Anders Larsson

The effect of polymer and surfactant adsorption on the colloidal stability and rheology of kaolin dispersions

Abstract We have investigated the effect of different water-soluble polymers and surfactants, commonly used as additives in paper coating formulations, on the rheology and the colloidal stability of concentrated kaolin dispersions. The adsorption of the different additives on kaolin with, and without, preadsorbed sodium polyacrylate (NaPAA) were studied at high pH. Highly negatively charged polymers like sodium polyacrylate and sodium carboxymethyl cellulose (NaCMC) polymers adsorb to a low extent on kaolin, while the adsorption of the uncharged polyvinyl alcohol (PVA) polymer is considerably higher. If the kaolin particles are predispersed with NaPAA, the adsorbed amount of negatively charged substances decreases considerably, probably due to competitive adsorption on the edges of kaolin. However, the adsorption of uncharged substances, like PVA or non-ionic surfactant, is almost unaffected by the presence of NaPAA at the surface. Addition of polymers or surfactants to kaolin dispersions influences the stability and rheology of the dispersions dramatically. Negatively charged substances such as NaPAA, NaCMC and anionic surfactant were found to stabilise the kaolin particles effectively through electrostatic repulsion, resulting in low relative viscosities for high solid content dispersions. However. for systems with PVA or non-ionic surfactant, NaPAA has to be added first in order to obtain efficient stabilisation. The relative viscosity of a kaolin slurry dispersed with NaPAA was always found to increase as a second polymer or surfactant was added.

Flocculation of cationic polymers and nanosized particles

Abstract The flocculation of large cationic polymers and nanosized particles is investigated. It is found that the molecular architecture of the polymer (linear or branched) is essential for the flocculation behavior. Only in the case of the linear polymer the degree of aggregation of the particles is important. The flocculation is a dynamic process where the particles affect the structure of the polyelectrolyte complex. The flocculation is affected by the presence of simple electrolytes that screen the highly charged particles and the cationic groups on the macromolecules.

Electrokinetic characterisation of cationic amylopectin starch; screening by salt and screening by nanosized silica particles

Abstract The screening of cationic amylopectin starch with salt has been investigated using the technique of electrokinetic sonic amplitude. The dynamic mobility was found to decrease as the electrolyte concentration increases. The experimental data were satisfactorily explained by applying a porous sphere model. The radius of the porous sphere could be used to evaluate the contraction of the amylopectin molecule as the electrolyte concentration increases. The screening of cationic amylopectin starch with nanosized silica particles was also followed using the technique of phase analysis light scattering. The formation of large macroscopic flocs could be explained in terms of available cationic and anionic sites of the initially formed polyelectrolyte complexes between one amylopectin molecule and a number of small silica particles. The screening of cationic amylopectin starch with salt has been investigated using the technique of electrokinetic sonic amplitude. The dynamic mobility was found to decrease as the electrolyte concentration increases. The experimental data were satisfactorily explained by applying a porous sphere model. The radius of the porous sphere could be used to evaluate the contraction of the amylopectin molecule as the electrolyte concentration increases. The screening of cationic amylopectin starch with nanosized silica particles was also followed using the technique of phase analysis light scattering. The formation of large macroscopic flocs could be explained in terms of available cationic and anionic sites of the initially formed polyelectrolyte complexes between one amylopectin molecule and a number of small silica particles.

Learning benefits of using 2D versus 3D maps: evidence from a randomized controlled experiment

The traditional important role of maps used for educational purposes has gained further potential with recent advances in GIS technology. But beyond specific courses in cartography this potential seems little realized in geography teaching. This article investigates the extent to which any learning benefits may be derived from the use of such technologies. A controlled experiment was conducted to examine whether information recall is improved when cartographic information on population distribution is presented in 2D versus 3D form. The results show statistically significant differences in learning benefits between the two formats, largely in favor of 2D representation. These findings suggest that learning benefits can be derived from paying greater attention to map format in educational settings.

Strengths and weaknesses of accessibility instruments in planning practice : Technological rules based on experiential workshops

ABSTRACT Accessibility instruments can play a valuable role in urban planning practice by providing a practical framework for exploring and testing relationships between land use and transport infrastructure. Despite many available accessibility instruments, they are still not widely used in planning practice. This paper explores the background of this problem by examining the findings of a EU-funded study on the usability and usefulness of existing accessibility instruments. The study applied 16 instruments in local planning contexts according to a standardized process protocol. The outcomes of these so-called experiential workshops were analysed through a standardized measurement protocol, which included participant observation along with pre- and post-workshop practitioner questionnaires. This broad investigation presents a rich analytical tool for understanding how different types of accessibility measures, spatial resolutions of output and levels of comprehensiveness affect usability and usefulness. Based on this we propose 10 technological rules that (a) can be used directly in practice to improve usability of accessibility instruments and (b) can provide hypotheses to be examined in further academic studies. Our results suggest that instead of striving for the ultimate accessibility measure, it would be more effective to identify which measures could successfully serve different user needs in accessibility planning.

Bridging the Knowledge-gap Between the Old and the New: Regional Marine Experience Production in Orust, Västra Götaland, Sweden

Abstract Today many regions in the industrialized world have to deal with a transformation from traditional industry such as agriculture or manufacturing to service-oriented production such as tourism. Nevertheless, few studies highlight the possibilities and limitations of inter-sectoral knowledge sharing among stakeholders representing these sectors and hence there seem to be missed opportunities for mutual collaboration in the era of experience production. Using an evolutionary perspective, this article aims to analyse how the leisure boat manufacturing and the tourism sectors in the municipality of Orust on the Swedish west coast, combine knowledge from these two sectors as a way to spur innovation in experience production. The article shows how there are a number of limitations to sectoral knowledge interaction. Some of them can be linked to the conservative nature of the traditional industry, and to the immature nature of the tourism sector, others to the role of policy. However, at the same time as there being a number of obstacles for collaboration, the article reveals some interesting possibilities to form inter-sectoral knowledge sharing.

THE STRUCTURE OF CATIONIC AMYLOPECTIN AS DETERMINED VIA MOBILITY DATA COMPARED TO MODEL CALCULATIONS

Abstract The structure of cationic amylopectin has been investigated by means of the electrokinetic sonic amplitude (ESA) technique. The obtained mobility data have been evaluated with model calculations. Static light-scattering data are also presented and compared with model calculations. It was found that cationic amylopectin has a heterogenous structure. The mobility data could roughly be modelled with a soft sphere. The light-scattering data are an intermediate between a linear chain and a homogenously branched polymer.

A multianalytical approach to characterize acidic adsorption sites on a quartz powder

Abstract In this paper three methods are described to estimate the number of adsorption sites and detect adsorption sites of differing nature on mineral surfaces. The methods are solution depletion adsorption isotherms, adsorption microcalorimetry, and desorption by solvent extraction followed by surface analysis using Electron Spectroscopy for Chemical Analysis (ESCA). The number of adsorption sites is obtained from the adsorbed amount of a test molecule on a mineral surface from the ESCA data using equations based on a substrate/overlayer model, and from the adsorption isotherms the number of sites available to accommodate a monolayer of test molecules is used. Information about whether the adsorption sites are of different or similar nature is provided by the desorption method using extraction in solvents of different polarities. More quantitative information concerning interactions between test molecules and adsorption sites, and possible interaction strength distribution due to sites of differing nature, is obtained from the adsorption enthalpies measured by microcalorimetry. The systems studied included strong basic test molecules (either a fatty diamine, octadecyl amine or pyridine) adsorbed on quartz powder from a nonpolar medium, n-octane. For the desorption study, subsequent extraction was carried out in pure n-octane, followed by ethanol. Adsorption/desorption of basic test molecules on quartz is important in applications of asphalt systems where fatty amines are often added to strengthen adhesion between bitumen and stone aggregates. The quartz powder studied here has acidic adsorption sites of differing nature on the surface. The strong interaction sites are consistent with iron oxide and/or oxohydroxide (strongest interactions with the fatty diamine where both nitrogen atoms can interact) and geminal hydroxyl groups. The weaker interaction sites are consistent with hydroxyl (silanol) groups forming hydrogen bonds with the basic test molecules.

Featured graphic: Spatial inequality and workplace accessibility: the case of a major hospital in Göteborg, Sweden

This map visualizes the interrelation between car/public transport workplace accessibility differences and place of residence.(1) The case is based on a hospital with 4500 employees and is the city’s single largest workplace with a majority of female workers. The analysis shows that 53% of the low-income female workers at the hospital can save between 30 and 60 minutes daily if they commute by car instead of public transport, compared with 46% of the high-income men. In addition, only 33% of the low-income women can save up to 30 minutes per day by using car instead of public transport, compared with 42% of the high-income men. The pattern of accessibility difference in the map indicates that low-income groups in general may be overrepresented in the semiperiphery of the city, refl ecting a gentrifi cation process of the inner-city areas, which often mismatches with the location of low-incomedominated workplaces. Thus, affordability of housing seems to be an important determinant for the place of residence choice, since most areas with the least difference between car and public transport accessibility are located in the city centre where property prices are high. Furthermore, the map shows a concentration of low-income female employees close to the hospital, with the number of commuters reduced drastically with increasing distance. This indicates that proximity to work is still an important determinant for the place of residence choice. Overall, there is a relatively small area in which employees at the hospital may live without having to spend signifi cantly longer time commuting by public transport compared with car. For groups with limited mobility resources (ie, without a car), this creates time– spatial restrictions on the home–workplace accessibility dynamics. One conclusion is that planners and policy makers need to be aware of the relative importance of public transport for different groups depending on factors such as gender, income, and place of work. The analysis illustrates how accessibility and travel opportunities are unevenly distributed among different groups in society, as well as across space. The map exemplifi es how infrastructure, gender, and income are important factors to explain this pattern (Church et al, 2000). Looking at spatial commuting patterns, the gendered labour-market structure provides an important component of analysis. The geography of workplaces is often spatially uneven, with central areas of the city dominated by women’s places of work and industrial and peripheral areas of the region dominated by male workplaces (Gil Solá, 2009). Mapping and analysis use register data from Statistics Sweden with a 100 meter geographical resolution, in this case aggregated to 500 meter cells. Accessibility calculations are based on the Swedish National Road Database and public transportation travel time data. For further description of the methodology see Elldér and Larsson (2011). The case was selected to represent a typically female-dominated workplace. One further limitation is made through the selection of a low-income group containing women with a yearly income below the national average for women (203 900 SEK /year). On the basis of these criteria we consider the selected group to be less likely to afford a car and hence more dependent on public transport or walking/bicycling for their daily trip to work.

Territorial Knowledge Dynamics and Knowledge Anchoring through Localized Networks: The Automotive Sector in Västra Götaland

James L., Vissers G., Larsson A. and Dahlström M. Territorial knowledge dynamics and knowledge anchoring through localized networks: the automotive sector in Västra Götaland, Regional Studies. Innovative firms often engage in knowledge interactions across regional boundaries, which is difficult to account for by territorial innovation models. The territorial knowledge dynamics perspective directs attention to the ways in which firms and other actors combine regional and extra-regional relations. It deals with the spatial aspects of innovation, emphasizing constantly evolving knowledge networks that are not confined to regional boundaries, which implies a new view on regional knowledge anchoring. The paper presents a case of innovation in the automotive sector in the Västra Götaland region of Sweden to show how a spatial pattern of knowledge interactions develops over time.