Adsorption Of Polymer Molecules Research Articles

Effect of Silica Particle Size on Polymer Adsorption. Morphological, Energetic and Conformational Relationships

AbstractA series of six chemically treated and untreated fumed silicas with increasing particle size (ranging from the nano‐ to the micrometer size) was prepared. Surface areas (and morphologies) and surface energies were determined by nitrogen adsorption and inverse gas chromatography, respectively. The adsorption of a series of PDMS with different and well‐defined molecular weights was studied at different polymer concentrations. Amounts of adsorbed polymer were determined by gravimetry and the energies of adsorption were assessed by flow‐microcalorimetry. Results are discussed in terms of particle surface energy and morphology effects on the conformation and the inter‐connectivity of adsorbed polymer molecules.

Micellization of non-surface-active diblock copolymers in water. Special characteristics of poly(styrene)-block-poly(styrenesulfonate).

Strongly ionized amphiphilic diblock copolymers of poly(styrene)-b-poly(styrenesulfonate) with various hydrophilic and hydrophobic chain lengths were synthesized by living radical polymerization, and their properties and self-assembling behavior were systematically investigated by surface tension measurement, foam formation, hydrophobic dye solubilization, X-ray reflectivity, dynamic light scattering, small-angle neutron scattering, small-angle X-ray scattering, and atomic force microscope techniques. These copolymer solutions in pure water did not show a decrease of surface tension with increasing polymer concentration. The solutions also did not show foam formation, and no adsorption at the air/water interface was confirmed by reflectivity experiments. However, in 0.5 M NaCl aq solutions polymer adsorption and foam formation were observed. The critical micelle concentration (cmc) was observed by the dye solubilization experiment in both the solutions with and without added salt, and by dynamic light scattering we confirmed the existence of polymer micelles in solution, even though there was no adsorption of polymer molecules at the water surface in the solution without salt. By the small-angle scattering technique, we confirmed that the micelles have a well-defined core-shell structure and their sizes were 100-150 A depending on the hydrophobic and hydrophilic chain length ratio. The micelle size and shape were unaffected by addition of up to 0.5 M salt. The absence of polymer adsorption at the water surface with micelle formation in a bulk solution, which is now known as a universal characteristic for strongly ionized amphiphilic block copolymers, was attributed to the image charge effect at the air/water interface due to the many charges on the hydrophilic segment.

Compaction of TiO2 suspension utilizing hydrophilic/hydrophobic transition of cationic thermosensitive polymers.

Compaction of TiO2 suspended particles utilizing the hydrophilic/hydrophobic transition of a cationic thermosensitive copolymer of N-isopropylacrylamide (NIPAM) and N-dimethylaminopropylacrylamide (DMAPAA) was examined. The surface of suspended TiO2 particles were sufficiently covered with the adsorbed polymer molecules at room temperature, and the suspension was subsequently heated above the transition temperature of the polymer. The thrusting motion of a plunger was used in order to provide an adequate mechanical force to compact the TiO2 suspended particles. The transition temperature was dependent on the DMAPAA content in the copolymer and the pH of the suspension. The transition temperature increased with increasing DMAPAA content and decreased with increasing pH. While suspended TiO2 particles were not compacted with poly(NIPAM), hard compacted sludge was readily obtained for cationic copolymer even if the content of DMAPAA groups was as low as 0.23 mol%. Furthermore, residual polymer molecules in the supernatant were not detected even if the polymer dosage was increased. These findings were attributed to the hydrophobic interaction of thermosensitive copolymer molecules adsorbed on TiO2 particles.

Polymer Micelle Formation without Gibbs Monolayer Formation: Synthesis and Characteristic Behavior of an Amphiphilic Diblock Copolymer Having Strong Acid Groups

A novel amphiphilic diblock copolymer having sulfonic acid groups in its hydrophilic chain with poly(diethylsilacyclobutane) as a hydrophobic segment was synthesized by living anionic polymerization followed by treatment with 1,3-propane sultone. The polymer backbone with a degree of polymerization of 18 (hydrophobic):37 (hydrophilic) was synthesized, and three kinds of diblock copolymers with different degrees of sulfonation (α = 0, 0.50, 0.81) were prepared as sodium salts. The surface tension of aqueous solutions of highly sulfonated polymers as including the α = 0 (all carboxylic acid) polymer did not decrease with polymer concentration. The solutions did not show foam formation even after vigorous shaking, and almost no adsorption of polymer molecules was observed at the air/water interface by X-ray reflectivity measurement. However, micelle formation with a radius of 140−200 Å was confirmed by dynamic light scattering and small-angle X-ray scattering experiments. Hence, this polymer showed “micelle formation” without “Gibbs monolayer formation” in water. The surface tension decrease in 0.5 M NaCl aqueous solution was also small, but adsorption of polymer was observed by X-ray reflectivity in addition to formation of foam by shaking. The strong ionic character of this novel class of amphiphilic polymer is thought to be the origin of this curious behavior.

SANS from adsorbed polymer layers

AbstractOne of the areas in which small‐angle neutron scattering (SANS) has had a profound impact over the last twenty years is the investigation of polymers and surfactants adsorbed at the solid/liquid and liquid/liquid interfaces. This is of course also an area of considerable commercial importance. Control of the structure of an adsorbed layer is thus a key priority of the colloid scientist. Equally important, however, is the ability to probe the arrangement of the adsorbed polymer molecules and to extract quantitative information from what might well be a complex, multicomponent system. SANS in combination with the principle of deuterium contrast variation is uniquely placed to provide this information.

Inorganic-organic functionally-graded films: The role of intermediate layers between TiO2 coatings and polymer substrates

An organic/inorganic-graded film was fabricated by a loop-tail-train-like adsorption of polymer molecules on polymer materials. Silicon dioxide (SiO2)/polymethyl metacrylate(PMMA)-graded film of 50nm was fabricated by optimal fabrication conditions such as an inorganic/organic ratio of prepared polymer, a concentration of solvent and coating processes. The fabricated-graded film was applied as an intermediate layer between the photo-active TiO2 and the polymer. Sunshine weatherometer examination was conducted on the fabricated samples including the PMMA intermediate layer, the SiO2 intermediate layer prepared from tetraethoxysilane (TEOS), and the fabricated-graded layer. The strong oxidation power of photo-excited TiO2 deteriorated the PMMA/TiO2 interface resulting in a hazy appearance after the sunshine weatherometer test. Microcracks instead of deterioration by photo-oxidation were observed on the SiO2 intermediate layer after the sunshine weatherometer test, and these microcracks resulted in the hazy appearance of the film. The formation of cracks was attributable to the brittleness of the SiO2 intermediate layer. However, there was no change in appearance on the film utilising the SiO2/PMMA-graded intermediate layer.

Surface and interfacial properties of polymer-intercalated layered double hydroxide nanocomposites

The surface and interfacial properties of the layered double hydroxide (LDH) phase Mg 6Al 2(OH) 16CO 3·4H 2O (LDHCO3) and its nanocomposites with poly(styrenesulfonate) (LDHPSS) and poly(vinylsulfonate) (LDHPVS) were characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, transmission electron microscopy, He pycnometry, and electrophoretic light scattering. Polymer incorporation within the inter-gallery space resulted in a shift of the d 003 reflection from 7.7 Å (LDHCO3) to 12.7 Å (LDHPVS) and 21 Å (LDHPSS). This increase in basal plane spacing caused the density of the LDH samples to decrease from 2.05 g/cm 3 (LDHCO3) to 1.83 and 1.41 g/cm 3 for LDHPVS and LDHPSS nanocomposites, respectively. LDHCO3 exhibited a positive electrophoretic mobility over the pH range from 4–11 with an isoelectric point (iep) at pH 11. However, the LDH nanocomposites displayed a negative electrophoretic mobility over the measured pH range, indicating that the surface properties of the LDH nanocomposites were dominated by negatively charged sulfonate groups from adsorbed polymer molecules.

Component interactions and the stability of some pigment/polymer dispersions

The sedimentation behavior of rutile and selected organic pigments dispersed in polymer solutions has been interpreted in terms of acid-base interactions at the polymer/pigment interface. The acid-base information was obtained from inverse gas chromatography. Moderate strengths of acid-base interaction were beneficial to the stability of dispersions, whereas both the absence of and excessive interaction resulted in the rapid deposition of solids. The effect is associated with the orientation of adsorbed polymer molecules, which must provide an adequate steric (entropic) barrier for the aggregation and deposition of solids. Implicated is the balance of interaction forces at pigment/polymer and polymer/solvent contacts. Rheological data for the dispersions have been used to obtain a parameter related to the thickness of the adsorbed polymer layer, by way of amplifying on the state of the pigment/polymer interface. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 245–253, 1998

The role of polyelectrolytes in the stabilisation and destabilisation of colloids

The aim of this study was to investigate the adsorption of polyelectrolytes on charged colloids with regard to their different modes of action in the destabilisation or stabilisation of colloidal suspensions. Polyvinyl pyridine was employed as polyelectrolyte and polystyrene latexes bearing sulfonate or carboxylate groups as colloids. Adsorption of the polyelectrolyte was followed using a radiolabelling technique which allowed determination of (i) the concentration of polymer remaining in the supernatant liquid phase and (ii) the rate of establishment of the interfacial layer at very low polymer concentrations. In fact, this situation generally led to destabilisation of the colloidal suspension. Changing the rate of polymer supply to the adsorbent enabled characterisation of the interfacial reconformation of the adsorbed polymer molecules. Slow supply rates limited the amount of polymer instantaneously adsorbed, while fast rates induced a desorption of the macromolecules in excess. Destabilisation and stabilisation processes were investigated using a particle counting method (Coulter Counter TA 11, Coultronics). This technique provides a histogram which is analysed to give the size (mass) frequency curve of the aggregates c(n,t) vs. n and the weight S(t) and number N(t) average sizes of the aggregates. The experimental data were interpreted with the aid of results from numerical and theoretical studies. Self-similarity of the aggregate and fragment size distributions throughout aggregation and fragmentation could be demonstrated, while modifications of the reduced size distribution revealed changes in the rate limiting phenomena. Dynamic scaling laws were derived to describe the temporal variations of the aggregation and fragmentation processes. According to the relative values of the dynamic exponents z and w and the exponent of the power-law cluster size distribution τ it was possible to determine the aggregation mechanism. In fragmentation however the situation appeared to be more complex. No clear correlation could be established between the dynamic exponents λ and μ of the rates of variation of S(t) and N(t) and the exponents of the reduced size distribution λ′ and ν determined at large and small values of the fragment size n. Whereas λ and μ were functions of the interfacial and solution characteristics, λ′ and ν depended on the mode of aggregate formation.

Adsorption of Polymer on Dispersion Particles

The kinetic behavior of the adsorption of polymer molecules onto the surfaces of dispersed particles is examined theoretically. Under the assumptions that the surface coverage of a particle by polymer is low and the adsorption is irreversible, the distribution of the probability of the number of adsorbed polymer molecules can be approximated by a Poisson distribution (Kislenko et al., J. Colloid Interface Sci.156, 508, 1993). A more detailed analysis reveals that, regardless of the reversibility of the adsorption process, a binomial distribution appears to be more appropriate. The deviation of the approximate Poisson distribution from the corresponding binomial distribution depends on the number of sites on a particle, S. In particular, the Poisson distribution is close to the latter only for a certain range of S; the former does not approach to the latter as S increases infinitely.

Electrooptic Study of Colloid Dispersions Stabilized by Polyelectrolyte Adsorption

Several electrooptic parameters can be used to follow the stages of polyelectrolyte adsorption on colloid particle surfaces. The process of electrostatic stabilization, achieved by polyelectrolyte surface recharging, is investigated for a series of samples and the results are compared to those obtained for low molecular surfactant stabilization. The results indicate a significant decrease of the relaxation frequency of particle electric polarizability in the presence of polyelectrolyte coverage. Evidence is given for the direct relation of the electrooptic relaxation frequency to the type of the adsorbed polymer molecule.

Effect of hydrophobically modified comb-like polymer on interfacial properties of coal

Hydrophobically modified polymers arc known to exhibit interesting interfacial properties and here surface modification of coal by a comb-type hydrophobic-hydrophilic copolymer (DAPRAL) was studied. Floatability tests revealed the coal to become more hydrophobic with increasing DAPRAL concentration regardless of its original floatability, suggesting that free segments of adsorbed polymer molecules can reorient with the hydrocarbon chains protruding into the gas phase. Zeta potential measurements it pH 3.5 and 7 showed the minimum DAPRAL concentrations needed to mask completely the surface charge of coal to correspond to those required to increase the coal floatability to the maximum. Hydrophobicity measured using a new reliable film-levitation technique also showed the coal to become more hydro-phobic with increasing polymer concentration but only until a plateau is reached. Further increase in DAPRAL concentration caused a decrease in the hydrophobicity which is suggested to be due to the consumption of the hydrocarbon chains on unadsorbed polymer segments by the formation of micellar aggregates.

Transient collision efficiency of polymer-induced flocculation

The temporal variation of the collision efficiency of primary particles in polymer-induced flocculation is investigated. A kinetic model is introduced assuming that the flocculation and the adsorption of polymer molecules are second order, and the desorption of polymer molecules is first order. The adsorption of polymer molecules is assumed to be reversible, and an adsorbed polymer molecule is allowed to rearrange itself. The result of numerical calculations reveals that, depending on the ratio (number of sites on the polymer molecules/number of sites on the surfaces of the colloidal particles) and the relative magnitude of the adsorption rate constant and the desorption rate constant, the collision efficiency calculated by the conventional analysis may be either underestimated or overestimated. Thus, care must be taken in predicting the rate of polymer-induced flocculation through the collision efficiency approach.

Adsorption of polyacrylamide on gold and iron from acidic aqueous solutions

The adsorption behaviour of polyacrylamide (PAA) on gold, and mild steel from sulphuric and hydrochloridic acid was studied using cyclic voltammetry with simultaneous monitoring of the double layer capacity. Adsorption isotherms, obtained by capacity measurements (using the two-condenser model), and corresponding thermodynamic parameters of the adsorption processes strongly depend upon the molecular mass of the polymer, electrode potential and temperature. In all cases the experimentally-obtained results show the best fit with Frumkin's isotherm (Langmuir and Flory—Huggins isotherms were tested as well). It was found that nearly complete coverage (θ = 1) can be reached at extremely low polymer concentrations in the solution (10 −8−10 −7 m) which can be explained by a significant participation of the directly attached segments of the polymer molecules (trains) at the metallic surface and weak lateral interactions. This conclusion was proved by comparison of the polymer adsorption with the adsorption behaviour of the monomer itself. Capacity measurements predict flat orientation of the polymer molecules at the metal/solution interface with an average thickness of the adsorbed layer of about 0.8 nm. Thermodynamic parameters of the polymer adsorption on gold, at low anodic potentials, are comparable with those obtained from corrosion measurements on iron and mild steel. At high anodic potentials adsorption of PAA on gold is an endothermic process which can be explained by a substitutional adsorption (Polym (aq) + xH 2O (s) = Polym (s) + xH 2O (aq)) and conformation changes of the adsorbed polymer molecule. Thus, the calculated values of Δ H 0 ads and Δ S 0 ads correspond to the whole process; adsorption of polymer molecules and desorption of x-water molecules per polymer molecule.

Hydrodynamic layer thickness of poly(ethylene oxide) adsorbed on polystyrene latex

The adsorption of poly(ethylene oxide) onto polystyrene latex particles is investigated by means of dynamic light scattering. The data suggest that the polymer adsorption process consists of three main stages: (i) diffusion of polymer molecules to the bare surface and subsequent changes in configuration of the first layer; (ii) the formation of a dense layer until apparent full coverage; and (iii) attainment of the equilibrium layer thickness. Data on kinetics reveal the presence of an energy barrier in stages (ii) and (iii) probably due to the hindered diffusion of polymer molecules through the adsorption layer. The effect of tail configurations is investigated by comparing adsorbed polymer molecules with and without an anchor end group and it is found that adsorption of polymer molecules without anchors leads to a thicker hydrodynamic adsorption layer, in agreement with theoretical expectations.

Light scattering with incident evanescent waves: A method for studying the properties of adsorbed polymers

A new method for studying the properties of adsorbed polymer molecules is proposed. If polymer molecules are adsorbed on the low refractive index side of an interface between two transparent dielectric media, they can scatter the evanescent radiation generated by total internal reflection of light incident on the interface from the high refractive index medium. Analysis of the angular distribution of the scattered light yields information about the mean extension of the polymer perpendicular to the interface and its mean extension parallel to the interface. As an example, the theory is illustrated for the case of rods, anchored at one end to the interface, and with uniform angular distribution in the half space of the low refractive index medium. Both analytical and numerical analyses are presented.

Enhancing Mechanical Properties of Polymer Composites by Modification of Surface Acidity or Basicity of Fillers

AbstractThe surface of a powdered glass has been treated to optimize its performance as a filler in polymer composites cast from solution. The aim has been to enhance acid-base interactions between the functional sites of polymers and the surface sites of the glass particles so as to insure complete coverage of the glass particles by adsorbed polymer molecules, and to thereby enhance both the adhesion and dispersion of the filler. The glass chosen for this study is a magnesium aluminum silicate of very low alkali metal content, and its surface sites have negligible basicity and only moderate acidity, as evidenced by weak adsorption of polymethylmethacrylate and negligible adsorption of chlorinated polyvinylchloride from solution in methylene chloride. Because of the negligible surface basicity of the filler, acidic polymers such as polyvinylbutyral and polyvinyl chloride are not adsorbed sufficiently to promote adhesion or dispersibility, and brittle or weak composites result.Surface treatments to enhance surface acidity or basicity of the glass particles were evaluated by electrophoresis in organic solvents, in which acidic particles had negative zeta-potentials and basic particles had positive zeta-potentials; untreated glass particles had zero zetapotentials. The most effective treatments were done with silane coupling agents; amino-silanes provided strong negative zeta-potentials and methacryloxy-silanes provided strong positive zeta-potentials. Angleresolved ESCA spectra showed that the adsorbed amino-silanes averaged about a monolayer in thickness and that half of the nitrogens bonded to the surface as ammonium groups and half were in the outer surface as basic amine groups; the carbonyl oxygens of the methacryloxy-silanes appeared to be bonded to the surface.Heavily-loaded polymer composites were made with the silane-treated and with untreated glass powders, using two acidic binders and a basic binder. The acidic binders were a polyvinylbutyral (PVB) binder cast from solution in a methanol-MIBK mixture, and a post-chlorinated polyvinylchloride (CPVC) binder cast from solution in a mixture of cyclohexane and tetrahydrofuran (THF): the glass transition temperature (Tg) for CPVC is about 140 C, but for PVB it is only about 35 C. The basic polymer (PEHM, polyethyl-hexylmethacrylate) has a Tg well below room temperature. Thus the extension to break in tensile tests was about 1% for CPVC, 10% for PVB, and 20 % for PEHM. About ten stress-strain Instron tests were made on each composite, and the composites with appreciable acid-base interactions between the matrix polymer and the surface sites of the treated glass fillers were in all cases much tougher than those without such acid-base interactions. The brittleness of the polyvinylbutyral composites filled with untreated glass powders was not observed at all on silane-treated glass powders.

Enhanced polyelectrolyte adsorption

The amounts of hydrolysed polyacrylamide adsorbed onto cationic polystyrene latex have been compared after achieving the same final conditions of the dispersion medium via different experimental routes. The configuration of the adsorbed polymer molecules, following the different procedures, has also been assessed. For example, adsorption from 0.5 mol dm −3 NaCl followed by redispersion in 0.002 mol dm −3 NaCl leads to significant enhancement in the amount adsorbed compared to direct adsorption from the latter medium. In addition, the configuration, as indicated by ESR spectral data, has a much greater proportion of segments in loops and tails following the indirect route. Similar observations were made after adsorption from water (pH 3) followed by redispersion into water (pH 6.5–7.0). The results are explained in terms of the balance between the increase in lateral electrostatic repulsions and the energy of desorption resulting from the change in solvent conditions.

Preparation and properties of very thin films of syndiotacticity‐rich poly(vinyl alcohol)

AbstractVery thin films of poly(vinyl alcohol) could be prepared by utilizing the adsorption of polymer molecules at air/water interface from the aqueous solutions of the poly(vinyl alcohol) derived from vinyl trifluoroacetate. The films prepared by the bubble method were thinner than those obtained by the frame method. The minimum thickness of the former films was 260 Å and that of the latter was 1800 Å. These very thin films resisted water at temperatures below 55°C. The maximum Young's modulus of the drawn/annealed films prepared from these samples was 30 GPa. The permeability of water, Jw/δP, was 2–6 × 10−3 cm · s−1 atm−1 (0–55°C) for the untreated film (thickness: 1800 Å) prepared by the frame method and 0.8–2.2 × 10−2cm · s−1 · atm−1 (5–55°C) for the untreated film (360 Å) prepared by the bubble method, and depended on the thickness of film.

The Growth Kinetics of Polyethylene Twins: Evidence for Nucleation and Growth Processes

We have succeeded in obtaining the nucleation rate and velocity of the travelling of steps from the nucleation and growth processes of polymer crystallization, utilizing the enhanced growth at re-entrant corners of {110} twinned crystals of polyethylene. The supercooling dependence of nucleation rate is two times as strong as that of growth rate; this fact suggests that the growth is by multi-nucleation (regime II). The velocity of steps is proportional to the concentration of solution and nucleation rate is independent of the concentration over the usual concentration range. These relalions suggest that the growth face is saturated with adsorbed polymer molecules and the travelling of steps is controlled by the volume diffusion of polymer in the solution. The method described can be applied to other systems which have the same type of re-entrant corner.