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Thermal field-flow fractionation (ThFFF) was designed to investigate the retention behavior of a series of dendritic polyethylenes synthesized using a chain walking catalyst (cwPE) with variations ...

Thermal field-flow fractionation (ThFFF) was used to characterize the architecture of aromatic-aliphatic polyesters with varying degrees of branching. Thermal diffusion and Soret coefficients (DT and ST, respectively) provide a novel route to polymer architecture analysis. This paper demonstrates an innovative strategy to extract architecture information from the physicochemical separation parameters embedded in ThFFF retention times without explicit separation of linear and branched samples. A Soret contraction factor (g″), defined as the ratio of the ST of a branched polymer to the ST of a molecular weight equivalent linear analogue, is introduced as a metric to indicate degree of branching (DB). This approach circumvents several challenges associated with the analysis of high molar mass polymers with a high degree of branching. The g″ value is shown to be proportional to the degree of branching for linear (DB, 0%), gradually branched (DB

Field-flow fractionation (FFF) is a family of techniques that was created especially for separating and characterizing macromolecules, nanoparticles, and micrometer-sized analytes. It is coming of age as new nanomaterials, polymers, composites, and biohybrids with remarkable properties are introduced and new analytical challenges arise due to synthesis heterogeneities and the motivation to correlate analyte properties with observed performance. Appreciation of the complexity of biological, pharmaceutical, and food systems and the need to monitor multiple components across many size scales have also contributed to FFF's growth. This review highlights recent advances in FFF capabilities, instrumentation, and applications that feature the unique characteristics of different FFF techniques in determining a variety of information, such as averages and distributions in size, composition, shape, architecture, and microstructure and in investigating transformations and function.

Colloidal hybrid nanoparticles integrate two or more material domains into a single construct to achieve multifunctionality and synergistic properties. The synthesis of these complex multicomponent hybrid nanoparticles often yields size and composition distributions that subsequently impact observed properties and complicate structure–function studies. Analyses of nanoparticle systems such as these that contain multiple simultaneously occurring distributions are highly challenging. In this work, we introduce thermal field-flow fractionation (ThFFF) as an analytical method to separate and characterize iron oxide (Fe3O4), platinum (Pt), and multicomponent platinum–iron oxide (Pt–Fe3O4) hybrid nanoparticles by composition. The transport of matter by a temperature gradient or thermal diffusion is exploited in the ThFFF separation and characterization of inorganic nanoparticles. Thermal diffusion coefficient (DT) values are determined from measured ThFFF retention times and translational diffusion coefficients...

High- and low-density lipoproteins (HDL and LDL) are attractive targets for biomarker discovery. However, ultracentrifugation (UC), the current methodology of choice for isolating HDL and LDL, is tedious, requires large sample volume, results in sample loss, and does not readily provide information on particle size. In this work, human plasma HDL and LDL are separated and collected using semi-preparative asymmetrical flow field-flow fractionation (SP-AF4) and UC. The SP-AF4 and UC separation conditions, sample throughput, and liquid chromatography/mass spectrometry (LC/MS) lipidomic results are compared. Over 600 μg of total proteins is recovered in a single SP-AF4 run, and Western blot results confirm apoA1 pure and apoB100 pure fractions, consistent with HDL and LDL, respectively. The SP-AF4 separation requires ~ 60 min per sample, thus providing a marked improvement over UC which can span hours to days. Lipidome analysis of SP-AF4-prepared HDL and LDL fractions is compared to UC-prepared HDL and LDL samples. Over 270 lipids in positive MS mode and over 140 lipids in negative MS mode are identified by both sample preparation techniques with over 98% overlap between the lipidome. Additionally, lipoprotein size distributions are determined using analytical scale AF4 coupled with multiangle light scattering (MALS) and dynamic light scattering (DLS) detectors. These developments position SP-AF4 as a sample preparation method of choice for lipoprotein biomarker characterization and identification. Graphical abstract ᅟ.

Mesoporous silica nanoparticles (MSN) with enlarged pores were prepared and characterized, and reversibly dissociated subunits of concanavalin A were entrapped in the mesopores, as shown by multiple biochemical and material characterizations. When loaded in the MSN, we demonstrated protein stability from proteases and, upon release, the subunits reassociated into active proteins shown through mannose binding and o-phthalaldehyde fluorescence. We have demonstrated a versatile and facile method to load homomeric proteins into MSN with potential applications in enhancing the delivery of large therapeutic proteins.

The synthesis of mesoporous silica thin films on nontraditional conductive substrates using an electro-assisted self-assembly (EASA) technique is described. This work extends prior demonstrations of EASA by exploring the effects of precursor sol pH, temperature, and substrate roughness and describes a new approach to synthesizing a mesoporous silica film that is detachable from the substrate. The latter uses a conductive polymer as a planarization layer for successful EASA on indium-tin oxide coated glass (ITO) and as a sacrificial layer that can be subsequently dispersed in water to release the silica film. This is a particularly important development because it opens up possibilities for synthesizing perpendicularly aligned nanoporous silica on a broad range of surfaces and non-conductive substrates and producing free standing nanostructured thin films. The silica films that are produced have well ordered hexagonally packed mesopores that are vertical to the substrate surface. The thicknesses of these mesoporous silica films were examined by scanning electron microscopy (SEM) and determined to be controllably variable between ∼100 and 200 nm. Transmission electron microscopy (TEM) showed organized porous structural features that were approximately 3 nm in diameter. Grazing-incidence small angle X-ray scattering (GISAXS) analysis yielded an ∼4.2 nm pore-to-pore distance and confirmed that a p6mm orientation persisted throughout the 6 cm2 mesoporous silica film samples.

We report a mild, effective, room-temperature method for brominating and functionalizing colloidal hydrogen-terminated silicon quantum dots (H-SiQDs) using N-bromosuccinimide (NBS) as the bromination reagent. This post-synthesis bromination overcomes a long-standing challenge of producing emissive SiQDs through the functionalization of directly synthesized halogen-terminated colloidal SiQDs.

Chemical mechanical polishing (CMP) is an essential technology used in the semiconductor industry to polish and planarize a variety of materials for the fabrication of microelectronic devices (e.g., computer chips). During the high shear (~1,000,000 s(-1)) CMP process, it is hypothesized that individual slurry particles are driven together to form large agglomerates (≥0.5 μm), triggering a shear thickening effect. These shear-induced agglomerates are believed to cause defects during polishing. In this study, we examined the shear thickening of a 25 wt % fumed silica slurry with 0.17 M added KCl using in situ small-angle light scattering during rheological characterization (rheo-SALS). The salt-adjusted slurry displays a ~3-fold increase in viscosity at a critical shear rate of 20,000 s(-1) during a stepped shear rate ramp from 100 to 25,000 s(-1). As the shear rate is reduced back to 100 s(-1), the slurry displays irreversible thickening behavior with a final viscosity that is 100-times greater than the initial viscosity. Corresponding rheo-SALS images indicate the formation of micrometer scale structures (2-3 μm) that directly correlate with the discontinuous and irreversible shear thickening behavior of the fumed silica slurry; these micrometer scale structures are 10-times the nominal particle diameter (~0.2 μm). The scattering patterns from the 25 wt % slurry were corroborated through rheo-SALS examination of 27 and 29 wt % slurries (C(KCl) = 0.1 M). All slurries, regardless of ionic strength and solids loading, display scattering patterns that are directly associated with the observed thickening behavior. Scattering was only observable during and after thickening (i.e., no scattering was detected in the absence of thickening). This work serves as the first in situ observation of micrometer scale structures within the fumed silica CMP slurry while under shear.

During the chemical mechanical polishing (CMP) process, it is believed that shear thickening of the slurry, caused by particle agglomeration, has the potential to result in a significant increase in particle-induced surface defects (i.e. scratches, gouges, pits, etc.). In this study, we have developed a methodology for the synchronized measurement of rheological behavior while polishing a semiconductor wafer, the first of its kind (a technique termed rheo-polishing). We investigate the shear thickening of a 25 wt% fumed silica slurry with 0.15 M added KCl and its impact on polishing performance and subsequent surface damage. The thickened slurry displays a ∼5-fold increase in viscosity with increasing shear rate. As the shear rate is reduced back to zero, the slurry continues to thicken showing a final viscosity that is ∼100× greater than the initial viscosity. Optical microscopy and non-contact profilometry were then utilized to directly link slurry thickening behavior to more severe surface scratching of “polished” TEOS wafers. The thickened slurry generated up to 7× more surface scratches than a non-thickened slurry. Both slurry thickening and surface scratching were associated with a dramatic increase in the population of “large” particles (≥300 nm) which were undetectable in the non-thickened slurry. These “large” and potentially scratch-generating particles are believed to instigate measurable surface damage.

International audience; Polymer self-assemblies joining oppositely charged chains, known as polyion complexes (PICs), have been formed using poly(ethyleneoxide – b – acrylic acid)/poly(l-lysine), poly(ethyleneoxide-b-acrylic acid)/dendrigraft poly(l-lysine) and poly[(3-acrylamidopropyl) trimethylammonium chloride – b – N – isopropyl acrylamide]/poly(acrylic acid). The self-assemblies have been first characterized in batch by Dynamic Light Scattering. In a second step, their analysis by Flow Field-Flow Fractionation techniques (FlFFF) was examined. They were shown to be very sensitive to shearing, especially during the focus step of the fractionation, and this led to an incompatibility with asymmetrical FlFFF. On the other hand, Frit Inlet FlFFF proved to be very efficient to observe them, either in its symmetrical (FI-FlFFF) or asymmetrical version (FI-AsFlFFF). Conditions of elution were found to optimize the sample recovery in pure water. Spherical self-assemblies were detected, with a size range between 70–400nm depending on the polymers. Compared to batch DLS, FI-AsFlFFF clearly showed the presence of several populations in some cases. The influence of salt on poly(ethyleneoxide-b-acrylic acid) (PEO-PAA) 6000-3000/dendrigraft poly(l-lysine) (DGL 3) was also assessed in parallel in batch DLS and FI-AsFlFFF. Batch DLS revealed a first process of swelling of the self-assembly for low concentrations up to 0.8M followed by the dissociation. FI-AsFlFFF furthermore indicated a possible ejection of DGL3 from the PIC assembly for concentrations as low as 0.2M, which could not be observed in batch DLS.

The impact of asymmetrical flow field-flow fractionation (AF4) on protein aggregate species is investigated with the aid of multiangle light scattering (MALS) and dynamic light scattering (DLS). The experimental parameters probed in this study include aggregate stability in different carrier liquids, shear stress (related to sample injection), sample concentration (during AF4 focusing), and sample dilution (during separation). Two anti-streptavidin (anti-SA) IgG1 samples composed of low and high molar mass (M) aggregates are subjected to different AF4 conditions. Aggregates suspended and separated in phosphate buffer are observed to dissociate almost entirely to monomer. However, aggregates in citric acid buffer are partially stable with dissociation to 25% and 5% monomer for the low and high M samples, respectively. These results demonstrate that different carrier liquids change the aggregate stability and low M aggregates can behave differently than their larger counterparts. Increasing the duration of the AF4 focusing step showed no significant changes in the percent monomer, percent aggregates, or the average Ms in either sample. Syringe-induced shear related to sample injection resulted in an increase in hydrodynamic diameter (dh) as measured by batch mode DLS. Finally, calculations showed that dilution during AF4 separation is significantly lower than in size exclusion chromatography with dilution occurring mainly at the AF4 channel outlet and not during the separation. This has important ramifications when analyzing aggregates that rapidly dissociate (∼2s) upon dilution as the size calculated by AF4 theory may be more accurate than that measured by online DLS. Experimentally, the dhs determined by online DLS generally agreed with AF4 theory except for the more well retained larger aggregates for which DLS showed smaller sizes. These results highlight the importance of using AF4 retention theory to understand the impacts of dilution on analytes.

The development of an asymmetrical field-flow fractionation (AsFlFFF) method for separating gold nanorods (GNR) is reported. Collected fractions containing GNR subpopulations with aspect ratios, sizes, and shapes which are more narrowly dispersed than the original population were further characterized by UV-vis spectroscopy and transmission electron microscopy. This ability to obtain different sizes and shapes of nanoparticles enabled the evaluation of a new approach to estimating the retention time and hydrodynamic size of nanorods and the investigation of GNR optical properties at a previously unattainable level of detail. Experimental results demonstrate that the longitudinal surface plasmon absorption maximum of GNRs is correlated with the effective particle radius in addition to the aspect ratio. This may account for some of the variabilities reported in published empirical data from different research groups and supports reports of simulated absorption spectra of GNRs of different physical dimensions. The use of AsFlFFF with dual UV-vis detection to rapidly assess relative changes in GNR subpopulations was demonstrated for irregularly shaped gold nanoparticles formed at different synthesis temperatures.

Chemical mechanical polishing (CMP) is a fundamental technology used in the semiconductor manufacturing industry to polish and planarize electronic materials. During the high shear (≥1,000,000 s − 1) polishing process, it is hypothesized that individual slurry particles begin to interact and collide with one another forming large agglomerates (≥0.5 μm). These agglomerates are suspected of causing defects such as scratches or gouges during polishing, which costs the semiconductor industry billions of dollars annually. We have developed a method for investigating the shear thickening behavior of fumed silica slurries (20–34 wt.%) under high shear using a parallel-plate geometry in a conventional rotating rheometer. The CMP slurries displayed irreversible thickening at shear rates exceeding 10,000 s − 1. Viscous heating and sample evaporation are shown to be inconsequential to the witnessed shear thickening behavior. Also, the observed thickening is not a result of a critical rheometer speed, as the thickening was independent of the experimental gap height. In agreement with previous work, the slurries thickened at lower shear rates as silica concentration was increased. The shear thickening of the fumed silica slurries is truly shear-induced, and therefore, the thickening of CMP slurries can be examined using a rotational rheometer at small gap heights (≤100 μm).

Silicon nanoparticles (Si NPs) were synthesized by plasma enhanced chemical vapor deposition (PECVD) using silane as a silicon source. Allylamine was used as passivation ligands to form water-soluble Si NPs. Finally, aqueous asymmetric flow field-flow fractionation was used to successfully separate the polydisperse Si NPs into monodisperse Si NP fractions.

The purpose of this study is to develop a novel bacterial analysis method by coupling the flow field-flow fractionation (flow FFF) separation technique with detection by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The composition of carrier liquid used for flow FFF was selected based on retention of bacterial cells and compatibility with the MALDI process. The coupling of flow FFF and MALDI-TOF MS was demonstrated for P. putida and E. coli. Fractions of the whole cells were collected after separation by FFF and further analyzed by MALDI-MS. Each fraction, collected over different time intervals, corresponded to different sizes and possibly different growth stages of bacteria. The bacterial analysis by flow FFF/MALDI-TOF MS was completed within 1 h with only preliminary optimization of the process.

Thermal field-flow fractionation (ThFFF) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) have been coupled to yield a powerful combination of techniques for polymer analysis. Thermal FFF's high molecular weight (MW) selectivity and sensitivity to chemical composition are used to separate polydisperse polymers and polymer mixtures into the narrow polydispersity and homogeneous chemical composition fractions essential for MALDI-TOFMS analyses. On the other hand, MALDI-TOFMS's ability to directly measure molecular weight alleviates the need for polymer standards for ThFFF. In this first-time coupling of ThFFF and MALDI-TOFMS, compatibility issues were addressed and optimum conditions and procedures were identified and developed to maximize the capabilities of the combined technique. Depending on the polymer MW and the method of MALDI sample deposition, fractions from 1-10 ThFFF runs were combined for MALDI-TOFMS analysis. Binary solvents were used to enhance ThFFF retention and resolution of low-MW (15-kDa) polymers, and methods were developed to allow routine MALDI-TOFMS analyses of polystyrene polymers up to 575 kDa. Overall, the MW compatibility of the two techniques was extended from several kilodaltons to several hundred kilodaltons. Polymer fractions were collected after separation by ThFFF and analyzed either by MALDI-TOFMS or reinjection into the ThFFF system. Good agreement was observed between the MW distribution data obtained by MALDI-TOFMS and ThFFF. The application of ThFFF/MALDI-TOFMS to polydisperse polymers and polymer mixtures was demonstrated. This combined technique was also shown to be a viable means for preparing standards from the original polymer sample.

Thermal field-flow fractionation (ThFFF) is capable of separating a wide molecular mass range of polymers by their molecular mass (Mr) and chemical composition. However, retention and resolution decrease significantly for polymers with Mr

Field-flow fractionation (FFF) techniques were used to separate various strains of bacteria and differentiate live from dead bacteria. The sedimentation, flow, and electrical FFF separations were accomplished in less than 15 minutes using the rapid hyperlayer mode. The bacteria used in these studies include Pseudomonas putida, Escherichia coli, and Staphylococcus epidermidis. Sedimentation FFF gives the highest resolution separations of a mixture of spherical and rod-shaped bacteria, and a mixture of two rod-shaped bacteria.