Interactions of Core−Shell Silica Nanoparticles in Liquid Carbon Dioxide Measured by Dynamic Light Scattering

• Published in: Industrial & engineering chemistry research 2006-08, Vol.45 (16), p.5603-5613
• Main Authors: Dickson, Jasper L, Adkins, Stephanie S, Cao, Ti, Webber, Stephen E, Johnston, Keith P
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie051372p

The effects of solvent density on interparticle interactions between dispersed core−shell silica nanoparticles in liquid CO2 were investigated in terms of diffusional second virial coefficients measured by dynamic light scattering. A porous cross-linked polymeric shell was formed about a hydrophilic silica core with a trifunctional silylating agent, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxy silane. The addition of the porous polymeric shell weakened the Hamaker interactions between particles enabling dispersibility at low CO2 pressures, even as low as the vapor pressure, with only a stir bar. With dynamic light scattering, the particle size and degree of aggregation were measured in ethanol, the solvent used for synthesis of the shells, and in CO2 as a function of both the silane:silica (wt:wt) ratio and the silane addition rate. Particles in ethanol with thick shells could be dried and redispersed in CO2, whereas particles with thin shells were dispersible in CO2 only when added to CO2 while still dispersed in ethanol. At the highest pressures, the diffusional second virial coefficients were only slightly negative in CO2, indicating weak attractive interactions. The coefficients became more negative as the CO2 density was lowered. Inorganic colloidal particles, with diameters on the order of a few hundred nanometers, may be dispersed in CO2 at the vapor pressure for tens of minutes with porous cross-linked polymeric shells, whereas such stabilization has not been achievable with either non-cross-linked polymeric or low molecular weight stabilizers.