High-resolution Particle Size Analysis Research Articles

Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized Nanoparticles.

A series of model sterically stabilized diblock copolymer nanoparticles has been designed to aid the development of analytical protocols in order to determine two key parameters: the effective particle density and the steric stabilizer layer thickness. The former parameter is essential for high resolution particle size analysis based on analytical (ultra)centrifugation techniques (e.g., disk centrifuge photosedimentometry, DCP), whereas the latter parameter is of fundamental importance in determining the effectiveness of steric stabilization as a colloid stability mechanism. The diblock copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using RAFT aqueous emulsion polymerization: this approach affords relatively narrow particle size distributions and enables the mean particle diameter and the stabilizer layer thickness to be adjusted independently via systematic variation of the mean degree of polymerization of the hydrophobic and hydrophilic blocks, respectively. The hydrophobic core-forming block was poly(2,2,2-trifluoroethyl methacrylate) [PTFEMA], which was selected for its relatively high density. The hydrophilic stabilizer block was poly(glycerol monomethacrylate) [PGMA], which is a well-known non-ionic polymer that remains water-soluble over a wide range of temperatures. Four series of PGMAx–PTFEMAy nanoparticles were prepared (x = 28, 43, 63, and 98, y = 100–1400) and characterized via transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). It was found that the degree of polymerization of both the PGMA stabilizer and core-forming PTFEMA had a strong influence on the mean particle diameter, which ranged from 20 to 250 nm. Furthermore, SAXS was used to determine radii of gyration of 1.46 to 2.69 nm for the solvated PGMA stabilizer blocks. Thus, the mean effective density of these sterically stabilized particles was calculated and determined to lie between 1.19 g cm–3 for the smaller particles and 1.41 g cm–3 for the larger particles; these values are significantly lower than the solid-state density of PTFEMA (1.47 g cm–3). Since analytical centrifugation requires the density difference between the particles and the aqueous phase, determining the effective particle density is clearly vital for obtaining reliable particle size distributions. Furthermore, selected DCP data were recalculated by taking into account the inherent density distribution superimposed on the particle size distribution. Consequently, the true particle size distributions were found to be somewhat narrower than those calculated using an erroneous single density value, with smaller particles being particularly sensitive to this artifact.

A sediment record of barrier estuary behaviour at the mesoscale: Interpreting high-resolution particle size analysis

At present, limited understanding of mesoscale (years–decades–centuries) back-barrier lagoon, barrier estuary behaviour is a critical shortcoming for resource managers and decision makers. In this paper, high-resolution particle size analysis of a sediment core from an intermittently open and closed barrier estuary is utilised to reconstruct a history of back-barrier environmental change at mesoscale temporal resolution. Sediments from Pescadero Marsh, California, were analysed for their particle size distribution at consecutive 2-mm intervals down-core. Site selection, informed by a time series of maps and aerial photographs coupled with a robust core chronology, ensured that the particle size data primarily reflect changing hydrodynamics of the back-barrier area over the European–American era (1850 to the present). Following more traditional plotting of particle size data and summary statistics, and statistical analysis of particle size end-members, visual analysis and categorisation of particle size distribution curves (PSDCs) provide an effective basis for the identification of recurring modal sizes and subpopulations. These particle size windows (PSWs) are interpreted as reflecting different modes of sediment transport and deposition, i.e., suspension and saltation loads, the varying prominence of which is interpreted as being modified by barrier integrity. When considered together, the down-core mean particle size (MPS) trend and individual PSDCs offer considerable insight into mesoscale system behaviour at subannual resolution over multiple years. This behaviour is expressed in the recurrence of characteristic barrier estuarine environments (closed lagoon, tidal lagoon, tidal marsh, and open estuary) and the overall barrier regime, and their persistence over the last c. 150years. Subannual and multiannual fluctuations in back-barrier environmental configuration are seen to be superimposed on a longer-term quasi-stable barrier regime, demonstrating the value of the applied methodology with regard to bridging the estuarine evolution (long-term, stratigraphic) and process (short-term, geomorphic) knowledge bases. The documented behaviour suggests a level of innate morphological resilience in the system over the long term despite episodic disturbance by high-energy storms. Such empirical demonstrations of resilient behaviour in coastal environments are rare at the mesoscale.

Meso-scale barrier estuary disturbance, response and recovery behaviour: Evidence of system equilibrium and resilience from high-resolution particle size analysis

Establishing the future trajectories of coastal wetlands, especially the nature of their disturbance, response and recovery regimes, is of critical importance for a wide range of stakeholders and environmental managers. Reconstructing meso-scale behaviour in coastal environments can serve to attune coastal resource management strategies to natural scales of system operations, thus fostering genuine sustainability. Sediments from Pescadero Marsh, a back-barrier coastal wetland in California, were analysed down-core for their particle size distribution in consecutive 2-mm sections. The particle size data reflect changing hydrodynamics in the back-barrier area driven by past variations in barrier coherence. When considered together, the down-core mean particle size trend and particle size distribution curve styles provide considerable insight into meso-scale system behaviour, revealing barrier/back-barrier disturbance–response–recovery regimes, regime shifts and the role of aperiodic high-energy events in disturbing these regimes. Over sub-annual and multi-annual time periods, the behaviour of the Pescadero system was consistently characterised by both dynamic response to disturbance and recovery through negative feedback. Furthermore, over the duration of the analysed core section, that is, 1200–2300 years, the system was determined to have adopted a series of static equilibrium states. The barrier estuary behaviour reconstructed from the Pescadero sediment record is indicative of innate environmental resilience.

Particle-size evidence of estuary evolution: A rapid and diagnostic tool for determining the nature of recent saltmarsh accretion

A conceptual model of saltmarsh sedimentation based on high-resolution particle-size analysis has been tested on short cores (c. 0.5m) of known age from the Dee estuary, NW England, UK. Here, two components of the particle-size distribution (PSD) are interpreted as the traction load deposited by the faster tidal flow velocities (‘fast tide’) and the suspension load that settles during the turn of the tide (‘slow tide’). The feasibility of this model for diagnosing the driving mechanism of estuary evolution in both time and space is tested with reference to historical evidence of saltmarsh accretion, up-core trends in dated saltmarsh cores, and the PSDs of present-day saltmarsh surface sediments. Cores that show an up-core progression from very fine-skewed to near symmetrical PSDs are interpreted in the context of estuary infilling due to a positive sediment budget (sediment surplus), whilst those that show a persistence of near-symmetrical, (very) poorly sorted, mesokurtic particle-size distributions in the fine to very fine silts size range are considered to be the result of ‘slow tide’ sedimentation. The influences of the two ‘end-member’ styles of saltmarsh accretion, i.e. (i) infilling due to sediment surplus and (ii) ‘slow tide’ settling linked to sea level, exhibit spatial and temporal trends as predicted, particularly in cores from mid- and lower saltmarsh locations. The upper saltmarsh cores also show evidence of estuary infilling due to ‘slow tide’ sedimentation at rates in excess of sea-level rise. The results confirm that the diagnostic approach can be applied as a ‘pre-filtering’ method for assessing the suitability of saltmarsh sediments for reconstructing sea-level trends, and for providing input data for improved estuary morphological modelling.

Loess and floods: late Pleistocene fine-grained valley-fill deposits in the Flinders Ranges, South Australia

Terrace remnants of late Pleistocene fine-grained valley-fills, at present eroded by ephemeral traction-load streams, are reported from many semi-arid and arid parts of the world. While they present promising palaeo-environmental archives for recent geological times such as the Last Glacial Maximum (LGM) for which few other terrestrial depositional records exist, their poorly understood nature has limited their significance. This study examines the fine-grained valley-fill deposits from the Flinders Ranges in South Australia, here called Flinders Silts. It establishes the timing, mode and environmental controls of deposition as opposed to their advancing erosion under the current climate. A regional chronostratigraphy based on 124 numerical dates is discussed, of which 43 radiocarbon and 22 luminescence ages were obtained from 12 sections across three major catchments within the scope of this thesis. Regionally significant intervals of rapid aggradation, relative surface stability and erosion are established. Regional climatic controls are differentiated from intrinsic catchment- and site-specific effects on the system. Further, individual age proxies and age models are critically assessed in how far they reflect depositional events. The final aggradational interval bracketing the extended LGM is discussed in detail on a continuous layered to laminated stratigraphic sequence. The provenance question of the fine-grained sediments and the depositional environment of the Flinders Silts are further addressed by high-resolution particle-size analysis. In order to study the subtle variations within the fine-grained partially-aggregated material, an original parametric sediment-sizing approach is employed. Finally, a range of traditional and emerging analytical techniques are applied to improve our understanding of palaeo-environments promoting aggradation. In conclusion, arid intervals throughout the last glacial cycle resulted in significant quantities of proximal dust being deposited as loess mantles within the catchments of the Flinders Ranges, acting as a near-longitudinal dust trap in the centre of the late Pleistocene “dust bowl”. The fine-grained aeolian accessions were repeatedly eroded by low-frequency high-magnitude precipitation events and redistributed as loess-derived alluvium, congesting narrow gorges and raising the base level for tributaries. Locally, backflooding resulted in the aggradation of layered to laminated slackwater deposits, the most continuous recording at least 12 large and numerous smaller flood events between 24 ka and 18 ka. The synchronous termination of the Flinders Silts coincides with early Deglacial climatic amelioration. The re-establishment of a perennial plant cover stabilising both dune fields and slope mantes is discussed as a potential scenario that would have discontinued dust supply to the fluvial system, in turn promoting incision and erosion. The studied aeolian-fluvial interplay of loess and floods has large implications for our understanding of landscape evolution in…

Testing foraminiferal taphonomy as a tsunami indicator in a shallow arid system lagoon: Sur, Sultanate of Oman

The tsunami produced by the 1945 Makran Trench earthquake is considered to be the second deadliest in the Indian Ocean after the 26 December 2004 Indonesian event. The tsunami struck Iran, Pakistan, India and Oman; however, historical records outside of India and Pakistan are sparse due to limited populations in those regions and little communication with larger cities. Sur Lagoon, Oman, a small microtidal lagoon, contains stratigraphic evidence of the 1945 tsunami. The goal of this study is to test the utility of foraminiferal provenance and taphonomy as an indicator of the 1945 event and examine its potential in detecting older events in the geologic record. Foraminiferal (taxa and taphonomy) and high resolution particle size analysis show that high abundances of predominantly marine taxa (Amphistegina spp., Ammonia inflata, and planktics) associated with the tsunami bed indicate an outside marine origin for the sediment. Influxes of large test sizes and fossil specimens support a shallow marine provenance. Findings indicate that foraminiferal analysis, when combined with other proxies (e.g. mollusc taphonomy, particle size distribution), can be used to delineate tsunami units from normal background sedimentation in intertidal systems. This technique holds potential for detecting older events in Sur Lagoon which are documented in historical texts, but as of yet, have not been ‘ground-truthed’.

Particle-size distribution of inferred tsunami deposits in Sur Lagoon, Sultanate of Oman

The sedimentary characteristics of shell beds within an interpreted tsunami deposit from Sur Lagoon, Oman were examined using shell taphonomy and high-resolution particle-size analysis. The tsunami bed was deposited by the 28 November, 1945 tsunami generated by the Makran subduction zone. Q-mode cluster analysis of particle-size data was evaluated as a means of discriminating individual tsunamite shell layers from lagoonal intertidal deposits. Results showed that the tsunami shell bed was more poorly sorted, and heterogeneous (in both the digested and undigested samples) than the background lagoonal sediments. The tsunami bed thickness correlated generally with the thickness of the shell-bed, however, cluster analysis extended the tsunami unit several centimeters above or below the shell bed in some cores. The particle-size analysis also showed subtle textural trends in the tsunami unit, suggesting that the tsunami bed was deposited in several distinctive phases during tsunami incursion into Sur Lagoon. The findings indicate that cluster analysis of particle-size data can be used to identify tsunami beds in intertidal environments and holds potential for identifying paleotsunami deposits in sediments from embayed intertidal–subtidal siliciclastic systems where obvious sedimentary structures may be absent.

Changing sedimentation patterns due to historical land-use change in Frenchman’s Bay, Pickering, Canada: evidence from high-resolution textural analysis

This study examines the anthropogenic alteration of sedimentation in Frenchman’s Bay in Lake Ontario, using high-resolution particle size analysis in two 200 cm cores. Lithofacies were determined using the particle size data of both the terrigenous sediment and terrigenous sediment + diatom fractions. Terrigenous particle size data from the centre of the lagoon provided the most representative record of anthropogenic impacts. Three distinctive lithofacies were recognized: (1) a Natural Wetland (NW) lithofacies (106–200 cm) had an average mean particle size of 49.4 μm, a mode of 29.4 μm and an average standard deviation of 119.1 μm; (2) an Agricultural and Deforestation (AD) lithofacies (40–105 cm) had a statistically significant lower average mean (30.8 μm), mode (13.5 μm), and standard deviation (48.5) μm; (3) an Urbanized (U) lithofacies (0–40 cm) showed a continued trend towards smaller particle sizes with an average mean of 21.2 μm, a mode of 9.4 μm, and an average standard deviation of 32.7 μm. The lithofacies correlated with previously identified trends in thecamoebian biofacies and magnetic susceptibility data showing post-colonial lagoon eutrophication and increased overland soil erosion. The up-core trend towards finer and less variable particle sizes is attributed to erosion of fine-grained watershed sediments (glacial Lake Iroquois silts and clay) during land-clearance and modification of natural drainage patterns. The influx of silts and clays into the lagoon is also recorded by increased sediment accumulation rates and a reduction in seasonal sediment variability in the wetland. Based on the 210Pb dates, sedimentation rates increased at 1850 ±56 AD (AD lithofacies) and suggest an exponentially increasing trend in accumulation rates. Increasing sedimentation rates can be attributed to the progressive loss of native vegetation and intensified erosion of Lake Iroquois deposits via stream and hillslope erosion. Ecologically, the increased input of fine-grained sediments into the wetland has resulted in reduced water clarity and has altered the wetland substrate contributing to wetland loss in Frenchman’s Bay.

High-Resolution Particle Size Analysis of Naturally Occurring Very Fine-Grained Sediment Through Laser Diffractometry

ABSTRACT In this paper, we present results from a large number of experiments aimed at quantifying method and instrument uncertainty associated with laser diffraction analysis. We analyzed the size distribution of fine-grained sediment ( 24 hours prior to analysis and using 60 seconds of ultrasonication during analysis. (2) Obscuration--a measure of the concentration of the suspension during analysis--produced the most reproducible results at about 20%. (3) Variations in refractive-index settings can significantly alter estimated grain-size distributions. (4) Assumed values for absorption (the degree to which sediment grains absorb the light) can have a profound effect on grain-size results. Absorption settings near 0 resulted in unexpected bimodal grain size distributions for sediments in the < 10 µm size fraction and significantly skewed the fine-grained tail of coarser samples, probably because of sub-optimal diffraction by particles with a diameter similar in size to the laser wavelength. Absorption settings closer to 1 produced very reproducible results and unimodal grain-size distributions over a wide range of refractive indexes. Our study has shown that laser diffraction can measure very fine-grained sediments (< 10 µm) quickly, with high precision ( 5% at 2 standard deviations), and without the need for extensive mineralogical determinations. These results make possible a new generation of studies in which high-resolution time-series data sets of sediment grain size can be used to infer subtle changes in paleohydrology.

The evolution of coupling of Asian winter monsoon and high latitude climate of Northern Hemisphere

The evolution and driving mechanism of the Asian winter monsoon system are of great importance to understanding the present-day climate. Through high-resolution particle size analysis of the oldest loess-red clay sequence known so far (with a basal age of about 8 Ma) and comparison of the results with oxygen isotope curves from North Atlantic marine sediments, 4 stages of the evolution of the Asian winter monsoon were clearly demonstrated. During the first stage, between about 8.1 and 4.3 Ma, there was no relation between Asian winter monsoon and Northern Hemisphere ice volume and high latitude climate inferred from marine sediments. A weak relation developed during the second stage, about 4.3 to 3.5 Ma. During the third stage (3.5 to 2.6 Ma) an Asian winter monsoon system similar to the present formed, initiating a stronger relation between the winter monsoon and Northern Hemisphere ice volume and high latitude climate. In the final stage (2.6 to 0 Ma) the present Asian winter monsoon system was fortified and stabilized and changes in the winter monsoon system were almost in phase with Northern Hemisphere ice volume and climate. The staggered uplift of Tibetan Plateau at ≈8, 3.6, 2.6 Ma and later might be the driving force for the evolution of the Asian winter monsoon.

The evolution of coupling of Asian winter monsoon and high latitude climate of Northern Hemisphere ——Grain evidence from 8.1 Ma loess-red clay sequence on the Chinese central Loess Plateau

The evolution and driving mechanism of the Asian winter monsoon system are of great importance to understanding the present-day climate. Through high-resolution particle size analysis of the oldest loess-red clay sequence known so far (with a basal age of about 8 Ma) and comparison of the results with oxygen isotope curves from North Atlantic marine sediments, 4 stages of the evolution of the Asian winter monsoon were clearly demonstrated. During the first stage, between about 8.1 and 4.3 Ma, there was no relation between Asian winter monsoon and Northern Hemisphere ice volume and high latitude climate inferred from marine sediments. A weak relation developed during the second stage, about 4.3 to 3.5 Ma. During the third stage (3.5 to 2.6 Ma) an Asian winter monsoon system similar to the present formed, initiating a stronger relation between the winter monsoon and Northern Hemisphere ice volume and high latitude climate. In the final stage (2.6 to 0 Ma) the present Asian winter monsoon system was fortified and stabilized and changes in the winter monsoon system were almost in phase with Northern Hemisphere ice volume and climate. The staggered uplift of Tibetan Plateau at ~8, 3.6, 2.6 Ma and later might be the driving force for the evolution of the Asian winter monsoon.

High-Resolution Particle Size Analysis from Nanometres to Microns

AbstractModem disc centrifuge technology has extended the range of application of sedimentation particle size analysis to include the submicron region. An overall size range of approximately 10 nm to 100 pm is now accessible. The principles of both the disc centrifuge photosedimentometer, which employs optical detection with full Mie light scattering corrections, and the X-ray disc centrifuge are described. Examples of their application to a variety of samples are given to illustrate the performance characteristics of the instruments including a direct comparison of resolving power with that of the laser diffraction technique.

Aerosol classification by electric mobility: apparatus, theory, and applications

An improved version of the Hewitt (differential) electric mobility analyzer was developed and its classifying characteristics were determined theoretically. The central mobility of the classified aerosol was found to be ( q c + q m )/4 πΛV, where q c and q m are the clean air and main outlet flows, respectively, Λ is a geometric factor, and Λ is the center rod voltage. The half-width of the mobility band was found to be ( q a + q s )/4 πΛV, where q a and q s are the aerosol and sampling outlet flows, respectively. These expressions were verified by the tests with a monodisperse aerosol of known size and low charge. A major advantage of this device is that the classified aerosol fraction remains airborne, ready for further use or analysis. Thus, one application of the device is the production of monodisperse test aerosols of known size, charge, and concentration by classification of a polydisperse aerosol. Other current applications include accurate measurement of particle electric mobility moments and high-resolution particle size analysis for polydisperse aerosols in the 0.005–1.0 μm size range.