Analysis of thermosensitive core–shell colloids by small-angle neutron scattering including contrast variation

Abstract

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.

Thermosensitive core-shell particles as model systems for studying the flow behavior of concentrated colloidal dispersions

“…18 A comprehensive characterization of these particles has been done recently by a combination of small-angle x-ray scattering ͑SAXS͒ and small-angle neutron scattering ͑SANS͒. 45,46 The main result of this work was to show that the shell of these core-shell particles is rather compact. This can be traced back to the method of polymerization.…”

Flow curves of dense colloidal dispersions: Schematic model analysis of the shear-dependent viscosity near the colloidal glass transition

“…Moreover, an analysis of these particles by a combination of small-angle neutron and X-ray scattering revealed that the shell is well-defined and the particles exhibit a narrow size distribution 32,33 . Their interaction in water is purely repulsive 31 if the temperature is not raised over 30 0 C.…”

Small-Angle Neutron Scattering on a Core−Shell Colloidal System: A Contrast-Variation Study

“…In particular, they can be studied in great detail using contrast-variation methods, 24 achieved most readily in the context of small-angle neutron scattering (SANS), although several studies make use of light [25][26][27] or X-ray [28][29][30] http://doc.rero.ch Through contrast variation, via the variation of scattering contrast by selective isotopic substitution of protons for deuterium in SANS, small-scale structures can be discriminated. This has been amply demonstrated in the past for, e.g., polymer-coated particles, [31][32][33] self-assembled surfactant [34][35][36][37] and block copolymer [38][39][40][41] systems. In addition, the quantitative modeling of SANS data for the same system under variable contrast is a far more stringent test of the models used and can therefore deliver more reliable values for structural parameters.…”