| 1. |
- Gane, P. A. C., et al.
(författare)
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Comparison of NMR cryoporometry, mercury intrusion porosimetry, and DSC thermoporosimetry in characterizing pore size distributions of compressed finely ground calcium carbonate structures
- 2004
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 43:24, s. 7920-7927
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates for the first time how mercury intrusion porosimetry (MIP), NMR-based cryoporometry, and DSC-based thermoporosimetry compare in revealing the porous characteristics of ground calcium carbonate structures compacted over a range of pressures. The comparison is made using the same source samples throughout. MIP, a much-used method in the characterization of porous structures, has the drawback that the high pressure needed to intrude the mercury may either distort the skeletal porous structure of the sample, especially when compressible materials such as cellulose or binders/latex are present, or lead to a reduction in the measured number of large pores due to the shielding by smaller pores. These effects have previously been addressed using bulk modulus corrections and by modeling the structure permeability to account for the potential shielding. Cryoporometry gives detailed information about the pore size distribution of an imbibition saturated structure. Thermoporosimetry is a relatively new candidate in this field, and it yields both pore size distribution and pore volume. Currently it is somewhat limited in the pore size range detectable, but it is relevant to pigmented coatings. Its potential is identified for capturing the pores involved in the progress of imbibition before saturation is reached.
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| 2. |
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| 3. |
- Vyörykkä, J., et al.
(författare)
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Characterization of paper coatings - Review and future possibilities
- 2006
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Ingår i: 2006 TAPPI Advanced Coating Fundamentals Symposium. ; , s. 32-57
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Konferensbidrag (refereegranskat)abstract
- Paper coating obviously plays an important role in printing and converting performance and thus a thorough knowledge of coating structure and chemistry, its generation from the wet state of the colour layer and its reaction to downstream processing, end-use and recycling, is needed to understand current products as well as to develop new products. Coating characterization methods may be divided into two subcategories; research methods and quality control methods. The latter category typically contains methods based on standards and are fast tools to evaluate the quality of the coatings, on-line, at-line or off-line. The instruments used in paper coating research aim to provide absolute rather than relative information, with the goal of offering greater insight into mechanisms underlying paper performance. These methods are accordingly often more demanding in terms of sample preparation and analysis time, and in some cases are still under development. This paper summarizes the achievements, limitations and future challenges faced by established analysis methods as well as emerging methods which could be used in paper coating characterization.
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| 4. |
- Fogden, A, et al.
(författare)
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Beyond the harmonic bending theory of ionic surfactant interfaces
- 1998
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Ingår i: Phys Rev E. - 2470-0053. ; 57, s. 5694-5706
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Tidskriftsartikel (refereegranskat)abstract
- There is now a broad understanding of how electrostatics, described by the nonlinear Poisson-Boltzmann equation, contributes to the phenomenological coupling (bending) constants of the flexible surface model as applied to ionic surfactant interfaces when the curvature energy density is truncated at harmonic order. Here, we extend this to the constants associated with anharmonic terms, specifically at third order in the interfacial curvatures, using model aggregates of spherical and cylindrical geometry. We analyze in detail the two limits of excess added salt and counterions only, and also provide a simple construction for bridging these two extremes using the theory of theta functions. Further, we investigate the asymptotic nature of the curvature expansion for ionic membranes, showing that it progressively deteriorates as the aggregate curvature is increased, and offer an alternative approximation scheme for the full free energy, using the method of Pade approximants.
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| 5. |
- Furó, I, et al.
(författare)
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NMR cryoporometry: a novel method for the investigation of the pore structure of paper and paper coatings
- 1999
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 14, s. 221-225
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Tidskriftsartikel (refereegranskat)abstract
- Many of the properties that paper coatings are designed to modify are determined to varying degrees by the nature of the pore space that interweaves the consolidated matrix. It is therefore highly useful to characterize the pore size distribution of paper coatings. Commonly used methods include mercury porosimetry, image analysis of scanning electron micrographs, and stain imbibition. Here, we describe a method, NMR cryoporometry, which is novel in its application to pores in paper and paper coating and is particularly suitable for measuring small pore sizes in the range of 1 to 100 nm. Such pore sizes are difficult to access with other techniques. The method is based on the principle of the freezing and melting temperature suppression of fluids entrapped within pores. A general outline of the technique is given, and an example of a cryoporometry measurement on a coated paper sample is described.
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| 6. |
- Kugge, C, et al.
(författare)
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A scanning electron microscope study of the surface structure of model paper coatings
- 2004
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 238, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the structure of model paper coating layers, composed of mineral pigments, latex binders and polymeric thickeners and dispersants, using Scanning Electron Microscopy (SEM). The main aim of the study is to identify how systematic variations in the composition of the coating, including pigment type (calcium carbonate, clay), the glass transition temperature of the binder, type (CMC, EHEC) and molecular weight of the polymeric thickener affect the surface features of the coating layer, including surface roughness and porosity and, consequently, gloss. The samples are investigated mainly in conventional high-vacuum SEM mode; however some studies are also performed with the environmental feature (ESEM mode) at higher pressures and humidities, in order to track dynamic changes drying and rewetting. The results are compared to those of recent measurements on the same systems obtained with Atomic Force Microscopy (AFM), where the local latex film formation process has been carefully studied
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| 7. |
- Kugge, C, et al.
(författare)
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Compressional rheology of model paper coatings
- 2001
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Ingår i: The Science of Papermaking. - Lancashire : FRC, Pulp & Paper Fundamental Research Society. ; , s. 1183-1202
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Bokkapitel (refereegranskat)abstract
- The surface treatment of paper is commonly undertaken in order to improve a set of key end-use properties, including optical response and printability. These properties can be influenced, to a significant extent, by the sub-surface structure of the coating layer. The nature of coating dewatering also has strong implications for machine runnability. Thus, there is a clear need to understand in suitable detail the nature of the coating consolidation process. In this study, we have applied a novel approach to characterising the equilibrium consolidation state of calcium carbonate sediments, both with and without polymeric thickener. The aim is to provide a quantitative link between the structure of consolidated layers and their network strength, though the compressive yield stress. A suspension, prepared at a given volume fraction of solid, is centrifuged to produce a consolidated particle sediment (or gel). The solidity variation of that sediment as a function of depth is then measured using one-dimensional magnetic resonance imaging (MRI), and the compressive yield stress calculated directly from the volume fraction profile. The results obtained are discussed in the light of particle network structure, the effect of polymer on particle consolidation, and the relation to viscoelastic properties of the suspensions. The link to the dewatering of coating suspensions, and structure formation in coating layers, is also considered.
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| 8. |
- Kugge, C, et al.
(författare)
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Pressure filtration of cellulose fibres
- 2005
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 31, s. 95-100
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Tidskriftsartikel (refereegranskat)abstract
- The compressional rheology of cellulose fibre suspensions has been studied using a pressure filtration technique. The dewatering of these systems is thus described in terms of various key properties of the suspension, including the compressive yield stress, permeability and solids diffusivity, permitting a quantitative characterisation of the consolidation process. We investigate as a particular example the effect of a commercial debonding agent additive on the compressional properties of a fibre suspension. Such agents are commonly used in the production of hygiene products where they are added to decrease the strength of fibre-fibre bonds. Here we investigate their effect on the compressive response of fibre suspensions as an example of how measurements of this type can be used to characterise the effect of additives on bulk properties. The results indicate that addition of debonder causes a somewhat higher dewatering tendency as the solids level is increased.
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| 9. |
- Kugge, C, et al.
(författare)
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Shear response of concentrated calcium carbonate suspensions
- 2004
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 271, s. 241-248
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Tidskriftsartikel (refereegranskat)abstract
- The rheology of concentrated calcium carbonate suspensions is investigated with respect to addition of solution and dispersion polymers. System materials and composition are chosen to be similar, generically, to those in use in the coating of paper. Specifically, we investigate the particle volume fraction dependence of the relative viscosity, using both capillary and steady-shear concentric cylinder measurement methods to cover a broad range of concentrations. The results are interpreted in terms of semi-empirical models, such as the Krieger–Dougherty model. Oscillatory shear measurements are also employed to investigate the viscoelastic behavior of the concentrated suspensions. The measurements indicate that a common solution polymer thickener, carboxymethyl cellulose (CMC), causes depletion flocculation of calcium carbonate suspensions.
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| 10. |
- Ninham, BW, et al.
(författare)
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Lifshitz theory of Casimir forces at finite temperature
- 1998
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 57, s. 1870-1880
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Tidskriftsartikel (refereegranskat)abstract
- We reexamine the Casimir and Lifshitz theories of intermolecular forces at nonzero temperature. For dilute media and atomic interactions, the limits of validity of the London-van der Waals potential between atoms at finite temperature are established by a detailed asymptotic analysis. In the retarded limit, the Casimir-Polder interaction potential is shown to be rigorously correct only in the limit of zero temperature. At any non-zero temperature a different analytic form obtains and is derived. We then consider Casimir forces between perfectly conducting plates. Existing results for the case of intervening vacuum are recovered by a novel method. Moreover, we show that the Mellin transform technique and theory of generalized zeta functions allows a detailed asymptotic treatment of a system of perfectly conducting plates with an intervening electron plasma, useful in the modeling of forces between metal plates, where the finite metallic skin-depth is an important consideration.
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