N. Prince, M. Ashwin, D. P. Woodruff, N. Singh, W. Walter, Robert G. Jones
The relative insensitivity of the Bragg condition to the exact angle of incidence to the scattering plane near normal incidence means that the X-ray standing wavefield absorption method can be applied to typical (imperfect) surface-science single-crystal samples in this special geometry. The method is highly complementary to the SEXAFS experiment that can be performed with the same instrumentation and we demonstrate this with examples of structures associated with Cl, CH3S— and S on Cu(111) and Hg on Ni(100). The combined approach is particularly valuable in cases in which the adsorbed species induce substrate reconstruction, and in particular reasonably definitive structures of considerable complexity have been identified for the two S-containing surfaces.
{"title":"Normal-incidence standing X-ray wavefield absorption and SEXAFS studies of adsorption structures on Cu and Ni surfaces","authors":"N. Prince, M. Ashwin, D. P. Woodruff, N. Singh, W. Walter, Robert G. Jones","doi":"10.1039/DC9908900301","DOIUrl":"https://doi.org/10.1039/DC9908900301","url":null,"abstract":"The relative insensitivity of the Bragg condition to the exact angle of incidence to the scattering plane near normal incidence means that the X-ray standing wavefield absorption method can be applied to typical (imperfect) surface-science single-crystal samples in this special geometry. The method is highly complementary to the SEXAFS experiment that can be performed with the same instrumentation and we demonstrate this with examples of structures associated with Cl, CH3S— and S on Cu(111) and Hg on Ni(100). The combined approach is particularly valuable in cases in which the adsorbed species induce substrate reconstruction, and in particular reasonably definitive structures of considerable complexity have been identified for the two S-containing surfaces.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"16 1","pages":"301-310"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88079846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The structure of the passive film that protects iron and iron/chromium alloys from corrosion has been investigated in situ in an aqueous environment using X-ray absorption spectroscopy, with fluorescence yield detection. From an analysis of the EXAFS and XANES it has been shown that the film formed on iron consists of FeO6 octahedra, linked together by sharing edges to form what are probably sheets, or chains. When the iron is alloyed with chromium, or when it is exposed to a solution containing chromate ions, the passive film becomes more disordered and the distance between neighbouring iron atoms increases slightly. More significantly, from the passivation point of view, it has been shown that the chromium is incorporated into the passive layer as a phase essentially identical to Cr(OH)3, i.e. CrO6 octahedra linked by hydrogen bonds into an amorphous three-dimensional phase. It is this phase that appears to give rise to the enhanced corrosion resistance that chromium imparts to iron alloys.
{"title":"In situ structural studies of the passive film on iron and iron/chromium alloys using X-ray absorption spectroscopy","authors":"M. Kerkar, James Robinson, A. J. Forty","doi":"10.1039/DC9908900031","DOIUrl":"https://doi.org/10.1039/DC9908900031","url":null,"abstract":"The structure of the passive film that protects iron and iron/chromium alloys from corrosion has been investigated in situ in an aqueous environment using X-ray absorption spectroscopy, with fluorescence yield detection. From an analysis of the EXAFS and XANES it has been shown that the film formed on iron consists of FeO6 octahedra, linked together by sharing edges to form what are probably sheets, or chains. When the iron is alloyed with chromium, or when it is exposed to a solution containing chromate ions, the passive film becomes more disordered and the distance between neighbouring iron atoms increases slightly. More significantly, from the passivation point of view, it has been shown that the chromium is incorporated into the passive layer as a phase essentially identical to Cr(OH)3, i.e. CrO6 octahedra linked by hydrogen bonds into an amorphous three-dimensional phase. It is this phase that appears to give rise to the enhanced corrosion resistance that chromium imparts to iron alloys.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"133 1","pages":"31-40"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86235458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The adsorption of xenon has been studied by SEXAFS on a Cu(111) surface in the monolayer and in the multilayer range. At temperatures ranging between 18 and 47 K, the Xe monolayer has been shown to be incommensurate because (i) the Xe—Xe spacing differs from the distance between easy three-fold-hollow sites (aCu√3) and (ii) the coefficient of thermal expansion of the Xe adlayer is much higher than that of copper. In addition, we have found an Xe—Cu distance of 0.345 nm, which compares well with the value determined by a hard-sphere model.
{"title":"Study of xenon layers on a Cu(111) surface","authors":"J. Jupille, J. Ehrhardt, D. Fargues, A. Cassuto","doi":"10.1039/DC9908900323","DOIUrl":"https://doi.org/10.1039/DC9908900323","url":null,"abstract":"The adsorption of xenon has been studied by SEXAFS on a Cu(111) surface in the monolayer and in the multilayer range. At temperatures ranging between 18 and 47 K, the Xe monolayer has been shown to be incommensurate because (i) the Xe—Xe spacing differs from the distance between easy three-fold-hollow sites (aCu√3) and (ii) the coefficient of thermal expansion of the Xe adlayer is much higher than that of copper. In addition, we have found an Xe—Cu distance of 0.345 nm, which compares well with the value determined by a hard-sphere model.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"22 1","pages":"323-328"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80788488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A brief review is given of experiments aimed at elucidating the structure of adsorbed layers on single-crystal metal surfaces using synchrotron radiation. The techniques based on the phenomena of photoabsorption or photoemission, which require no long-range order in the adlayer and may prove to be of wider applicability than electron or X-ray diffraction, particularly for absorbed molecules. To illustrate the potential of the various methods the adsorption systems Cu{110}(2 × 1)/O and Cu{110}/H.CO2 are considered in more detail. In the case of the ordered oxygen overlayer, recent low-energy electron diffraction structural analyses are available for comparison. The application of a range of techniques is of particular advantage in this system because of the relative complexity of the structure: the adsorbate induces a so-called missing-row reconstruction. The energetics of such surface restructuring processes are also briefly discussed. In the case of the surface formate species the molecular orientation and adsorption site have been determined by X-ray absorption spectroscopy and photoelectron diffraction, respectively. This adsorption system shows no long-range order, a feature common to most adsorbed molecular fragments formed via simple heterogeneous reactions. Finally, some consideration is given to the requirement of high spectral brilliance for surface structural experiments, particularly in view of the construction of third-generation synchrotron radiation sources.
{"title":"Introductory lecture. Structural investigations of adsorbed layers using synchrotron radiation","authors":"A. Bradshaw","doi":"10.1039/DC9908900001","DOIUrl":"https://doi.org/10.1039/DC9908900001","url":null,"abstract":"A brief review is given of experiments aimed at elucidating the structure of adsorbed layers on single-crystal metal surfaces using synchrotron radiation. The techniques based on the phenomena of photoabsorption or photoemission, which require no long-range order in the adlayer and may prove to be of wider applicability than electron or X-ray diffraction, particularly for absorbed molecules. To illustrate the potential of the various methods the adsorption systems Cu{110}(2 × 1)/O and Cu{110}/H.CO2 are considered in more detail. In the case of the ordered oxygen overlayer, recent low-energy electron diffraction structural analyses are available for comparison. The application of a range of techniques is of particular advantage in this system because of the relative complexity of the structure: the adsorbate induces a so-called missing-row reconstruction. The energetics of such surface restructuring processes are also briefly discussed. In the case of the surface formate species the molecular orientation and adsorption site have been determined by X-ray absorption spectroscopy and photoelectron diffraction, respectively. This adsorption system shows no long-range order, a feature common to most adsorbed molecular fragments formed via simple heterogeneous reactions. Finally, some consideration is given to the requirement of high spectral brilliance for surface structural experiments, particularly in view of the construction of third-generation synchrotron radiation sources.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"28 1","pages":"1-20"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84676554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The rate of colloidal deposition of carbon black onto a microscope slide coated with tin-doped indium oxide has been measured using light scattered from the evanescent wave of a light beam passing through the slide. The rate can be measured in real time and the ITO coat allows the electrode potential of the surface to be changed. The mass transport of the particles is controlled by using the hydrodynamics of the impinging jet; depending on the size of the jet the hydrodynamics can either be wall-pipe or wall-jet. When the potential of the surface is positive there is no barrier to the deposition of the negatively charged particles; under both the wall-pipe and wall-jet regimes the particles deposit as the mass transport-controlled rate. Good agreement is found between the values of the diffusion coefficient of the particles measured in the two regimes. Depending on the age of the slide, when the potential is negative the particles either do not deposit or they deposit into the secondary minimum. The radial variation under the wall-jet regime shows that if they do deposit they do so again at the mass transport-controlled rate. The position of the secondary minimum can be calculated and it is shown that there is good agreement between the calculated position and the penetration of the evanescent wave. For ionic strengths > 10 mmol dm–3 there is no barrier and the particles deposit at all potentials. From this result we estimate a value of the Hamaker constant of 23.8 kBT. Using this value one can then calculate for lower ionic strengths the potential at which the barrier collapses and the particles transfer from the secondary into the primary minimum. Reasonable agreement is found between the theoretical and experimental results.
{"title":"Colloidal deposition under conditions of controlled potential","authors":"W. Albery, R. A. Fredlein, G. O'Shea, A. L. Smith","doi":"10.1039/DC9909000223","DOIUrl":"https://doi.org/10.1039/DC9909000223","url":null,"abstract":"The rate of colloidal deposition of carbon black onto a microscope slide coated with tin-doped indium oxide has been measured using light scattered from the evanescent wave of a light beam passing through the slide. The rate can be measured in real time and the ITO coat allows the electrode potential of the surface to be changed. The mass transport of the particles is controlled by using the hydrodynamics of the impinging jet; depending on the size of the jet the hydrodynamics can either be wall-pipe or wall-jet. When the potential of the surface is positive there is no barrier to the deposition of the negatively charged particles; under both the wall-pipe and wall-jet regimes the particles deposit as the mass transport-controlled rate. Good agreement is found between the values of the diffusion coefficient of the particles measured in the two regimes. Depending on the age of the slide, when the potential is negative the particles either do not deposit or they deposit into the secondary minimum. The radial variation under the wall-jet regime shows that if they do deposit they do so again at the mass transport-controlled rate. The position of the secondary minimum can be calculated and it is shown that there is good agreement between the calculated position and the penetration of the evanescent wave. For ionic strengths > 10 mmol dm–3 there is no barrier and the particles deposit at all potentials. From this result we estimate a value of the Hamaker constant of 23.8 kBT. Using this value one can then calculate for lower ionic strengths the potential at which the barrier collapses and the particles transfer from the secondary into the primary minimum. Reasonable agreement is found between the theoretical and experimental results.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"47 1","pages":"223-234"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88702777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present experimental evidence for reversible phase transitions in aqueous dispersions of acrylic lattices upon addition of two types of hydrophobically modified water-soluble polymers: hydroxyethyl cellulose with randomly placed hydrophobes, and poly(ethylene oxide) with hydrophobic end groups. In the limit of very weak polymer–particle associations flocculation occurs via depletion attraction, while strong associations lead to bridging flocculation with restabilization at higher polymer concentrations. Our observations for the end-modified poly(ethylene oxide) agree well with the predictions of our pseudo-one-component model, which we review briefly. This theory predicts the dependence of the phase transition on the polymer molecular weight and hydrophobic substitution, as well as the nature of the phase transition (fluid–fluid or fluid–solid) and the compositions of the resulting phases.
{"title":"Experimental and theoretical study of phase transitions induced in colloidal dispersions by associative polymers","authors":"M. Santore, W. Russel, R. Prud’homme","doi":"10.1039/DC9909000323","DOIUrl":"https://doi.org/10.1039/DC9909000323","url":null,"abstract":"We present experimental evidence for reversible phase transitions in aqueous dispersions of acrylic lattices upon addition of two types of hydrophobically modified water-soluble polymers: hydroxyethyl cellulose with randomly placed hydrophobes, and poly(ethylene oxide) with hydrophobic end groups. In the limit of very weak polymer–particle associations flocculation occurs via depletion attraction, while strong associations lead to bridging flocculation with restabilization at higher polymer concentrations. Our observations for the end-modified poly(ethylene oxide) agree well with the predictions of our pseudo-one-component model, which we review briefly. This theory predicts the dependence of the phase transition on the polymer molecular weight and hydrophobic substitution, as well as the nature of the phase transition (fluid–fluid or fluid–solid) and the compositions of the resulting phases.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"39 1","pages":"323-333"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78233896","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. W. O'Brien, B. R. Midmore, A. Lamb, R. J. Hunter
From electroacoustic theory it is now possible to determine the dynamic electrophoretic mobility of colloidal particles from measurements in any suspension for which the particle size is small compared to the sound wavelength (R. W. O'Brien, J. Fluid Mech., 1990, 212, 81); for dilute suspensions of spherical particles there is a simple formula for calculating the zeta potential from such mobility measurements (R. W. O'Brien, J. Fluid Mech., 1988, 190, 71). In this paper we present experimental verification of the theory for a latex and a cobalt phosphate sol, both of which are monodisperse, over a range of electrolyte concentrations and pH. We also present electroacoustic titration data on two polydisperse TiO2 sols, and discuss the discrepancies that result when these data are compared with the monodisperse theory.
从电声理论出发，现在可以通过测量任何悬浮液中胶体颗粒的动态电泳迁移率，其中颗粒尺寸与声波波长相比较小(R. W. O'Brien, J.流体力学)。， 1990, 212, 81);对于球形颗粒的稀悬浮液，有一个简单的公式可以从这种迁移率测量中计算ζ势(R. W. O'Brien, J.流体力学)。， 1988, 190, 71)。在本文中，我们对乳胶和磷酸钴溶胶的理论进行了实验验证，这两种溶胶都是单分散的，在一定的电解质浓度和ph值范围内。我们还提供了两种多分散TiO2溶胶的电声滴定数据，并讨论了将这些数据与单分散理论进行比较时产生的差异。
{"title":"Electroacoustic studies of moderately concentrated colloidal suspensions","authors":"R. W. O'Brien, B. R. Midmore, A. Lamb, R. J. Hunter","doi":"10.1039/DC9909000301","DOIUrl":"https://doi.org/10.1039/DC9909000301","url":null,"abstract":"From electroacoustic theory it is now possible to determine the dynamic electrophoretic mobility of colloidal particles from measurements in any suspension for which the particle size is small compared to the sound wavelength (R. W. O'Brien, J. Fluid Mech., 1990, 212, 81); for dilute suspensions of spherical particles there is a simple formula for calculating the zeta potential from such mobility measurements (R. W. O'Brien, J. Fluid Mech., 1988, 190, 71). In this paper we present experimental verification of the theory for a latex and a cobalt phosphate sol, both of which are monodisperse, over a range of electrolyte concentrations and pH. We also present electroacoustic titration data on two polydisperse TiO2 sols, and discuss the discrepancies that result when these data are compared with the monodisperse theory.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"47 15 1","pages":"301-312"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76327291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
X-ray diffraction has been used to determine the structure of surfaces over the past decade or so. The concepts involved in surface structure determination may be extended to the study of buried interfaces. A formalism for the determination of the structure of epitaxial interfaces is outlined, together with its application to the NiSi2/Si(111) interface. The use of a grazing incidence diffraction geometry to investigate strain relaxation in latticemismatched epilayers on the monolayer scale is discussed. The technique has been employed to monitor strain relaxation in thin Ge overlayers on Si(001) substrates with greater sensitivity than is attainable using other techniques. The results indicate that strain relaxation in this system relates primarily to islanding on the surface rather than the formation of misfit dislocations.
{"title":"X-Ray scattering from semiconductor interfaces","authors":"J. E. MacDonald","doi":"10.1039/DC9908900191","DOIUrl":"https://doi.org/10.1039/DC9908900191","url":null,"abstract":"X-ray diffraction has been used to determine the structure of surfaces over the past decade or so. The concepts involved in surface structure determination may be extended to the study of buried interfaces. A formalism for the determination of the structure of epitaxial interfaces is outlined, together with its application to the NiSi2/Si(111) interface. The use of a grazing incidence diffraction geometry to investigate strain relaxation in latticemismatched epilayers on the monolayer scale is discussed. The technique has been employed to monitor strain relaxation in thin Ge overlayers on Si(001) substrates with greater sensitivity than is attainable using other techniques. The results indicate that strain relaxation in this system relates primarily to islanding on the surface rather than the formation of misfit dislocations.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"119 1","pages":"191-200"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81694119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
X-Ray diffraction using synchrotron radiation from the National Synchrotron Light Source at Brookhaven has been used to study the clean Pt(110) surface prepared in ultrahigh vacuum. Three-dimensional crystallographic data show the structure to be ‘missing row’ with alternate [01] rows of atoms vacant in the top layer. Significant lateral relaxations are seen down to the fourth layer. Above 1080 K the surface undergoes a phase transition somewhat like that of Au(110). However, a distinct shifting of the half-order peak reveals the transition to involve the appearance of surface steps, and so it must be classified as a roughening transition instead of a simple 2D Ising model.
{"title":"Structure and roughening of the Pt(110) surface","authors":"I. Robinson, E. Vlieg, K. Kern","doi":"10.1039/DC9908900159","DOIUrl":"https://doi.org/10.1039/DC9908900159","url":null,"abstract":"X-Ray diffraction using synchrotron radiation from the National Synchrotron Light Source at Brookhaven has been used to study the clean Pt(110) surface prepared in ultrahigh vacuum. Three-dimensional crystallographic data show the structure to be ‘missing row’ with alternate [01] rows of atoms vacant in the top layer. Significant lateral relaxations are seen down to the fourth layer. Above 1080 K the surface undergoes a phase transition somewhat like that of Au(110). However, a distinct shifting of the half-order peak reveals the transition to involve the appearance of surface steps, and so it must be classified as a roughening transition instead of a simple 2D Ising model.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"68 1","pages":"159-168"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80924558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To describe the stabilization of colloid particles on addition of polymers, the osmotic pressure of a colloid, relative to its supernatant, has been studied. The traditional way to calculate the osmotic pressure, is to use a truncated virial expansion. The problem with such an approach, however, is the fact that the virial expansion is valid only at very low volume fractions of colloid and polymer. To extend the range of validity of the theory to finite volume fractions, we use an established theory of the liquid state. In the approach adopted it is assumed that repulsive forces exist at short distances and attractive forces exist at longer distances between the constituents of the colloid–polymer mixture. The phase behaviour of the system has been calculated as a function of the volume fractions of the colloid particles and of the polymer particles, and as a function of the degree of attraction. Various characteristic phase behaviours have been obtained: (i) depletion flocculation, (ii) bridging flocculation at low polymer concentration followed by restabilisation at higher polymer concentration, and (iii) conditions where the mixture is stable at all volume fractions of colloid and polymer. The theoretical analyses forwarded here reveal that the three-body interaction colloid–polymer–colloid plays an important role in the phase behaviour.
{"title":"Stability of colloid–polymer dispersions","authors":"R. D. Groot, W. Agterof","doi":"10.1039/DC9909000271","DOIUrl":"https://doi.org/10.1039/DC9909000271","url":null,"abstract":"To describe the stabilization of colloid particles on addition of polymers, the osmotic pressure of a colloid, relative to its supernatant, has been studied. The traditional way to calculate the osmotic pressure, is to use a truncated virial expansion. The problem with such an approach, however, is the fact that the virial expansion is valid only at very low volume fractions of colloid and polymer. To extend the range of validity of the theory to finite volume fractions, we use an established theory of the liquid state. In the approach adopted it is assumed that repulsive forces exist at short distances and attractive forces exist at longer distances between the constituents of the colloid–polymer mixture. The phase behaviour of the system has been calculated as a function of the volume fractions of the colloid particles and of the polymer particles, and as a function of the degree of attraction. Various characteristic phase behaviours have been obtained: (i) depletion flocculation, (ii) bridging flocculation at low polymer concentration followed by restabilisation at higher polymer concentration, and (iii) conditions where the mixture is stable at all volume fractions of colloid and polymer. The theoretical analyses forwarded here reveal that the three-body interaction colloid–polymer–colloid plays an important role in the phase behaviour.","PeriodicalId":12210,"journal":{"name":"Faraday Discussions of The Chemical Society","volume":"17 1","pages":"271-280"},"PeriodicalIF":0.0,"publicationDate":"1990-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90652720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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