Adhesion of latex films; influence of surfactants

The aim of the work presented in this article was to investigate the role of surfactants on adhesion properties of latex films. Several polymer/surfactant/support systems were used. Polymers were poly(2-ethyl hexyl methacrylate) or a methyl methacrylate/ethyl acrylate copolymer partially grafted onto a hydrophilic polyester. Surfactants were sodium dodecyl sulfate (SDS), hexadecyl pyridinium chloride (HPCI), or ethoxylated nonyl phenol containing 10 or 30 segments of ethylene oxide (NP10 or NP30). Supports were glass plates or poly(ethylene terephthalate) films. Adhesion was measured by a peel test at 180°. Loci of failure were determined by multitechnique analysis of the surfaces revealed after peeling. At medium and high peel rates, the peel energy versus surfactant concentration curves show either a maximum or a minimum, depending on the surfactant. When the peel rate is decreased, these maxima and minima flatten out and, at zero peel rate (extrapolated values), the peel energy becomes independent of the surfactant concentration. Surfaces analyses revealed that the surfactant is always present at the locus of failure. Rupture takes place in a thick (above 10 nm) (SDS), in a thin (a few nanometers) (NP30), or at the top of a surfactant layer (HPCI). The locus of failure is independent of the peel rate and of the surfactant concentration. The conclusion is that the surfactant strongly influences adhesion properties of latex films but several points remain unexplained.     

Adhesion of latex films. Part II. Loci of failure

In order to continue our work on surfactant effects on the adhesion properties of latex films, we investigated a new system based on an acrylic copolymer, synthesized in the presence of a hydrophilic polyester. The surfactants were either sodium dodecyl sulfate (SDS) or an ethoxylated nonyl phenol containing 30 ethoxy groups (NP30). As substrates, either glass plates or poly(ethylene terephthalate) (PET) films were used. This article describes the analysis of the loci of failure after peeling of the films. The analytical techniques used were X-ray photoelectron spectroscopy (XPS) (or ESCA), static secondary ion mass spectrometry (SSIMS), and contact angle measurements. It was shown that the loci of failure were independent of the peel rate and of the nature of the substrate. The failure occurs in a thick surfactant layer for SDS, and in a thin one for NP30. The thickness of the layer increases with the concentration of surfactant in the latex film. The surfactant is located near the surface of the substrate, on top of a layer of hydrophilic polyester. The consequences of the structure of the film-substrate interface on the adhesion properties is presented in Part III in this series.     

Surface and interfacial FTIR spectroscopic studies of latexes. II. Surfactant–copolymer compatibility and mobility of surfactants

Whereas molecular level interactions between sulfonate groups of SDOSS surfactant and COOH groups of EA/MMA copolymer have been discussed in part I of this series, the major focus of this work is to establish the effect of compatibility on the distribution of surfactants at the film–air and the film–substrate interfaces. It is found that the exudation of anionic surfactants is inhibited in neutralized ethyl acrylate/methacrylic acid latex films. On the other hand, nonionic surfactants do not exhibit enrichment at the film interfaces. The inhibited exudation of anionic surfactants is attributed to the increased compatibility resulting from surfactant penetration into the swollen latex particles. This is followed by the formation of solubilized polymer–surfactant complexes through the adsorption of surfactant onto the hydrophobic polymer segments. The effect of neutralization of the carboxylic acid groups on the exudation of anionic surfactants suggests the formation of hydrophobic interactions that overwhelm surface tension effects and prevent surfactant enrichment at either interface.     

Alkali-soluble resins (ASR) and acrylic blends: influence of ASR distribution on latex film and paint properties

Alkali-soluble resins (ASRs) are a special type of polymeric surfactant containing both hydrophobic moieties and carboxylic acid functional groups. Upon ionization, ASRs provide electrosteric stabilization to the latex particles, thus allowing reduction or even elimination of conventional surfactants while maintaining or improving latex stability. The distribution of ASR in the dried film depends on its miscibility with the latex polymer. Its presence in the blend system is expected to alter the film formation process and consequently performance properties of paint products based on the latex blends containing ASR. In this study, the effects of a high Tg, alkali-soluble resin (ASR), poly(styrene/alpha-methylstyrene/acrylic acid) terpolymer on the properties of latex and paint films were examined. The film formation of a soft acrylic latex in the absence and presence of the ASR was evaluated using a variety of analytical techniques. As expected, paint properties such as scrub resistance, wet adhesion, and block resistance were also affected by the inclusion of ASR. The results provide new insights into the structure and surface morphology of latex and paint films containing ASRs, as well as their impact on mechanical and the performance properties.     

Effect of surfactant systems on the water sensitivity of latex films

The effects of three different types of surfactant systems (ionic, polymeric, and electrosteric stabilizers) on the water sensitivity of poly(butyl acrylate‐co‐methyl methacrylate) latex films was examined. The water sensitivity was found to be strongly dependent on the surfactant system used in their preparation. A number of factors, such as the surfactant mobility and crystallinity and surfactant/polymer polarity appeared to affect the water uptake of the films. Highly mobile and crystallizable surfactants yielded high water sensitivity for films containing ionic surfactants, whereas the surfactant polarity had a greater effect on latices stabilized by polymeric surfactants, with the more hydrophilic systems providing greater water uptake. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1813–1823, 2004     

Surfactant concentration and morphology at the surfaces of acrylic latex films

The final outcome of surfactants during latex film formation is a topic of ongoing concern and interest. In this study of an acrylic latex containing an anionic surfactant, two notable phenomena are observed. (1) A higher surfactant concentration is present at the air surface of the latex films, regardless of the film-forming temperature and time. In some cases, surfactant is not visible in an atomic force microscope (AFM) image as a separate phase, but compositional profiles obtained with Rutherford backscattering spectrometry (RBS) reveal an enhanced concentration of surfactant over a depth from the surface that is comparable to the latex particle diameter. (2) The surfactant features that are imaged with the AFM evolve from a thin uniform layer, to a ‘finger-like' morphology, to small flat droplets, and finally to larger, hemispherical ‘blobs.' We suggest that surfactant is first deposited from the air/water interface onto the latex surface during the drying process. During this progression in the morphology of the surfactant, the ratio of the surface area-to-volume decreases. We speculate that this phenomenon is driven by a reduction in surface energy.     

一种富马酸类可聚合乳化剂的合成及其乳液性能研究

马来酸酐和十四醇在80℃酯化反应1 h得马来酸单十四酯;然后和PCl3在60℃反应2 h得单十四酯马来酰氯;最后与N-甲基牛磺酸钠在70℃反应1 h得白色粉末状固体,用w(CH3CH2OH)=95%的乙醇重结晶,得到一种富马酸类磺酸盐阴离子可聚合乳化剂——N-甲基-N-十四醇单酯马来酰基-牛磺酸钠。用质谱和1HNMR鉴定了目标化合物,结构正确。将所合成的可聚合乳化剂用于醋酸乙烯酯-丙烯酸丁酯-叔碳酸乙烯酯-甲基丙烯酸六氟丁酯乳液聚合,单体转化率97.75%,凝胶率0.02%,乳液固体份质量分数43.52%,乳液多分散性系数(PDI)0.02,呈单分散性。作为对比,非可聚合阴离子乳化剂十二烷基硫酸钠(SDS)同样应用到该乳液聚合体系中,结果发现:由可聚合乳化剂制得的乳液,在耐电解质性能和贮存稳定性方面有所提高,在成膜耐水性方面,可聚合乳化剂制得的乳胶膜浸入水中30 d后,吸水率为13.70%,SDS的吸水率是103.09%,是前者的7.52倍,可聚合乳化剂很好地提高了乳液成膜后的耐水性。     

Surfactants in heterophase polymerization: A study of film formation using force microscopy

Film formation of three different latices was studied using atomic force microscopy. The latices were made from a mixture of butyl acrylate, styrene, and acrylic acid using either a polymerizable or an unreactive anionic surfactant as an emulsifier. Sodium 11-crotonoyloxyundecan-1-ylsulfate and sodium 3-(sulfopropyl)tetradecylmaleate were used as a reactive surfactant and the unreactive surfactant was sodium dodecylsulfate (SDS). The conventional surfactant was found to migrate to the surface of the latex film to a much greater extent than did the reactive surfactants; however, also, the latter were incompletely anchored to the particle. The maleate surfactant was bound to a higher degree than was the crotonate, a finding which is in line with the relative reactivities of the two surfactants. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 187–198, 1997     

Synergisms in Binary Mixtures of Anionic and pH‐Insensitive Zwitterionic Surfactants and Their Precipitation Behavior with Calcium Ions

This work aims to investigate synergy in anionic and zwitterionic surfactant mixtures, as they result in better interfacial properties and micellization behavior. Various mixtures of the pH‐insensitive zwitterionic surfactant 3‐(decyldimethylammonio) propanesulfonate (Zwittergent 3–10) and sodium dodecylsulfate (SDS) were prepared in aqueous solution at a range of pH values between 2 and 13. The thermodynamic parameters during mixed surfactant adsorption at the air/water interface are obtained and the results show the mixed surfactant systems having superior properties to the constituent surfactants. Experimentally, the mixed surfactant solutions clearly improve the surface activities by lowering the critical micelle concentration (CMC) and lowering the surface tension at the air/water interface. The synergisms are investigated through the interaction parameters estimated from regular solution theory that is used to quantitatively describe the nonideality of surfactant mixtures. High negative interaction parameters are obtained from these surfactant mixtures. Experimental precipitation phase boundaries of SDS in the presence of CaCl₂ were also investigated in mixtures containing pH‐insensitive zwitterionic surfactant at different pH levels from 2 to 13 and SDS mole fractions of 0.25, 0.50, 0.75, and 1.00. Changes in the precipitation phase boundaries are due to the changes in the speciation or activities of the major components both below and above the CMC. As a result, the precipitation phase boundaries are pH dependent. In addition, mixed micellization and counterion binding to the micelle also change the precipitation phase boundary above the CMC. The activity‐based solubility product of calcium dodecylsulfate is also determined from the precipitation phase boundaries below the CMC. X‐ray diffraction patterns and SEM images confirm that only calcium dodecylsulfate precipitates in the soap scum for all pH and surfactant compositions studied.     

Wettability of Polymeric Solids by Aqueous Solutions of Anionic and Nonionic Surfactant Mixtures

Measurements of the surface tension (γ _LV) and advancing contact angle () on poly(tetrafluoroethylene) (PTFE) and poly(methyl methacrylate) (PMMA) were carried out for aqueous solutions of sodium decyl sulfate (SDS) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (TX100) and their mixtures. The results obtained indicate that the values of the surface tension and contact angles of solutions of surfactants on PTFE and PMMA surfaces depend on the concentration and composition of the surfactant mixtures. Calculations based on the Lucassen-Reynders equation indicate that for single surfactants and their mixtures at a given concentration in the bulk phase the values of surface excess concentration of surfactants at water–air and PTFE–water interfaces are nearly the same, so the adsorption of the surfactants at water–air and PTFE–water interfaces should also be the same. However, the adsorption of TX100 and its mixtures with SDS at water–air interface is higher than that at PMMA–water interface, which is confirmed by the ratio of absolute values of molecular interaction parameters at these interfaces calculated on the basis of Rosen approach. If we take into account the hydration of the poly(ethylene oxide) chains of TX100 and acid and base parameters of the surface tension of water it appears that the PMMA surface is covered by the 'pure' water molecules from the solution or molecules connected with the chain of nonionic surfactant. On the other hand, the lack of SDS molecules at the PMMA–water interface may result from the formations of its micelles which are connected with the TX100 chain.     

Morphological and Physical Properties of Triblock Copolymers of Methyl Methacrylate and 2‐Ethylhexyl Methacrylate

Summary: Triblock copolymers of methyl methacrylate (MMA) and 2‐ethylhexyl methacrylate (EHMA) [that is, poly(MMA–EHMA–MMA)] were prepared by an emulsion atom‐transfer radical polymerization. The relationships of their structural, morphological, and physical properties were investigated. The latex particles had core‐shell morphologies and the block copolymers experienced phase separation. Small latex particles with a low number of cores could deform and wet silicon‐wafer surfaces, but the deformation of large latex particles was restricted by the internal two‐phase morphology of the particles. Latex casting produced continuous pinhole‐free films, in which hard poly(MMA) (PMMA) cores of different latex particles merged and provided interparticle connections. The morphology of solution‐cast films depended on block composition, solvent type, and film thickness. For all the prepared polymer samples, thick films cast in toluene had poly(EHMA) (PEHMA) materials at air surface, whereas those cast in tetrahydrofuran had a sponge‐like PMMA surface structure. Thin toluene‐cast films from P(MMA–EHMA–MMA) with the block degrees of polymerization ( ) 200–930–200 showed spherical PMMA domains and those from 380–930–380 yielded a protruded worm‐like PMMA structure. The copolymer materials were coated on a glass surface for peeling tests. The films gave good hot‐melt adhesion properties when the of the PEHMA block was over 600. The peeling strength depended on the lengths of both PEHMA and PMMA blocks. The P(MMA–EHMA–MMA) sample with of 310–930–310 yielded the highest peeling strength of 7.4 kgf · inch^?1. The developed material is demonstrated to be a good candidate for a solvent‐free, hot‐melt, pressure‐sensitive adhesives for special‐purpose applications such as medical tapes and labels.

     

Interfacial Dynamic Properties and Dilational Rheology of Sulfonate Gemini Surfactant and its Mixtures with Quaternary Ammonium Bromides at the Air–Water Interface

The dynamic interfacial properties and dilational rheology of gemini sulfonate surfactant (SGS) and its mixtures with quaternary ammonium bromides (DTAB, CTAB) at the air–water interface were investigated using drop shape analysis. Results suggest that the adsorption process of these surfactants is diffusion-controlled at dilute concentrations, whereas the adsorption mechanism gradually shifts to a mixed kinetic-diffusion control with increasing surfactant concentration. The mixed surfactant system possesses the best surface activity when the molar ratios of SGS/DTAB and SGS/CTAB mixtures are 9:10. The formation of catanionic complexes shields the electrostatic repulsion between surfactant molecules and lowers the electrostatic adsorption barrier. Therefore, SGS/DTAB and SGS/CTAB mixtures exhibit higher adsorption rates than either component alone. The effects of oscillating frequency and surfactant concentration on the surface dilational properties of SGS, DTAB, CTAB, SGS/DTAB, and SGS/CTAB mixtures were also determined. As the oscillating frequency increases, the dilational elasticity of these surfactants gradually increases. The dilational elasticity peaks at a certain concentration, which is less than the critical micelle concentration (CMC). Results show that the dilational elasticity of SGS/DTAB and SGS/CTAB mixtures is higher than that of either component, resulting from the formation of a denser monomolecular adsorption layer at the air–water interface. Our study provides a basis for understanding the interaction mechanism of catanionic surfactant mixtures containing Gemini surfactant at the air–water interface.     

Reactive surfactants in heterophase polymerization. XVII. Influence of the surfactant on the mechanical properties and hydration of the films

In the context of a European union‐supported network on “Reactive Surfactants for Heterophase Polymerization,” different polymerizable surfactants (surfmers) have been synthesized and engaged in the emulsion polymerization of styrene, butyl acrylate, and acrylic acid. The thermomechanical properties of films cast from these different latices are reported in this article. The evolution of the mechanical properties with temperature and the effect of water molecules on these properties are studied. We observed that the studied surfactants do not influence the properties of the dry films. However, some differences due to grafting of reactive surfactants appeared when the films were wet. The amount of water uptake is drastically decreased when only reactive surfactants are present in the film. Concerning the mechanical behavior of the wet films, a decrease of the plastic flow stress is observed for all the samples whatever the nature of the surfactant (reactive or conventional). Hence, calorimetric measurements and dynamic mechanical analysis are used to identify the possible mechanisms that induce the change in the mechanical behavior of the latex films. In the case of reactive surfactant grafted to the polymer, the very low value of water uptake is accompanied by a plasticization of the polymer. In contrast, no plasticizing effect is observed in the case of nonreactive surfactant, even if the amount of water is very large. Finally, the tensile behavior of the styrene–butyl acrylate copolymer versus temperature is analyzed in the frame of the quasi point defects (qpd) model. Both rubber elasticity and chain orientation effects are taken into account to describe the behavior laws at large extensions (i.e., ? ≈ 1.2). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1686–1700, 2002; DOI 10.1002/app.10548     

Influence of surfactant properties on thermal behavior and sol–gel transitions in surfactant‐HPMC mixtures

Four surfactants, namely, sodium n‐decyl sulfate (SDeS), sodium n‐hexadecyl sulfate (SHS), sodium n‐dodecyl sulfate (SDS), and Triton X‐100, were used as additives to study thermal behavior and sol–gel transformations in dilute aqueous hydroxypropyl methyl cellulose (HPMC)/surfactant mixtures using micro‐differential scanning calorimetry. The influence of anionic surfactant, SDS on the gelation varied with SDS concentration where the sol–gel transition started at a higher temperature. Shape of the thermograms changed from single mode to dual mode at the SDS concentration of 6 mM and higher. SDeS and SHS, however, resulted in “salt‐in” effect of a different magnitude during gelation. Triton X‐100, being a non‐ionic surfactant, showed a minor “salt‐out” effect on the thermo‐gelation process. On the basis of different thermal behavior of anionic and non‐ionic surfactant/HPMC systems, a mechanism is proposed explaining how the chemical structure and electro‐charge of the surfactants affect the polymer/surfactant binding and polymer/polymer aggregation because of hydrophobic interaction during the sol–gel transition. © 2009 Wiley Periodicals, Inc. Journal of Applied Polymer Science, 2009     

Adhesion of latex films. Part III. Surfactant effects at various peel rates

In order to study the effect of surfactants on the adhesion of latex films, peel energy versus surfactant concentration curves were established at various peel rates. The main latex polymer was a methyl methacrylate (MMA)/ethyl acrylate (EA) copolymer synthesized in the presence of a hydrophilic polyester. Another polymer, less extensively studied, a styrene/butyl acrylate/methacrylic acid terpolymer, was also used for comparison purposes. The surfactants were either sodium dodecyl sulfate (SDS) or ethoxylated nonyl phenol containing 30 segments of ethylene oxide (NP30). The substrates were glass plates or poly(ethylene terephthalate) films. It was found that with SDS-containing films, whatever the substrate or the polymer, the curves went through a maximum, whereas with NP30 they went through a minimum, at medium or high peel rates. When the peel rate was decreased, the curves flattened out and at zero peel rate (extrapolated values), they became horizontal. The peel energies at zero peel rate were three to four times higher than the reversible works of adhesion. Qualitative interpretations are proposed for these results.     

Viscoelastic properties of latex paint films in tension: Influence of the inorganic phase and surfactants

The tensile properties of latex coatings were investigated with a set of custom formulated artist-type paints at an age of 1 year. All films in the study contained a poly(methyl methacrylate-cobutyl acrylate) binder exhibiting a glass-transition at approximately 10 °C. The viscoelastic behaviour of the latex matrix is first highlighted through a series of experiments involving different strain histories and temperatures. Influence of the inorganic particle concentration and geometry is then illustrated using TiO₂ and calcined kaolin for the secondary phase. Experimental data from a wide range of conditions are summarised through master curves of secant modulus and failure strains using time–temperature superposition. The results indicate that the latex films behave in a rheologically simple manner and it is possible to predict the response outside of the experimental time-scale. An analysis by similar methods is also given for TiO₂ pigmented films with/without surfactant removed by immersion in water. Differential scanning calorimetry and atomic force microscopy were also used in conjunction with mechanical tests. The combined findings suggest that a fraction of surfactant migrates to the TiO₂ interface during film formation, where it interferes with adhesion of the acrylic matrix.     

Molecular dynamics simulation on the structure–activity relationship between the Gemini surfactant and foam properties

The structure–activity relationship between the molecular structure of Gemini surfactants and foam properties has not yet been deeply revealed. In this study, we clarified for the first time the structure–activity relationship between foam properties and molecular structure of Gemini surfactant by discussing the variation characteristics of parameters such as free energy of interface formation, radial distribution function, and mean square displacement calculated by molecular simulation method. The research results show that (1) the Gemini surfactant with the sulfonic acid head group has the most excellent foam properties; (2) the foam properties increase monotonously with the increase of the hydrophobic tail chain length; (3) the foam properties decrease monotonously with the increase of the spacer group length. It is hoped that this article can further broaden the application range of surfactants as foaming agents in industrial fields such as oil and gas exploitation.     

复配表面活性剂对油水界面行为和性质影响的模拟研究

含复配表面活性剂的油田废水是一种多组分复杂体系,研究其中的分子作用关系有助于后续废水处理方案的确定。采用分子动力学(MD)模拟方法建立界面模型,通过定义表面活性剂的关键扭转点及相应的分子夹角、定义协同作用能,结合界面处的密度分布函数等性能模拟和界面张力测试结果,多角度分析两类阴阳离子表面活性剂复配对油水界面特性的影响。结果表明,与含单组分表面活性剂的油水体系相比,复配表面活性剂的相反电荷极性头基间静电吸引作用提高了油水界面稳定性;相较于十二烷基磺酸钠/十六烷基三甲基溴化铵(SLS/CTAB)复配体系,十二烷基硫酸钠/十六烷基三甲基溴化铵(SDS/CTAB)中分子间的协同作用可更好地提高体系的稳定性;当复配表面活性剂的配比为8/10~12/6时的油/水界面稳定效果较优、12/6时稳定性最好。研究结果可为石油开采及油水分离方案的确定提供依据。     

复配表面活性剂对油水界面行为和性质影响的模拟研究

含复配表面活性剂的油田废水是一种多组分复杂体系,研究其中的分子作用关系有助于后续废水处理方案的确定。采用分子动力学(MD)模拟方法建立界面模型,通过定义表面活性剂的关键扭转点及相应的分子夹角、定义协同作用能,结合界面处的密度分布函数等性能模拟和界面张力测试结果,多角度分析两类阴阳离子表面活性剂复配对油水界面特性的影响。结果表明,与含单组分表面活性剂的油水体系相比,复配表面活性剂的相反电荷极性头基间静电吸引作用提高了油水界面稳定性;相较于十二烷基磺酸钠/十六烷基三甲基溴化铵(SLS/CTAB)复配体系,十二烷基硫酸钠/十六烷基三甲基溴化铵(SDS/CTAB)中分子间的协同作用可更好地提高体系的稳定性;当复配表面活性剂的配比为8/10~12/6时的油/水界面稳定效果较优、12/6时稳定性最好。研究结果可为石油开采及油水分离方案的确定提供依据。     

Effects of Surfactant Headgroups on Oil-in-Water Emulsion Droplet Formation: An Experimental and Simulation Study

Nonpolar oils such as kerosene and diesel oil are common collectors in coal flotation. Surfactants are usually added to the pulp to emulsify the oil collectors. The present study used dodecane as the oil collector and anionic sodium dodecyl sulfonate (SDS) and nonionic tetraethylene glycol monododecyl ether (C₁₂EO) with different headgroups and identical chain alkyls to investigate the effect of the surfactant headgroups on oil-in-water emulsion droplet formation. The morphology and stability of dodecane emulsions were determined experimentally. Density functional theory (DFT) and molecular dynamics (MD) simulations were used to explain the microscopic mechanism. The results of DFT indicated a larger interaction between SDS and the water molecules than that between C₁₂EO and water molecules. The results obtained by MD suggested that the SDS headgroup exhibited a loose arrangement and a relatively large gap size, thereby weakening the interaction between SDS and water molecules at the dodecane/water interface. In contrast, the headgroups of C₁₂EO were bent and interwoven with others to form a tight reticulation at the interface. According to the simulation results, the ability of the surfactant to form dodecane-in-water emulsion droplets depends on the arrangement of the surfactants at the oil–water interface rather than on the interaction strength between the headgroups of the surfactants and water molecules. The presented microscopic mechanism of the surfactant headgroup formation of oil-in-water emulsion droplets offers surfactant selection and design references.