Interactions between hairy rod anionic conjugated polyelectrolytes and nonionic alkyloxyethylene surfactants in aqueous solution: observations from cloud point behaviour

The effect of three anionic, hairy-rod fluorene based conjugated polyelectrolytes on the cloud points of the alkyloxyethylene surfactants C10E3, C12E4, C12E5, and C12E6 has been studied in aqueous solution. Although the association behaviour of these rigid polymers with surfactants is different from that of more flexible polyelectrolytes, both types of polymers are seen to increase the cloud points, probably as a consequence of associative interactions. The possible importance of Coulombic interactions is suggested by the decrease in cloud points with these systems in the presence of NaCl. With the conjugated polyelectrolytes, the effect appears to be most pronounced with poly[9,9-bis(4-phenoxybutylsulfonate)fluorene-co-2,5-thienylene], which may result from specific interactions between oxyethylene groups and the thiophene ring. The value of cloud point behaviour in designing water based formulations for preparation of devices of these conjugated polyelectrolytes is discussed.     

Benzylic and pyridinium head groups controlled surfactant-polymer aggregates of mixed cationic micelles and anionic polyelectrolytes

The oppositely charged electrostatic interactions between cationic single and mixed micelles of benzyldimethylhexadecylammonium chloride (BHDACl), hexadecylpyridinium bromide (HPyBr), hexadecylpyridinium chloride (HPyCl), and their mixtures with anionic polyelectrolytes, namely carboxymethylcellulose sodium salt (CMC) and polystyrene sulfonate sodium salt (PSS) were studied with the help of conductivity (), viscosity (), turbidity (), and NMR studies. showed single aggregation process, which was represented by apparent critical micelle concentration, acmc, of each surfactant in aqueous polyelectrolyte solution. Both and demonstrated strong electrostriction effects in the case of BHDACl-polyelectrolyte systems due to weak electrostatic interactions in view of steric hindrances created by benzylic group of BHDACl. ¹H NMR results showed that the head group proton resonances of BHDACl upon incorporation of HPyBr or HPyCl in the presence of CMC or PSS remained identical to that in pure water, which demonstrated very weak interactions between BHDACl and polyelectrolytes. A less shielding of pyridinium head group protons by BHDACl in the presence of polyelectrolytes in comparison to that in pure water indicated favorable electrostatic interactions between pyridinium head groups and anionic polyelectrolytes. HPyBr in comparison to HPyCl showed stronger interactions with polyelectrolytes.     

Pseudo-Gated Adsorption with Negligible Volume Change Evoked by Halogen-Bond Interaction in the Nanospace of MOFs

The enhancement of gas adsorption utilizing weak interactions in porous compounds is highly demanding for the design of energy-efficient storage materials. Here, we present a rational design for such an adsorption process by using synergistic functions between dynamic motion in a local module and weak but specific host–guest interactions, that is, halogen-bond (XB) interactions in metal–organic frameworks (MOFs). We designed a new porous coordination polymer (PCP), that is, Br-PCP, the pore surfaces of which are decorated with −CH₂Br groups and could be useful for interaction with CO₂ molecules. In accordance with our anticipation, in-situ studies suggest that the adsorption step at approximately 54 kPa during CO₂ adsorption is indeed facilitated by XB interactions with little change in the structural volume. This approach of integrating flexible XB modules in rigid PCPs is applicable for designing advanced gas storage systems.     

Stimuli-Responsive Delivery of Antimicrobial Peptides Using Polyelectrolyte Complexes

Antimicrobial peptides (AMPs) are antibiotics with the potential to address antimicrobial resistance. However, their translation to the clinic is hampered by issues such as off-target toxicity and low stability in biological media. Stimuli-responsive delivery from polyelectrolyte complexes offers a simple avenue to address these limitations, wherein delivery is triggered by changes occurring during microbial infection. The review first provides an overview of pH-responsive delivery, which exploits the intrinsic pH-responsive nature of polyelectrolytes as a mechanism to deliver these antimicrobials. The examples included illustrate the challenges faced when developing these systems, in particular balancing antimicrobial efficacy and stability, and the potential of this approach to prepare switchable surfaces or nanoparticles for intracellular delivery. The review subsequently highlights the use of other stimuli associated with microbial infection, such as the expression of degrading enzymes or changes in temperature. Polyelectrolyte complexes with dual stimuli-response based on pH and temperature are also discussed. Finally, the review presents a summary and an outlook of the challenges and opportunities faced by this field. This review is expected to encourage researchers to develop stimuli-responsive polyelectrolyte complexes that increase the stability of AMPs while providing targeted delivery, and thereby facilitate the translation of these antimicrobials.     

Dye-surfactant interactions: a review

The present state of knowledge of the mechanisms of dye-surfactant interactions for "normal" aqueous micelles is surveyed. The nature of the forces which lead to the binding of dye molecules in micelles, the influence of the cationic, anionic or non-ionic character of a surfactant on the absorption and/or fluorescence behaviour (below and above the critical micelle concentration), ion-association processes and the influence of additives on these processes are discussed. Some discussion along these lines on related systems (reverse micelles, vesicles, polyelectrolytes) is included.     

Electrosteric Stabilization of Al(2)O(3), ZrO(2), and 3Y-ZrO(2) Suspensions: Effect of Dissociation and Type of Polyelectrolyte

The mechanisms of eight anionic polyelectrolytes stabilizing colloidal sized alpha-Al(2)O(3), pure ZrO(2), and Y(2)O(3)-doped ZrO(2) particles in aqueous solution are discussed. The polyelectrolytes studied were the Na(+) and NH(4)(+) salts of polyacrylic acid and polymethacrylic acid having different molecular weights. The particle-dispersant interactions were studied by measuring adsorption isotherms, particle size, thickness of adsorbed layer, and zeta potentials by elektrokinetic sonic analysis at different powder volume fractions (straight phi=0.01-0.3), pH, and electrolyte (KCl) content. The dissociation of the polyelectrolytes was studied by potentiometric titrations. The dissociation constant of the polymethacrylates was found to be 0.6 pH unit higher than that for the polyacrylates. High-affinity adsorption isotherms were observed over the pH range when the polyelectrolytes were fully ionized. The results show good correlation between adsorption isotherms and zeta potential data in systems of dispersed, dilute alumina particles. When particles and polymers were of equal charge (the same sign of charge) the polymer shell was thicker. At higher volume fractions (straight phi=0.3), and when alumina particles/added ammonium polyelectrolyte were of equal charge, a maximum in the absolute value of zeta potential resulted. Due to adsorption all the anionic polyelectrolytes studied provided electrosteric stabilization of the alpha-Al(2)O(3), and Y(2)O(3)-doped ZrO(2) suspensions by enhancing the zeta potential to 40 mV or over and by shifting the isoelectric point to lower pH, the low-molecular-weight polyelectrolytes decreasing the isoelectric point more than the polyelectrolytes having higher molecular weight. The polyelectrolytes studied failed to stabilize pure monoclinic ZrO(2) particles. Due to the shortness of the chain of polyelectrolytes studied, no bridging was observed between oppositely charged polyelectrolyte/alumina particles. Copyright 2000 Academic Press.     

Multi‐Stimuli‐Responsive Polymer Materials: Particles,Films, and Bulk Gels

Stimuli‐responsive polymers have received tremendous attention from scientists and engineers for several decades due to the wide applications of these smart materials in biotechnology and nanotechnology. Driven by the complex functions of living systems, multi‐stimuli‐responsive polymer materials have been designed and developed in recent years. Compared with conventional single‐ or dual‐stimuli‐based polymer materials, multi‐stimuli‐responsive polymer materials would be more intriguing since more functions and finer modulations can be achieved through more parameters. This critical review highlights the recent advances in this area and focuses on three types of multi‐stimuli‐responsive polymer materials, namely, multi‐stimuli‐responsive particles (micelles, micro/nanogels, vesicles, and hybrid particles), multi‐stimuli‐responsive films (polymer brushes, layer‐by‐layer polymer films, and porous membranes), and multi‐stimuli‐responsive bulk gels (hydrogels, organogels, and metallogels) from recent publications. Various stimuli, such as light, temperature, pH, reduction/oxidation, enzymes, ions, glucose, ultrasound, magnetic fields, mechanical stress, solvent, voltage, and electrochemistry, have been combined to switch the functions of polymers. The polymer design, preparation, and function of multi‐stimuli‐responsive particles, films, and bulk gels are comprehensively discussed here.     

Tuning smart microgel swelling and responsive behavior through strong and weak polyelectrolyte pair assembly

The layer-by-layer (LbL) assembly of polyelectrolyte pairs on temperature and pH-sensitive cross-linked poly(N-isopropylacrylamide)-co-(methacrylic acid), poly(NIPAAm-co-MAA), microgels enabled a fine-tuning of the gel swelling and responsive behavior according to the mobility of the assembled polyelectrolyte (PE) pair and the composition of the outermost layer. Microbeads with well-defined morphology were initially prepared by synthesis in supercritical carbon dioxide. Upon LbL assembly of polyelectrolytes, interactions between the multilayers and the soft porous microgel led to differences in swelling and thermoresponsive behavior. For the weak PE pairs, namely poly(L-lysine)/poly(L-glutamic acid) and poly(allylamine hydrochloride)/poly(acrylic acid), polycation-terminated microgels were less swollen and more thermoresponsive than native microgel, whereas polyanion-terminated microgels were more swollen and not significantly responsive to temperature, in a quasi-reversible process with consecutive PE assembly. For the strong PE pair, poly(diallyldimethylammonium chloride)/poly(sodium styrene sulfonate), the differences among polycation and polyanion-terminated microgels are not sustained after the first PE bilayer due to extensive ionic cross-linking between the polyelectrolytes. The tendencies across the explored systems became less noteworthy in solutions with larger ionic strength due to overall charge shielding of the polyelectrolytes and microgel. ATR FT-IR studies correlated the swelling and responsive behavior after LbL assembly on the microgels with the extent of H-bonding and alternating charge distribution within the gel. Thus, the proposed LbL strategy may be a simple and flexible way to engineer smart microgels in terms of size, surface chemistry, overall charge and permeability.     

Formation and Physicochemical Features of Hybrid Threadlike Micelles in Aqueous Solution

We investigate the construction of long, stable hybrid threadlike micelles consisting of polyelectrolytes and oppositely charged surfactants in aqueous solution and examine the physicochemical features such as their structure and viscoelastic behavior in aqueous solution. The most important point for their construction is the careful control of interactions, especially electrostatic interactions, caused between the surfactants and polyelectrolytes. Incorporated polyelectrolytes are fully extended in these hybrid threadlike micelles irrespective of the molecular weight of the polymer. The viscoelastic behavior of the hybrid threadlike micellar solution is similar to that of ordinary threadlike micellar systems consisting of low‐molecular‐weight substances. However, the inclusion of polymers in the micelles causes differences in their mechanical properties.     

Human serum albumin self-assembly on weak polyelectrolyte multilayer films structurally modified by pH changes

Adsorption of proteins onto film surfaces built up layer by layer from oppositely charged polyelectrolytes is a complex phenomenon, governed by electrostatic forces, hydrogen bonds, and hydrophobic interactions. The amounts of the interacting charges, however, both in polyelectrolytes and in proteins adsorbed on such films are a function of the pH of the solution. In addition, the number and the accessibility of free charges in proteins depend on the secondary structure of the protein. The subtle interplay of all these factors determines the adsorption of the proteins onto the polyelectrolyte film surfaces. We investigated the effect of these parameters for polyelectrolyte films built up from weak "protein-like" polyelectrolytes (i.e., polypeptides), poly(L-lysine) (PLL), and poly(glutamic acid) (PGA) and for the adsorption of human serum albumin (HSA) onto these films in the pH range 3.0-10.5. It was found that the buildup of the polyelectrolyte films is not a simple function of the pure charges of the individual polyelectrolytes, as estimated from their respective pKa values. The adsorption of HSA onto (PLL/PGA)n films depended strongly on the polyelectrolyte terminating the film. For PLL-terminated polyelectrolyte films, at low pH, repulsion, as expected, is limiting the adsorption of HSA (having net positive charge below pH 4.6) since PLL is also positively charged here. At high pH values, an unexpected HSA uptake was found on the PGA-ending films, even when both PGA and HSA were negatively charged. It is suggested that the higher surface rugosity and the decrease of the alpha-helix content at basic pH values (making accessible certain charged groups of the protein for interactions with the polyelectrolyte film) could explain this behavior.     

Weak polyelectrolytes tethered to surfaces: Effect of geometry,acid–base equilibrium and electrical permittivity

The structural and thermodynamical properties of weak polyelectrolytes end-tethered to surfaces of arbitrary geometry are studied using a molecular theory. The theory is based on writing down the free energy functional of the system including all the basic interactions and the explicit acid–base equilibrium for the chargeable groups of the polymer. The theory explicitly includes the size, shape, conformations, and charge distribution of all the molecular species. The electrostatic interactions include a density-dependent dielectric function, modeled with the Maxwell–Garnett mixing formula, to account for the composition-dependent permittivity. The minimization of the free energy leads to the distribution of all molecular species and their dependence on bulk pH and salt concentration. We apply the theory to polymer chains end-tethered to planar, cylindrical, and spherical surfaces. The radius of the curved surfaces is small to enhance the curvature effect. We find that when the grafting surfaces are uncharged, the approximation of a constant dielectric function works very well for both structural and thermodynamic properties. The structure of weak polyelectrolytes tethered on cylindrical and spherical surfaces is different from that of polymers tethered on planar surfaces due to the available volume as a function of the distance from the surface. Specifically, the degree of dissociation increases with increasing curvature of the surface. This is a manifestation of the coupling between the local density of protons, counterions, and polymer segments. The results can be interpreted in terms of the local Le Chatelier principle for the acid–base equilibrium, with proper account of the three local contributions: counterions, protons, and chargeable groups. We find that one can achieve local changes of pH between one to two units within 1–2 nm. The thickness of the tethered layers as a function of bulk pH shows a large increase when the pH is equal to the bulk pK. However, the variation with salt concentration is different for the different geometries. The largest swelling is found for cylindrical surfaces. The predictions from scaling theories of a maximum in the thickness of the film as a function of salt concentration is found for planar films, but not for curved surfaces. Finally, the interactions between cylinders with tethered polyelectrolytes is very different from the equivalent planar surfaces. These results are important for the interpretation of force measurements with nanoscale AFM tips. The implications of the results for the rational design of responsive tethered polymer layers is discussed together with the limitations of the theoretical approach. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2638–2662, 2006     

Film stability during postassembly morphological changes in polyelectrolyte multilayers due to acid and base exposure

The mechanism of the transition from a continuous morphology to a porous morphology within polyelectrolyte multilayers (PEMs) of linear poly(ethylene imine) (LPEI) and poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) and PAA assembled by the layer-by-layer (LbL) technique is examined. These morphological changes were created by both acidic and basic postassembly treatments. Basic postassembly treatment is shown to create different types of porosity than acidic postassembly treatment. The morphological variation from the introduction of porosity to the collapse of these porous structures and the dissolution of films under postassembly treatments was observed by AFM, optical microscopy, quartz crystal microbalance (QCM), and SEM. These morphological transitions which are a result of structural rearrangement of weak polyelectrolytes due to pH changes are closely related to the neutralization of the polycations and the ionization of polyanions. Results obtained from FTIR spectroscopy and QCM confirm that polyelectrolytes are being selectively or partially released from the polyelectrolyte multilayers thin films (PEMs) in response to the pH treatment as a function of exposure time. In conclusion, here new information is presented about the structural reorganization found in a number of weak polyelectrolyte systems. This information will be useful in designing functional materials based on polyelectrolytes.     

Complex formation of poly(4-vinyl-N-alkylpyridinium) salts or polymer containing flavin mononucleotide with indole derivatives

A charge-transfer-type complex formation between poly(4-vinyl-N-propylpyridinium bromide) (C3PVP), poly(4-vinyl-N-butylpyridinium bromide) (C4PVP) or poly(4-vinyl-N-benzylpyridinium chloride) (BzPVP), and indole derivatives or between polymer containing flavin mononucleotide residues and indole derivatives was studied in the presence of simple and polyelectrolytes. The association constant (K) of the complex formation with indole acetate increased in the order BzPVP > C4PVP > C3PVP, which indicated an important contribution by hydrophobic interaction. The addition of simple and polyelectrolytes decreased the association constants. This was explained by the “secondary salt effect” of the salts. The importance of the electrostatic interactions in the complexation systems was obvious. The influence of simple electrolytes on the K values was discussed theoretically according to Manning's theory.     

Polymers as matrices for whole cell immobilization

The immobilization of whole microbial cells has become an important tool in the development of biocatalytic processes in the pharmaceutical and food industry. Not only dead, i.e. non growing cells, but recently with higher priority living and growing cells are the biological species, for which simple and efficient polymeric carriers had to be found. In comparison to other methods, like adsorption or encapsulation, entrapment into a polymer network is the most widely used technique. The network can be formed on the basis of a)ionic interactions (ionotropic gelation of polyelectrolytes), b) of polycondensation reactions (epoxides, polyurethanes, silicones) or c) of polymerization reactions (crosslinking polymerization of vinylic monomers, oligomers or polymers). The characteristic features and the efficiency-controlling parameters of some immobilized cells systems are discussed as illustrative examples.     

Self-Assembly of Supramolecular Aggregates Based on Sector- and Cone-Shaped Dendrons and Bolaamphiphiles

Using a number of classes of such sector-shaped macromolecules as derivatives of 2,3,4- and 3,4,5- tri(dodecyloxy)benzenesulfonic acid and dendrimers based on gallic acid as an example, the main stages in the formation of supramolecular ensembles are considered: the formation of individual supramolecular aggregates due to the weak noncovalent interactions of mesogenic groups, and the subsequent ordering within these aggregates, which lowers the free energy of a system. Supramolecular aggregates are in turn organized into two- or three-dimensional supramolecular lattices. It is shown that the shape of the supramolecular aggregates and its change along with temperature are functions of the chemical structure of the mesogenic group (resulting in the controlled design of complex self-organizing systems with a given response to external stimuli).     

Selective Adsorption of Functionalized Nanoparticles to Patterned Polymer Brush Surfaces and Its Probing with an Optical Trap

The site‐specific attachment of nanoparticles is of interest for biomaterials or biosensor applications. Polymer brushes can be used to regulate this adsorption, so the conditions for selective adsorption of phosphonate‐functionalized nanoparticles onto micropatterned polymer brushes with different functional groups are optimized. By choosing the strong polyelectrolytes poly(3‐sulfopropyl methacrylate), poly(sulfobetaine methacrylate), and poly[2‐(methacryloyloxy)ethyl trimethylammonium chloride], it is possible to direct the adsorption of nanoparticles to specific regions of the patterned substrates. A pH‐dependent adsorption can be achieved by using the polycarboxylate brush poly(methacrylic acid) (PMAA) as substrate coating. On PMAA brushes, the nanoparticles switch from attachment to the brush regions to attachment to the grooves of a patterned substrate on changing the pH from 3 to 7. In this manner, patterned substrates are realized that assemble nanoparticles in pattern grooves, in polymer brush areas, or substrates that resist the deposition of the nanoparticles. The nanoparticle deposition can be directed in a pH‐dependent manner on a weak polyelectrolyte, or is solely charge‐dependent on strong polyelectrolytes. These results are correlated with surface potential measurements and show that an optical trap is a versatile method to directly probe interactions between nanoparticles and polymer brushes. A model for these interactions is proposed based on the optical trap measurements.     

Assessment of polyelectrolyte coating stability under dynamic buffer conditions in CE

Dynamic buffer conditions are present in many electrophoretically driven separations. Polyelectrolyte multilayer coatings have been employed in CE because of their chemical and physical stability as well as their ease of application. The goal of this study is to measure the effect of dynamic changes in buffer pH on flow using a real-time method for measuring EOF. Polyelectrolyte multilayers (PEMs) were composed of pairs of strong or completely ionized polyelectrolytes including poly(diallyldimethylammonium) chloride and poly(styrene sulfonate) and weak or ionizable polyelectrolytes including poly(allylamine) and poly(methacrylic acid). Polyelectrolyte multilayers of varying thicknesses (3, 4, 7, 8, 15, or 16 layers) were also studied. While the magnitude of the EOF was monitored every 2 s, the buffer pH was exchanged from a relatively basic pH (7.1) to increasingly acidic pHs (6.6, 6.1, 5.5, and 5.1). Strong polyelectrolytes responded minimally to changes in buffer pH (<1%), whereas substantial (>10%) and sometimes irreversible changes were measured with weak polyelectrolytes. Thicker coatings resulted in a similar magnitude of response but were more likely to degrade in response to buffer pH changes. The most stable coatings were formed from thinner layers of strong polyelectrolytes.     

Block polyelectrolytes in aqueous environments

Analogous to the self-assembly of low-molecular-weight amphiphiles in aqueous solutions, the formation of spherical micelle-like aggregates has been observed in systems of amphiphilic block copolymers in water. The aggregates, often called micelles due to structural similarities with surfactant associates, are found to exist above the critical micelle concentration (cmc). The micellization of amphiphilic block copolymers has been investigated using a wide range of techniques, such as size-exclusion chromatography (SEC), static and dynamic light scattering (SLS and DLS), small-angle x-ray scattering (SAXS), small-angle neutron scattering (SANS), transmission electron microscopy (TEM), viscometry, and steady-state fluorescence spectroscopy. The present lecture is a review of recent work in our laboratory concerning the micellization of ionic block copolymers. These high-molecular-weight amphiphiles may contain one or more of a variety of ionic blocks, such as poly(4-vinylpyridinium alkyl halides), poly(metal acrylates), poly(metal methacrylates) and sulfonated polystyrene. In water, such polymers are referred to as block polyelectrolytes, as they combine the colloidal behavior of block copolymers with the long-range electrostatic interactions of polyelectrolytes. Early work in this field has been reviewed by Selb and Gallot.¹     

Functionalizing inorganic solids: towards organic-inorganic nanostructured materials for intelligent and bioinspired systems

The design, preparation, and properties of organic-inorganic hybrid compounds are described and discussed with respect to their potential uses as intelligent and bioinspired materials. Several synthesis strategies based on intercalation in 2D solids, the grafting of organic groups onto silica and silicates, and the self-assembly of organo-silica materials are presented, focusing on the soft procedures that are used to modify the functionality of the inorganic substrates. The combination of both organic and inorganic moieties at the nanometer level forms the basis for preparing multifunctional solids that are provided with specific functions in response to different types of stimuli. In some cases these resemble materials that are found in biological systems. Examples include organic-inorganic membranes that are based on intercalated macrocyclic compounds and bi-layer vesicles that consist of alkyl long-chains arranged either in the confined region of layered silicates or as self-organized organo-silica micelles. The role of certain hybrid materials such as membranes provides a different approach to the development of artificial liposomes and other mimetic systems that have an organic-inorganic composition and nanostructural organization. Their potential uses for DDS or DNA-dense phases are also discussed and novel alternatives to bioinspired systems development are proposed.     

Polyelectrolyte multilayer capsules as vehicles with tunable permeability

This review is devoted to a novel type of polymer micro- and nanocapsules. The shell of the capsule is fabricated by alternate adsorption of oppositely charged polyelectrolytes (PEs) onto the surface of colloidal particles. Cores of different nature (organic or inorganic) with size varied from 0.1 to 10 mum can be used for templating such PE capsules. The shell thickness can be tuned in nanometer range by assembling of defined number of PE layers. The permeability of capsules depends on the pH, ionic strength, solvent, polymer composition, and shell thickness; it can be controlled and varied over wide range of substances regarding their molecular weight and charge. Including functional polymers into capsule wall, such as weak PEs or thermosensitive polymers, makes the capsule permeability sensitive to correspondent external stimuli. Permeability of the capsules is of essential interest in diverse areas related to exploitation of systems with controlled and sustained release properties. The envisaged applications of such capsules/vesicles cover biotechnology, medicine, catalysis, food industry, etc.