Charged Fibrils Research Articles

Preparation of para-aramid aerogel fiber structurally colored by light scattering through wet spinning and supercritical drying

This research is an investigation of the preparation conditions for para-aramid aerogel fibers that are structurally colored by Rayleigh scattering, an angle-independent structural color. It is well known that structural color has the angle dependence of colors. However, there is currently a desire for materials with angle-independent structural color. During the fibers’ spinning process, the microstructures of the fibers are generated. The effect of spinning conditions is investigated by measuring the optical properties of the wet gel fibers. The neutralization speed of negatively charged PPTA fibrils has a significant impact on the formation of the dense microstructure. Spinning under the fast neutralization speed condition makes it possible to achieve the blue-colored fiber derived from Rayleigh scattering. The influence of neutralization speed on the microstructure of the fibers is confirmed by FE-SEM characterization. Furthermore, spinning using a narrow inner diameter needle decreases the whiteness component derived from Mie scattering of the fibers, resulting in a more vivid blue color. The angle-independent structurally colored fibers hold great promise for application in clothing, interiors, and industrial materials.

Elastoplastic behavior of anisotropic, physically crosslinked hydrogel networks comprising stiff, charged fibrils in an electrolyte.

Fibrillar hydrogels are remarkably stiff, low-density networks that can hold vast amounts of water. These hydrogels can easily be made anisotropic by orienting the fibrils using different methods. Unlike the detailed and established descriptions of polymer gels, there is no coherent theoretical framework describing the elastoplastic behavior of fibrillar gels, especially concerning anisotropy. In this work, the swelling pressures of anisotropic fibrillar hydrogels made from cellulose nanofibrils were measured in the direction perpendicular to the fibril alignment. This experimental data was used to develop a model comprising three mechanical elements representing the network and the osmotic pressure due to non-ionic and ionic surface groups on the fibrils. At low solidity, the stiffness of the hydrogels was dominated by the ionic swelling pressure governed by the osmotic ingress of water. Fibrils with different functionality show the influence of aspect ratio, chemical functionality, and the remaining amount of hemicelluloses. This general model describes physically crosslinked hydrogels comprising fibrils with high flexural rigidity - that is, with a persistence length larger than the mesh size. The experimental technique is a framework to study and understand the importance of fibrillar networks for the evolution of multicellular organisms, like plants, and the influence of different components in plant cell walls.

Foaming of oxidized nanocellulose for the preparation of high-flux water filters

Treatment of polluted water is an important task to secure access to clean water also for future generations. Filters are an efficient means to reject various pollutants on a wide range of size scales either by size-exclusion or electrostatic interaction, respectively. Commonly, filters and membranes from various synthetic materials are employed for these applications. Recently, filters based on renewable (nano) cellulose papers and coatings emerged as sustainable alternative to synthetic materials usually utilized. However, fabrication of such paper network structures from aqueous suspension by filtration processes is a time-consuming process caused by the high water holding capacity of highly hydrophilic and negatively charged nanocellulose fibrils. To optimize the preparation of nanocellulose coated filters, substitution of water by air and thus generating nanocellulose foams that are collapsed onto a substrate would be an appealing approach. Here we present the development of foams from negatively charged TEMPO-oxidized nanocellulose by screening various surfactants and concentrations to generate a foam stable enough to be transferred onto a viscose substrate. Foams were collapsed by oven consolidation, positive pressure filtration, or hot-pressing, respectively. Consolidated filters were tested for their water permeance and rejection of heavy metal ions using copper ions as model system. Very high permeances competitive to commercial filters based on synthetic polymers were achieved. Furthermore, adsorption capacities for copper of up to 70 mg/g were found. This is close to adsorption capacities reported for negatively charged TEMPO-oxidized nanocellulose in conventional batch-wise static adsorption. However, in the current process adsorption takes place during filtration of water through filters in a continuous process which constitutes a tremendous advantage.Graphical

The effect of ethanol on fibrillar hydrogels formed by glycyrrhizic acid monoammonium salt

MotivationThe monoammonium salt of glycyrrhizic acid (AGA) is known to form fibrillar hydrogels and few studies regarding self-assembly of AGA have been published. Yet, the understanding of the fibrillar microstructures and the gelation remains vague. Thus, we attempt to achieve a deeper understanding of the microstructures and the gelation process of binary solutions of AGA in water. Further, we examine the effect of ethanol on the microstructures to pave the way for potential enhancement of drug loading in AGA hydrogels. ExperimentsA partial room temperature phase map of the ternary system AGA/ethanol/water was recorded. Small-angle X-ray and neutron scattering experiments were performed over wide ranges of compositions in both binary AGA/water and ternary AGA/ethanol/water mixtures to get access to the micro-structuring. FindingsBinary aqueous solutions of AGA form birefringent gels consisting of a network of long helical fibrils. ‘Infinitely’ long negatively charged fibrils are in equilibrium with shorter fibrils (≈25 nm), both of which have a diameter of about 3 nm and are made of around 30 stacks of AGA per helical period (≈9nm), with each stack consisting of two AGA molecules. The interaxial distance (order of magnitude ≈20 nm) varies with an almost two-dimensional swelling law. Addition of ethanol reduces electrostatic repulsion and favors the formation of fibrillar end caps, reducing the average length of shorter fibrils, as well as the formation of small, swollen aggregates. While the gel network built by the long fibrils is resilient to a significant amount of ethanol, all fibrils are finally dissolved into small aggregates above a certain threshold concentration of ethanol (≈30 wt%).

Preparation of nanochitin hydrogel with adjustable inter-structure by sequencial genipin crosslinking and ice-templating under acid condition

In this work, genipin crosslinked chitin nanofibril hydrogels/cryogels were successfully prepared. Due to the acidic disperse nature of positively charged chitin fibrils, the pH nature for the chemical crosslinking between chitin nanofibrils and genipin was restricted under 5.0. The pH nature and crosslinking temperature were found greatly influence the efficient chemical crosslinking between chitin nanofibril and genipin. Further ice templated crosslinking was found effective enhancing the mechanical properties of resulting chitin nanofibril hydrogels/cryogels. The cryogel prepared by genipin-crosslinked DEChNs showed interconnected pores, presenting a state of stacking layers. In addition, the deposition of hydroxyapatite (HA) on the surface of chitin nanofibril scaffolds was found effective for improving chondrocyte attachments and growths. The cells viability indicated the good cell compatibility of the cryogel. All the results indicated that the cryogel prepared by genipin-crosslinked DEChNs showed a potential for tissue engineering applications.

Anticoagulant activity and pleiotropic effects of heparin.

The recognized therapeutic effect of heparins is an anticoagulant activity (anti-Xa and anti-IIa) acting in an indirect manner (cofactor of antithrombin) but which is carried by only 20% at best of the glycan chains composing any commercial preparation of heparin, whether unfractionated or low molecular weight. However, the effects of glycan chains that participate in the therapeutic but also potentially adverse effects of heparin preparations must also be considered. These specific effects of glycans are potentially different for each commercial preparation of heparins and, in particular, low molecular weight heparins (LMWH) compared with unfractionated heparin (UFH) and LMWH between them. The glycanic nature of heparin is responsible for its very particular pharmacology: exchange with the glycocalyx of cells in particular endothelial. Exchanges which depend on the length and structure of the glycan chains therefore different between UFH and LMWH between the different heparin preparations between them but also according to the state of glycocalyx differently altered according to the underlying diseases and their degree of evolution. If the anticoagulant effects of heparins can potentially be replaced with those of new oral anticoagulants, the glycan effects of heparins cannot be replaced by synthetic non-glycan molecules. This replacement will undoubtedly limit certain risks such as heparin-induced thrombocytopenia (HIT) but other beneficial effects participating to the overall efficacy of heparin (whose relative importance remains to be ascertained), will also disappear: effects on surfaces, anti-inflammatory effects, antineoplastic and anti-metastatic effects, ancillary anticoagulant effects (not dependent on antithrombin), effect on endothelial dysfunction. This review will be focused on all of these related/pleiotropic effects of heparins that are in fact the effects of the glycan nature of heparin. Among the antithrombotic effects not dependent on antithrombin one has been more recently highlighted: the passivation/neutralization of the positively charged fibrils of Netosis, by the negatively charged glycan chains of heparin. This also has clinical implications: in the era of generics and biosimilars where biosimilar heparins begin to appear, it is important to know that accordingly to FDA and EMEA rules: their biosimilarity is judged only on the "classical" anticoagulation effect cofactor of antithrombin (anti-IIa/anti-Xa) but that all glycan effects that are potentially beneficial or potentially deleterious are not taken into consideration in their assessment.

International abstracts

The recognized therapeutic effect of heparins is an anticoagulant activity (anti-Xa and anti-IIa) acting in an indirect manner (cofactor of antithrombin) but which is carried by only 20% at best of the glycan chains composing any commercial preparation of heparin, whether unfractionated or low molecular weight. However, the effects of glycan chains that participate in the therapeutic but also potentially adverse effects of heparin preparations must also be considered. These specific effects of glycans are potentially different for each commercial preparation of heparins and, in particular, low molecular weight heparins (LMWH) compared with unfractionated heparin (UFH) and LMWH between them. The glycanic nature of heparin is responsible for its very particular pharmacology: exchange with the glycocalyx of cells in particular endothelial. Exchanges which depend on the length and structure of the glycan chains therefore different between UFH and LMWH between the different heparin preparations between them but also according to the state of glycocalyx differently altered according to the underlying diseases and their degree of evolution. If the anticoagulant effects of heparins can potentially be replaced with those of new oral anticoagulants, the glycan effects of heparins cannot be replaced by synthetic non-glycan molecules. This replacement will undoubtedly limit certain risks such as heparin-induced thrombocytopenia (HIT) but other beneficial effects participating to the overall efficacy of heparin (whose relative importance remains to be ascertained), will also disappear: effects on surfaces, anti-inflammatory effects, antineoplastic and anti-metastatic effects, ancillary anticoagulant effects (not dependent on antithrombin), effect on endothelial dysfunction. This review will be focused on all of these related/pleiotropic effects of heparins that are in fact the effects of the glycan nature of heparin. Among the antithrombotic effects not dependent on antithrombin one has been more recently highlighted: the passivation/neutralization of the positively charged fibrils of Netosis, by the negatively charged glycan chains of heparin. This also has clinical implications: in the era of generics and biosimilars where biosimilar heparins begin to appear, it is important to know that accordingly to FDA and EMEA rules: their biosimilarity is judged only on the “classical” anticoagulation effect cofactor of antithrombin (anti-IIa/anti-Xa) but that all glycan effects that are potentially beneficial or potentially deleterious are not taken into consideration in their assessment.

Liposomes Integrated with Amyloid Hydrogels: a Novel Composite Drug Delivery Platform

The present study was undertaken to evaluate the possibility of designing the composite drug delivery platform by integration of the liposomes into the network of amyloid hydrogels. The efficiency of drug entrapment into the combined lipid-protein systems was assessed using the two anticancer agents, viz., the hydrophilic positively charged drug doxorubicin (DOX) and the hydrophobic europium coordination complex, referred to here as V7. The lipid vesicles were composed of the neutral lipid phosphatidylcholine (PC) and its mixture with anionic lipid cardiolipin (CL, 10 mol%), while the amyloid fibrils were obtained from the egg yolk lysozyme (LzF) and the bovine serum albumin (BSAF). The cumulative results from the fluorescence and equilibrium dialysis studies revealed that the negatively charged albumin fibrils favor the DOX encapsulation into PC multilamellar liposomes but exert opposite effect in the case of CL-containing liposomes. However, no sensitivity to the presence of fibrillar protein was observed in the systems PC/DOX/LzF and CL10/DOX/LzF. Likewise, neither LzF nor BSAF affected the extent of V7 encapsulation into the lipid vesicles. These findings highlight the possibility of increasing the payload efficiency of hydrophilic drugs through combining the liposomes with amyloid hydrogels.

Fibril Charge Affects α-Synuclein Hydrogel Rheological Properties.

In this paper, we have investigated the interactions between α-synuclein fibrils at different pH values and how this relates to hydrogel formation and gel properties. Using a combination of rheology, small-angle X-ray scattering, Raman spectroscopy, and cryo-transmission electron microscopy (cryo-TEM) experiments, we have been able to investigate the relationship between protein net charge, fibril-fibril interactions, and hydrogel properties, and have explored the potential for α-synuclein to form hydrogels at various conditions. We have found that α-synuclein can form hydrogels at lower concentrations (50-300 μM) and over a wider pH range (6.0-7.5) than previously reported. Over this pH range and at 300 μM, the fibril network is electrostatically stabilized. Decreasing the pH to 5.5 results in the precipitation of fibrils. A maximum in gel stiffness was observed at pH 6.5 (∼1300 Pa), which indicates that significant attractive interactions operate at this pH and cause an increase in the density of hydrophobic contacts between the otherwise negatively charged fibrils. We conclude that fibril-fibril interactions under these conditions involve both long-range electrostatic repulsion and a short-range hydrophobic attractive (sticky) component. These results may provide a basis for potential applications and add to the understanding of amyloids.

Amyloid Fibrils with Positive Charge Enhance Retroviral Transduction in Mammalian Cells.

Amyloid fibrils are cross-β-sheet-rich protein/peptide fibrils that are typically associated with neurodegenerative diseases such as Parkinson's and Alzheimer's disease. Recently, functional amyloids have been discovered where amyloids are implicated in performing normal physiological functions of the host organism rather than creating diseases. The ability of amyloids to interact with the cell membrane and other small biomolecules exhibits its great potential to be used as a biomaterial for cell adhesion and gene delivery system. Given the established ability of semen-derived amyloids to concentrate HIV in semen and that of charged polymers as an enhancer of retroviral gene transfer, we hypothesized that charged amyloid fibrils can augment virus-mediated delivery system. We show that amyloids of α-synuclein formed in the presence and absence of cationic polymers chitosan and amyloid of poly-l-lysine can interact with lentiviral particles and enhance transduction efficiency in cells. The amyloid nanofibrils increase transduction efficiency up to ∼4 fold similar to widely used cationic polymer Polybrene. This study shows that amyloid nanofibril scaffolds may be used as targeted gene delivery systems.

Positively and Negatively Charged Collagen Nanohydrogels: pH‐responsive Drug‐releasing Characteristics

Researchers are facing many challenges in developing a strategy for site‐specific delivery in the gastrointestinal tract that can maximize therapeutic response and reduce side effects. The objective of this article was to develop a site‐specific drug delivery system for the gastrointestinal tract using natural polymer collagen (CG). For this, two types of pH‐responsive CG nanohydrogels (negatively charged pH‐CGNH‐COOH and positively charged pH‐CGNH‐NH2) were prepared using negatively and positively functionalized carbon nanotubes, CNT‐COOH and CNT‐NH2, respectively. The pH‐CGNH‐COOH and pH‐CGNH‐NH2 nanohydrogel samples comprising negatively and positively charged fibrils (CG/CNT‐COOH and CG/CNT‐NH2) were physicochemically characterized by Fourier‐transform infrared spectrometry, Zeta sizer, thermogravimetric analysis, and field emission scanning electron microscopy. They also revealed the pH‐responsive release of bovine serum albumin at pH 9 and cytochrome C at pH 2. These results strongly indicate that these drug carriers can be useful for site‐specific delivery in the gastrointestinal tract.

Foams Stabilized by β-Lactoglobulin Amyloid Fibrils: Effect of pH.

β-Lactoglobulin fibrils could serve as a surface-active component and form adsorption layers at the air/water interface. In this study, the physical parameters related to the surface adsorption, foaming, and surface properties of β-lactoglobulin fibrils as a function of pH (2-8) were investigated. Results showed that an increase of pH from 2 to 5 led to a rise of the viscoelastic modulus of the surface adsorption layer and half-life time (t1/2) of foams, but it decreased foamability. When the pH was close to its isoelectric point (5.2), fibrils had the lowest electrostatic repulsion and entangled at the air/water interface resulting in a tightly packaged adsorption layer around bubbles to prevent coalescence and coarsening. When the pH (7-8) was higher than the pI of fibrils, the negatively charged β-lactoglobulin fibrils possessed good foamability (∼80%) and high foam stability (t1/2 ≈ 8 h) simultaneously even at low concentration (1 mg/mL). It demonstrated that β-lactoglobulin fibrils with negative charges presented a good foaming behavior and could be a potential new foaming agent in the food industry.

Impact of TEMPO-oxidization strength on the properties of cellulose nanofibril reinforced polyvinyl acetate nanocomposites

Nanocomposites of polyvinyl acetate (PVAc) reinforced with two different TEMPO-oxidized cellulose nanofibrils (CNF) were prepared by casting/evaporation method. These two sets of CNF, designed as CNF-O-5min (5min of oxidation) and CNF-O-120min (120min of oxidation), are different by their surface charge, geometrical characteristics and crystallinity index. The weight fraction of CNF was changed from 1 to 10wt%. The mechanical and thermal properties of the nanocomposite films were studied by dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests, and their morphology was investigated by scanning electron microscopy (SEM). For all nanocomposites, increasing amounts of CNF led to a significant increase in the mechanical properties (increase in Young’s modulus and tensile strength) and in the water uptake. On the other hand, the lost of transparency became very significant when the weight fraction of CNF exceeded 3wt%. The comparison between the two sets of CNF showed that PVAc/CNF-O-5min nanocomposite films had a tendency to display higher tensile strength and elastic modulus than those of PVAc/CNF-O-120min films. In addition, the water uptake is higher for PVAc/CNF-O-120min. Finally, the thermal stability analyses for PVAc/CNF films show that shorter and more charged fibrils (CNF-O-120min) appear to slightly increase the thermal stability compared to other larger and less charged fibrils (CNF-O-5min). All these results are discussed in connection with the CNFs characteristics.

Alternating potentials assisted electrochemical deposition of mineralized collagen coatings

Mineralized collagen coatings were synthesized by electrochemical deposition with alternating negative and positive potentials. The obtained coatings demonstrated a multi-layer structure alternating consisting of weakly and highly mineralized collagen layers and the proportion of each layer could be controlled by adjusting the deposition time. The coatings deposited using alternating potentials assisted electrochemical deposition (AP-ECD) showed significantly enhanced osteoblasts proliferation, and rhBMP-2 loading capability compared to those of the coatings deposited using constant potential electrochemical deposition (CP-ECD). The enhanced cytocompatibility and rhBMP-2 loading capability of the coatings might be attributed to their high proportion of weakly mineralized collagen layer. Furthermore, the deposition mechanism for alternating potentials is proposed as that positive potential induces deposition of negatively charged collagen fibrils to form a weakly mineralized collagen layer. Our results suggest that the present deposition method could be a promising approach to engineer mineralized collagen coating with better biological performances.

Counter-ion specificity explored in abnormal expansion of supra-molecular aggregates in aqueous solution of alkaline metal salts.

Ionic effects in aqueous solution of macro-ions showing specificity and unconventional characters, respectively, receive a lot of interests recently; however, the complexity of specific ion effects in unconventional phenomena remains ambiguous. In this study, the effects of univalent ions on aggregation of supra-molecular nano-fibrils with charged carboxylate groups on the surface as a prototype of macro-ions are investigated by Small Angle X-ray Scattering (SAXS) in aqueous solutions of alkaline metal chlorides. It is found that the columnar bundles of charged fibrils are expanded in certain salt concentration range contradicting the conventional screening effects of salts. The degree of expansion is dominated by cations as Na(+) induces drastic effects in comparison to rather gentle changes from K(+) and Cs(+). The specific cations effects observed by SAXS correlate with the pH behavior of the solutions, an indicator of surface charge, or number of carboxylate groups along the supra-molecular fibrils. It is postulated that while Na(+) with stronger affinity to carboxylates apparently reduces the surface charge, K(+) and Cs(+) only weakly interact with carboxylates and induce minor changes, accounting for the cation-sensitive aggregation behavior of fibrils observed by SAXS. By probing the bundling aggregation of charged supra-molecular nano-fibrils in salty water, we provide direct evidence of specific counter-ion effects in unusual expansion caused by univalent salts.

A Colloidal Description of Intermolecular Interactions Driving Fibril-Fibril Aggregation of a Model Amphiphilic Peptide.

We apply a kinetic analysis platform to study the intermolecular interactions underlying the colloidal stability of dispersions of charged amyloid fibrils consisting of a model amphiphilic peptide (RADA 16-I). In contrast to the aggregation mechanisms observed in the large majority of proteins and peptides, where several elementary reactions involving both monomers and fibrils are present simultaneously, the system selected in this work allows the specific investigation of the fibril-fibril aggregation process. We examine the intermolecular interactions driving the aggregation reaction at pH 2.0 by changing the buffer composition in terms of salt concentration, type of ion as well as type and concentration of organic solvent. The aggregation kinetics are followed by dynamic light scattering, and the experimental data are simulated by Smoluchowski population balance equations, which allow to estimate the energy barrier between two colliding fibrils in terms of the Fuchs stability ratio (W). When normalized on a dimensionless time weighted on the Fuchs stability ratio, the aggregation profiles under a broad range of conditions collapse on a single master curve, indicating that the buffer composition modifies the aggregation kinetics without affecting the aggregation mechanism. Our results show that the aggregation process does not occur under diffusion-limited conditions. Rather, the reaction rate is limited by the presence of an activation energy barrier that is largely dominated by electrostatic repulsive interactions. Such interactions could be reduced by increasing the concentration of salt, which induces charge screening, or the concentration of organic solvent, which affects the dielectric constant. It is remarkable that the dependence of the activation energy on the ionic strength can be described quantitatively in terms of charge screening effects in the frame of the DLVO theory, although specific anion and cation effects are also observed. While anion effects are mainly related to the binding to the positive groups of the fibril surface and to the resulting decrease of the surface charge, cation effects are more complex and involve additional solvation forces.

Using solution state NMR spectroscopy to probe NMR invisible gelators.

Supramolecular hydrogels are formed via the self-assembly of gelator molecules upon application of a suitable trigger. The exact nature of this self-assembly process has been widely investigated as a practical understanding is vital for the informed design of these materials. Solution-state NMR spectroscopy is an excellent non-invasive tool to follow the self-assembly of supramolecular hydrogels. However, in most cases the self-assembled aggregates are silent by conventional (1)H NMR spectroscopy due to the low mobility of the constituent molecules, limiting NMR spectroscopy to following only the initial assembly step(s). Here, we present a new solution-state NMR spectroscopic method which allows the entire self-assembly process of a dipeptide gelator to be followed. This gelator forms transparent hydrogels by a multi-stage assembly process when the pH of an initially alkaline solution is lowered via the hydrolysis of glucono-δ-lactone (GdL). Changes in the charge, hydrophobicity and relative arrangement of the supramolecular aggregates can be followed throughout the assembly process by measuring the residual quadrupolar couplings (RQCs) of various molecular probes (here, (14)NH4(+) and isopropanol-d8), along with the NMR relaxation rates of (23)Na(+). The initially-formed aggregates comprise negatively charged fibrils which gradually lose their charge and become increasingly hydrophobic as the pH falls, eventually resulting in a macroscopic contraction of the hydrogel. We also demonstrate that the in situ measurement of pH by NMR spectroscopy is both convenient and accurate, representing a useful tool for the characterisation of self-assembly processes by NMR.

Sol–gel transition of charged fibrils composed of a model amphiphilic peptide

We characterized the sol–gel transition of positively charged fibrils composed of the model amphiphilic peptide RADARADARADARADA (RADA 16-I) using a combination of microscopy, light scattering, microrheology and rheology techniques, and we investigated the dependence of the hydrogel formation on fibril concentration and ionic strength. The peptide is initially present as a dispersion of short rigid fibrils with average length of about 100nm. During incubation, the fibrils aggregate irreversibly into longer fibrils and fibrillar aggregates. At peptide concentrations in the range 3–6.5g/L, the fibrillar aggregates form a weak gel network which can be destroyed upon dilution. Percolation occurs without the formation of a nematic phase at a critical peptide concentration which decreases with increasing ionic strength. The gel structure can be well described in the frame of the fractal gel theory considering the network as a collection of fibrillar aggregates characterized by self-similar structure with a fractal dimension of 1.34.

Carboxymethylated nanofibrillated cellulose: effect of monovalent electrolytes on the rheological properties

The effect of the ionic strength on the properties of a carboxymethylated nanofibrillated cellulose (NFC) system was investigated through rheological studies. It was shown that homogenization of pulp suspensions containing a high amount of a monovalent electrolyte leads to the production of NFC systems displaying a lower magnitude in the rheological response as compared with systems prepared at lower ionic strengths conditions. It was further shown that increasing the ionic strength of NFC suspensions after their manufacturing also results in a lowering of the rheological response. The decreased rheological response in the former case was postulated to be caused by a lowering of the delamination deficiency of the homogenization process, due to decreased swelling of the carboxymethylated pulp, caused by the screening of the charges. In the latter case (post-addition of the electrolyte), the lowering of the rheological response was postulated to be due to the compression of the electrostatic double layer, when the electrostatic repulsion between the charged fibrils diminished in the presence of the electrolyte.

Specific ion effects induced by mono-valent salts in like charged aggregates in water.

While salt mediated association between similarly charged poly-electrolytes occurs in a broad range of biological and colloidal systems, the effects of mono-valent salts remains little known experimentally. In this communication we systematically study influences of assorted mono-valent salts on structures of and interactions in two dimensional ordered bundles of charged fibrils assembled in water using Small Angle X-ray Scattering (SAXS). By quantitatively analyzing the scattering peak features, we discern two competing effects with opposite influences due to partitioning of salts in the aqueous complex. While electrostatic effects from salts residing between the fibrils suppress attraction between fibrils and expand the bundles, it is compensated by external osmotic pressure from peripheral salts in the aqueous media. The balance between the two effects varies for different salts and gives rise to ion-specific equilibrium behavior as well as structure of ordered bundles in salty water. The specific ions effects in like charged aggregates can be attributed to preferential distribution of ions inside or outside the bundles, correlated to the ranking of ions in Hofmeister series for macromolecules. Unlike conventional studies on Hofmeister effects by thermodynamic measurements relying on modeling for data interpretation, our study is based directly on structural analysis and is model-insensitive.