W0383
Evaluating Organoclays for Nanocomposites by Small Angle
Scattering. Derek L. Ho1, 2 and Charles J. Glinka1,
1Center for Neutron Research, National Institute of Standards and
Technology, Gaithersburg, MD 20899, 2Dept. of Materials and Nuclear
Engineering, Univ. of Maryland, College Park, MD 20742.
Understanding the interaction between organically modified
clay (organoclay) platelets and organic solvent molecules as well as the
corresponding structure of organoclays in a suspension is a critical step toward
tailoring and characterizing nanocomposites formed by organoclays in a polymer
matrix. Recently, nanocomposites composed of clays and polymers have been found
to have improved mechanical properties as well as enhanced thermal stability.
The improved properties are related to the degree of dispersal and exfoliation
of the clay platelets in the polymer matrix. In order to understand and optimize
potential processing conditions, organoclays were dispersed in a number of
organic solvents covering a range of solubility parameters and characterized
using small-angle neutron scattering and wide-angle x-ray scattering techniques.
With Hansen's solubility parameters, δo2 =
δd2 + δp2 +
δh2, the correlation between the degree of
exfoliation of organoclays and the solvent in which the clay platelets are
dispersed/mixed has been analyzed. It has been found that the dispersion force
of the solvent, reflected by δd, is the principal factor
determining whether the clay platelets remain suspended in the solvent while the
polar (δp) and hydrogen-bonding (δh) forces
affect primarily the tactoid formation/structure of the suspended platelets. The
organically modified clays studied in this work precipitated in any solvent with
molecules with moderately strong hydrogen-bonding groups. The correlation found
has been used to correctly identify a solvent, trichloroethylene, which
completely exfoliates the organoclays studied in this work.