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Common superplasticizers (dispersants) for cementitious materials such as concrete include carboxylated comb polymers which strongly chelate Ca2+ ions. Thus, a substrate holding Ca2+ ...as docking site on its surface and of a narrow particle size distribution was expected to produce reliable values for the adsorbed layer thickness (ALT) of polycarboxylate comb polymers, as measured via dynamic light scattering. ALT presents a key parameter which controls the dispersion power of these polymers and provides the steric hindrance effect between cement particles.
Using octadecyl phosphate as emulsifier, phosphate modified polystyrene nanoparticles (dH(z)~86 nm) of narrow size distribution were successfully synthesized and characterized via scanning electron microscopy, dynamic light scattering (DLS) and zeta potential measurements. The particles allowed to measure concentration dependent adsorbed layer thicknesses of a series of structurally different, self-synthesized polycarboxylate superplasticizers.
The phosphate-modified polystyrene nanoparticles were found to present a suitable substrate for ALT measurements of adsorbed polycarboxylate comb polymers. DLS measurements revealed that with progressing adsorption, these polymers develop a concentration-dependent isothermal ALT. At saturation point, layer thicknesses of 3 to 8 nm were observed. The values correlate well with molecular properties of the polymers whereby increasing side-chain length, side-chain density and molecular weight provoke higher ALTs.
Flocculation performance of polyelectrolytes is affected by their molecular branching. To unravel the mechanisms involved, we performed flocculation experiments of negatively charged polystyrene ...latex particles using three cationic polyacrylamide-based polyelectrolytes differing only in the degree of molecular branching. In the experiment, a simple linear chain molecule and two branched polyelectrolytes were tested. The initial rate of flocculation under the condition of standardized mixing, the value of resulted electrophoretic mobility of particles coated with polyelectrolytes, and their hydrodynamic layer thickness by means of particle tracking of Brownian motion were monitored to compare the effect of branching degree. The rate of flocculation was found to increase with an increase in the degree of branching, as corresponding to the hydrodynamic adsorbed layer thickness. These results suggested the importance of the relaxation process polymer chain from coil-like solution conformation to flattened adsorbed state on the surface of colloidal particles. Branched polymers retain their shape after arriving on the surface due to the presence of branches that disturb smooth movement resulting in slow relaxation on the surface of the colloidal particle. Subsequently, forming thick adsorbed layer and enhances the rate of flocculation. Thus, explaining the commonly observed trend where branched polymers achieve better flocculating abilities than linear ones.
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The molecular composition of Acacia senegal and Acacia seyal gum exudate samples were studied using transmission electron microscopy. The molecules observed in both samples were found to have ...diameters of either ∼20 μm, ∼60 μm or ∼10 μm. These most likely represent the arabinogalactan (AG), arabinogalactan-protein (AGP) and glycoprotein (GP) molecules present in Acacia gum exudates. Micrographs obtained for gum solutions that had been left to stand for up to 5 days, indicated that molecular aggregation had occurred, this was particularly evident for the Acacia senegal sample. This aggregation process was attributed to intermolecular electrostatic interactions. The adsorbed layer thickness of the gums adsorbed onto polystyrene latex particles was determined using dynamic light scattering. For the Acacia senegal gum sample, it was found that the adsorbed layer thickness increased over time and after 14 days had a value of 61 nm. These findings are indicative of multilayer adsorption, through intermolecular electrostatic interaction. For the Acacia seyal gum sample the adsorbed layer thickness was only ∼3 nm and did not increase over time. Transmission electron microscopy revealed the presence of a distinct, thick adsorbed layer for the Acacia senegal gum and the presence of a much thinner, more diffuse layer for the Acacia seyal gum sample. Emulsification studies showed that the Acacia senegal gum was more effective at stabilising limonene oil-in-water emulsions than the Acacia seyal sample and that this was because markedly more Acacia senegal gum adsorbed at the oil-water interface compared to the Acacia seyal gum exudate.
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•Acacia gums in solution display molecular association.•Acacia senegal gum forms multilayers at the solid/liquid interface.•Acacia gum composition observed using TEM and STEM.
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•Temporal change of δH and EPM of PSL particle coated with oppositely charged polyelectrolyte after over dosage incubation was monitored.•Charge density of polyelectrolyte chain is ...confirmed to have significant influences on the morphological relaxation of adsorbed polyelectrolytes.•Effects of the diameter of particle and ionic strength were clarified.
Temporal change of hydrodynamic layer thickness (δH) and electrophoretic mobility (EPM) of polystyrene sulfate latex (PSL) particles adsorbed by oppositely charged polyelectrolytes were monitored herein to clarify the relaxation behavior after overshooting. Two linear polyelectrolytes with nominal molecular weight of 5 million differing in chain charge density, σ = 100 % (PTMA5M) and σ = 4 % (PTMC5M), and PSL particles of different diameters were used in the experiment. With the former polyelectrolyte, a remarkably thick layer that is formed at the incubation decays with the time scale of several tens of minutes and the EPM remains constant. The value of δH decreases with the increase of particle size, whereas with the latter polyelectrolyte, the initial value of δH is several times smaller than that of the former. There is a case wherein the EPM decreases with time, although δH remains constant. The initial δH is independent of the particle size. Ascribing the reason for the relaxation phenomena to desorption of overshot polyelectrolytes attached with meta-stable conformation in the initial stage, we have obtained an approximate picture of the conformational change for the chain of different charge density.
The different desorption concepts of the two polyelectrolytes PTMA5M and PTMC5M, which have similar molecular weights and differ in the charge density on the polystyrene sulfate latex (PSL) particles ...by 25 times, and with various charge densities in a long incubation, were systematically investigated based on hydrodynamic adsorbed layer thickness (δH) and electrophoretic mobility (EPM) under two ionic strengths in the present study. Herein, in the case of highly charged polyelectrolyte PTMA5M, desorption continued for 4 h and re-adsorbing proceeded after a longer incubation time higher than 4 h. Meanwhile, in the case of lowly charged polyelectrolyte PTMC5M, an adsorption–desorption equilibrium was suggested to take into account the unchanging of both δH and EPM.
In the temperature range –10–30°С the influence of thermo-oxidative aging, frequency and deformation on the interfacial interaction according to the parameters
K–B–G*
and
К–В–
δ in asphalt mastics ...and modified mastics based on bitumen grade BND 60/90 has been investigated. The filler was introduced into bitumen in the ratio of 1/1 by weight. Active powder of discretely devulcanized rubber (APDDR) as a modifier was introduced in the ratio bitumen/APDDR = 87.5/12.5 by weight. It is shown that the modification of APDDR provides a greater thickness of adsorbed layer on the surface of filler particles under various conditions of external influences compared to mastic, and this thickness depends on the sequence of introduction of filler and APDDR.
Pressure drop in liquid chromatography Podgornik, Aleš
Journal of separation science,
January 2019, 2019-Jan, 2019-01-00, 20190101, Letnik:
42, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Measurement of pressure drop is routinely performed during chromatographic runs. In many cases this information is only used for regulation of mobile phase flow rate to keep pressure drop below ...defined limit. However, pressure drop can provide additional important information about performance of chromatographic process. In this review different parameters affecting pressure drop such as compressibility of chromatographic media, nature of applied sample and mobile phase flow regime are discussed. Detailed analysis correlating organization of particle based chromatographic media and pressure drop is presented together with its extension to convective media such as membranes and monoliths but also novel 3D printed media. Finally, estimation of layer thickness formed by adsorbed molecules based on a pressure drop data is presented and its applicability is discussed.
•Dynamic light scattering was used to study adsorbed layer thicknesses (ALTs) of polymers.•Cationic polystyrene nanoparticles (d∼77nm) were utilized as adsorbents.•Various anionic polyelectrolytes ...representing functional polymers in cement were tested.•Highly reproducible values for ALTs were obtained, even at pH∼13.•Adsorbed conformation of the polymers accessible from comparison of ALT with rh values.
Dynamic light scattering (DLS) was found to present a facile method to directly measure the adsorbed layer thickness (ALT) of various functional polymers. Monodisperse polystyrene nanoparticles (d∼77nm) modified with zinc palmitate to attain a positive surface charge were identified as a suitable adsorbent. These particles are chemically inert and stable even at very high pH values, e.g. of ∼13. As polymers, two cement dispersants, two retarders and four water-retention admixtures were investigated. At first, adsorption isotherms were developed to probe whether single or multiple polymer layers were present on the particles’ surfaces. Next, the adsorbed layer thickness of each polymer on polystyrene nanoparticles was measured using DLS and the results were compared with the hydrodynamic radius of the polymers in solution. From this data, the adsorbed conformation of the polymers was assessed. The method allows quick determination of the ALT at reasonable accuracy.
•Colloidal stability of natural rubber particles has been studied.•Surfactant is strongly adsorbed providing very effective steric stabilization.•The thickness of the adsorbed surfactant layer has ...been measured.•Stability can be modulated, from highly stable to coagulated dispersions.•Suspensions consisting of weakly flocculated particles produce more uniform films.
The effect of a graft copolymer of inulin (linear polyfructose with degree of polymerization greater than 23) on which several C12 alkyl chains are grafted (INUTEC NRA surfactant) on the stability of vulcanized natural rubber was investigated. This surfactant showed a high adsorption affinity to latex surface, and the adsorption isotherms could be fitted to Langmuir equation. The plateau adsorption is approximately 3.4molm−2, corresponding to an area per INUTEC molecule of 4.9nm2. The polymeric surfactant adsorbed layer thickness was determined using zeta potential and dynamic light scattering (PCS techniques). This gave an electrokinetic layer thickness at the plateau adsorption of 3.5nm and a hydrodynamic thickness of 3.1nm. These values indicate that the surfactant can increase the colloidal stability of rubber latex particles, by steric repulsion. The stability of the rubber particles with the surfactant was determined by measuring the critical coagulation concentration (CCC) of calcium nitrate. The adsorption of the surfactant causes a large increase in particle stability; and it was found that the CCC of rubber particles containing the copolymer surfactant increased with the increase in surfactant concentration. Three stability regions were distinguished, namely the coagulation region, the weak flocculation region and the stable dispersion region. The weakly flocculated region may allow the formation of a more uniform layer of latex, which is a very important objective in the industry of glove manufacturing. Thin films of latex have been prepared by a dipping method, and the results clearly demonstrate that smoother films are obtained as a result of a weak flocculation behaviour induced by the presence of surfactant. The results described in this paper may allow the formation of more homogeneous thin films of latex.
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