Interfaces in Composite Materials - Biointerfaces: Where Material Meets Biology - page 157

high surface area/volume ratio contributes to much greater effects of the
interface on the composite properties. The structure of this interface is in-
fluenced by the number of anchoring points the polymer matrix chains
make with the filler 51 (Figure 7.1, panel I). An effective adsorption of the
polymer chains onto the surface of the filler particles produces a compact
interface. A diffuse interface with long polymer loops and tails, however,
would result from poor adsorption of the polymer chains on the surface of
filler particles. 62 The strength of interaction of polymer chains with the filler
particles controls both the conformations of the polymer chains at the
interface and the entanglement distribution in a larger region surrounding
the filler particles. 51 This will then be reflected on the overall elastic moduli
and behavior

d n 3 r 4 n g | 1

(e.g., necking and drawing after yielding) of nano-

composites. 50

7.2.1.1 Methodology of Examination
The filler-matrix interface has been investigated using many different
techniques. The structure and density of the interface, for example, has been
examined using thermal gravimetric analysis (TGA), transmission electron
microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) 51 and
molecular dynamic simulation (MDS). 50 Analysis of surface chemistry by
X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES)
and time of flight secondary ion mass spectrometry (ToF-SIMS) has also
been attempted. Thermodynamics of the interface has been investigated
using dynamic contact angle analysis (DCAA) and inverse gas chroma-
tography (IGC). 41 The gap between the filler and matrix has been monitored
using optical microscopy, light attenuation and scanning electron micro-
scopy. 63 Dispersion and spatial distribution of the filler within the matrix
has been quantified using coarse-grained molecular dynamics simulation 43
and scanning electron microscopy. 64 The reinforcing effect of the filler has
been assessed through mechanical testing 64 and stress-transfer between
phases by X-ray diffraction. 61 Information on the interaction of the coupling
agent with the filler and matrix has also been gained using thermogravi-
metric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). 55

.

7.2.2 Composite-surrounding Environment
The traditional concept of biocompatibility relied on the use of inert ma-
terials that do not instigate toxic effects. More recently, this concept has
shifted to the use of reactive, stimuli responsive materials that interact with
the local environment for full tissue integration. Studying the interface be-
tween a biomaterial and surrounding environment provides new insights on
biophysical phenomena and molecular mechanisms underlying complex
biological processes. At this interface, the circulating cells can attach,
spread, proliferate and differentiate or die. The circulating biomolecules can
also be adsorbed, bound to - and/or released from - a biomaterial surface.