Enhanced flocculation of colloidal dispersions by polymer mixtures

Bridging flocculation and electrolyte coagulation of negatively charged colloidal dispersions in the presence and absence, respectively, of uncharged polymers and polymer mixtures were studied. The relative coagulation and flocculation rates of particles in the presence of electrolyte and small polymer amounts were measured and the stability ratios have been calculated at various ionic strengths. Also, the structure of polymer layers formed in individual adsorption of polymers and in simultaneous competitive adsorption from binary polymer mixtures at particle/solution interfaces was investigated. The electrophoretic mobility and the diffusion coefficient of particles with and without adsorbed polymer were measured by laser Doppler-electrophoresis and photon correlation spectroscopy, respectively, and the electrophoretic and the hydrodynamic thickness of adsorbed polymer layers have been calculated. It was found that the adsorbed polymers may enhance or diminish the rate of successsful encounters between particles, even at low surface coverages, depending on the magnitude of the interparticle electrostatic repulsion. In addition, competitive adsorption of chemically different polymers for particle surfaces may result in considerable alteration in the conformation of macromolecules in the mixed adsorption layer. Close correlation was found between the effectiveness of polymers as flocculants and the thickness of adsorbed polymer layers formed at optimum polymer dosages on the particle surfaces. Binary mixtures of suitable polymers proved to be very efficient flocculants for the dispersions. The enhanced flocculating effect of some mixtures can be ascribed to extended polymer layers formed in competitive adsorption of chemically different macromolecules at particle/solution interfaces. These findings have relevance in many environmental technologies and offer a way of improving the effectiveness of solid–liquid separation processes.     

Time dependent wettability of mineral and metal surfaces in the presence of thiol surfactants

The decrease in wettability of mineral and metal surfaces due to the adsorption of surfactants is crucial for flotation recovery and upgrading of these materials in mineral processing. Because of limited residence time in flotation processing, the kinetics of the wettability changes of the mineral surface becomes an important issue. The time dependent wettabilities of silver and galena (PbS) surfaces in aqueous solutions of di-isobutyl dithiophosphinate, a commercial flotation reagent, were determined from in situ measurements of advancing and receding bubble contact angles. Kinetic parameters were calculated from these data. By comparing the in situ measurements with ex situ measurements of water contact angles and external reflection FTIR of the adsorbed organic films on silver, a physical interpretation of the wettability data is given in terms of the evolution of these thin organic films on the mineral surfaces.     

Application of polymer nanoparticle coating for tuning the hydrophobicity of cellulosic substrates

Nanoparticles of partially imidized poly(styrene–maleic anhydride) were applied from an aqueous dispersion as a one- or two-layer coating onto paper substrates, for controlling the paper surface hydrophobicity and improving the water barrier resistance. The effect of deposition conditions and thermal treatments on the topography and properties of the coating was studied by scanning electron microscopy, atomic force microscopy (AFM), contact angle measurements, and friction measurements. The wettability of paper surfaces with adsorbed nanoparticles can be controlled by tuning the chemical and topographical surface parameters: the water contact angles were found to increase at higher imide content as determined by Raman spectroscopy (depending on synthesis and thermal treatment), and higher average surface roughness determined by AFM (depending on the deposition method). The present technique may serve as a unique replacement for chemical treatments hydrophobizing fibrous substrates.     

Contact angle measurements and interpretation: wetting behavior and solid surface tensions for poly(alkyl methacrylate) polymers

Low-rate dynamic contact angles of a large number of liquids were measured on a poly(ethyl methacrylate) (PEMA) polymer using an automated axisymmetric drop shape analysis profile (ADSA-P). The results suggested that not all experimental contact angles can be used for the interpretation in terms of solid surface tensions: eight liquids yielded non-constant contact angles and/or dissolved the polymer on contact. From the experimental contact angles of the remaining four liquids, we found that the liquid-vapor surface tension times the cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γlv cos ζ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is again in harmony with those from other methacrylate polymer surfaces of different compositions and side-chains. The solid-vapor surface tension of PEMA calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 33.6 ± 0.5 mJ/m2 from the experimental contact angles of the four liquids. The experimental results also suggested that surface tension component approaches do not reflect physical reality. In particular, experimental contact angles of polar and nonpolar liquids on polar methacrylate polymers were employed to determine solid surface tension and solid surface tension components. Contrary to the results obtained from the equation-of-state approach, we obtained inconsistent values from the Lifshitz-van der Waals/acid-base (van Oss and Good) approach using the same sets of experimental contact angles.     

Adsorption of poly(dimethyl siloxanes) from solution on silica: 2

The adsorption energy (Δε_s), the change in energy on breaking a solvent-adsorbent bond and forming a segment-adsorbent bond, for poly(dimethyl siloxane) at the solution/silica interface has been measured under actual adsorption conditions. The effect of the adsorption energy on the extent of mass adsorption and on the conformation of the adsorbed polymer layer was evaluated. At low surface coverage, it is primarily the adsorption energy which determines the conformation of the adsorbed polymer layer as a function of the molecular weight. This effect is opposed by an entropy lowering, resulting from a restriction of the configuration of the adsorbed polymer molecules. At high surface coverage, lateral interactions between the adsorbed polymer molecules became an important factor causing a decrease in the fraction of directly adsorbed segments per molecule with increasing coverage.     

Contact Angles and Coating Film Thickness

The effect of film thickness and surface preparation techniques on contact angles of water, 1-bromonaphtalene, and n-hexadecane on Teflon® AF 1600 polymeric surfaces is studied. It was found that contact angles of water on different thicknesses of spin-coated films ranging from 27?nm to 420?nm are essentially constant. This is due to the homogeneity and smoothness of the coating layers as shown by the scanning force microscopy of the samples. Furthermore, the contact angle measurements with these three liquids on both dip-coated and spin-coated films suggested that the film preparation technique does not affect contact angles dramatically. Interestingly, slightly higher contact angles on dip-coated surfaces were measured. It is also argued that the anomaly of the water contact angle—in the sense that the measured contact angle is much higher than the expected ideal value—is due to specific interactions between water and Teflon®.     

AFM measurements of hydrophobic forces between a polyethylene sphere and silanated silica plates- the significance of surface roughness

Recently, substantial research effort has been devoted to the study of non-DLVO forces between hydrophobic surfaces. However, the significance of surface roughness in the analysis of these hydrophobic attractive forces has not been given sufficient consideration and research is now in progress to attend to this issue. Fused silica plates covered with adsorbed octadecyltrichlorosilane (OTS) were characterized by water contact angle measurements and atomic force microscopy (AFM). Surfaces with different surface coverages and different contact angles were obtained by variation of the adsorption time. OTS formed patches on the silica surfaces, the lateral size and height of which depended on the adsorption time. Such surfaces exhibit differences in roughness at the sub-nanometer level. Using the AFM colloidal probe technique, forces between a polyethylene sphere and silanated silica surfaces were measured in water. Long-range attractive forces were found, usually referred to as hydrophobic forces. The resulting force vs. distance curves were fitted with a double exponential function. The magnitude of the short-range part of the force curves seems to correlate with water contact angles at silanated silica surfaces. On the other hand, the range of the long-range force correlates with the roughness of the silanated silica surface. These results with silanated silica surfaces were compared with the AFM results for polyethylene and graphite surfaces and on the basis of these experimental efforts, it appears that the nature of these hydrophobic attractive forces is related to surface roughness.     

Photo-optical and electrochemical behavior of novel heterocyclic copoly(naphthylimide-amide)s

In this work, core–shell-structured silica-based surface molecularly imprinted nanoadsorbents (SMIPs) were prepared using a facile and general method that combined reverse atom transfer radical precipitation polymerization (RATRPP) and a surface imprinting nanotechnique. The resulting nanoadsorbents were then used to improve selective recognition and achieve the rapid removal of sulfamethazine (SMZ) from water. A modified one-step Stöber method was used to prepare monodisperse vinyl-functionalized silica spheres 250 nm in size. Subsequently, an imprinted polymer nanoshell (only 25 nm thick) was uniformly coated onto the surfaces of the hybrid silica spheres in a two-step polymerization process. The characteristics (i.e., isotherms, kinetics, and mechanism) of the adsorption of SMZ onto SMIPs from aqueous solution were systematically studied using batch experiments. The adsorption capacity increased with increasing initial concentration and contact time. The nonlinear Langmuir, Freundlich, and Temkin models were used to analyze equilibrium data, and these data were found to be best represented by the Langmuir isotherm, which yielded a high maximum monolayer adsorption capacity of 76.34 μmol g^?1 due to the effective sites located in the thin imprinted nanoshell. The adsorption process rapidly reached equilibrium and the data were best described by a pseudo-second-order rate model. The adsorption mechanism was mainly governed by intraparticle diffusion. The SMIPs adsorbed more SMZ than nonimprinted nanoadsorbents did, and they adsorbed much more of the template than other antibiotics, suggesting that the SMIPs show excellent selective recognition. Reusable SMIPs were shown to be a potentially efficient nanoadsorbent for the selective and fast removal of antibiotic residues from aqueous environments.     

Effects of hydroxypropyl cellulose and hydroxyethyl cellulose adsorption on the wetting of low energy solid surfaces

Advancing and receding contact angles on paraffin (PF) and poly(methyl methacrylate) (PMMA) have been measured for solutions of hydroxypropyl cellulose (HPC) and hydroxycthyl cellulose (HEC), two hydrophohic polymers differing considerably in their surface activity at the air-water interface. Consistent with observations made previously with hydrocarbon-chain surfactant solutions, advancing contact angles with PF are the same as those observed with pure liquids having the same surface tension, while those with PMMA are considerably greater. Receding contact angles for these polymer solutions appear to he the same as those observed with pure liquids. Consequently, this leads to less wettability in an advancing mode and greater apparent contact angle hysteresis than might be expected. Concurrent studies of HPC and HEC adsorption with the same PMMA samples used in the wetting studies and estimates of adsorption of HPC and HEC at the air-water interface indicate that these effects on wetting are due primarily to greater nonspecific polymer adsorption to the air-water interface than to the more polar PMMA-water interface.     

On Origins of Time-Dependence in Contact Angle Measurements

Time-dependent variations have been observed in the contact angles of wetting fluids on surfaces of homopolymers poly(styrene) (PS) and poly(methyl methacrylate) (PMMA), and copolymers of styrene and 4-vinyl pyridine (P(S-4VP)) and styrene and methacrylic acid (P(S-MAA)). Variations in the case of PS were unimportant, but significant variations occurred with the other polymers, allowing for the definition of both initial and equilibrium contact angle values. The total change in contact angles was strongly dependent on the acid-base contribution to the free energy of adsorption of the wetting fluids on the respective polymer surfaces, as determined from inverse gas chromatography experiments. A tentative correlation also linked the total change in contact angle with the ability of the polymer surfaces to reorganize when in contact with the polar wetting fluids of this study. Careful consideration must be given to the possibility of polymer surface reorganization when selecting fluids for use in the collection of reliable contact angle data.     

On Origins of Time-Dependence in Contact Angle Measurements

Time-dependent variations have been observed in the contact angles of wetting fluids on surfaces of homopolymers poly(styrene) (PS) and poly(methyl methacrylate) (PMMA), and copolymers of styrene and 4-vinyl pyridine (P(S-4VP)) and styrene and methacrylic acid (P(S-MAA)). Variations in the case of PS were unimportant, but significant variations occurred with the other polymers, allowing for the definition of both initial and equilibrium contact angle values. The total change in contact angles was strongly dependent on the acid-base contribution to the free energy of adsorption of the wetting fluids on the respective polymer surfaces, as determined from inverse gas chromatography experiments. A tentative correlation also linked the total change in contact angle with the ability of the polymer surfaces to reorganize when in contact with the polar wetting fluids of this study. Careful consideration must be given to the possibility of polymer surface reorganization when selecting fluids for use in the collection of reliable contact angle data.     

An experimental study of adsorption of polymers on activated carbon: Butadiene—styrene polymers and poly(methyl methacrylate)

An experimental study of the extents and rates of adsorption of several polymers from various solvents onto activated carbon has been carried out. The polymers studied included polystyrene, polybutadiene, butadiene–styrene copolymers and poly(methyl methacrylate). The solvents included toluene, cumene, decalin, 2-pentanone, and methyl ethyl ketone (MEK). Polystyrene is adsorbed from the different solvents in the order MEK, 2-pentanone, cumene, toluene, decalin. The adsorption from toluene, decalin, and cumene is in the order polystyrene, polybutadiene butadiene—styrene copolymer. The fact that the copolymer is adsorbed less than either homopolymer is striking. The variation of molecular weight distribution with extent of adsorption has been studied. It was found that low molecular weight polymer was preferentially adsorbed in the early stages of the experiment, but high molecular weight polymer was adsorbed at longer times. The apparent adsorption rate constants have been evaluated for the various systems and resolved into external mass transfer, internal (intraparticle) mass transfer, and adsorption rate constants. The experimental data have been applied to the prediction of the elution of the polymers from chromatographic columns packed with activated carbon.     

Tailored surface properties of semi-fluorinated block copolymers by electrospinning

Diblock copolymers based on polystyrene (PS) macroinitiators and four different fluorinated monomers (perfluorooctyl ethyl methacrylate (FMA), pentafluorostyrene (FS), perfluorooctyl-ethylene oxymethyl styrene (EMS), 2,3,5,6-tetrafluoro-4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecaoxy)styrene (FSF)) were synthesized via atom transfer radical polymerization (ATRP). The lengths of the PS and fluorinated blocks were altered and the surface and self-assembling properties of the polymers were compared with respect to the fluorinated monomer used and the fluorine content. The surface properties, contact angles and surface tension, were enhanced by the existence of the CF₃ groups at the end of the alkyl chains compared with poly(pentafluorostyrene). Hydrophobicity of the surfaces was further enhanced by electrospinning the polymer solutions, which yielded superhydrophobic surfaces with water contact angles >150° for polymers having CF₃ groups.     

Surface energy changes produced by ultraviolet-ozone irradiation of poly(methyl methacrylate), polycarbonate,and polytetrafluoroethylene

Contact angles of water and methylene iodide were measured as a function of UV/O₃ treatment time for three polymers: poly(methyl methacrylate) (PMMA), polycarbonate, and polytetrafluoroethylene (PTFE). Surface roughnesses were also measured. Surface free energies were then calculated using relationships developed by Kaelble and Neumann. The surface energy of polycarbonate was found to increase (～ 60%) during UV/O₃ treatment. However, calculations on PMMA were hampered by the formation of a water soluble surface product. On PTFE surfaces, the UV/O₃ treatment etched the surface, causing large increases in surface roughness, rendering contact angle measurements impossible. It is concluded that care must be taken in interpreting contact angle measurements and surface energy calculations on UV/O₃ treated polymer surfaces.     

Über das verhalten von sulfonierten naphthalin- und phenol-formaldehyd-kondensationsharzen an grenzflächen

The wetting mechanism of solids by the examined polymers basically differs from the wetting mechanism of surfactants. Aqueous solutions of polymers are not surface-active and show on solids the same contact angle as water. At hydrophobic solids such as graphite or polyethylene, a reversible monomolecular physisorption occurs, which can be described by the LANGMUIR'S equation. In contrast, on polycarbonate plastics, kaolin and porcelain, a largely irreversible adsorption occurs. The irreversibly adsorbed polymer molecules hydrophilize the surfaces of solids, which then retain their hydrophilic properties and can be wettedd even after repeated rinsing. With adsorption on graphite, the adsorbed amount of substance is independent on the ratio liquid volume/adsorbent, whereas with adsorption on kaolin and porcelain the amount of polymers adsorbed in equilibrium increases with an increasing ratio. The adsorption depends upon the external surface area, consequently, the equilibrium adsorption decreases significantly with an increasing grain radius.     

Influence of the coating method on the formation of superhydrophobic silicone–urea surfaces modified with fumed silica nanoparticles

Effect of the coating method on the formation of superhydrophobic polydimethylsiloxane–urea copolymer (TPSC) surfaces, modified by the incorporation of hydrophobic fumed silica nanoparticles was investigated. Four different coating methods employed were: (i) layer-by-layer spin-coating of hydrophobic fumed silica dispersed in an organic solvent onto TPSC films, (ii) spin-coating of silica–polymer mixture onto a glass substrate, (iii) spray coating of silica/polymer mixture by an air-brush onto a glass substrate, and (iv) direct coating of silica–polymer mixture by a doctor blade onto a glass substrate. Influence of the coating method, composition of the polymer/silica mixture and the number of silica layers applied on the topography and wetting behavior of the surfaces were determined. Surfaces obtained were characterized by scanning electron microscopy (SEM), white light interferometry (WLI) and advancing and receding water contact angle measurements. It was demonstrated that superhydrophobic surfaces could be obtained by all methods. Surfaces obtained displayed hierarchical micro-nano structures and superhydrophobic behavior with static and advancing water contact angles well above 150° and fairly low contact angle hysteresis values.     

A facile method of using sulfobetaine‐containing copolymers for biofouling resistance

Antifouling materials are desirable for many biomedical applications. In this work, the poly(sulfobetaine methacrylate‐co‐butyl methacrylate) (PSB) copolymers were investigated for their antifouling properties. The copolymers were synthesized via a simple free‐radical polymerization with feed ratio of the zwitterionic sulfobetaine methacrylate (SBMA) varying from 0 to 20 mol %. The polymer composition was verified by nuclear magnetic resonance. The enzyme‐linked immunosorbent assay and surface plasmon resonance were used to evaluate protein adsorption on a series of PSB copolymers from the single protein solution of fibrinogen, undiluted human blood serum, and undiluted human blood plasma. Results show that the protein adsorption amount decreased with the increasing content of SBMA in the copolymers. The adsorption levels achieved by PSB containing 20 mol % SBMA (PSB20) were only 4, 17, and 15 ng/cm² from fibrinogen, serum, and plasma, respectively, which represented 99%, 90%, and 90% reduction compared with the adsorption amounts on poly(butyl methacrylate) with no SBMA. The PSB20 film also completely inhibited endothelial cell attachment. Fouling resistance of PSB polymers can be well correlated with their receding water contact angles, which represent the polymer surface compositions in aqueous environment. The excellent antifouling abilities of PSB copolymers, combined with the facial synthesis method, commercial availability of all monomers, and low cost, render them highly promising for wide practical applications. The polymers can be applied versatilely as both solvent‐cast films and surface coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40789.     

Submicrometer-scale heterogeneous surfaces by PS-PMMA demixing

Patterned surfaces were created using two polymers: polystyrene (PS) on the one hand, and either poly(methyl methacrylate) (PMMA) or poly(methyl methacrylate)-poly(methacrylic acid) (PMMA-PMAA) on the other hand. PMMA was dissolved in a solvent of PS; this solution was then spin-coated on a PS support that partially dissolved during the process. The materials were analyzed by water contact angle measurement, XPS, ToF-SIMS and AFM. The effect of the solvent on the final surface morphology was strongly marked. With chloroform, the acrylic polymer was the major surface constituent, possibly because of the high evaporation rate of this solvent. With toluene, which is a better solvent for PS compared to PMMA, the obtained surface was almost exclusively constituted of PS. The use of chlorobenzene provided inclusions of acrylic polymer in PS, both polymers being exposed at the outermost surface. The surface morphology presented rings, the interior of which consisted of the acrylic polymer, while the rest of the surface was made of PS.     

Effect of polyacrylate binding layers on adhesion of UV-cured epoxyacrylate protective coatings on optical fibers

Polymer coatings on optical fibers were made of homopolymers of methyl methacrylate, poly(butyl acrylate) and poly(nonyl acrylate), the random copolymer of methyl methacrylate with 5% of methacrylic acid and asymmetric block copolymers of the same acrylates with short polar block of poly(5-tert-butyl-peroxy-5-methyl-1-hexen-3-yne-co-maleic anhydride) (50 : 50 mol %). They were obtained by means of physisorption of the polymers from the solution on the surface of two sorts of fused silica rods and plates preliminary heated at 200 and 900°C. The contact angle method was employed to evaluate the structure of adsorbed polymer films in the conditions of poor solvent. The fraction of the silica surface capped by the polymer, and surface free energy and its polar and dispersive components were estimated. The results were correlated with the data of adhesion tests between covered silica rods and ultraviolet (UV)-cured epoxyacrylate and discussed in terms of interpenetration of chains of the preliminary adsorbed polymer and polymer matrix. The chains of binding layer (adsorbed polymer) pull-out from the matrix and pull-off from the substrate failure mechanisms were suggested to explain the adhesion data for different sorts of silica rods. The efficiency of the polymer binding layer increases in the following order: asymmetric block copolymer < copolymer < homopolymer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1913–1923, 1998