On the indirect polyelectrolyte titration of cellulosic fibers. Conditions for charge stoichiometry and comparison with ESCA

The effect of electrolyte (NaHCO3) concentration on the adsorption of poly-DADMAC (poly-diallyldimethylammonium chloride) onto cellulosic fibers with different charge profiles was investigated. Surface carboxymethylated fibers were obtained by grafting carboxymethyl cellulose (CMC) onto the fiber surface and bulk carboxymethylated fibers were obtained by reacting the fibers with monochloroacetic acid. It was shown that nonionic interactions do not exist between cellulose and poly-DADMAC, rather electrostatic interactions govern the adsorption. Charge stoichiometry prevails under electrolyte-free conditions, whereas surface charge overcompensation occurs at higher electrolyte concentrations. It was shown that charge stoichiometry prevails if the thickness of the electric double layer kappa(-1) was larger than the mean distance between the charges on the fiber surface, as predicted by polyelectrolyte adsorption theories, taking lateral correlation effects into account. In a second set of experiments the ESCA technique served to independently calibrate the polyelectrolyte titrations for determining the surface charge of cellulosic fibers. Various molecular masses of poly-DADMAC were adsorbed to carboxymethylated fibers having different charge profiles. The adsorption of low M(w) poly-DADMAC (7.0 x 10(3)), analyzed by polyelectrolyte titration, was about 10 times higher than that of the high M(w) poly-DADMAC (9.2 x 10(5)). Despite the difference in accessibility of these two polyelectrolytes to the fiber cell wall, ESCA surface analysis showed, as expected, only slight differences between the two polyelectrolytes. This gives strong credibility to the idea that surface charge content of cellulosic fibers can be analyzed by means of adsorption of a high-molecular-mass cationic polymer, i.e., by polyelectrolyte titration.     

The fiber charge measurement depending on the poly-DADMAC accessibility to cellulose fibers

Cellulose fiber charge is a significant parameter for porous cellulose fibers, and strongly affects the swelling ability of cellulose fibers and the properties of cellulose-based materials as well. Actually, it includes surface charge and inner charge. The surface charge is mentioned often in papermaking wet-end chemistry, however, the inner charge or the total charge is paid less attention to. In this study, the cationic polydiallyldimethyl ammonium chloride (poly-DADMAC) with different molecular weight (Mw) was applied for the accessibility evaluation to the cellulose fiber charges by using polyelectrolyte adsorption technique. Results showed that higher fiber charge was detected by lower Mw poly-DADMAC (7.5–15 kDa) due to its highly efficient penetration into the fiber cell walls and neutralization with inner charges, while lower fiber charge was obtained by using higher Mw poly-DADMAC (higher than 100 kDa) because of its adsorption onto fiber surface. As a consequence, high-Mw poly-DADMAC was used to determine the surface charge of cellulose fibers, and low-Mw poly-DADMAC could be used to measure the total charge under the saturated adsorption and low ionic strength (or salts concentration). This was confirmed by SEM–EDS analysis. The low-Mw poly-DADMAC adsorption had a good agreement with conventional conductometric titration, and a linear regression equation with slope of 1.03 and regression coefficient of 0.99 was obtained.     

EFFECT OF RADIATION ON HIGH-CHARGE-DENSITY POLYDIALLY-DIMETHYL AMMONIUM CHLORIDE IN DILUTE AQUEOUS SOLUTION

The effect of radiation on high-charge-density cationic polymer, polydiallyl-dimethyl ammonium chloride (poly-DADMAC), in dilute aqueous solution was investigated. The irradiated samples were characterized in terms of reducedviscosity and electric conductivity. The crosslinking reaction of polyDADMAC chains occurs preferentially in the irradiatedsamples at a concentration of polyDADMAC higher than 1.3 g/100 mL that was induced indirectly by the OH radicals, oneof the radiolysis products of water. In more dilute samples (less than 0.8 g/100 mL) the chain scission of macro radicalsappears to be the main reaction. N_2O atmosphere enhances the crosslinking due to the extra OH radicals produced byreaction between N_2O and e_(aq), another radiolysis products of water. Methanol and some mineral salts such as KCl, KBr inhibit the crosslinking to a certain extent. The mechanism of sensitization and inhibition is discussed in detail.     

Rheological behavior of highly loaded cellulose nanocrystal/poly(vinyl alcohol) composite suspensions

Recent emphasis on the pilot scale production of cellulosic nanomaterials has increased interest in the effective use of these materials as reinforcements for polymer composites. An important, enabling step to realizing the potential of cellulosic nanomaterials in their applications is the materials processing of CNC/polymer composites through multiple routes, i.e. melt, solution, and aqueous processing methods. Therefore, the objective of this research is to characterize the viscoelastic behavior of aqueous nanocomposite suspensions containing cellulose nanocrystals (CNCs) and a water-soluble polymer, poly(vinyl alcohol) (PVA). Specifically, small amplitude oscillatory shear measurements were performed on neat PVA solutions and CNC-loaded PVA suspensions. The experimental results indicated that the methods used in this study were able to produce high-quality nanocomposite suspensions at high CNC loadings, up to 67 wt% with respect to PVA. Additionally, the structure achieved in the nanocomposite suspensions was understood through component attributes and interactions. At CNC loadings near and less than the percolation threshold, a polymer mediated CNC network was present. At loadings well above the percolation threshold, a CNC network was present, indicated by limited molecular weight dependence of the storage modulus. Overall, these results provide increased fundamental understanding of CNC/PVA suspensions that can be leveraged to develop advanced aqueous processing methods for these materials.     

Adsorption of cationic cellulose derivative/anionic surfactant complexes onto solid surfaces. II. Hydrophobized silica surfaces

The effect of the anionic surfactant SDS (sodium dodecyl sulfate) on the adsorption behavior of cationic hydroxyethyl cellulose (Polymer JR-400) and hydrophobically modified cationic cellulose (Quatrisoft LM-200) at hydrophobized silica has been investigated by null ellipsometry and compared with the previous data for adsorption onto hydrophilic silica surfaces. The adsorbed amount of LM-200 is found to be considerably larger than the adsorbed amount of JR-400 at both surfaces. Both polymers had higher affinity toward hydrophobized silica than to silica. The effect of SDS on polymer adsorption was studied under two different conditions: adsorption of polymer/SDS complexes from premixed solutions and addition of SDS to preadsorbed polymer layers. Association of the surfactant to the polymer seems to control the interfacial behavior, which depends on the surfactant concentration. For the JR-400/SDS complex, the adsorbed amount on hydrophobized silica started to increase progressively from much lower SDS concentrations, while the adsorbed amount on silica increased sharply only slightly below the phase separation region. For the LM-200/SDS complex, the adsorbed amounts increased progressively from very low SDS concentrations at both surfaces, and no large difference in the adsorption behavior was observed between two surfaces below the phase separation region. The complex desorbed from the surface at high SDS concentrations above the critical micelle concentration. The reversibility of the adsorption of polymer/SDS complexes upon rinsing was also investigated. When the premixed polymer/SDS solutions at high SDS concentrations (>5 mM) were diluted by adding water, the adsorbed amount increased due to the precipitation of the complex. The effect of the rinsing process on the adsorbed layer was determined by the hydrophobicity of the polymer and the surface.     

Adsorption behavior of cationic polymers on bentonite

The adsorption behavior of a series of cationic water-soluble polymers poly(diallyldimethylammonium chloride) with different molar masses onto raw bentonite was investigated through the elaboration of their adsorption isotherms and the quantification of the water content of the clay/polymer complexes formed. It was found that the type of adsorption isotherms obtained depends on the chain length of the polymer. The study showed a correlation between the amount of adsorbed polymer and the water content of the clay, after the adsorption experiments. The lower the molar mass of the polymer used, the larger was the reduction on water content of the complexes.     

Adsorption of low charge density polyelectrolytes to an oppositely charged porous substrate

The adsorption behavior of a low charge density cationic polyelectrolyte to cellulosic fibers has been studied. Cationic dextran served as a model polyelectrolyte, as it can be prepared over a range in molecular mass and charge density. The adsorption behavior of the cationic dextran was measured in electrolyte-free conditions using polyelectrolyte titration techniques. By fluorescent labeling the cationic dextran, the extent to which adsorption occurs inside the porous structure was further determined by fluorescent confocal laser scanning microscopy. Cationic dextran having a sufficiently low charge density adsorbed into the pores, although the extent the cationic dextran adsorbed was governed by the molecular mass. The adsorption behavior of the cationic dextran was also studied in various electrolyte concentrations. The adsorbed mass monotonically decreased with increasing electrolyte, as the electrostatic interaction with the substrate was more effectively screened. This behavior also suggests that the interactions between adsorbed polyelectrolyte chains, i.e. lateral correlation effects, are negligible for low charge density polyelectrolytes. Finally, the effect of having a preadsorbed layer of cationic dextran on the adsorption behavior was determined in electrolyte-free conditions using fluorescent double staining techniques. The preadsorbed cationic dextran had almost no effect on the adsorption of low molecular mass fractions. Low molecular mass fractions directly adsorbed into the pore structure, as opposed to adsorbing to a free surface and diffusing into the pores. It was also shown that cationic dextran can be selectively adsorbed to different locations, such that the surface of a porous substrate can be treated uniquely from the bulk.     

Tough nanocomposite hydrogels from cellulose nanocrystals/poly(acrylamide) clusters: influence of the charge density,aspect ratio and surface coating with PEG

Cellulose-derived materials are usually characterized by sophisticated structures, leading to unique and multiple functions, which have been a source of inspiration for the fabrication of a wide variety of nanocomposites. Cellulose nanocrystals/poly(acrylamide) (CNCs/PAM) nanocomposite hydrogels were synthesized via in situ polymerization in the CNC suspension. The cellulose from pulp fiber under different sulfuric acid hydrolysis conditions, examined by conductometric titration and transmission electron microscopy, was applied to study how the effects of the surface charge and aspect ratio affect CNCs’ mechanical reinforcement in nanocomposites. The results indicated that the higher surface charge concentration resulted in better dispersibility in aqueous suspension, leading to a more efficient energy dissipation process. The CNC reinforcement behavior followed the percolation model where the greater aspect ratio of CNC contributed to higher mechanical properties. The preferential adsorption of poly(ethylene glycol) (PEG) on the CNC surface was characterized by zeta potential measurements where the fracture strength and fracture elongation of nanocomposites decreased with increasing PEG concentration. The adsorption of PEG on the CNC surface occupied the active sites for polymer chain propagation, which hindered the PAM cross-linking effect on the CNC surface and decreased the cross-linking density of the network.     

All-cellulose multilayers: long nanofibrils assembled with short nanocrystals

Self-organized multilayer films were formed by sequential addition of oppositely charged cellulose I nanoparticles. The all-cellulosic multilayers were prepared via adsorption of cationicially modified cellulose nanofibrils (cat NFC) and anionic short crystalline cellulose (CNC) at pH 4.5 and pH 8.3. The properties and build-up behavior of layer-by-layer-constructed films were studied with microgravimetry (QCM-D) and the direct surface forces in these systems were explored with colloidal probe microscopy to gain information about the fundamental interplay between cat NFC and anionic CNC. The importance of the first layer on the adsorption of the consecutive layers was demonstrated by comparing pure in situ adsorption in the QCM-D with multilayer films made by spin coating the first cationic NFC layer and then subsequently adsorbing the following layers in situ in the QCM-D chamber. Differences in adsorbed amount and viscoelastic behavior were observed between those two systems. In addition, a significant pH dependence of cat NFC charge was found for both direct surface interactions and layer properties. Moreover the underlying cellulose layer in multilayer film was established to influence the surface forces especially at lower pH, where the cat NFC chains extensions were facilitated and overall charge was affected by the cationic counterpart within the layers. This enhanced understanding the effect of charge and structure on the interaction between these renewable nanoparticles is valuable when designing novel materials based on nanocellulose.     

Body temperature-responsive gels derived from hydroxypropylcellulose bearing lignin II: adsorption and release behavior

The lower critical solution temperature (LCST) of hydroxypropylcellulose bearing lignin (HPC-L) prepared from unbleached pulp depends on the amount of residual lignin. An HPC-L gel having thermal properties reflective of original HPC-L was prepared using ethyleneglycol diglycidylether as a crosslinker, as previously reported [Uraki et al. (2004) Carbohydr. Polym. 58:123–130], and the volume transition temperature was detected as an endothermic peak by differential scanning calorimetry (DSC). The adsorption and release behavior of the guest molecules to/from this gel was then examined. When the adsorption of cationic and anionic guests was compared, cationic methylene blue (MB) was adsorbed in larger amounts than anionic methyl orange (MO). In addition, MB adsorption into the HPC-L gel was greater than MB adsorption into the HPC gel prepared from commercially available HPC. This suggests that residual lignin affects the adsorption of organic dyes. Significant differences were not observed with respect to the release of MB from HPC-L at 38 °C and lower temperatures. In the adsorption of surfactants, marked adsorption at around the critical micelle concentration of the ionic surfactants and gel swelling were observed. Such swelling did not occur in the aqueous nonionic surfactant solution, although the nonionic surfactant was adsorbed into the gel. Gel swelling may have been caused by the electrostatic repulsion of the ionic surfactants adsorbed onto the polymer chains within the gel structure.     

Biointeractive antibacterial fibres using polyelectrolyte multilayer modification

Contact-active antibacterial surfaces are a novel tool in the antibacterial battle. The preparation of such surfaces usually involves harsh reaction conditions and organic solvents. A more sustainable alternative would involve physical adsorption of water-soluble polyelectrolytes using a renewable substrate. Here, highly charged cationic polyvinylamines (PVAm), with or without hydrophobic modifications, have been adsorbed onto the naturally anionic cellulosic wood-fibres. To increase the amount of PVAm, polyelectrolyte multilayers were prepared using polyacrylic acid as the anionic polyelectrolyte. The modified fibres were characterised for PVAm content, water retention and antibacterial properties. The use of multilayers increased the total polymer content without notably reducing the water swelling. The fibres were shown to have excellent bioactive properties and reduced waterborne Escherichia coli and Bacillus subtilis by more than 99.9 %, which is a generally accepted definition of an antibacterial material. A large reduction in bacterial growth was observed upon addition of nutrients, although minor growth was detected after 24 h. The results further show that one adsorbed polymer layer was sufficient to obtain a contact-active surface, which makes the PVAm multilayer system seemingly unique. No polymer leaching from any of the samples was detected, indicating that the fibres work via a contact-active antibacterial mechanism. The results show the feasibility of constructing a sustainable antibacterial material using a renewable substrate and water-based solutions in the material construction process.     

Adsorption and controlled release of Chlortetracycline HCl by using multifunctional polymeric hydrogels

Adsorption and controlled release of Chlortetracycline HCl to and from multifunctional polymeric materials (HEMA/MAA) hydrogels were investigated. P(HEMA/MAA) hydrogels were synthesized by gamma radiation-induced copolymerization of 2-hydroxyethylmethacrylate (HEMA) and methacrylic acid (MAA) in aqueous solution. The influence of copolymer composition and pH value of the surrounding medium on the type of water diffusion into the glassy polymer were discussed. Drug, Chlortetracycline HCl containing hydrogels, with different drug concentration to polymer ratios, was loaded by direct adsorption method. The influence of MAA content in the gel on the adsorption capacities of hydrogel was studied. Chlortetracycline HCl adsorption capacity of hydrogels was found to increase from 8 to 138 mg Chlortetracycline HCl per gram dry gel with increasing amount of MAA in the gel system and drug concentration. The effect of pH on the releasing behavior of Chlortetracycline HCl from gel matrix was investigated. In vitro drug release studies in different buffer solutions show that the basic parameters affecting the drug release behavior of hydrogel are the pH of the solution and MAA content of hydrogel.     

Diffusion into and adsorption of polyethylenimine on porous silica gel

The polyethyleneimine (PEI)–water–silica gel absorption system was used as a model system to investigate the relationship between diffusion into the porous structure, adsorption rate, and molecular weight of the polymer. Three silica gels, Porasil A, B, and and C having a range of characteristic porosity were used as adsorbents. Adsorption of PEI on Porasil C, which has the majority of its pores much larger than the dimensions of the adsorbate molecule, increased initially with increased molecular weight but became nearly constant at higher molecular weight. Little increase in adsorption occurred for this silica gel with increased ionic strength or with increased pH between 9.5 and 10.8. In contrast, adsorption increased sharply with increased ionic strength and for the same pH range on Porasil A. Molecular weight dependence was reversed. Adsorption decreased with increased molecular weight on Porasil A. In this case, the molecular size of PEI investigated was the same as the majority of pore apertures in the adsorbent. Solution environments (i.e., pH and ionic strength) that decrease the size of the PEI molecule and its affinity for the anionic silica gel surface, thus enabling it to more readily diffuse into the smaller porous regions of the adsorbent, are the apparent causes of the very large adsorption increase. Electrostatic repulsion between PEI molecules do not appear greatly to affect adsorption. Similar adsorption behavior has been reported in the literature for the PEI–cellulosic fiber adsorption system. Maximum adsorption on Porasil A occurred at pH 10.8, the same maximum generally reported for adsorption of PEI on cellulosic fibers. In this case, the silica gel (Porasil A) was found to have a pore size distribution and specific surface area of the same magnitude as cellulosic fibers prepared in the expanded state.     

Sulfonated Hollow Covalent Organic Polymer: Highly‐Selective Adsorption toward Cationic Organic Dyes over Anionic Ones in Aqueous Solution

A sulfonated hollow covalent organic polymer (sh‐COP‐P) was prepared by post sulfonation of hollow covalent organic polymer (h‐COP‐P) synthesized through poly‐condensation of tetrabiphenylporphyrin (TBPP). In comparison with h‐COP‐P, sh‐COP‐P exhibits significantly enhanced adsorption capacity of organic cationic dyes in aqueous solutions accompanied with notably reduced adsorption capacity of anionic dyes. This gives sh‐COP‐P a satisfactory performance in selectively separating cationic organic dyes from anionic ones, mainly attributed to the electrostatic interaction between polymer backbone and the guest molecules.     

Adsorption of branched-linear polyethyleneimine-ethylene oxide conjugate on hydrophilic silica investigated by ellipsometry and Monte Carlo simulations

The adsorption of and conformation adopted by a branched-linear polymer conjugate to the hydrophilic silica-aqueous solution interface have been studied by in situ null ellipsometry and Monte Carlo simulations. The conjugate is a highly branched polyethyleneimine structure with ethyleneoxide chains grafted to its primary and secondary amino groups. In situ null ellipsometry demonstrated that the polymer conjugate adsorbs to the silica surface from water and aqueous solution of 1 mM asymmetric divalent salt (calcium and magnesium chloride to emulate hard water) over a large pH range. The adsorbed amount is hardly affected by pH and large charge reversal on the negatively charged silica surface occurred at pH = 4.0, due to the adsorption of the cationic polyelectrolyte. The Monte Carlo simulations using an appropriate coarse-grained model of the polymer in solution predicted a core-shell structure with no sharp boundary between the ethyleneimine and ethyleneoxide moieties. The structure at the interface is similar to that in solution when the polymer degree of protonation is low or moderate while at high degree of protonation the strong electrostatic attraction between the ethyleneimine core and oppositely charged silica surface distorts the ethyleneoxide shell so that an "anemone"-like configuration is adopted. The adsorption of alkyl benzene sulfonic acid (LAS) to a preadsorbed polymer layer was also investigated by null ellipsometry. The adsorption data brought additional support for the existence of a strong polymer adsorption and showed the presence of a binding which was further enhanced by the decreased solvency of the surfactant in the salt solution and confirmed the surface charge reversal by the polymer adsorption at pH = 4.0.     

Adsorption and inactivation behavior of horseradish peroxidase on cellulosic fiber surfaces

The physical immobilization behavior of horseradish peroxidase (HRP) on cellulosic fiber surfaces was characterized using adsorption and inactivation isotherms measured by the depletion method followed by fitting of Langmuir’s and Freundlich’s models to the experimental data. The adsorption and inactivation behavior of simpler and relatively non-porous high and low crystalline cellulosic substrates (microcrystalline cellulose and regenerated cellulose) as well as more complex and porous cellulosic pulp fibers (bleached kraft softwood fibers) were investigated. The effect of the sorbent surface energy on HRP adsorption was demonstrated by increasing the hydrophobicity of the cellulosic fibers using an internal sizing agent. The influence of the fiber surface charge density on HRP adsorption was studied via modification of the cellulosic fibers using TEMPO (2,2,6,6-tetramethyl-1-piperidiniloxy radical)-mediated oxidation methods. Results showed that hydrophobic interactions had a much larger effect on HRP adsorption than electrostatic interactions. More hydrophobic fiber surfaces (lower polar surface energy) result in larger enzyme-fiber binding affinity constants and higher binding heterogeneity. It was also found that oxidation of the cellulosic fiber substrate reduces enzyme adsorption affinity but significantly increases the loading capacity per unit weight of the surface.     

The effect of the amphiprotic nature of human hair keratin on the adsorption of high charge density cationic polyelectrolytes

Adsorption of the cationic polymers poly(methacrylamidopropyltrimethyl ammonium chloride) (PMAPTAC) and poly(1,1-dimethylpiperidinium-3,5-diallylmethylene chloride) (PDMPDAMC) on human hair was studied by measurements of the amount of polymer adsorbed and by the streaming potential method. Results reflect the amphoteric nature of the keratin surface and show that the excess of anionic sites at pH values above 4 is the main driving force for the adsorption of cationic polyelectrolytes. Lowering the pH below 4 or addition of neutral salt (KCl) reduces the amount of adsorbed polymer. It was shown that the adsorption of cationic polymer in the concentration range 0.01 to 0.1 % and at neutral pH reverses the overall character of the surface from anionic to cationic. Keratin fibers modified in this manner do not exhibit amphoteric character and bear excess positive charge in the pH range 2–9.5. The value of the amount of the polymer adsorbed at saturation concentration (2 mg/g) as well as the lack of molecular weight effect in the range (5 · 10⁴ – 10⁶) on the amount of polymer adsorbed suggest that polymer chains adopt a rather extended conformation on the fiber surface. Some data concerning the formation of a complex between adsorbed cationic polymer and anionic detergents or polyelectrolytes are also presented.     

Foaming and foam stability for mixed polymer-surfactant solutions: effects of surfactant type and polymer charge

Solutions of surfactant-polymer mixtures often exhibit different foaming properties, compared to the solutions of the individual components, due to the strong tendency for formation of polymer-surfactant complexes in the bulk and on the surface of the mixed solutions. A generally shared view in the literature is that electrostatic interactions govern the formation of these complexes, for example between anionic surfactants and cationic polymers. In this study we combine foam tests with model experiments to evaluate and explain the effect of several polymer-surfactant mixtures on the foaminess and foam stability of the respective solutions. Anionic, cationic, and nonionic surfactants (SDS, C(12)TAB, and C(12)EO(23)) were studied to clarify the role of surfactant charge. Highly hydrophilic cationic and nonionic polymers (polyvinylamine and polyvinylformamide, respectivey) were chosen to eliminate the (more trivial) effect of direct hydrophobic interactions between the surfactant tails and the hydrophobic regions on the polymer chains. Our experiments showed clearly that the presence of opposite charges is not a necessary condition for boosting the foaminess and foam stability in the surfactant-polymer mixtures studied. Clear foam boosting (synergistic) effects were observed in the mixtures of cationic surfactant and cationic polymer, cationic surfactant and nonionic polymer, and anionic surfactant and nonionic polymer. The mixtures of anionic surfactant and cationic polymer showed improved foam stability, however, the foaminess was strongly reduced, as compared to the surfactant solutions without polymer. No significant synergistic or antagonistic effects were observed for the mixture of nonionic surfactant (with low critical micelle concentration) and nonionic polymer. The results from the model experiments allowed us to explain the observed trends by the different adsorption dynamics and complex formation pattern in the systems studied.     

The adsorption of cationic and amphoteric copolymers on glass surfaces: zeta potential measurements,adsorption isotherm determination,and FT Raman characterization

The adsorption of cationic and amphoteric copolymers onto controlled pore glass (CPG) powders has been studied by measurement of the powder particle zeta (zeta) potential, by determination of the adsorption isotherm, and by FT Raman measurements of the polymer-coated powder. The cationic polymers consisted chiefly of homopolymers of dimethyldiallylammonium chloride (DMDAAC) or copolymers of DMDAAC and acrylamide. The amphoteric polymers studied included copolymers of DMDAAC and acrylic acid. The comonomer ratio was varied to explore the dependence of cationic charge density on the extent and effect of adsorption. Both types of polymers adsorb onto the anionic glass surface via an ion-exchange mechanism. Consequently, a correspondingly higher mass of a low-charge-density copolymer adsorbs than of a cationic homopolymer. The presence of the anionic portion in the amphoteric polymers does not significantly alter this picture. The zeta potential, however, reflects the overall nature of the polymer. Cationic polymers effectively neutralize the glass surface, while amphoteric polymers leave the zeta potential net negative. Adsorption isotherms, determined via the depletion technique using colloidal titration, were used to "calibrate" a FT Raman method. The latter was used to determined the amount of adsorbed polymer under solution conditions in which colloidal titration could not be performed.     

Adsorption of PEO-PPO-PEO triblock copolymers with end-capped cationic chains of poly(2-dimethylaminoethyl methacrylate)

We study the adsorption of a symmetric triblock copolymer of ethylene oxide, EO, and propylene oxide, PO, end-capped with quarternized poly(2-dimethylaminoethyl methacrylate), DMAEMA (DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24)). Light scattering and tensiometry are used to measure the relative size of the associated structures and surface excess at the air-liquid interface. The adsorbed amount, the amount of coupled water, and the viscoelasticity of the adsorbed polymer layer are measured on hydrophobic and hydrophilic surfaces (polypropylene, cellulose, and silica) by using quartz crystal microgravimetry (QCM) and surface plasmon resonance (SPR) at different ionic strengths and temperatures. The results of the experiments are compared with those obtained after adsorption of the uncharged precursor copolymer, without the cationic end-caps (EO(132)PO(50)EO(132)). DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) possesses higher affinity with the negatively charged silica and cellulose surfaces while the uncharged copolymer adsorbs to a larger extent on polypropylene surfaces. In this latter case, adsorption increases with increasing solution ionic strength and temperature. Adsorption of EO(132)PO(50)EO(132) on silica surfaces has little effect on the water contact angle (WCA), while adsorption of DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) increases the WCA of silica to 32°, indicating a large density of exposed PPO blocks upon adsorption. After adsorption of EO(132)PO(50)EO(132) and DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) on PP, the WCA is reduced by ≈14° and ≈28°, respectively, due to the exposed hydrophilic EO and highly water-soluble DMAEMA segments on the surfaces. The extent of surface coverage at saturation at the polypropylene/liquid interfaces (≈31 and 40 nm(2)/molecule obtained by QCM and SPR, respectively) is much lower, as expected, when compared with results obtained at the air/liquid interface, where a tighter packing is observed. The percentage of water coupled to the adsorbed cationic polymer decreases with solution ionic strength. Overall, these observations are ascribed to the effects of electrostatic screening, polymer hydrodynamic size, and solvency.