The accurate characterization of submicrometer and nanometer sized particles presents a major challenge in the diverse applications envisaged for them including cosmetics, biosensors, renewable energy, and electronics. Size is one of the principal parameters for classifying particles and understanding their behavior, with other particle characteristics usually only quantifiable when size is accounted for. We present a comparative study of emerging and established techniques to size submicrometer particles, evaluating their sizing precision and relative resolution, and demonstrating the variety of physical principles upon which they are based, with the aim of developing a framework in which they can be compared. We used in-house synthesized Stöber silica particles between 100 and 400 nm in diameter as reference materials for this study. The emerging techniques of scanning ion occlusion sensing (SIOS), differential centrifugal sedimentation (DCS), and nanoparticle tracking analysis (NTA) were compared to the established techniques of transmission electron microscopy (TEM), scanning mobility particle sizing (SMPS), and dynamic light scattering (DLS). The size distributions were described using the mode, arithmetic mean, and standard deviation. Uncertainties associated with the six techniques were evaluated, including the statistical uncertainties in the mean sizes measured by the single-particle counting techniques. Q-Q plots were used to analyze the shapes of the size distributions. Through the use of complementary techniques for particle sizing, a more complete characterization of the particles was achieved, with additional information on their density and porosity attained.

The ability to control the speed and polarisation of light pulses will allow for faster data flow in optical networks of the future. Optical delay and switching have been achieved using slow-light techniques in various media, including atomic vapour. Most of these vapour schemes utilise resonant narrowband techniques for optical switching, but suffer the drawback of having a limited frequency range or high loss. In contrast, the Faraday effect in a Doppler-broadened slow-light medium allows polarisation switching over tens of GHz with high transmission. This large frequency range opens up the possibility of switching telecommunication bandwidth pulses and probing of dynamics on a nanosecond timescale. Here we demonstrate the slow-light Faraday effect for light detuned far from resonance. We show that the polarisation dependent group index can split a linearly polarised nanosecond pulse into left and right circularly polarised components. The group index also enhances the spectral sensitivity of the polarisation rotation, and large rotations of up to 15π rad are observed for continuous-wave light. Finally, we demonstrate dynamic broadband pulse switching, by rotating a linearly polarised nanosecond pulse from vertical to horizontal with no distortion and transmission close to unity.

The attachment of proteins, and other biomolecules, to nanoparticles is of critical interest both in the development of medical products using nanoparticles and in understanding the behaviour and fate of nanoparticles in biological systems. Measuring the amount of protein attached to the particles is a fundamental step in these regards and there are a variety of methods available for this purpose. In this work, we compare the use of three methods which measure particle diameter: Dynamic Light Scattering (DLS), Nanoparticle Tracking Analysis (NTA) and Differential Centrifugal Sedimentation (DCS). The choice of gold particles also permits measurement of the amount of adsorbed protein through a shift in plasmon frequency in UV-visible spectroscopy. When the protein layer is complete, the results from all methods are consistent to within $20% scatter and suggest that IgG adsorption on these 20 nm to 80 nm nanoparticles is rather similar to adsorption on flat gold surfaces with a water content of $60% by volume. We note an excellent correlation between plasmon frequency shift and DCS sedimentation times which indicates that both DCS and analytical ultracentrifugation can provide precise measurement of the thickness of complete protein shells on dense nanoparticles, but also show that these methods will fail for particles with a density of $1.38 g cm À3 . In the low protein coverage regime, the measured amount of protein depends upon the technique: NTA and DLS provide, as expected, similar values that also correlate well with plasmon frequency shift. DCS analysis underestimates protein shell thicknesses in this regime and this may be explained through redistribution of the protein shell which reduces the frictional force during sedimentation. Crown copyright ª2013. Reproduced with the permission of the controller of HMSO.

We report phase diagrams for amphiphilic block copolymers prepared via ring-opening metathesis polymerization (ROMP). A library of 30 block copolymers with variable hydrophilic functionality, block ratios, and degrees of polymerization was prepared, and the resulting assemblies were analyzed by small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). A phase diagram of the self-assemblies was constructed for each of the various copolymer systems screened, representing the first of its kind for polynorbornene block copolymers in dilute solutions. Furthermore, we take advantage of kinetic control in the preparation of an array of particle morphologies accessed from the same polymer structure. ■ INTRODUCTIONIn the design of nanomaterials, morphology is a key consideration in determining fundamental properties. Examples relevant to soft material design include arranging DNA on micelle coronas to increase resistance to nuclease degradation, 1,2 varying circulation patterns and clearance mechanisms of different particle shapes in vivo, 3−8 and shape effects for cellular uptake of nanoparticles in vitro. 9−11 Given the strong correlation between morphology and function, much effort has been expended in the attempt to define particle structure through the design of block copolymer amphiphiles. 12−18 However, it is known that the conditions under which a given micelle is formulated will greatly influence the outcome despite best efforts to dictate results through chemical structure. 15,16,19−25 Over the past few decades, experimental and theoretical studies have explored properties that contribute to selfassembly events of block copolymers (BCPs) in solution. 16,26−30 It has been established that the nanoparticle morphology is a result of a reduction in free energy achieved via three main parameters: (i) stretching of the hydrophobic core block, (ii) interfacial tension between the core and solvent, and (iii) repulsion between corona strands. 12,15,16,20,26,30,31 Each of these components involves contributions from myriad variables in the polymer structure and environment. To complicate the matter further, a delicate balance and interplay between thermodynamically and kinetically driven solution phase particle formation processes has a large influence over the final morphology of the nanostructure. 13,16,18−20,22−25,27−35 For many kinetically trapped systems, unimer exchange may be so unfavorable that the assemblies generated are stable on a time scale of months or years without outside perturbation, and no change in morphology is observed. 36,37 In contrast to BCPs in the bulk, where the influence of kinetics on morphology is less important, constructing phase diagrams for self-assemblies in solution is particularly challenging given that it is impossible to change one component of the polymer or solution without also perturbing the kinetic landscape of assembly. For example, small changes in core block size will not only alter polymer molecular weight or the hydrophilic−hydrophobi...