The volume transition in thermosensitive colloidal core–shell particles is investigated by small-angle x-ray scattering (SAXS), small-angle Neutron scattering (SANS), and dynamic light scattering (DLS). The latex particles are dispersed in water and consist of a solid poly(styrene) core with a diameter of 100 nm. The thermosensitive shell is made up of poly(N-isopropylacrylamide) (PNIPA) chains crosslinked by 2.5 mol % N,N’-methylenbisacrylamide (BIS). Water is a good solvent for PNIPA at room temperature but becomes a poor solvent above 32 °C. The PNIPA network of the shell undergoes a volume transition at this temperature. As a result the diameter of the particle shrinks. The scattering intensities of the particles measured by SAXS and SANS as a function of temperature may be decomposed into a part deriving from the overall structure and a part originating from the fluctuations within the network. The analysis of the overall structure leads to the volume fraction of the swollen network at different temperatures. SANS in conjunction with contrast variation demonstrates that the network is confined in a well-defined shell. SAXS and SANS data therefore allow the phase diagram of the network in the shell of the particles to be derived, i.e., the average volume fraction of the network in the shell can be determined as a function of temperature. DLS corroborates this result but demonstrates that there is a small fraction of chains exceeding the outer radius derived from SAXS and SANS. The static intensity caused by the fluctuations of the network becomes the leading contribution at high scattering angles. SAXS data show that this part can be described by a Lorentzian both below and above the volume transition. The analysis demonstrates that critical fluctuations of the network around the transition temperature are fully suppressed. This finding is explained by the strong steric constraint of the network by its confinement within a shell of colloidal dimension. The swelling and shrinking can only take place along the radial direction and the chains are bound to the solid surface of the cores which remains constant during the transition.

We present an investigation of thermosensitive coreÈshell particles by small-angle neutron scattering (SANS). The particles consist of a solid poly(styrene) core and a shell of crosslinked poly(N-isopropylacrylamide) (PNIPA) chains. These latex particles are dispersed in water and have a diameter of ca. 150 nm. At ambient temperature the PNIPA-network in the shell is swollen but at higher temperature water is expelled and the shell undergoes a continuous volume transition. The radial extension of the shell is investigated as a function of temperature by use of SANS. The analysis by SANS is performed at di †erent contrasts using appropriate mixtures of and It demonstrates that the shell has a well-deÐned compact structure above theO. volume transition. The swelling of the shell upon cooling can be described in terms of an affine expansion of the network. This is followed by a slight decrease of the volume fraction with increasing distance to the surface of the cores. The analysis by SANS demonstrates that the phase behavior of the network in the shell may be undertaken in terms of average volume fractions. It thus supplements the previous analysis by SAXS in a decisive manner.

We discuss the analysis of the volume transition in thermosensitive colloidal core‐shell particles by synchrotron small‐angle X‐ray scattering. The latex‐particles are dispersed in water and consist of a solid poly(styrene) core (diameter: 107 nm) and a shell of a thermosensitive crosslinked polymer chains. The thermosensitive shell is built up from poly(N‐isopropylacrylamide) chains (PNIPA) crosslinked by N,N'‐methylenbisacrylamide (BIS). The scattering intensities measured as function of temperature may be decomposed into a part deriving from the overall structure and a part originating from the fluctuations within the network. The analysis of the overall structure leads to the volume fraction of the swollen network at different temperatures. The intensity caused by the fluctuations of the network becomes the leading contribution at high scattering angles. It may be described by a Lorentzian below and above the volume transition. The analysis demonstrates that critical fluctuations of the network around the transition temperature are fully suppressed. This finding is explained by the strong steric constraint of the network by its confinement within a shell of colloidal dimensions: i) The swelling and shrinking can only take place along the radial direction, and ii) the chains are bound to the solid surface of the cores which remains constant during the transition.

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We present the study of the adsorption of a non-ionic surfactant onto latex particles by small-angle X-ray scattering (SAXS). The analysis of the process of adsorption by SAXS is discussed in detail. It is demonstrated that SAXS allows to monitor the gradual built-up of the surface layer with increasing amount of added surfactant. SAXS also allows to obtain the radial volume fraction of the hydrophilic tails of the surfactant. Possible limitations of this analysis are discussed.