The analysis of a dendrimer of fifth generation by small-angle neutron scattering (SANS) in solution is presented. The contrast of the solute toward the solvent dimethylacetamide (DMA) is changed systematically by measurements of the dendrimer in mixtures of deuterated with protonated DMA. Additional SANS measurements at highest contrast and varying dendrimer concentrations allowed to determine the structure factor of the dendrimers in solution. SANS intensities measured at different contrast are shown to yield the contrast F j -F m where F j is the average scattering length density of the dissolved dendrimer and Fm is the scattering length density of the solvent. This allows to determine the molecular weight of the dendrimer in an unambiguous fashion. The comparison of the measured and the calculated molecular weight demonstrates that the dendritic structure under consideration here is not fully perfect. The analysis of the radial structure of the dendrimer rests on the decomposition of the measured intensities into terms depending on powers of the contrast F j -F m. The leading term which scales with the square of the contrast leads to the determination of the scattering intensity referring to infinite contrast. This allows to elucidate the radial scattering length density in an unambiguous manner. The analysis demonstrates that the present dendrimer, composed of flexible units, has a compact structure where the density has its maximum at the center of the molecule. This is in accord with recent theoretical deductions.

Using small-angle neutron scattering and liquid integral equation theory, we relate the structure factor of flexible dendrimers of fourth generation to their average shape. The shape is measured as a radial density profile of monomers belonging to a single dendrimer. From that, we derive an effective interaction of Gaussian form between pairs of dendrimers and compute the structure factor using the hypernetted chain approximation. Excellent agreement with the corresponding experimental results is obtained, without the use of adjustable parameters. The present analysis thus strongly supports the previous finding that flexible dendrimers of low generation present fluctuating structures akin to star polymers.

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The analysis of the equilibrium structure of a dendrimer of fourth generation by small‐angle neutron scattering (SANS) is described. The analysis presented here is based on measurements of the SANS intensities at different contrasts ρ–ρm with ρ being the average scattering length density of the dissolved dendrimer and ρm the scattering length density of the solvent dimethylacetamide (DMA). In this study ρm was changed by using mixtures of protonated and deuterated DMA. On varying the contrasts of solute towards solvent, the average scattering length density of the dissolved dendrimer ρ can be obtained unambiguously. Contrast variation leads to determination of the molecular weight of the dendrimer which is shown to be in excellent agreement with the calculated value. The measured scattering intensity I (q) (q = (4π/λ) sin (θ/2); λ: wavelength of radiation; θ: scattering angle) can be decomposed into terms depending on the contrast ρ–ρm and a term independent of it. Contribution of the latter is mainly given by incoherent scattering of the numerous protons present in the structure of the dendrimer. Experimental data presented here demonstrate that this contribution must be removed in order to obtain meaningful structural information. The term scaling linearly with ρ–ρm is negligible within given margins of error. The structural information is embodied in the contribution which scales with contrast ρ–ρm in the square and may be regarded as scattering intensity extrapolated to infinite contrast. Fourier‐inversion of this term leads to a radial segment density distribution which has its maximum at the center of the molecule. This is in agreement with recent theoretical predictions and shows that the dendrimer of fourth generation studied here is a strongly fluctuating structure akin to branched or star polymers.

Small-angle X-ray scattering (SAXS) is a tool which allows the study of the structure and the interaction of polymer latexes with great accuracy. The low electron density of the polymers used for the synthesis of latex particles as e.g. polystyrene allows the matching of the contrast by adding sucrose to the serum. Thus, scattering intensities measured at different contrast, i.e., at different excess electron densities can be evaluated (contrast variation). This yields precise information on the radial electron density of the particles. In this article recent SAXS-investigations on latex particles are reviewed. It is demonstrated that core-shell latexes can be analyzed precisely by contrast variation. The same method can be applied to swollen latex particles to examine the polymer concentration near the boundary to the water phase. Here it is shown that the depletion of the polymer molecules near this boundary is very small which points to a minute wall-repulsion effect. Since the excess electron density of polystyrene latex particles in water is very small, the scattering from adsorbed layers of surfactants dominates the measured intensity in this particular system. Therefore the adsorption equilibrium of a given surfactant as well as the competitive adsorption of two different surfactants on a polystyrene latex can be assessed by SAXS.