Ebook: Characterisation of Interfaces in Micro- and Nano-composites

Abstract
There is a current industrial requirement for the development of suitable test-
methodology that is capable of in-situ mechanical and physical characterisation of
the interface and interfacial region in composite materials. The most promising tool
for micro- and nano-scale measurements is the atomic force microscope (AFM)
although, for suitable test-methodology to be realised, further development is
required. The work contained within this thesis documents the development of AFM
procedures for the measurement of elastic moduli variation across the interface and
considers the physical size of the interfacial region.
The first AFM procedure is for the analysis of multiple (AFM) indentations and the
quantification of each indentation (in terms of reduced elastic moduli). Results of
interfacial testing using this procedure highlighted short transition regions of
apparently increased elastic moduli between the glass reinforcement and the
polymeric matrix. It was not possible to identify whether the increase in elastic
moduli was representative of an interphase due to the possibility that the
indentations in this region were restricted by the presence of the glass fibre-
reinforcement. A second, novel procedure was then developed to independently
verify whether or not any indentations were restricted, and identify whether a
measured transition is representative of an interphase. This procedure was based
on the principle that the any indentation performed in close proximity to the glass
fibre-reinforcement would have an uneven distribution of loading between the
surface and the indenter tip. The uneven distribution of loading resulted in torsion of
the indenter tip, which was measured during multiple indentations across the
interface of a glass fibre-reinforced phenolic composite. It was found that the
apparent increase in elastic moduli measured across the interface was directly
related to restriction due to, and contact with, the proximity of the glass fibre-
reinforcement.
Finally, the latest AFM technique with the potential for quantitative measurement, is
reviewed. The work has shown that AFM nanomechanical mapping has the potential
to be a useful supplement to liT for measuring the small-scale elastic modulus of a
polymer surface.
It was found that the technique can provide repeatable
measurements of polymer moduli for a number of different probes provided that
careful calibration procedures are used.