Cylindrical Polyelectrolyte Brushes Research Articles

Cylindrical brushes with ionized side chains: Scaling theory revisited.

We revisit the classic scaling model of a cylindrical polyelectrolyte (PE) brush focusing on molecular brushes with stiff backbones and dispersions of polymer-decorated nanorods. Based on the blob representation we demonstrate that similarly to the case of planar PE brushes, separation of intra- and intermolecular repulsions between charges leads to novel scaling regimes for cylindrical PE brushes in salt-added solution and a sharper decrease in its thickness versus salt concentration dependence. These theoretical predictions may inspire further comprehensive experimental research and computer simulations of synthetic and biopolyelectrolyte cylindrical brushes.

Scaling Theory of Strongly Charged Cylindrical Polyelectrolyte Brushes

Scaling theory of charged cylindrical polyelectrolyte brushes is developed. The dependence of brush thickness on the grafting density, charge fraction, and chain length is analyzed. A full phase diagram is established. Characteristics and boundaries between different regimes of cylindrical polyelectrolyte brushes are summarized. Special attentions are paid to electrostatic interaction induced stiffening and counterion condensation effects. If the Bjerrum length of the solution is larger than the Kuhn length of the polyelectrolyte chains, counterion condensation occurs in the strongly charged polyelectrolyte brushes. On the contrary, the electrostatic interaction stretches the strongly charged grafted polyelectrolyte chains to their contour length.

A Facile Polymer Templating Route Toward High‐Aspect‐Ratio Crystalline Titania Nanostructures

High-aspect-ratio rutile and anatase hybrid nanowires are produced via a template-directed process using a novel cylindrical polyelectrolyte brush template. Loading the highly negatively charged 1D templates with pre-synthesized TiO(2) nanocrystals, results in the fabrication of soluble crystalline TiO(2) hybrid nanowires.

Association of a Cylindrical Polyelectrolyte Brush with Tetravalent Counterions

Cylindrical poly(styrene sulfonate) brushes were combined with a tetravalent double-DABCO based counterion. With increasing addition of counterion, hydrodynamic radius and radius of gyration decrease and AFMreveals a conformation change from wormlike to curled structures. Rg/Rh changes from 1.3 to 0.9. Above charge stoichiometry, brushes become interconnected into finite size assemblies, which are stable in aqueous solution for charge ratios (ratio of the molar concentration of charged counterion groups to the molar concentration of charged monomer units of the polymer brush) 1 < l < 1.2. They are compact and consist of the brushes in curled (bent) conformation, which is in difference to network-like aggregates from cylindrical poly(styrene sulfonate) brushes with tetravalent porphyrin counterions (Gröhn et al. Macromolecules 2009) and to a wormlike - bent conformation - helix transition found for another brush counterion system (Müller et al. Soft Matter 2009).

Direct Synthesis of Poly(potassium 3-sulfopropyl methacrylate) Cylindrical Polymer Brushes via ATRP Using a Supramolecular Complex With Crown Ether

A supramolecular complex between an ionic monomer 3-sulfopropyl methacrylate (SPMAK) and crown ether 18-crown-6 (18C6) has been employed to prepare a strong anionic cylindrical polyelectrolyte brush poly(potassium 3-sulfopropyl methacrylate) (PSPMAK) by atom transfer radical polymerization (ATRP) in polar solvent dimethyl sulfoxide (DMSO). This strategy solved the problem of the solubilities of the incompatible hydrophobic poly-initiator and hydrophilic ionic monomer. The formation of the PSPMAK brush is well proven by (1) H NMR, aqueous gel permeation chromatography (GPC), dynamic light scattering (DLS), static light scattering (SLS), atomic force microscopy (AFM), and cryogenic transmission electron microscopy (cryo-TEM) measurements. Cleavage of the side chains and further analysis reveal that the initiating efficiency of the polymerization is as low as 0.35.

Nanomechanical behaviors of microcantilever-based single-stranded DNA chips induced by counterion osmotic effects

Experiments show that deflections of microcantilever-DNA chip can be induced by many factors, such as grafting density, hybridization efficiency, concentration, length and sequence of DNA molecules, buffer salt concentration, time, and temperature variation. However, there are few theoretical works on microcantilever-DNA chips. The present paper is aimed to study the influence of counterion effects of single-stranded DNA (ssDNA) polyelectrolyte solution on the nanomechanical behaviors of microcantilever-based ssDNA chips during packing process. First, the effect of osmotic pressure induced by ingress of counterions into DNA brush structures is studied with Hagan's model for a cylindrical polyelectrolyte brush system on the basis of Poisson-Boltzmann distribution hypothesis. Second, Zhang's two-variable method for a laminated cantilever is used to formulate a four-layer energy model for ssDNA chips with weak interactions. Third, the influence of grafting density, ssDNA chain length, and salt concentration on packing deflection is investigated using the principle of minimum energy. The predictive tendency is qualitatively similar to those observed in some related ssDNA chip experiments. The difference between the four-layer model and the simplified two-layer model for ssDNA chips is also discussed.

Manipulating the Morphologies of Cylindrical Polyelectrolyte Brushes by Forming Interpolyelectrolyte Complexes with Oppositely Charged Linear Polyelectrolytes: An AFM Study

We present a study on water-soluble interpolyelectrolyte complexes (IPECs) formed by cationic cylindrical polyelectrolyte brushes (CPBs) and linear anionic poly(sodium styrenesulfonate) (PSSNa) using atomic force microscopy (AFM). The IPECs were prepared by dialysis of salt-containing solutions of the two polymeric components. The morphologies of the IPECs could be tuned by changing the charge ratio between the two polyelectrolytes, Z(-/+). Addition of increasing numbers of short PSSNa chains induced morphology changes of host CPBs from worms through intermediate pearl-necklace structures to fully collapsed spheres. Extremely long guest PSSNa caused the full collapse of the brushes to spheres even at very low charge ratios without intermediate states. In both cases we observe "disproportionation", that is, inhomogeneous distribution of the PSS chains between the CPB for Z(-/+) < 1. Unexpected micrometer-scale core-shell cylindrical objects were found by directly mixing CPBs with long PSSNa, which might be nonequilibrium structures caused by the kinetically controlled IPEC formation.

Soft matter nanoparticles with various shapes and functionalities can form through electrostatic self-assembly

Electrostatic self-assembly is an important area presenting fascinating opportunities for the design of functional and responsive nanostructures. In this contribution we highlight a recent approach that allows the formation of nanoscale assemblies with a variety of shapes – spheres, rods, hollow spheres, networks and rings – from macroions and multivalent organic counterions as building blocks. Combination of electrostatics and secondary forces is key to a directed structure formation, while the charged nature of the assembled nanoparticles gives rise to their stability in solution. The concept allows the formation of nanoassemblies which respond to external stimuli. Macroionic building blocks can range from linear polyelectrolytes over ionic dendrimers to cylindrical polyelectrolyte brushes, and counterions can be ionic dye molecules, porphyrins or other stiff or semiflexible ions. The versatility and potential of the strategy are discussed.

Numerical Self‐Consistent Field Theory of Cylindrical Polyelectrolyte Brushes

AbstractA single cylindrical polyelectrolyte brush is studied by self‐consistent field (SCF) theory and the results compared with predictions from scaling theory. It is shown that the SCF theory results give the general trends as well as insight into the crossover regions between different regimes. The density profiles of the polyions and small ions indicate that the systems are locally electroneutral. The salted brush bears characteristics similar to those of a neutral brush. Counter‐intuitively, the chains are not uniformly stretched in the osmotic regime. The free‐end monomers shift to the outer region and an exclusion zone appears and grows with decreasing of salt concentration.magnified image

Influence of Counterion Valency on the Conformational Behavior of Cylindrical Polyelectrolyte Brushes

Using a dissipative particle dynamics approach, we study the conformations and interactions of a cylindrical polyelectrolyte brush (CPB) with added salt. The effects of counterion valency on the conformational behaviors of the CPB are analyzed in detail by considering various parameters like the distribution of bond lengths, the mean distance between two grafting points, the order parameter of side chains, etc. The lyotropic behavior of the CPB is also investigated through examining the backbone persistence. Our simulations demonstrate that the presence of the multivalent counterions can induce the collapse of the CPB, leading to various conformations. We identify a horseshoe to helical to coil-like conformation transition with increasing counterion valency. An important factor for the collapse of the CPB is the fact that the strong condensation of counterions induced by the higher electrostatic correlations decreases the osmotic pressure inside the brush. It is found that the ratio of the backbone persistence to the diameter of the CPB, l(p)/d, can only be affected to a slight extent by changing the counterion valency and the side chain length. These results may provide a valuable guideline that can be used to tailor the microstructure of the systems and to yield desired macroscopic behaviors.

Dissipative Particle Dynamics Simulations of Complexes Comprised of Cylindrical Polyelectrolyte Brushes and Oppositely Charged Linear Polyelectrolytes

Dissipative particle dynamics (DPD) approach is used to investigate the conformational behaviors and interactions of the complex between a cylindrical polyelectrolyte brush (CPB) and linear polyelectrolytes (LPs) with opposite charges. The effective complex between CPB and LPs and its dependence on the amount and length of LPs are examined. It is found that the CPB conformation presents collapse and reswelling with the increasing amount of LPs. The collapse is caused by the replacement of monovalent CPB counterions by LPs and the condensation of LPs on the CPB which reduce the osmotic pressure inside the brush. The swelling of the collapsed CPB is induced by the excluded volume effects of additionally absorbed LPs and LP counterions. The results show that the addition of LPs can not enhance the effective complex between the CPB and LPs when the total charge of LPs exceeds that of CPB. Our simulation also demonstrates that the increase of the LP length leads to a shrinking of the CPB which consequently exhibits rod-like or spherical conformations. The most effective complex between a CPB and LPs can be reached only when the contour length of LPs is not less than that of the CPB side chain.

Finite-Size Networks from Cylindrical Polyelectrolyte Brushes and Porphyrins

We report on the electrostatic self-assembly of negatively charged cylindrical polystyrenesulfonate (NaPSS) brushes and stiff organic counterions of different valency. In particular, the tetravalent cationic porphyrin meso-tetrakis(4-(trimethylammonium)phenyl)porphyrin (TAPP) yielded two new supramolecular architectures that are stable in aqueous solution. The porphyrin binds to the polyelectrolyte brush due to electrostatic and secondary π−π interactions and can further interconnect the brushes to nanoscale networks. In salt solution individual porphyrin-decorated cylindrical brushes were obtained. Structures formed are characterized by UV−vis spectroscopy, atomic force microscopy (AFM), cryo-transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS), and dynamic light scattering (DLS). In order to study porphyrin aggregates by DLS, an IR laser setup (λ = 831.5 nm) was used. The new morphologies have potential as functional structures in molecular electronics and pharmaceutics.

Dissipative particle dynamics simulations on overcharged cylindrical polyelectrolyte brushes with multivalent counterions

Employing a dissipative particle dynamics (DPD) approach, we investigate the overcharging behaviors of a cylindrical polyelectrolyte brush (CPB) in the presence of multivalent counterions. The conformational change of the CPB is considered with the increasing concentration of multivalent counterions. We gain insight into the re-expansion mechanism of the CPB by examining various parameters. The influence of the overcharging on the possibility of lyotropic behavior for the CPB is discussed based on the ratio of the persistence length (lp) to the diameter of the CPB (d). Our simulations demonstrate that the CPB can exhibit a horseshoe–rod–helix–rod–horseshoe conformational change from the collapse to the re-expansion regimes. The excluded-volume effects of the multivalent counterions and the monovalent positive ions absorbed by the CPB in the re-expansion regime increase its size, causing a re-expansion of the brush. Our simulations show that the increase of the ratio lp/d turns to be much slower in the expansion regime, demonstrating that excess addition of the salt with multivalent counterions does not improve efficiently the lyotropic behavior of the CPB. These findings provide guidelines for tailoring the structures of the CPB and thereby controlling the interaction between the CPB and couterions.

Nano-patterned structures in cylindrical polyelectrolyte brushes assembled with oppositely charged polyions

We demonstrate that the electrostatically driven association of cylindrical polyelectrolyte brushes (CPBs) with oppositely charged linear polyelectrolytes (PEs) in dilute aqueous solution gives rise to well-defined and colloidaly stable (not undergoing secondary aggregation with time) polymeric nano-assemblies representing novel water-soluble interpolyelectrolyte complexes (IPECs). Each complex particle comprises a single “host” CPB whose charge is undercompensated by the “guest” PE chains. Molecular dynamics (MD) simulations were used to probe the structural organization of these nano-assemblies. We find that they spontaneously adopt the shape of a necklace of complex coacervate pearls which comprise charged monomer units of CPB and those of the guest PEs in approximately stoichiometric (1:1) ratio. Each complex coacervate pearl is decorated by a star-like PE corona formed by the branches of the CPB not involved in the interpolyelectrolyte complexation. Repulsive interactions between these coronas stabilize the periodic intra-molecular structure and assure aggregative stability of the IPEC derived from the single CPB. AFM images of the complex particles deposited on mica unambiguously support their pearl-necklace structural organization. Our work theoretically predicts and experimentally confirms a possibility to tune the periodicity of one-dimensional intramolecular nano-patterned structures at will by a variation of the base-molar ratio between the oppositely charged macromolecular building blocks incorporated in the polymeric nano-assembly, that is, by a variation of the stoichiometry of the IPECs.

Effect of the Ionic Strength and pH on the Equilibrium Structure of a Neurofilament Brush

Using the numerical model of Scheutjens and Fleer, we investigated, on a self-consistent field level, the equilibrium structure of the neurofilament brush formed by projection domains of the constituent NF-H, NF-M, and NF-L proteins. The phosphorylation of such a brush is a major regulatory process that triggers the relocation of the H tails from the NF core to the brush periphery. We explore how the pH and the ionic strength affect the rearrangements in the NF brush structure upon phosphorylation. We demonstrate that the translocation of H tails in an individual NF occurs as a sharp cooperative transition below and up to the physiological salt concentration. Regularities of this process are reminiscent of the collapse-to-stretching transition in a cylindrical polyelectrolyte brush in a poor solvent. The effect of pH at physiological ionic strength is noticeable only in the acidic range and is more pronounced for a dephosphorylated NF.

730 Preparation of poly- and monoclonal antibodies against Alzheimer's PS-1 molecule

Using the numerical model of Scheutjens and Fleer, we investigated, on a self-consistent field level, the equilibrium structure of the neurofilament brush formed by projection domains of the constituent NF-H, NF-M, and NF-L proteins. The phosphorylation of such a brush is a major regulatory process that triggers the relocation of the H tails from the NF core to the brush periphery. We explore how the pH and the ionic strength affect the rearrangements in the NF brush structure upon phosphorylation. We demonstrate that the translocation of H tails in an individual NF occurs as a sharp cooperative transition below and up to the physiological salt concentration. Regularities of this process are reminiscent of the collapse-to-stretching transition in a cylindrical polyelectrolyte brush in a poor solvent. The effect of pH at physiological ionic strength is noticeable only in the acidic range and is more pronounced for a dephosphorylated NF.