Ola J. Karlsson - Academia.edu (original) (raw)

Papers by Ola J. Karlsson

International Journal of Environmental Research and Public Health, Nov 23, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Acoustics, Jul 4, 2020

Several room acoustic parameters have to be considered in ordinary public rooms, such as offices ... more Several room acoustic parameters have to be considered in ordinary public rooms, such as offices and classrooms, in order to present the actual conditions, thus increasing demands on the acoustic treatment. The most common acoustical treatment in ordinary rooms is a suspended absorbent ceiling. Due to the non-uniform distribution of the absorbent material, the classical diffuse field assumption is not fulfilled in such cases. Further, the sound scattering effect of non-absorbing objects such as furniture are considerable in these types of rooms. Even the directional characteristic of the sound scattering objects are of importance. The sound decay curve in rooms with absorbent ceilings often demonstrate a double slope. Thus, it is not possible to use reverberation time as room parameter as a representative standalone acoustic measure. An evaluation that captures the true room acoustical conditions therefore needs supplementary parameters. The aim of this experimental study is to show how various acoustical treatments affect reverberation time T 20 , speech clarity C 50 and sound strength G. The experiment was performed in a mock-up of a classroom. The results demonstrated how absorbers, diffusers and scattering objects influence room acoustical parameters. It is shown that to some extent the parameters can be adjusted individually by using different treatments or combination of treatments. This allows for the fine-tuning of the acoustical conditions, in order to fulfill the requirements for achieving a high-quality sound environment.

Journal of Applied Polymer Science, 1998

Carboxylated polystyrene latex was used as seed and isoprene as the second-stage monomer in an in... more Carboxylated polystyrene latex was used as seed and isoprene as the second-stage monomer in an inhibited, seeded emulsion polymerization recipe for studies of monomer swelling kinetics at 80°C during interval III of an emulsion polymerization. The isoprene was added to the reactor in small portions using a syringe, and changes in the reactor pressure were continuously measured. Isoprene was added until a free liquid monomer phase was formed; that was, interval II was reached, as indicated by no further pressure increase upon the addition of more monomer. When the observed pressure increment, Op i , per unit isoprene added was plotted as a function of the volume fraction of polymer in the latex particles, v p , the graph could be divided into 3 domains. The break points in the Op i curve could, in an analogous emulsion polymerization, be identified as the glass transition temperature for the polymer, the so-called gel point in interval III and the onset of interval III. In the second domain, where the v p was between the glass transition temperature, T g , for the seed polymer and the gel point, the value of Op i decreased significantly with increasing monomer concentration in the latex particles. This was due to the entropy of mixing and the monomer acting as a plasticizer in the seed polymer. The rate of sorption of monomer to the latex particles was low at high values of v p. It then increased rapidly with increasing monomer concentrations in the latex particles, [M] p , and a maximum was observed in domain 2. At lower values of v p the sorption rate decreased in domain 3 and finally became zero as the free liquid monomer phase started to form. Results from batch polymerization suggested that the rate of diffusion of adsorbed monomer and oligo radicals into the particles was retarded. A simplified form of the Vanzo equation was used to estimate the monomer partitioning. It predicted too high a value of [M] p , especially in domain 2 of the swelling process.

Angewandte Chemie International Edition, 2006

Acoustics, Jun 18, 2021

Buildings

In ordinary public rooms, such as classrooms and offices, an absorbent ceiling is the typical fir... more In ordinary public rooms, such as classrooms and offices, an absorbent ceiling is the typical first acoustic action. This treatment provides a good acoustic baseline. However, an improvement of specific room acoustic parameters, operating for specific frequencies, can be needed. It has been seen that diffusing elements can be effective additional treatment. In order to choose the right design, placement, and quantity of diffusers, a model to estimate the effect on the acoustics is necessary. This study evaluated whether an SEA model could be used for that purpose, particularly for the cases where diffusers are used in combination with an absorbent ceiling. It was investigated whether the model could handle different quantities of diffusing elements, varied diffusion characteristics, and varied installation patterns. It was found that the model was sensitive to these changes, given that the output from the model in terms of acoustic properties will be reflected by the change of diffu...

Traditionally, the room acoustic properties in an ordinary public room are defined by only one pa... more Traditionally, the room acoustic properties in an ordinary public room are defined by only one parameter, the reverberation time. However, research has showed that additional room acoustic parameters as sound strength and speech clarity are necessary to consider in order to achieve good acoustic conditions. In a room with acoustical ceiling treatment the effects of furniture and interiors on the room acoustic parameters are significant. In addition, by using diffusers with directional properties it is possible to individually control the room acoustic parameters. Room acoustical measurements have been carried out in a reverberation chamber with suspended absorbing ceiling and directional diffusing objects. The effect of different diffuser configurations has been examined regarding reverberation time, speech clarity and sound strength. The evaluation shows that the orientation and the amount of the diffusing elements have a significant influence on the room acoustic parameters and ca...

May 2010, 2010

Time-dependent changes in the surface properties of coated papers were studied as the evolution o... more Time-dependent changes in the surface properties of coated papers were studied as the evolution of surface hydrophobicity of laboratory and commercially coated papers. We measured the apparent contact angles on the papers during several weeks post-production. Hydrophobicity upon aging increased for all samples made from traditional coating colors on mechanical base stock and on base stock made from cotton linters. Accelerated aging by heat treatment intensified the increase of the apparent contact angles and accelerated the time-dependent behavior. A key mechanism in these changes may be the spreading of latex particles in a coating.

This thesis describes the preparation of heterogeneous latexes, which may serve as binders in coa... more This thesis describes the preparation of heterogeneous latexes, which may serve as binders in coating applications, and the characterization of these. The latexes were prepared in two-stage seeded emulsion polymerization. The seed latexes used were polystyrene, whose properties had been changed by copolymerization with methacrylic acid (MAA) or divinyl benzene. The second-stage polymers were copolymers of styrene-co-isoprene-co-MAA or styrene-co-butadiene-co-MAA with varying compositions. The monomers in the second stage of polymerization were added either as a batch, or as a semi-continuous operation during the whole of the second stage or during various periods. The hydrophilicity of the polymeric phases was found to affect the particle morphology to a great extent. It was possible to change the particle morphology from an inverted core-shell to a core-shell morphology simply by adding small amounts of MAA to the monomer mixture used in the second stage of polymerization. Crosslinking of the seed particles had an even stronger effect on the morphology development. Increased amounts of isoprene and MAA, as well as an increased phase ratio between the second-stage polymer and the seed was found to increase deviations between particle sizes obtained by TEM and QELS. Monomer swelling experiments showed that it was possible to estimate the monomer volume fraction at which the seed polymer glass transition temperature (Tg) and the so-called gel point occurred, through pressure measurements. When the pressure was monitored in the copolymerization of butadiene and styrene, the conversion at which crosslinking began was detected as an irregularity on the pressure curve plotted as a function of the second-stage monomer conversion. Films made from the heterogeneous latexes were found to consist of two phases with the hard seed particles remaining as particles within the films. Mechanical measurements on the films showed that films made from latexes with crosslinked seed particles having irregular shapes, had the highest mechanical strength due to inter-particle contacts. Films made from latexes with core-shell morphologies exhibited lower mechanical strength due to the smooth seed particle structures left in the film. When latexes with crosslinked seed particles of irregular shapes were used as binders in model paper coating applications, they increased the porosity, gave greater light scattering ability and higher coating gloss of the coating layer, compared with latexes having core shell morphologies, due to retarded shrinkage of the coating during drying.

Macromolecules, 2015

Hydrophobic fumed silica dispersions in organic monomers were explored as a pore-forming system i... more Hydrophobic fumed silica dispersions in organic monomers were explored as a pore-forming system in polymer synthesis. The method developed provides a simple and effective way of controlling the pore size in highly cross-linked polymers. Fumed silica suspensions in divinylbenzene were polymerized with subsequent etching of the silica particles, therefore creating the porosity in the polymer. The resulting polymers are mesoporous materials, exhibiting an extremely narrow pore size distribution with an average pore size of about 100 Å, replicating the size of the nanofiller. BET surface areas were found appreciably high (∼350 m 2 / g). Furthermore, the rheological behavior of the prepolymerization mixtures was studied to elucidate the formation of the porous network and showed that a tridimensional network of particles is formed at a minimum silica fraction (Φ v) of 0.08.

Aqueous Polymer Dispersions, 2004

Hybrid systems have been made by taking an acrylic latex dispersion and slowly dropping an alkyd ... more Hybrid systems have been made by taking an acrylic latex dispersion and slowly dropping an alkyd resin into the dispersion while stirring to achieve a solid content of 75–80%. The particle size distributions of alkyd droplets were studied with a laser diffraction instrument and the structure of the hybrid system in the liquid state has been studied by light microscopy.

Polymer Reaction Engineering, 2003

We have developed software to simulate the development of non‐equilibrium latex particle morpholo... more We have developed software to simulate the development of non‐equilibrium latex particle morphologies produced by seeded emulsion polymerization. The diffusion of second stage polymer radicals within seed particles controls the development of morphology in a large number of systems. Knowledge of the conditions present within the latex particles during the reaction is required in order to model this diffusion process,

Polymer, 2000

The surfactant characteristics of novel random block polyelectrolyte polyester emulsifiers, SMTAP... more The surfactant characteristics of novel random block polyelectrolyte polyester emulsifiers, SMTAPE, were investigated by analyzing the surface tension of a variety of SMTAPE with different molecular weights and different hydrophilicities in aqueous solution, and also by studying the change of surface tension of polystyrene (PS) latex with increasing SMTAPE emulsifier concentration. The SMTAPE emulsifier was found to lower the surface tension of water by about 15 mN/m at the CMC. All of the investigated SMTAPE emulsifiers show two CMC break points, which were attributed to their broad molecular weight distribution. A Langmuir type adsorption isotherm was observed in this system. The surface area occupied by an SMTAPE molecule on a PS latex particle at 25ЊC was found to be 187 Å 2 at saturation. The conformation of SMATAPE emulsifier molecule adsorbed on a PS latex particle is thought to be a hydrophobic segment "trains" anchored to the polymer surface.

Macromolecular Symposia, 2000

Journal of Colloid and Interface Science, 2008

Film formation from latex dispersions with varying concentrations of sodium dodecylsulfate (SDS) ... more Film formation from latex dispersions with varying concentrations of sodium dodecylsulfate (SDS) and sodium persulfate (NaPS) was studied with a sorption balance. The drying rate decreased significantly at a critical volume fraction of polymer (φ pc). Under constant drying conditions the φ pc varied due to differences in particle stabilization. In SDS containing samples, the droplets wetted larger areas, the film thicknesses decreased and, consequently, the initial evaporation rate was decreased. The decrease in the initial evaporation rate first continued with increasing SDS concentration but leveled off at an apparent critical micelle concentration (CMC). Samples containing NaPS had different types of film formation mechanisms with large variations in φ pc and the total drying time, which could be explained by differences in the electrostatic stabilization. For dialyzed dispersions containing no NaPS, φ pc was close to 0.7. In samples with medium high NaPS concentration a skin was formed at the air interface causing an early shift in the evaporation rate, resulting in 0.25 < φ pc < 0.7. At high NaPS concentration the particles coagulated and settled giving an apparent increase in φ pc , i.e., values above 0.7. Deviations from the skin formation behavior predicted by the Routh and Russel (RR) model were observed.

Surface Coatings International Part B: Coatings Transactions, 2005

ABSTRACT The development of new binders used for coatings has traditionally been driven by a comb... more ABSTRACT The development of new binders used for coatings has traditionally been driven by a combination of the need for technical improvements and increased environmental awareness, together with stricter legislation regarding VOC (volatile organic compound) emissions. One interesting way to achieve new types of binders is to combine already existing ones, thereby exploiting the positive properties of both. In the present study, a combination of an alkyd and an acrylic dispersion was used to produce a potential hybrid binder. The structures of the binders both in the liquid state and in films prepared from the hybrids were studied using several microscopy techniques. It was found that the preparation method of the hybrids affected the morphology to a large extent, and the structural information was also linked to the rheological behaviour of the hybrids as well as to the mechanical properties of the final binder films.