatic complex formed as a result of the reaction consists of lamellar type surfactant micelles embedded in a polyelectrolyte network. It is also shown that such complexes contain equimolar amount of surfactant ions and ionized polyelectrolyte units paired with amphiphil head groups. In other words a charged network is not able to bind surplus oppositely charged surfactant ions. However, it is still able to solubilize a substantial amount of a nonionized surfactant. Chemical structure of surfactants strongly affect internal structure of lamellae and stability of the complexes.