Tunable Order in Alginate/Graphene Biopolymer Nanocomposites
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Abstract
We
report on highly aligned graphene oxide or graphene sheets inside
an alginate matrix and their structure obtained for various compositions.
The order of the platelet particles with respect to one another has
been verified by environmental scanning electron microscopy (ESEM)
and 2-dimensional X-ray diffraction (2D XRD). The microscopic order
within the platelet particles has been analyzed by X-ray diffraction
(XRD) measurements in the Bragg–Brentano reflection configuration
as well as in Debye–Scherrer diffraction mode. The azimuthal
angle intensity profiles obtained from 2D XRD analysis have been fit
to Maier–Saupe and affine deformation model predictions, and
the affine deformation model proved to be the most reliable to quantify
the order parameter ⟨<i>P</i><sub>2</sub>⟩
values of graphene oxide/sodium alginate and graphene/calcium alginate
composites with different weight fractions of the filler. The ⟨<i>P</i><sub>2</sub>⟩ values for graphene oxide/sodium alginate
composites were found to show little dependence on the concentration
of graphene sheets above ∼10 wt %, with a maximum ⟨<i>P</i><sub>2</sub>⟩ value of 0.8 at 25 wt % graphene oxide
inside the sodium alginate matrix. The alignment of graphene sheets
inside the calcium alginate matrix has been observed to be lower,
with an average ⟨<i>P</i><sub>2</sub>⟩ value
of 0.7. We have not observed preferred orientation of graphene sheets
inside the barium alginate matrix. The formation of a highly aligned
graphene oxide/sodium alginate composite structure has been explained
by the affine deformation model, whereupon drying the developed yield
stress causes sheets to align in-plane with the polymer matrix. The
impaired orientation of graphene sheets inside the calcium alginate
matrix and absence of orientation in the barium alginate matrix have
been explained by the structure development in the polymer matrix
itself due to metal-ion-induced cross-linking