| 1. |
- Karlsson, Mattias, 1980, et al.
(författare)
-
Biomimetic nanoscale reactors and networks
- 2004
-
Ingår i: Annual Review of Physical Chemistry. - : Annual Reviews. - 0066-426X .- 1545-1593. ; 55, s. 613-49
-
Tidskriftsartikel (refereegranskat)abstract
- Methods based on self-assembly, self-organization, and forced shape transformations to form synthetic or semisynthetic enclosed lipid bilayer structures with several properties similar to biological nanocompartments are reviewed. The procedures offer unconventional micro- and nanofabrication routes to yield complex soft-matter devices for a variety of applications for example, in physical chemistry and nanotechnology. In particular, we describe novel micromanipulation methods for producing fluid-state lipid bilayer networks of nanotubes and surface-immobilized vesicles with controlled geometry, topology, membrane composition, and interior contents. Mass transport in nanotubes and materials exchange, for example, between conjugated containers, can be controlled by creating a surface tension gradient that gives rise to a moving boundary or by induced shape transformations. The network devices can operate with extremely small volume elements and low mass, to the limit of single molecules and particles at a length scale where a continuum mechanics approximation may break down. Thus, we also describe some concepts of anomalous fluctuation-dominated kinetics and anomalous diffusive behaviours, including hindered transport, as they might become important in studying chemistry and transport phenomena in these confined systems. The networks are suitable for initiating and controlling chemical reactions in confined biomimetic compartments for rationalizing, for example, enzyme behaviors, as well as for applications in nanofluidics, bioanalytical devices, and to construct computational and complex sensor systems with operations building on chemical kinetics, coupled reactions and controlled mass transport.
|
|
| 2. |
- Bergenholtz, Johan, 1964, et al.
(författare)
-
On-off dissociation dynamics of colloidal doublets
- 2013
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 104:1
-
Tidskriftsartikel (refereegranskat)abstract
- First-passage time theory is used to analyze the dissociation behavior of doublets of colloidal particles. The first-passage time distribution for particles interacting via a DLVO potential is determined numerically. For strongly attractive particles the distribution becomes broad such that the mean first-passage time becomes a poor measure of the dynamics. In spite of this, use can be made of the mean in a matching condition, which allows for reproducing distributions for strongly attractive doublets by a semi-analytical solution for particles interacting only through surface adhesion. The smallest eigenvalue in the analytical solution, which governs the long-time asymptotic behavior of the first-passage time distribution, is identified analytically for strongly attractive pairs of particles. In addition, in this limit the distribution is shown to asymptote to an exponential distribution, which means that the dissociation process can be simply captured by an on-off model, without sacrificing the effect of the surface chemistry, with a constant probability for dissociation. This probability is simply related to the surface-adhesive parameter and the separation distance at which the pair of particles ceases to be considered a doublet.
|
|
| 3. |
- Kaunisto, Erik, 1982, et al.
(författare)
-
A simple model for simulation of particle deaggregation of few-particle aggregates
- 2014
-
Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 60:5, s. 1863-1869
-
Tidskriftsartikel (refereegranskat)abstract
- A proper mechanistic understanding of the deaggregation process of small colloidal particle aggregates is of generic importance within many fields of science and engineering. The methodology for modeling colloidal deaggregation is currently limited to analytical solutions in the two-particle case and time consuming numerical algorithms, such as Brownian Dynamics (BD) simulations, for many-particle aggregates. To address this issue, a simplified alternative model that describes deaggregation of few-particle aggregates is presented. The model includes end-particle deaggregation and a particle reconfiguration mechanism, which are the two most important mechanisms for deaggregation. Comparison of the calculated first passage time distribution for various two-, three-, four-, and five-particle aggregates with the corresponding result using BD simulations confirms the validity of the model. It is concluded that the dominating mechanism behind deaggregation can be quantified using a deaggregation number, which reflects the time scale for reconfiguration relative to the time scale for end-particle deaggregation.
|
|
| 4. |
- Abbas, Zareen, 1962, et al.
(författare)
-
Synthesis, characterization and particle size distribution of TiO2 colloidal nanoparticles
- 2011
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 384:1-3, s. 254-261
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles of controlled size, well defined shape, pure phase and of clean surfaces are ideal model systems to investigate surface/interfacial reactions. In this study we have explored the possibility of synthesizing TiO2 nanoparticles in the size range of 7–20 nm under well controlled experimental conditions. A simple method based on the hydrolysis of TiCl4 was used to obtain particles having surfaces free from organics. Stable dispersions of TiO2 nanoparticles of various sizes were obtained by optimizing the reaction/dialysis time and temperature. The synthesized TiO2 particles were found to be predominantly of anatase phase and narrow particle size distributions were obtained. The TiO2 particles were characterized with respect to their phase, size and shape by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Particle size distribution in a colloidal dispersion was obtained by the electrospray scanning mobility particle sizer (ES-SMPS) method and compared with an average particle size determined from dynamic light scattering (DLS). The average particle sizes obtained by the DLS and ES-SMPS methods were in good agreement, while a primary particle size of 4 nm was found in X-ray diffraction irrespective of the particle size in solution. Early stages of the nucleation process were monitored by the ES-SMPS method. These results show that small particles of 4–5 nm are initially formed and it is highly likely that large particles are formed due to aggregation of primary particles.
|
|
| 5. |
|
|
| 6. |
- Abrahamsson, Christoffer, 1984, et al.
(författare)
-
Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability
- 2014
-
Ingår i: Soft Matter. - 1744-683X .- 1744-6848. ; 10:24, s. 4403-4412
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel selfassembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology.
|
|
| 7. |
- Ahlström, Bodil, 1968, et al.
(författare)
-
Prediction of structures and gel transitions in systems of colloids with moderate-range attractions
- 2007
-
Ingår i: Journal of Physics. Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19, s. 036102-036117
-
Tidskriftsartikel (refereegranskat)abstract
- Predictions of glass transitions from the idealized mode-coupling theory (MCT) are tested for systems with intermediate-range particle attractions. Liquid structure input to MCT is provided by the Asakura–Oosawa (AO) theory for the depletion interaction, used as an idealized model for structures in colloid–polymer mixtures. The effective one-component formulation of the AO theory is verified to capture the complete pair structure found from the binary version of the theory also for polymer–colloid size ratios somewhat larger than those for which an exact mapping of the two descriptions holds. The Percus–Yevick theory is shown to provide an accurate structural input to MCT, at least in the single-phase fluid region. With this combination of theories, very reasonable predictions for locations of glassy states in the experimental phase diagram are obtained for polymer–colloid size ratios somewhat larger than have been considered before. Simple approximations are also suggested for extracting the remaining pair structure from calculations of the one-component AO theory.
|
|
| 8. |
- Andersson Trojer, Markus, et al.
(författare)
-
Elastic strain-hardening and shear-thickening exhibited by thermoreversible physical hydrogels based on poly(alkylene oxide)-grafted hyaluronic acid or carboxymethylcellulose
- 2020
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 22:26, s. 14579-14590
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of strongly elastic physical gels based on poly(alkylene oxide)-grafted hyaluronan or carboxymethylcellulose, exhibiting both shear-thickening and strain-hardening have been studied using rheometry and explained using a slightly different interpretation of the transient network theory. The graft copolymers were prepared by a quantitative coupling reaction. Their aqueous solutions displayed a thermoreversible continuous transition from Newtonian fluid to viscoelastic solid which could be controlled by the reaction conditions. The evolution of all material properties of the gel could be categorized into two distinct temperature regimes with a fast evolution at low temperatures followed by a slow evolution at high temperatures. The activation energy of the zero shear viscosity and the relaxation time of the graft inside the interconnecting microdomains were almost identical to each other in both temperature regimes. This suggests that the number of microdomains remained approximately constant whereas the aggregation number inside the microdomains increased according to the binodal curve of the thermosensitive graft.
|
|
| 9. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
-
Quantitative Grafting for Structure-Function Establishment: Thermoresponsive Poly(alkylene oxide) Graft Copolymers Based on Hyaluronic Acid and Carboxymethylcellulose
- 2019
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20:3, s. 1271-1280
-
Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Chemical Society. A series of thermoresponsive graft copolymers, gelling at physiological conditions in aqueous solution and cell growth media, have been synthesized using quantitative coupling between a small set of amino-functionalized poly(alkylene oxide) copolymers (PAO) and the carboxylate of the biologically important polysaccharides (PSa) carboxymethylcellulose and the less reactive hyaluronate. Quantitative grafting enables the establishment of structure-function relationship which is imperative for controlling the properties of in situ gelling hydrogels. The EDC/NHS-mediated reaction was monitored using SEC-MALLS, which revealed that all PAOs were grafted onto the PSa backbone. Aqueous solutions of the graft copolymers were Newtonian fluids at room temperatures and formed reversible physical gels at elevated temperatures which were noncytotoxic toward chondrocytes. The established structure-function relationship was most clearly demonstrated by inspecting the thermogelling strength and the onset of thermogelling in a phase diagram. The onset of the thermogelling function could be controlled by the global PAO concentration, independent of graft ratio.
|
|
| 10. |
- Arteta, Marianna Yanez, et al.
(författare)
-
Successful reprogramming of cellular protein production through mRNA delivered by functionalized lipid nanoparticles
- 2018
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 115:15
-
Tidskriftsartikel (refereegranskat)abstract
- © 2018 National Academy of Sciences. All Rights Reserved. The development of safe and efficacious gene vectors has limited greatly the potential for therapeutic treatments based on messenger RNA (mRNA). Lipid nanoparticles (LNPs) formed by an ionizable cationic lipid (here DLin-MC3-DMA), helper lipids (distearoylphos-phatidylcholine, DSPC, and cholesterol), and a poly(ethylene glycol) (PEG) lipid have been identified as very promising delivery ve ctors of short interfering RNA (siRNA) in different clinical phases; however, delivery of high-molecular weight RNA has been proven much more demanding. Herein we elucidate the structure of hEPO modified mRNA-containing LNPs of different sizes and show how structural differences affect transfection of human adipocytes and hepatocytes, two clinically relevant cell types. Employing small-angle scattering, we demonstrate that LNPs have a disordered inverse hexagonal internal structure with a characteristic distance around 6 nm in presence of mRNA, whereas LNPs containing no mRNA do not display this structure. Furthermore, using contrast variation small-angle neutron scattering, we show that one of the lipid components, DSPC, is localized mainly at the surface of mRNA-containing LNPs. By varying LNP size and surface composition we demonstrate that both size and structure have significant influence on intracellular protein production. As an example, in both human adipocytes and hepatocytes, protein expression levels for 130 nm LNPs can differ as much as 50-fold depending on their surface characteristics, likely due to a difference in the ability of LNP fusion with the early endosome membrane. We consider these discoveries to be fundamental and opening up new possibilities for rational design of synthetic nanoscopic vehicles for mRNA delivery.
|
|
| 11. |
- Behrens, Manja A, et al.
(författare)
-
Temperature-Induced Attractive Interactions of PEO-Containing Block Copolymer Micelles
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:21, s. 6021-6029
-
Tidskriftsartikel (refereegranskat)abstract
- Interactions in a temperature sensitive-colloidal model system are investigated over a wide range of temperatures and concentrations to characterize the interparticle interactions within the system. This model system is composed of poly(ethylene oxide) end-capped with an octadecyl chain (C18E100), which by small-angle X-ray scattering (SAXS) have been shown to form spherical micelles in an aqueous salt solution. In the present study a 0.9 M NaF solution is used to shift the cloud point into the experimentally convenient temperature range. Densitometry and SAXS have shown no indication of specific interactions between the salt ions and the micelles. The spherical micelles are found to persist at elevated temperatures and a change in interparticle interaction is observed by viscometry and SAXS. The results are all consistent with the decreased solvent quality of water toward poly(ethylene oxide) with increasing temperature and it is seen that attractive interparticle interactions emerge in the vicinity of the cloud point.
|
|
| 12. |
- Bergenholtz, Johan, 1964, et al.
(författare)
-
Analysis of small-angle X-ray scattering data in the presence of significant instrumental smearing
- 2016
-
Ingår i: Journal of Applied Crystallography. - 0021-8898 .- 1600-5767. ; 49, s. 47-54
-
Tidskriftsartikel (refereegranskat)abstract
- A laboratory-scale small-angle X-ray scattering instrument with pinhole collimation has been used to assess smearing effects due to instrumental resolution. A new, numerically efficient method to smear ideal model intensities is developed and presented. It allows for directly using measured profiles of isotropic but otherwise arbitrary beams in smearing calculations. Samples of low-polydispersity polymer spheres have been used to show that scattering data can in this way be quantitatively modeled even when there is substantial distortion due to instrumental resolution.
|
|
| 13. |
- Bergenholtz, Johan, 1964
(författare)
-
Detachment dynamics of colloidal spheres with adhesive interactions
- 2018
-
Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 97:4
-
Tidskriftsartikel (refereegranskat)abstract
- Escape of colloidal-size particles from various kinds of solids, such as aggregates and surfaces, occurs in a wide variety of settings of both fundamental and applied scientific interest. In this paper an exact solution for the detachment of adhesive spheres from each other by means of diffusion is presented. The solution takes into account repeated detachment and reattachment events in the course of time on the way toward the permanently separated state. For strongly adhesive spheres this state is approached in an exponential manner essentially regardless of how the bound state is specified. The analytical solution is shown to capture semiquantitatively the escape from more realistic potential wells using a mapping procedure whereby equality of second virial coefficients is imposed.
|
|
| 14. |
- Bergenholtz, Johan, 1964, et al.
(författare)
-
Equilibration of fluid-phase coexistence in polydisperse particle systems with short- and moderate-range depletion attractions
- 2011
-
Ingår i: Fluid Phase Equilibria. - : Elsevier BV. - 0378-3812. ; 305:1, s. 9-18
-
Tidskriftsartikel (refereegranskat)abstract
- Gibbs ensemble Monte Carlo (GEMC) simulations have been done on polydisperse systems of particles interacting via the Asakura-Oosawa depletion potential. On restricting the range of the depletion attraction particles aggregate forming long-lived. unequilibrated structures and it becomes increasingly difficult to sample phase space. It is found that by simply equilibrating systems sequentially starting at longer ranges of attraction, the equilibrium fluid-fluid phase coexistence can be determined down to polymer-colloid size ratios approaching 10%. For such short ranges of the depletion interaction it becomes difficult to obtain reliable estimates of chemical potentials due to occasional particle insertions resulting in very low energies. The results show that full equilibrium is not reached at a polymer-colloid size ratio of 10% in spite of lengthy simulations due to persistent structures in the dense-fluid phase dominated by particles belonging to the larger size fraction. Free-volume theory with a polydisperse colloid component, modeled as a three-component mixture, is used for qualitative comparison with some of the results of the computer simulations.
|
|
| 15. |
|
|
| 16. |
- Bergenholtz, Johan, 1964, et al.
(författare)
-
Waiting-time distributions of particle entrapments in clustered states generated by short-range attractive, long-range repulsive (SALR) interactions
- 2019
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 126
-
Tidskriftsartikel (refereegranskat)abstract
- Brownian dynamics simulations have been carried out for so-called SALR systems, comprising fluids of particles interacting via competing short-range attractions and long-range repulsions. As the attraction is strengthened, particles form long-lived clusters with an internal structure that becomes ordered. This process is correlated with a slowing-down of the dynamics, which shows subdiffusive behavior in this regime with multiple dynamical time scales. Here we demonstrate that the waiting-time distribution of particle entrapments in clusters reflects these variations in the dynamics. Two- and many-body effects are cleanly delineated by computing these waiting times using a first passage time theory for excursions in the pair potential. For internally ordered clusters the accompanying slower time scale is found to be on the order of the escape time for a particle buried in a crystalline cluster.
|
|
| 17. |
- Braun, F N, et al.
(författare)
-
Glassy arrest in colloidal fluids with size polydispersity.
- 2007
-
Ingår i: The journal of physical chemistry. B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 111:40, s. 11626-8
-
Tidskriftsartikel (refereegranskat)abstract
- Short-range attraction between colloidal particles such as proteins can drive a glass-like structural arrest. For monodisperse systems, mode-coupling theory affords a simple asymptotic prediction of the transition. Here, using a depletion mapping framework, we extend this result to incorporate size polydispersity. For comparison, we also give an energy landscape formulation of the transition. We comment on the relevance to subcellular crowding, recombinant protein expression, and osmotic stress in microbial organisms.
|
|
| 18. |
- Bucciarelli, Saskia, et al.
(författare)
-
Unusual dynamics of concentration fluctuations in solutions of weakly attractive globular proteins
- 2015
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1089-5639. ; 6:22, s. 4470-4474
-
Tidskriftsartikel (refereegranskat)abstract
- The globular protein γB-crystallin exhibits a complex phase behavior, where liquid–liquid phase separation characterized by a critical volume fraction ϕc = 0.154 and a critical temperature Tc = 291.8 K coexists with dynamical arrest on all length scales at volume fractions around ϕ ≈ 0.3–0.35, and an arrest line that extends well into the unstable region below the spinodal. However, although the static properties such as the osmotic compressibility and the static correlation length are in quantitative agreement with predictions for binary liquid mixtures, this is not the case for the dynamics of concentration fluctuations described by the dynamic structure factor S(q,t). Using a combination of dynamic light scattering and neutron spin echo measurements, we demonstrate that the competition between critical slowing down and dynamical arrest results in a much more complex wave vector dependence of S(q,t) than previously anticipated.
|
|
| 19. |
- Eriksson, Maja, et al.
(författare)
-
Binding of Intercalating and Groove-Binding Cyanine Dyes to Bacteriophage T5
- 2007
-
Ingår i: The Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 111:5, s. 1139-1148
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction between four related cyanine dyes and bacteriophage T5 is investigated with fluorescence and absorption spectroscopy. The dyes, which differ in size, charge, and mode of DNA-binding, penetrate the capsid and bind the DNA inside. The rate of association decreases progressively with increasing dye size, from a few minutes for YO to more than 50 h for YOYO (at 37 °C). The relative affinity for the phage DNA is a factor of about 0.2 lower than for the same T5-DNA when free in solution. Comparison of groove-bound BOXTO-PRO and intercalating YO-PRO shows that the reduced affinity is not due to DNA extension but perhaps influenced by competition with other cationic DNA-binding agents inside the capsid. Although, the extent of dye binding to the phages decreases with increasing external ionic strength, the affinity relative to free DNA increases, which indicates a comparatively weak screening of electrostatic interactions inside the phage. The rate of binding increases with increasing ionic strength, reflecting an increase in effective pore size of the capsid as electrostatic interactions are screened and/or a faster diffusion of the dye through the DNA matrix inside the capsid as the DNA affinity is reduced. A combination of electron microscopy, light scattering, and linear dichroism show that the phages are intact after YO-PRO binding, whereas a small degree of capsid rupture cannot be excluded with BOXTO-PRO.
|
|
| 20. |
- Gibaud, Thomas, et al.
(författare)
-
Phase separation and dynamical arrest for particles interacting with mixed potentials—the case of globular proteins revisited
- 2011
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 7:2, s. 857-860
-
Tidskriftsartikel (refereegranskat)abstract
- We examine the applicability of the extended law of corresponding states (ELCS) to equilibrium and non equilibrium features of the state diagram of the globular protein lysozyme. We provide compelling evidence that the ELCS correctly reproduces the location of the binodal for different ionic strengths, but fails in describing the location of the arrest line. We subsequently use Mode Coupling Theory (MCT) to gain additional insight into the origin of these observations. We demonstrate that while the critical point and the connected binodal and spinodal are governed by the integral features of the interaction potential described by the normalized second virial coefficient, the arrest line is mainly determined by the attractive well depth or bond strength.
|
|
| 21. |
- Helttunen, Kaisa, et al.
(författare)
-
Solid lipid nanoparticles from amphiphilic calixpyrroles
- 2016
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 464, s. 59-65
-
Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: Macrocyclic amphiphiles form interesting self-assembling structures, including solid lipid nanoparticles, which have potential applications in drug encapsulation. Aryl-extended calixpyrroles, which act as anion binding hosts, are expected to form solid lipid nanoparticles, even though the alkyl chains have unusual perpendicular geometry with respect to the hydrophilic head group. The preparation conditions and the alkyl chain length should affect the size and stability of the particles. Experiments: Solid lipid nanoparticles of two aryl-extended calixpyrroles with resorcinol walls and either meso-dodecyl or meso-methyl alkyl chains were compared. Ethanolic solutions of the calixpyrroles were mixed with water and the resulting nanoparticle dispersions were studied with dynamic light scattering and nanoparticle tracking analysis. The effect of different calixpyrrole/ethanol/water ratios on particle size was tested. The surface charge of the particles at different pH and NaCl concentration was determined by zeta potential measurements. Findings: The meso-dodecyl calixpyrrole produced small nanoparticles with mean hydrodynamic diameters between 40 and 70 nm in 0.86–4.28 M ethanol. The particles were stable in solution for several months. Particles prepared from meso-methyl calixpyrrole were larger and less stable. The smallest particles were obtained with low calixpyrrole concentration and calixpyrrole/ethanol ratio. Larger ethanol/water ratio induced broader particle size distributions. Increasing pH aided the stability of the particles due to increased negative surface charge.
|
|
| 22. |
- Jonsson, Kristin, 1988, et al.
(författare)
-
Semi-batch synthesis of colloidal spheres with fluorinated cores and varying grafts of poly(ethylene glycol)
- 2017
-
Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X .- 1435-1536. ; 295:10, s. 1983-1991
-
Tidskriftsartikel (refereegranskat)abstract
- Fluorinated spheres with grafted poly(ethyleneglycol) (PEG) have been synthesized using a semi-batch emulsion polymerization in which the initiator is fed slowly to the reaction. In this way, PEG-grafted colloidal spherescan be fabricated with varying PEG chain length, different cores and varying degrees of crosslinking. The resulting batches have been characterized using disc centrifuge photo-sedimentometry and small-angle X-ray scattering. The size distribution is shown to be a sensitive function of the molar ratio of the reactive PEG macromonomer to fluorinated monomer, and with some optimization latices of very low polydispersity can be obtained with this simple synthesis method. For short PEG grafts too high a molar ratio results in a build up of smaller size particles and a broadening of the size distribution, whereas for longer grafts the mean particle size increases with decreasing molar ratio.
|
|
| 23. |
- Jonsson, Kristin, 1988, et al.
(författare)
-
Stabilizing Colloidal Particles against Salting-out by Shortening Surface Grafts
- 2019
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 35:36
-
Tidskriftsartikel (refereegranskat)abstract
- A dramatic improvement is reported in the stability of colloidalparticles when stabilizing surface grafts are systematically shortened from small polymers to single monomers. The colloidal dispersions consist of fluorinated latex particles, exhibiting a weak van der Waals attraction, with grafted steric layers of poly(ethylene glycol) (PEG) of different chain lengths. Using an effective salting-out electrolyte, Na2CO3, particle aggregates are detected above a threshold salt concentration that is independent of the particle concentration. The results are interpreted in terms of a sudden onset of nondispersibility of single particles, triggered by the solvent not completely wetting particle surfaces. By decreasing the PEG chain length, the threshold salt concentration is found to increase sharply. For grafts with just a single ethylene glycol group, dispersions remain stable up to exceedingly high concentrations of Na2CO3. However, on removal of the surface coverage altogether, the classical stability behavior of charge-stabilized dispersions is recovered. The behavior can be captured by a simple model that incorporates effective polymer−solvent interactions in the presence of an electrolyte.
|
|
| 24. |
- Kaunisto, Erik, 1982, et al.
(författare)
-
Fundamental mechanisms for tablet dissolution: Simulation of particle deaggregation via brownian dynamics
- 2013
-
Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 102:5, s. 1569-1577
-
Tidskriftsartikel (refereegranskat)abstract
- For disintegrating tablet formulations, deaggregation of small particles is sometimes one of the rate-limiting processes for drug release. Because the tablets contain particles that are in the colloidal size range, it may be assumed that the deaggregation process, at least qualitatively, is governed by Brownian motion and electrostatic and van der Waals interactions, where the latter two can be described by a Derjaguin–Landau–Verwey–Overbeek interaction potential. On the basis of this hypothesis, the present work investigates the applicability of Brownian dynamics (BD) simulations as a tool to understand the deaggregation mechanism on a fundamental level. BD simulations are therefore carried out to determine important deaggregation characteristics such as the so-called mean first passage time (MFPT) and first passage time distribution (FPTD) for various two-, three-, and four-particle aggregates. The BD algorithm is first validated and tuned by comparison with analytical expressions for the MFPT and FPTD in the two-particle case. It is then shown that the same algorithm can also be used for the three-particle case. Lastly, the simulations of three- and four-particle aggregates show that the initial shape of the aggregates may significantly affect the deaggregation time.
|
|
| 25. |
- Khavari, Adele, 1977, et al.
(författare)
-
On the percolation of alginate/calcium systems at low concentrations
- 2016
-
Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 137, s. 480-487
-
Tidskriftsartikel (refereegranskat)abstract
- The sol-to-gel transition of an alginate rich in β-d-mannuronic acid residues and at a concentration of 0.1% w/v in 15 mM NaCl in the presence of calcium ions of 0 to 3.5 mM was studied with dynamic light scattering. The dynamics of the different systems added further insight into the alginate gel forming mechanisms. Below a Ca2+ concentration of 0.7 mM, the build-up of small aggregates could be verified. Moreover, at a critical concentration, close to 0.9 mM Ca2+, a percolated, non-ergodic network started to form from some of these aggregates, with smaller aggregates still diffusing in the network. The system displayed strong non-ergodicy at high Ca2+ concentrations with a non-ergodicity parameter that appeared to form discontinuously from near zero to a clearly non-zero value at the critical Ca2+ concentration.
|
|
| 26. |
- Li, Weimin, et al.
(författare)
-
Concentration-Induced Association in a Protein System Caused by a Highly Directional Patch Attraction
- 2016
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120, s. 8953-8959
-
Tidskriftsartikel (refereegranskat)abstract
- Self-association of the protein lactoferrin is studied in solution using small-angle X-ray scattering techniques. Effective static structure factors have been shown to exhibit either a monotonic or a nonmonotonic dependence on protein concentration in the small wavevector limit, depending on salt concentration. The behavior correlates with a nonmonotonic dependence of the second virial coefficient on salt concentration, such that a maximum appears in the structure factor at a low protein concentration when the second virial coefficient is negative and close to a minimum. The results are interpreted in terms of an integral equation theory with explicit dimers, formulated by Wertheim, which provides a consistent framework able to explain the behavior in terms of a monomer–dimer equilibrium that appears because of a highly directional patch attraction. Short attraction ranges preclude trimer formation, which explains why the protein system behaves as if it were subject to a concentration-dependent isotropic protein–protein attraction. Superimposing an isotropic interaction, comprising screened Coulomb repulsion and van der Waals attraction, on the patch attraction allows for a semiquantitative modeling of the complete transition pathway from monomers in the dilute limit to monomer–dimer systems at somewhat higher protein concentrations.
|
|
| 27. |
- Nayeri, Moheb, 1979, et al.
(författare)
-
Measurements of screening length in salt solutions by total internal reflection microscopy: Influence of van der Waals forces and instrumental noise
- 2013
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 429, s. 74-81
-
Tidskriftsartikel (refereegranskat)abstract
- Total internal reflection microscopy (TIRM) measurements of colloidal spheres in aqueous electrolyte solutions have been carried out with focus on screening properties of various electrolytes and methods and analyses for reliably extracting them from TIRM measurements. Approximations based on Lifshitz theory of flat plates are found to yield van der Waals interactions that are too strong compared to measured interaction potentials. Allowing for some attenuation of these interactions due to surface roughness, a consistent set of screening lengths can be extracted by fitting a model of the interaction, comprising screened Coulomb, van der Waals, and gravitational interactions, to the TIRM data. With the exception of the 2:2 electrolytes, the screening lengths extracted from the TIRM measurements are well described by Debye–Hückel theory, including some surfactants below their critical micelle concentration and electrolytes with large size asymmetries between anion and cation. In 2:2 electrolytes the screening lengths are found to be larger than the corresponding Debye length by as much as 50% at the highest salt concentrations studied. While this deviation is significantly larger than predictions of theory based on the primitive model of electrolytes, similar magnitudes are found from analysis of BD simulations with added noise at realistic levels in the incident intensity. The work shows that care has to be taken when extracting parameters governing potentials in the presence of noise, particularly at high ionic strengths when potentials become steep at short separations.
|
|
| 28. |
|
|
| 29. |
- Nayeri, Moheb, 1979, et al.
(författare)
-
Surfactant effects on colloidal interactions: Concentrated micellar solutions of nonionic surfactant
- 2010
-
Ingår i: COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 368:1-3, s. 84-90
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of nonionic surfactants on interaction energies between polystyrene latex or silica spheres and a flat glass surface has been studied using total internal reflection microscopy (TIRM). The measurements reveal that both Triton X-100 and C12E5 contribute to the Debye screening length, an effect that is essentially removed on first exposing the surfactants to ion-exchange resin. Whereas particles can be embedded in Triton X-100 concentrations at least as high as 285 times the critical micelle concentration, the same particles become elastically tethered at intermediate separations from the glass surface in somewhat less concentrated micellar solutions of C12E5. The elastic energy is caused by a connecting structure between the particle and glass surface, which remains intact on dilution and on lowering the ionic strength of the solvent.
|
|
| 30. |
- Nordström, Jonas, 1980, et al.
(författare)
-
Concentration- and pH-dependence of highly alkaline sodium silicate solutions
- 2011
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 356:1, s. 37-45
-
Tidskriftsartikel (refereegranskat)abstract
- In this study two routes for the gelation of water glass have been investigated; the destabilization by a change in pH and by an increase in concentration through evaporation. Both methods produce optically transparent, highly viscous, homogeneous solutions. The structure and dynamics of the solutions along the two routes have been investigated with Dynamic Light Scattering, 29Si-Nuclear Magnetic Resonance spectroscopy, viscosity measurements and infrared spectroscopy. We find that the two routes are fundamentally different. Increasing the concentration of the sodium silicate system leaves the silica speciation apparently unchanged. Lowering the pH leads to condensation reactions, thus a change in the silica speciation.
|
|
| 31. |
- Oskolkova, Malin Zackrisson, 1974, et al.
(författare)
-
Concentration-dependent effective attractions between PEGylated nanoparticles
- 2015
-
Ingår i: RSC Advances. - 2046-2069. ; 5:32, s. 25149-25155
-
Tidskriftsartikel (refereegranskat)abstract
- Effective attractions between colloidal particles bearing a grafted poly(ethylene glycol) (PEG) layer in water have been studied and quantified by measurements of the collective diffusion coefficient and by quantitative analysis of small-angle neutron scatterin (SANS) data. Results for the collective diffusion coefficient in the dilute limit indicate that effective attractions develop gradually as carbonate anions are added to the dispersions. Analysis of SANS data within a square-well interaction model at a constant salt concentration allows for quantitative analysis of scattering patterns of samples prior to crossing into an aggregation regime, where particles form large clusters, reached either through increasing the temperature or the particle concentration. Aggregation is observed visually and is also evident in the scattering as a lowering of the intensity at intermediate wavevectors while leaving enhanced scattering in the forward direction, suggesting a nearby fluid–fluid phase transition. In addition, at low and moderate particle concentrations the attraction strength is shown to depend mainly on temperature but at high particle concentrations a much stronger temperature dependence is observed, which shows that the attraction acquires a dependence on particle concentration at sufficiently high concentrations. The concentration dependence is attributed to a decreased solvation of PEG chains due to an increased ratio of ethylene oxide segments to water.
|
|
| 32. |
- Perez-Holmberg, Jenny, 1977, et al.
(författare)
-
Near Room Temperature Synthesis of Monodisperse TiO2 Nanoparticles: Growth Mechanism
- 2013
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:10, s. 5453-5461
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrolysis of TiCl4 was used to form monodisperse nanoparticles of TiO2 with clean surfaces. The solid fraction and solution composition during synthesis were simulated using equilibrium data, and formation and growth was followed with two complementary techniques, an electrospray-scanning mobility particle sizer (ES-SMPS) and dynamic light scattering (DLS). In ES-SMPS the number density of particles is measured. Droplets formed in the spraying step mainly contain electrolyte, giving rise to residue particles that are detected together with the nanoparticles of interest. Discrimination between the two kinds of particles can be made by changing the flow conditions and applicability of the method for in situ measurements of particle size during growth is demonstrated. In DLS the hydrodynamic mobility is measured, and further insight into the initial growth mechanism was revealed by observation of slow, sustained oscillations in the scattered intensity, indicating a dissolution–precipitation mechanism at the lowest pH values. The size of the particles formed in the dissolution–precipitation step is most likely determined by the surface charge, and larger particles are formed by aggregation.
|
|
| 33. |
- Perez-Holmberg, Jenny, 1977, et al.
(författare)
-
Nonlinear Concentration Dependence of the Collective Diffusion Coefficient of TiO2 Nanoparticle Dispersions
- 2011
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115, s. 13609-13616
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersions of titania nanoparticles are shown to yield collective diffusion coefficients in dynamic light-scattering measurements that depend nonlinearly on particle concentration under dilute conditions. From theory, one expects a linear dependence for monodisperse systems except for strongly interacting charged particles in low ionic strength media. Angularly resolved dynamic light-scattering measurements reveal that aggregates are present, which explains the collective diffusion coefficient tending to lower values in the dilute limit than the Stokes Einstein diffusion coefficient of the nanoparticles. A simple theoretical model based on mixtures of charged nanoparticle spheres and small amounts of larger-sized neutral or weakly charged spheres, modeling the presence of aggregates, is applied and shown to yield predictions in qualitative accord with the experimental trends. In particular, the downward curvature of the collective diffusion coefficient on diluting the system arises in the model from nanoparticles being driven into close proximity to the larger particles by electrostatic interactions. Similar experimental trends observed in silica dispersions suggest that the behavior is not an isolated finding. This study clearly shows that a small number of larger aggregates dramatically change the measured value of the collective diffusion coefficient; thus, care must be exercised when characterizing nanoparticles with dynamic light scattering.
|
|
| 34. |
- Perez-Holmberg, Jenny, 1977, et al.
(författare)
-
Surface charge and interfacial potential of titanium dioxide nanoparticles: Experimental and theoretical investigations
- 2013
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 407:1, s. 168-176
-
Tidskriftsartikel (refereegranskat)abstract
- Size dependent surface charging and interfacial potential of titanium dioxide (TiO2) nanoparticles are investigated by experimental and theoretical methods. Commercially available TiO2 (P25) nanoparticles were used for surface charge determinations by potentiometric titrations. Anatase particles, 10 and 22 nm in diameter, were synthesized by controlled hydrolysis of TiCl4, and electrophoretic mobilities were determined at a fixed pH but at increasing salt concentrations. Corrected Debye–Hückel theory of surface complexation (CDH-SC) was modified to model the size dependent surface charging behavior of TiO2 nanoparticles. Experimentally determined surface charge densities of rutile and P25 nanoparticles in different electrolytes were accurately modeled by the CDH-SC theory. Stern layer capacitances calculated by the CDH-SC theory were in good agreement with the values found by the classical surface complexation approach, and the interaction of protons with OH groups is found to be less exothermic than for iron oxide surfaces. Moreover, the CDH-SC theory predicts that the surface charge density of TiO2 nanoparticles of diameter <10 nm is considerably higher than for larger particles, and pH at the point of zero charge (pHPZC) shifts to higher pH values as the particle size decreases. The importance of including the particle size in calculating the zeta potentials from mobilities is demonstrated. Smoluchowski theory showed that 10 nm particles had lower zeta potential than 22 nm particles, whereas a reverse trend was seen when zeta potentials were calculated by Ohshima’s theory in which particle size is included. Electrokinetic charge densities calculated from zeta potentials were found to be only one third of the true surface charge densities.
|
|
| 35. |
- Persson, Rasmus, 1985, et al.
(författare)
-
Efficient computation of the scattering intensity from systems of nonspherical particles
- 2016
-
Ingår i: Journal of Applied Crystallography. - 0021-8898 .- 1600-5767. ; 49:5, s. 1524-1531
-
Tidskriftsartikel (refereegranskat)abstract
- The analysis of the angle dependence of the elastic scattering of radiation from a sample is an efficient and non-invasive technique that is used in fundamental science, in medicine and in technical quality control in industry. Precise information on the shape, size, polydispersity and interactions of a colloidal sample is readily obtained provided an underlying scattering model, i.e. form and structure factors, can be computed for the sample. Here, a numerical method that can efficiently compute the form factor amplitude (and thus the scattering intensity) of nonspherical scatterers through an importance sampling algorithm of the Fourier integral of the scattering density is presented. Using the precomputed form factor amplitudes, the calculation of the scattering intensity at any particle concentration then scales linearly with the particle number and linearly with the number of q points for its evaluation. This is illustrated by an example calculation of the scattering by concentrated suspensions of ellipsoidal Janus particles and the numerical accuracy for the computed form factor amplitudes is compared with analytical benchmarks.
|
|
| 36. |
- Schantz Zackrisson, Anna, 1973, et al.
(författare)
-
A small-angle X-ray scattering study of aggregation and gelation of colloidal silica
- 2008
-
Ingår i: Colloids and surfaces. A, Physicochemical and engineering aspects. - : Elsevier BV. - 0927-7757. ; 315:1-3, s. 23-30
-
Tidskriftsartikel (refereegranskat)abstract
- Aggregation and gelation in colloidal silica dispersions have been studied by time-resolved, small-angle X-ray scattering. Two different ways of raising the ionic strength, leading to destabilization of the dispersions, have been examined. In situ destabilization by urease-catalyzed hydrolysis of urea has been used as well as an approach with simple mixing of sols with salt solutions. For concentrated dispersions different structures result from the two destabilization methods. Structures differ also in the gelled state, with essentially no fractal scattering from the directly mixed samples whereas fractal scattering on intermediate length scales is observed for the in situ destabilized samples. In contrast, for more dilute particle concentrations, similar structures are generated in both cases and at gelation structures are in close agreement. However, gel times differ drastically in some cases for the two methods, as do the conditions for gelation. These differences are tentatively rationalized by some degree of irreversible aggregation occurring in the mixing stage that, given sufficient time, leads to gelation.
|
|
| 37. |
- Schantz Zackrisson, Anna, 1973, et al.
(författare)
-
Concentration effects on irreversible colloid cluster aggregation and gelation of silica dispersions.
- 2006
-
Ingår i: Journal of colloid and interface science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 301:1, s. 137-44
-
Tidskriftsartikel (refereegranskat)abstract
- Effects of particle concentration on the irreversible aggregation of colloidal silica are studied using in situ destabilization via the ionic strength increase derived from the enzymatic hydrolysis of urea by urease. Aggregation is monitored by time-resolved optical density and dynamic light scattering measurements. It terminates at a gel boundary, signaled by a prominent increase of the optical density and incipient non-ergodicity. Raman scattering is used to demonstrate that the enzymatic reaction continues, well beyond gelation for the compositions studied here, until the urea is consumed. Calibration of the ionic conductivity permits for constructing stability diagrams in terms of particle and salt concentration. As with reversible gelation, the process exhibits a collective character in that lower ionic strengths are required for gelation of concentrated dispersions and vice versa. However, light scattering demonstrates that the gel boundary is preceded here by a line marking the transition from reversible to irreversible cluster formation, with the two transition boundaries tracking each other. Comparisons are made with dispersions destabilized by direct addition of salt solutions, which gel under very different conditions.
|
|
| 38. |
- Sharifi, Soheil, et al.
(författare)
-
Variations in Structure Explain the Viscometric Behavior of AOT Microemulsions at Low Water/AOT Molar Ratios
- 2012
-
Ingår i: Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics. - : Walter de Gruyter GmbH. - 0942-9352. ; 226:3, s. 201-218
-
Tidskriftsartikel (refereegranskat)abstract
- The viscosity of AOT/water/decane water-in-oil microemulsions exhibits a well-known maximum as a function of water/AOT molar ratio, which is usually attributed to increased attractions among nearly spherical droplets. The maximum can be removed by adding salt or by changing the oil to CCl4. Systematic small-angle X-ray scattering (SAXS) measurements have been used to monitor the structure of the microemulsion droplets in the composition regime where the maximum appears. On increasing the droplet concentration, the scattering intensity is found to scale with the inverse of the wavevector, a behavior which is consistent with cylindrical structures. The inverse wavevector scaling is not observed when the molar ratio is changed, moving the system away from the value corresponding to the viscosity maximum. It is also not present in the scattering from systems containing enough added salt to essentially eliminate the viscosity maximum. An asymptotic analysis of the SAXS data, complemented by some quantitative modeling, is consistent with cylindrical growth of droplets as their concentration is increased. Such elongated structures are familiar from related AOT systems in which the sodium counterion has been exchanged for a divalent one. However, the results of this study suggest that the formation of non-spherical aggregates at low molar ratios is an intrinsic property of AOT.
|
|
| 39. |
- Ulama, Jeanette, et al.
(författare)
-
Monodisperse PEGylated Spheres: An Aqueous Colloidal Model System
- 2014
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:9, s. 2582-2588
-
Tidskriftsartikel (refereegranskat)abstract
- Fluorinated core–shell spheres have been synthesized using a novel semibatch emulsion polymerization protocol employing slow feeding of the initiator. The synthesis results in aqueous dispersions of highly monodisperse spheres bearing a well-defined poly(ethylene glycol) graft (PEGylation). Measurements are consistent with the synthesis achieving a high grafting density that moreover consists of a single PEG layer with the polymer significantly elongated beyond its radius of gyration in bulk. The fluorination of the core of the particles confers a low index of refraction such that the particles can be refractive index matched in water through addition of relatively small amounts of a cosolvent, which enables the use of optical and laser-based methods for studies of concentrated systems. The systems exhibit an extreme stability in NaCl solutions, but attractions among particles can be introduced by addition of other salts, in which case aggregation is shown to be reversible. The PEGylated sphere dispersions are expected to be ideally suited as model systems for studies of the effect of PEG-mediated interactions on, for instance, structure, dynamics, phase behavior, and rheology.
|
|
| 40. |
- Ulama, Jeanette, et al.
(författare)
-
Polymer-Graft-Mediated Interactions between Colloidal Spheres
- 2016
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:12, s. 2882-2890
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersions of fluorinated colloidal spheres bearing grafted poly(ethylene glycol) (PEG) are studied as a function of salt and particle concentration with the aim of improving the understanding of interactions among polymer-grafted particles. These dispersions can sustain large concentrations of salt, but crystals nucleate in dilute dispersions when a sufficient Na2CO3 concentration is reached, which is attributed to the presence of attractions between particles. On further increasing the Na2CO3 concentration, the solvent is rapidly cleared of particles. Small-angle X-ray scattering and cryogenic transmission electron microscopy are employed in order to quantify the attractions. The former is used to extract a second virial coefficient, and the latter shows that the PEG-graft contracts as a function of increasing salt concentration. The contraction not only leads to a reduction in excluded volume but also is accompanied by attractions of moderate magnitude. In contrast, dispersion of the particles in ethanol, in which bulk PEG solutions crystallize, lead to fractal structures caused by strong attractions.
|
|
| 41. |
- Zackrisson, Malin, 1974, et al.
(författare)
-
Depletion interactions in model microemulsions.
- 2004
-
Ingår i: Langmuir : the ACS journal of surfaces and colloids. - 0743-7463. ; 20:8, s. 3080-9
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of temperature changes and polymer addition on the behavior of droplet microemulsions of nonionic surfactant, water, and decane are reported and analyzed within polymer depletion theory. Dilution viscometry and dynamic light scattering were used to confirm that these microemulsions behave essentially as hard-sphere dispersions, providing us with an ideal reference system. Addition of poly(ethylene glycol) (PEG) lowers the emulsification failure boundary, where excess oil is expelled, which can be qualitatively understood by an analysis of the available volume for the polymer. Sufficient addition of PEG causes a fluid-fluid phase separation in qualitative accord with experiments on mixtures of rigid colloidal hard spheres and nonadsorbing polymer. Addition of PEG or raising the temperature causes the collective diffusion coefficient D(C) to decrease. From theory, the initial linear slope of D(C) versus droplet concentration can be used to discriminate between attractions and repulsions. The measured D(C) data for the droplets in the presence of PEG are modeled using the Asakura-Oosawa theory of depletion. Fitting the theory to the measured D(C) data permits for extracting the only unknown parameter, the polymer radius of gyration. Quantitative agreement is found with literature data, demonstrating that polymer depletion occurs in the system and that the Asakura-Oosawa theory provides a faithful description of the phenomenon.
|
|
| 42. |
- Zackrisson, Malin, 1974, et al.
(författare)
-
Small-angle neutron scattering on a core-shell colloidal system: a contrast-variation study.
- 2005
-
Ingår i: Langmuir : the ACS journal of surfaces and colloids. - : American Chemical Society (ACS). - 0743-7463. ; 21:23, s. 10835-45
-
Tidskriftsartikel (refereegranskat)abstract
- Small-angle neutron scattering (SANS) measurements are reported on a sterically stabilized, core-shell colloidal system using contrast variation. Aqueous dispersions of polystyrene particles bearing grafted poly(ethylene glycol) (PEG) have been studied over a large range of particle concentrations and two different solvent conditions for the PEG polymer. SANS data are analyzed quantitatively by modeling the particles as core-shell colloids. In a good solvent and under particle contrast conditions, an effective hard-sphere interaction captures excluded-volume interactions up to high concentrations. Contrast variation, through isotopic substitution of both the core and solvent, expedite a detailed study of the PEG layer, both in the dilute limit and as a function of the particle concentration. Upon diminishing the solvent quality, subtle changes in the PEG layer translate into attractions among particles of moderate magnitude.
|
|
| 43. |
- Zackrisson, Malin, 1974, et al.
(författare)
-
Structure, dynamics, and rheology of concentrated dispersions of poly(ethylene glycol)-grafted colloids.
- 2006
-
Ingår i: Physical review. E, Statistical, nonlinear, and soft matter physics. - 1539-3755. ; 73:1 Pt 1
-
Tidskriftsartikel (refereegranskat)abstract
- A comprehensive experimental study of the dynamics and rheology of concentrated aqueous dispersions of poly(ethylene glycol)-grafted colloidal spheres is reported. The study focuses on good solvent conditions, for which excluded-volume interactions dominate. At high concentrations a glass transition is evident from the nondecaying component of the intensity correlation function measured with three-dimensional dynamic light scattering. Results for the linear viscoelastic and steady shear rheology on approaching the glass transition correlate well with the slowing of the diffusive dynamics; in particular, at, or close to, the concentration where the dynamics becomes nonergodic, the dispersions acquire a low-frequency plateau in the elastic shear modulus as well as a yield stress. The overall behavior of the dispersions conforms to that of hard-sphere dispersions; however, some qualitative differences are observed in the evolution of the dynamics and rheology with increasing concentration near the glass transition.
|
|
