Deposition of polymer latices on grafted Nylon 6 fiber

Deposition of polymer latices on a grafted Nylon 6 fiber was studied as a function of pH and the degree of grafting. The latices were polystyrene (PS), styrene/acrylamide copolymer (P(St/AAm)) and styrene/acrylic acid copolymer (P(St/AA)). The deposition of the latices on the grafted fiber decreased in every case with increasing pH and no deposition was observed at alkaline pH. The grafting of fiber with acrylic and methacrylic acid reduced the deposition of P(St/AAm) and P(St/AA) latices but had no influence on the deposition of PS latex. The relation between the deposition rates and the interaction energy at acidic pH indicates that the deposition of PS latex on the grafted fiber mainly depends on the electrostatic interaction. These results suggest that the expansion of water-soluble polyelectrolyte layer on the surface of grafted fiber plays an important role on the deposition.     

The effect of metallic cations on the electrophoretic properties of a pretreatedHevea latex

High-ammonia latex concentrate prepared from doubly-centrifuged fieldHevea latex was exhaustively dialysed to remove any residual water-soluble non-rubber constituents. The electrophoretic mobilities of the dialysed latex in the presence of various metallic cations were investigated as a function of electrolyte concentration. The mobility decreased with increasing concentration of the cations Na⁺, Ba²⁺, Mg²⁺ and Ca²⁺ in a manner consistent with the effect of simple electrolyte on compression of the electric double layer. Anomalous behaviour was noted for the divalent ion copper, in that it reversed the charge of the latex particles at a concentration even lower than that of uranyl ions. Multivalent cations (lanthanum, cerium and thorium) had a profound influence on the latex particles where very low charge reversal concentrations were observed. It is believed that strong adsorption of hydrolysed species from the metallic ions was responsible for reversing the charge of the originally negative latex particles. These experiments indicated that the efficiency with which the cations reversed the charge of the latex particle surface was in the order: lanthanum > cerium > copper > thorium > uranyl > calcium > magnesium > barium > sodium. The number of cation binding sites on the latex particle surface and the chemical free energies of cation adsorption were calculated. It was found that the interaction of the latex particle with the hydrolysable metallic cations was much more stronger than that with the simple divalent cations and that this intercation was comparable to that of biological surfaces.     

Preparation of composite fine particles by heterocoagulation

To prepare regular composite particles comprised of organic and inorganic compounds, based on heterocoagulation theory, the properties of the mixture of small amphoteric latices (2a=250 nm) and large spherical silica (2a=240–1590 nm) were investigated as a function of pH, particle number ratio, particle size ratio and electrolyte concentration in the medium. It is apparent that under suitable conditions, we may prepare a stable mixed suspension comprising uniform composite particles, which are made up of many latices regularly adsorbed on silica surfaces, and each composite particle is undergoing Brownian motion as an isolated unit. This new composite particle is very stable for electrolyte, base and acid medium, and its surface charges (sign and magnitude) can be controlled by changing the pH of the medium.     

Conformational changes of polyglutamic acid adsorbed on cationic polystyrene as characterized by microelectrophoresis technique

Polypeptides (polyglutamic acid in sodium form) of three different polymerization degrees have been adsorbed on cationic polystyrene latex. The electrokinetic behavior of the complex PG/PS has been studied by microelectrophoretic mobility. The effect of ionic strength and pH on electrokinetic properties of the complex PG/PS have also been studied. It has been found that the appearance of maximum inu _e -logc curves is related to coverage degree of polystyrene surface and the polymerization degree of polypeptides chains. Likewise, the form of such curves depends markedly on pH. An attempt has been made to explain the data in terms of conformational changes of the adsorbed polypeptides chains.Presented at the NATO Advanced Study Institut on Polymer Colloid, Strasbourg (France), July 1988.     

Chemical heterogeneity in emulsion copolymers of carboxylic monomers

Copolymer latices of butylacrylate (BA) with acrylic and methacrylic acid (AA and MAA) were prepared by batch type emulsion polymerization, and, for comparison, copolymers with identical monomer composition were prepared by batch type solution polymerization.The distribution of the carboxylic monomers in the latex particles and the serum was studied by density gradient and sedimentation experiments with the analytical ultracentrifuge. Dynamic mechanical measurements of films of these copolymers were used to determine the storage and loss moduli as a function of temperature. From these measurements the position and extension of the glass transition range on the temperature scale is obtained. For heterogeneous emulsion copolymers with two glass transition temperatures the distribution of the carboxylic monomer units in the different copolymer phases can be determined. Electron microscopy of ultra thin cross-sections of stained films gave further insight into the film morphology.The combination of the results obtained with the different methods gives rise to the following clues: In the BA/AA latices about 40% (by weight) of the total AA used in the recipe are found in the serum as a water soluble polymer, about 50% are found to increase the glass transition temperatureT _g of the bulk of the BA copolymer and, therefore, are thought to be incorporated into the interior of the latex particles, and the remaining 10% are, conclusively, located on the particle surface.In the BA/MAA latices no water soluble copolymer could be detected in the serum, about 90% of the MAA used is found in the bulk of the copolymer, and about 10% form a second hard phase on the surface of the latex particles.Dynamic mechanical measurements on the copolymer latex films show at least two phases with different glass transition temperatures: the bulk of the copolymer with a relatively low content of (M)AA units and a glass transition range at low temperatures, and a second (M)AA rich phase with a highT _g.The latter phase forms a honeycomb-like structure surrounding the packed latex particles. That results in a three-dimensional network of polymer with a highT _g extending throughout the latex film. In spite of the fact that this phase is built from a small fraction of the total copolymer only, it has a very pronounced influence on the performance behaviour of latex films.Dedicated to Professor Dr. R. Manecke on the occasion of his 70th birthday.     

Preferential adsorption of bovine serum albumin dimer onto polymer microspheres having a heterogeneous surface consisting of hydrophobic and hydrophilic parts

The adsorption behaviors of bovine serum albumin (BSA) containing both dimeric and monomeric species onto polymer microspheres were examined using various homopolymers and poly(2-hydroxyethyl methacrylate)/polystyrene composite microspheres which were produced by the emulsifier-free (seeded) emulsion polymerization technique. The preferential adsorption of the BSA dimer was clearly observed in an optimum region of the surface hydrophilicities of the polymer microspheres. The preferential adsorption of the BSA dimer onto the composite polymer microspheres having heterogeneous surfaces consisting of hydrophilic and hydrophobic parts was more marked than those onto the homopolymer and copolymer microspheres having homogeneous surfaces.     

The pH dependence of dispersion of TiO2 particles in aqueous surfactant solutions

The pH dependence of dispersion of titanium dioxide (TiO₂) particles has been examined in the presence of surfactant molecules in water. Whereas particles were dispersed in water at acid and alkaline regions rather than at neutral region, the dispersion was enhanced at neutral region in an aqueous sodium dodecyl sulfate (SDS) solution and at acid and alkaline regions in an aqueous dodecyldimethylamine oxide (C₁₂DAO) solution. Considering the pH dependence of zeta potential, the adsorption models of surfactant molecules on a particle were estimated on the basis of the modes of hemimicelle and double-layer compression. While the particles that adsorbed Al³⁺ were remarkably dispersed around pH 6, their dispersion does not largely depend on pH in the addition of SDS, indicating the adsorption of SDS molecules to form double-layer compression in the whole pH region. Dynamic light-scattering measurement and electron microscopic observation suggested that the particles were dispersed in water as small flocs.     

Adsorption of anionic surfactants on positively charged polystyrene particles II

In the case of cationic polystyrene latex, the adsorption of anionic surfactants involves a strong electrostatic interaction between both the particle and the surfactant, which may affect the conformation of the surfactant molecules adsorbed onto the latex-particle surface. The adsorption isotherms showed that adsorption takes place according to two different mechanisms. First, the initial adsorption of the anionic surfactant molecules on cationic polystyrene surface would be due to the attractive electrostatic interaction between both ionic groups, laying the alkyl-chains of surfactant molecules flat on the surface as a consequence of the hydrophobic interaction between these chains and the polystyrene particle surface, which is predominantly hydrophobic. Second, at higher surface coverage the adsorbed surfactant molecules may move into a partly vertical orientation with some head groups facing the solution. According to this second mechanism the hydrophobic interactions of hydrocarbon chains play an important role in the adsorption of surfactant molecules at high surface coverage. This would account for the very high negative mobilities obtained at surfactant concentration higher than 5×10^–7 M. Under high surface-coverage conditions, some electrophoretic mobility measurements were performed at different ionic strength. The appearance of a maximum in the mobility-ionic strength curves seems to depend upon alkyl-chain length. Also the effects of temperature and pH on mobilities of anionic surfactant-cationic latex particles have been studied. The mobility of the particles covered by alkyl-sulphonate surfactants varied with the pH in a similar manner as it does with negatively charged sulphated latex particles, which indicates that the surfactant now controls the surface charge and the hydrophobic-hydrophilic character of the surface.Dedicated to the memory of Dr. Safwan Al-Khouri IbrahimPresented at the Euchem Workshop on Adsorption of Surfactants and Macromolecules from Solution, Åbo (Turku), Finland, June 1989     

Effect of surface charge on adsorption of bovine serum albumin 2. Interaction of protein molecules with an anionic monolayer,as studied by ellipsometry,radiotracer and surface tension measurements

The adsorption of bovine serum albumin (BSA) onto an anionic monolayer of sodium docosylsulfate (SDocS) spread at the air/water interface was studied by ellipsometry. The adsorption behavior of BSA was estimated from the observed changes in phase differences and in the ratio of reflection coefficients. The dynamic process of BSA adsorption was measured after the injection of BSA solution into the aqueous substrate of SDocS monolayer. The gentle stirring of the substrate solution for 10 min was found to be enough to make the solution homogeneous without damaging the monolayer. The adsorption characteristics of BSA onto a negatively charged surface was compared with that onto a positively charged surface previously reported.The amount of adsorption depended on time and showed a maximum with an initial rapid rise, followed by gradual decrease toward the ultimate equilibrium value. The amount and time of the maximum adsorption depended on the concentration of BSA added to the aqueous substrate.Separate radiotracer measurement, using³⁵S-labeled SDocS monolayer, which is insoluble by itself, revealed that SDocS is solubilized into the bulk solution when BSA is added to the aqueous substrate.     

Swelling of poly(methacrylic acid) gels and adsorption of L-lysine and its polymer on the gels

Poly (methacrylic acid) gels (PMAA gels) of various degrees of crosslinking were prepared and the dissociation behavior of these gels was examined; the swelling behavior was investigated as a function of the solution pH values. A reentrant phenomenon of swelling was observed and interpreted based on the Flory-Huggins equation and the Donnan equilibrium formula. Moreover, adsorption of L-lysine, oligo(L-lysine)s (Lys-n,n=3, 9, and 19) and poly(L-lysine) onto PMAA gels from aqueous solutions was investigated under different conditions of pH and concentration of adsorbate. The adsorption ratio of L-lysine onto PMAA gel is dependent on both the pH of solution and the degree of crosslinking. In a pH range between 8 and 9, the protonated form of L-lysine is strongly adsorbed on the PMAA gel by electrostatic interactions. Oligomers and polymer of L-lysine are adsorbed in a somewhat different way from the monomeric L-lysine. In addition, the desorption behavior of L-lysine from PMAA gels by a change in pH was also investigated.     

Contribution of steric and electrostatic repulsion forces to the stability of styrene latices copolymerized with acrylic acid

Acrylic acid (AA) is used in many emulsion polymerization formulations to improve the colloidal stability of the latex product. The improved stability originates from electrostatic repulsion complemented with steric repulsion. The strength of the electrostatic and steric repulsion forces in a styrene (S)/AA copolymer latex was investigated at different pH values, electrolyte concentrations, and temperatures. A comparison was made with an S homopolymer latex. Transmission electron microscopic pictures, combined with visual inspections, provided understanding of the mechanisms leading to coagulation in polystyrene (PS)/AA copolymer latices. Colloidal stability of the unswollen sodium dodecyl sulfate stabilized PS latex is based on electrostatic repulsion. Destabilization by sodium chloride resulted in aggregation. The acidic PS/AA latex remained stable against aggregation at high electrolyte concentrations because of steric repulsion. The acidic PS/AA latex showed a strong tendency to flocculate at increasing electrolyte concentrations. Flocculation was not observed for high‐pH PS/AA latices at high electrolyte concentrations. Steric repulsion of the acid PS/AA latex was lost at temperatures higher than the critical coagulation temperature (35 °C), and flocculation was followed by aggregation and coalescence. The high‐pH PS/AA latex was stable even at high electrolyte concentrations and temperatures up to 80 °C because of strong electrosteric stabilization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2985–2995, 2003     

Polystyrene(1)/poly(butyl acrylate-methacrylic acid)(2) core-shell emulsion polymers. Part I. Synthesis and colloidal characterization

Polystyrene (PS) (1)/Poly(n-butyl acrylate (BA)-methacrylic acid (MAA)) (2) structured particle latexes were prepared by emulsion polymerization using monodisperse polystyrene latex seed (118 nm) and different BA/MAA ratios. Three main aspects have been investigated: i) the polymerization kinetics; ii) the particle morphology as a function of reaction time; iii) the distribution of MAA units between the water phase and the polymer particles.The amount of MAA in the shell copolymer was found to be the main factor controlling the particle shape and morphology. The shape of the structured particles was, generally, non-spherical, and the shape irregularities increased as a particles was, generally, non-spherical, and the shape irregularities increased as a function of reaction time. At the beginning of the second stage reaction, new small particles were observed, which coalesced onto the PS seed as the polymerization proceeded. The distribution of the MAA groups in the latex particles and the serum was analyzed by alkali/back-acid titration, using ionic exchanged latexes. No MAA groups were detected in the latex serum. Due to the lowTg of the BA-MAA copolymers, alkali conductimetric titrations accounted for all the MAA groups on and within the polymer particles. Therefore, for these systems, this method is not only limited to a thin surface layer, as it is often assumed.     

Characterization of wood fibers modified by phenol-formaldehyde

Wood-fiber phenol-formaldehyde-resin (PFR) modified surfaces, obtained from the adsorption of a PFR/water solution, are investigated as a function of the nature and the amount of PFR adsorbed. Surface are measurements are performed by using krypton adsorption at 77 K. Chemical modification is monitored by the electron spectroscopy for chemical analysis (ESCA) technique and the surface energy by the inverse phase gas chromatography (IPGC) method at infinite dilution. The London dispersive componentγ _S ^L of the surface energy shows a relationship to the concentration of carbon and oxgen at the fiber surface.γ _S ^L increases from 27.5 mN·m⁻¹ for the untreated fiber to 42.5 mN·m⁻¹ for the fibers treated with 20% high molecular-weight-grade phenol-formaldehyde. The surface atomic ratio O/C determined using the ESCA technique exhibits a decrease from 44% for untreated to 31% for treated samples. Surface area also decreases from 2.09 m²/g to 1.50 m²/g. The PFR adsorbed by wood fibers is observed as the dispersive component of surface energy starts to increase, as the surface oxygen concentration decreases, and on the surface area of the wood fiber.     

Polymer adsorption on fine particles; the effects of particle size and its stability

The effects of particle size on polyacrylamide (PAAm,M _w =59×10⁴, 500×10⁴) adsorption were investigated using a series of well-characterized hematite (-Fe₂O₃) dispersions. The -Fe₂O₃ particles with highly monodisperse and nearly spherical shape ranged in radius from 23 nm to 300 nm. the maximum amount of PAAm adsorption (M _m ) in each system, showed a steady increase with decreasing particle radius and was influenced strongly by particle concentrations in the medium. Furthermore, it was realized that the diameter of -Fe₂O₃ particles after treatment with PAAm under different particle concentrations decreased with increasing particle concentration. The relation between particle concentration in the medium and particle size after treatment was also influenced by the medium pH, i.e., at the medium pH close to the isoelectric point of -Fe₂O₃ particles (pH^o=9.2), the particle size after treatment increased with increasing particle concentration. All these results suggest that in the system of ultra-fine particles, the mixing process between particle-particle and polymerparticle will play an important role on the conformation of adsorbed polymer layer.     

Polyacrylamide Na-kaolinite interactions: Effect of electrolyte concentration on polymer adsorption

The variation in polyacrylamide adsorption on Na-kaolinite as a function of the electrolyte concentration of the clay suspension, was determined under three pH conditions, where the clays display varying charge characteristics. Interpretation of the results is based on two arguments: non-charged polyacrylamide adsorption is restricted to the edge faces of the colloidal platelets and hydrogen bonding between the amide groups of the polymer and the isolated hydroxyl sites of these faces is the mode of surface attachment. At constant pH, when Na-kaolinite bears charged surface groups, the polymer adsorption, which is related to the density of the anchoring sites, parallels the state of ionization of the edge surface. The mechanism by which the salt modifies the adsorption properties of the kaolinite in neutral medium is not established with certainty. Nevertheless, no polymer-clay association occurs if the surface is entirely uncharged. This result is in line with the fact that while hydroxyl groups are engaged in internal hydrogen bonds, they cannot hydrogen-bond to the polyacrylamide. Variations in the clay-polymer affinity are attributed to a modification of the interfacial structure of the adsorbed polymer, associated with changes in the surface density of the anchoring groups.     

Adsorption of polyethylene glycol from aqueous solution on montmorillonite clays

Adsorption rates and capacities of polyethylene glycol (PEG) were investigated for five montmorillonite clays. The adsorption of PEG for all the montmorillonite clays was rapid, and equilibrium was attained within 30 min. The adsorption isotherms of PEG for all the montmorillonites conformed to the Freundlich equation. The adsorption heats were 7.3 and 11.6 kJ · mol^–1(mw.:2000), and 8.7 and 14.2 kJ · mol^–1(mw.:20000) for the montmorillonite and the bentonite II-Ca, respectively. Adsorption capacities for all the clay samples approached constants for the molecular weight of PEG over 2000, though they increased with the increase of molecular weight under 2000. The adsorption capacities were slightly influenced by a nearly neutral pH. The montmorillonite clays which had different interlayer cations showed quite different adsorption capacities. The bentonite II-Ca, the acid clay, and the activated clay showed large adsorption capacities that were 30–50 % of that of an activated carbon.     

Changes in electrokinetic properties of natural rubber latex after surface chemical modifications

High-ammonia latex concentrate prepared from doubly-concentrifuged fieldHevea latex was exhaustively dialyzed to remove any residual water-soluble non-rubber constituents. The specially purified latex was then treated with specific chemical reagents to modify the surface ionogenic groupings originally present on the latex particle surface. The electrophoretic mobility of the modified latexes was investigated as a function of pH. The change in electrokinetic properties of the surface-modified latex was explained in terms of chemical modification to the ionogenic groups of the adsorbed layer of proteins and long chain fatty acid soaps on the latex particle surface, the negative charges of which are primarily responsible for the colloidal stability of the latex. For comparison direct extraction of the long-chain fatty acid soaps from the specially purified latex by solvent was also carried out. Present results indicate that the number of carboxyl groups from the adsorbed long-chain fatty acid soaps plays a major role in the stabilization of the latex concentrate. In comparison the contribution of negative charges from the adsorbed proteins towards the stability of the latex is of less importance.     

XPS analysis (ESCA) of the surface composition of poly(styrene/2-hydroxyethyl methacrylate) microspheres produced by emulsifier-free emulsion polymerization

Polymer microspheres composed of various compositions of styrene and 2-hydroxyethyl methacrylate (HEMA) were produced by batch emulsifier-free emulsion polymerization. The HEMA content at the surface, [HEMA] _s , of the microspheres powdered by freeze-drying was determined by both quantitativeC ^1s /O ^1s analysis andC ^1s peak shape analysis of the x-ray photoelectron spectroscopic spectra. When the HEMA content in the microsphere, [HEMA] _p , was less than about 5 mole%, the [HEMA] _s values determined by the two different methods showed good agreement. At [HEMA]_p above 5 mole %, [HEMA]_s values determined by the first method were about 15 mole % greater than those determined by the second. They both showed a similar tendency with the [HEMA] _s being higher than the [HEMA] _p , e.g., when [HEMA] _p was 1 mole %, [HEMA] _s was 11 mole %. The intensity of the satellite peak due to the ^* transition of the benzene ring of the styrene component decreased with an increase in [HEMA] _p , to zero at 5 mole % of [HEMA] _p . These results indicate that the HEMA component is localized at the surface.Part CVIII of the series Studies on Suspension and Emulsion.     

Adsorption of quaternary ammonium chlorides with various hydrocarbon chain lengths to glass

Contact angles, measured with various liquids, have been employed to calculate the surface free energies of glass after adsorption of quaternary ammonium chlorides with a variable hydrocarbon chain length 8n16. The thickness of the adsorbed layers has been determined ellipsometrically. A clear relation is observed between the measured parameters and the hydrocarbon chain lengthn, if only the extremesn=8 andn=16 are considered. Surface free energies decrease from 138 erg.cm^–2 for clean glass to 101 and 64 erg.cm^–2 forn=8 andn=16, respectively, at the highest concentration tested (7.5 mM). The adsorbed layer thickness of C₈ amounts to approximately 50 % of the thickness observed for C₁₆. No clear relation between the measured parameters is observed for the intermediate hydrocarbon chain lengths, which presumably reflects the many configurations possible in these adsorbed layers. It is envisaged that adsorption of C₈ as well as C₁₆ is restricted to a monolayer, which is completed at approximately 2 mM. In the case of C₈ electrostatic repulsion between the polar headgroups will inhibit further adsorption, whereas in the case of C₁₆ the van der Waals attraction from the adsorbed layer and the glass will probably not be sufficient to stimulate further adsorption.