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In core–shell nanoparticle analysis, the determination of size distributions of the different particle parts is often complicated, especially in liquid media. Density matching is introduced as a method for analyzing core–shell nanoparticles using Analytical Ultracentrifugation (AUC), making it possible to obtain the core size distribution in liquid dispersions. For this approach, the density of the dispersion is adjusted to the density of the shell. Oil filled nanocapsules are utilized with component densities of around 1 g mL−1 to demonstrate this technique. The shell size distribution is calculated supposing the particle size distribution as a convolution of the shell‐ and core size distributions. Finally, the distributions of core size, shell thickness, particle size, and particle density and thus particle composition are obtained. To clarify the effect of swelling, AUC measurements are combined with further size characterization methods like Particle Tracking Microscopy and Dynamic Light Scattering. [ABSTRACT FROM AUTHOR]

Abstract A pulsed light emitting diode, coupled with a properly configured spectrometer is implemented in open source analytical ultracentrifugation detection hardware, allowing for spectral acquisition spanning the visible to near infrared. Details of the challenges arising with the new hardware are described, along with the necessary solutions to overcome them. The system is successfully tested with polystyrene and gold nanoparticles, demonstrating effectiveness for different material and particle geometries. Sedimentation coefficient distributions and analytically extracted spectra are presented for the multiwavelength datasets extending into the near infrared. Additionally, deconvolution algorithms are applied as a further demonstration of tools applicable to these datasets and the resolving power possible. The results of gold nanoparticle analysis presented here show effective near infrared spectral acquisition is now possible for multiwavelength analytical ultracentrifugation, opening the door for analysis of many important samples with spectral properties in this range, including rich classes of metal and semiconductor nanoparticles. Graphical abstract Image 1 Highlights • NIR spectral analysis now possible with analytical ultracentrifugation. • Pulsed LEDs provide NIR illumination for multiwavelength AUC. • Gold nanoparticle distributions and spectral properties may be recovered. • Method applicable to a broad range of plasmonic and semi-conductor nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: Molar mass distributions are of high interest in macromolecular chemistry because they directly determine the physical and chemical properties of polymers. A principal approach to obtain and control the shape of broad molar mass distributions is adjusting the initiator concentration in free radical polymerizations. A controlled gradient of the initiator concentration should potentially lead to tailored molar mass distributions. Here we use analytical ultracentrifugation (AUC) to adjust and measure a macroinitiator's concentration gradient. Subsequent photopolymerization of a uniformly distributed monomer leads to desired chain length distributions. Resulting distributions are described and calculated by a Schulz–Flory approach. The desired concentration profiles are simulated in advance and can be detected anytime by the optical systems in the centrifuge. Therefore, tailored broad molar mass distributions can now be produced using predictions from simulations using the established theory of AUC. [ABSTRACT FROM AUTHOR]

Controlled Suzuki-Miyaura coupling polymerization of 7′-bromo-9′,9′-dioctyl-fluoren-2′-yl-4,4,5,5-tetramethyl-[1,3,2]dioxaborolane initiated by bromo(4- tert-butoxycarbonylamino-phenyl)(tri- tert-butylphosphine)palladium ( 1) or bromo(4-diethoxyphosphoryl-phenyl)(tri- tert-butylphosphine)palladium ( 2) yields functionalized polyfluorenes (Mn = 4 × 103 g mol−1, Mw/Mn < 1.2) with a single amine or phosphonic acid, respectively, end-group. High temperature synthesis of cadmium selenide quantum dots with these functionalized polyfluorenes as stabilizing ligands yields hybrid particles consisting of good quality (e.g. emission full width at half maximum of 30 nm; size distribution σ < 10%) inorganic nanocrystals with polyfluorene attached to the surface, as corroborated by transmission electron microscopy analysis and analytical ultracentrifugation. Sedimentation studies on particle dispersions show that a substantial portion (ca. half) of the phosphonic acid terminated polyfluorene ligands is bound to the inorganic nanocrystals, versus ca. 5% for the amino-functionalized polyfluorene ligands. Single particle micro-photoluminescence spectroscopy shows an efficient and complete energy transfer from the polyfluorene layer to the inorganic quantum dot. [ABSTRACT FROM AUTHOR]

Analytical ultracentrifugation (AUC) is a classical absolute technique for polymer analysis. However, it is also a very powerful technique for the characterization of nanoparticles as already established almost 80 years ago by the pioneering work of Svedberg and coworkers. AUC allows for sample fractionation either due to size (sedimentation velocity/sedimentation equil ibrium) or due to the chemical structure expressed as particle density (density gradient). Thus, the direct measurement of particle size resp. particle density distributions is possible with high statistical accuracy and a very high resolution even in complicated mixtures. Beside an introduction to AUC, this article will outline these possibilities for nanoparticles with sizes ranging over the entire colloidal range and also for organic-inorganic hybrid particles, showing the versatility of AUC. Also, a guide to AUC textbooks, internet discussion platforms, and modern free evaluation software is provided. The combination with other techniques such as light scattering or field-flow-fractionation can gain a deep insight into complex hybrid particle mixtures. This points toward future global analysis possibilities for the simultaneous determination of distributions of several particle characteristics such as size and density. [ABSTRACT FROM AUTHOR]

Analytical ultracentrifugation (AUC) is a powerful technique to observe colloidal nanocrystals (NCs) directly in solution and obtain critical information about their physical-chemical properties. Nevertheless, a more comprehensive implementation of AUC for the characterisation of such a class of crystalline colloids has been traditionally impaired by the requirement of having a priori knowledge of the complex, multilayered structure formed by NC in solution. This includes the nature (density and mass) of the surface ligands (SLs) that provide NC colloidal stability and the shell of solvent molecules formed on it. Herein, we propose a methodology to determine the NCs size by using SLs with a density equal to that of the solvent. Thereby, the buoyancy force of the SL shell is neutral, and the density of the NCs is sufficient a priori knowledge to calculate their related mass and size distributions. The simplicity and reliability of the method are evaluated with cetyltrimethylammonium bromide (CTAB) stabilized spherical gold NCs (AuNCs) of dimensions ranging from 1 to 17 nm. The proposed method has great potential to be transferred to any non-crystalline and crystalline colloids of different nature and composition, which have a density that is equal to the bulk and can be stabilized by SLs having a density that matches that of the solvent. [ABSTRACT FROM AUTHOR]

Gold nanoclusters consisting of a specific atom number have gained popularity in research in recent years due to their outstanding properties. Due to their molecule-like behavior, their properties depend strongly on their size. Although they represent the link species between atoms and nanoparticles and are the subject of current research, a high-resolution characterization is still missing. Here, we used the band forming experiment in analytical ultracentrifugation (AUC) to characterize the gold nanoclusters in the moment of their generation using thioglycerol as a stabilizer. The concentration variation of the gold precursor, reducing agent, and stabilizer was investigated. The formation of different cluster species from the smallest Au4 up to Au911 could be observed. Very stable clusters of Au55 appear in every experiment and other cluster sizes more rarely. The extracted UV/Vis spectra could additionally be correlated to every cluster. The variation in the concentration of sodium borohydride and the stabilizer did not lead to a clear trend, but the gold ion concentration directed the size of the formed clusters. A decrease seemed to promote the generation of a higher abundance of smaller clusters accompanied by less big clusters, and vice versa. These results present the characterization of the different nanocluster generations directly in the formation process of nanoparticles and therefore are a contribution to the understanding of their formation. [ABSTRACT FROM AUTHOR]

Abstract: Osmotic pressure is a key parameter to understand the thermodynamics and the interactions in colloidal systems. We present here four examples to demonstrate the variety of information that can be extracted from it. The equation of state, i.e. the osmotic pressure versus concentration curve, could be established using analytical ultracentrifugation in binary clay–water mixtures. This method allows a quick and efficient determination of the phase boundaries, and the equation of state shows a good agreement with a Poisson–Boltzmann model. In ternary mixtures of water–anionic surfactant–cationic surfactant, phase separation with a different partitioning of the surfactant in both phases could be evidenced. In the monophasic domains, the surface charge density of the objects could be estimated from the equation of state. In mixtures of polyelectrolytes, different behaviours of the osmotic pressure with respect to the composition could be interpreted in terms of microphase separation, or homogeneous complexation, depending on the composition in polyelectrolyte. Finally, in a colloidal dispersion of spheres coated with polyelectrolytes, three different colloid–colloid interaction regimes could be identified, depending if the polyelectrolyte shells are collapsed onto the colloid, swollen, or non-overlapping. These examples illustrate the variety of information that osmotic pressure can give in a large variety of situations, making this technique an indispensable tool for the physico-chemist. [Copyright &y& Elsevier]