ABSTRACT
I. Introduction ................................................................. 280 II. Basic Aspects of Micro-Indentation: Contact
Geometry...................................................................... 282 III. Structure Development in Polymer Glasses:
Influence of Temperature and Time of Crystallization ............................................................. 284
IV. Dependence of Microhardness on Nanostructure of Semicrystalline Polymers: Mechanisms of Deformation ................................................................. 289
V. Study of Polymorphism in Polymers by Microhardness ............................................................. 295
VI. Application to Polymer Composites ........................... 296 VII. Structural Features of Block Copolymers:
Influence of Composition, Structure and Physical Aging ............................................................................ 298
VIII. Microhardness: Morphology Correlations in Blends of Glassy Polymers ...................................................... 300
IX. Outlook......................................................................... 304 Acknowledgements............................................................... 306 References............................................................................. 306
I. INTRODUCTION
Indentation hardness offers a convenient way to probe the mechanical properties of a polymer surface [1]. The method is based on the local deformation produced on a material surface by a sharp indenter upon application of a given load. Some of the advantages of indentation testing, in relation to other procedures for mechanical characterization, are the possibility of testing the mechanical properties of a device in its original assembly, and the ability to spatially map the surface mechanical properties in the micron or sub-micron range. The latter is of fundamental importance for inhomogeneous polymer systems. Additionally, it has been shown that hardness,
H
, of homogeneous polymer materials is related to other macroscopic mechanical properties such as the yield stress,
σ
, and the elastic modulus,
E
[2,3]. The compressive yield stress is shown to correlate with hardness, following the mechanical models of elastoplastic indentation, i.e, tending towards
H
≈
σ
(Tabor’s relation for a fully plastic deformation) with decreasing elastic strain (higher
E
/
σ
ratio). The method most widely used in determining the hard-
ness of polymers is based on the direct imaging of the residual indentation [1]. Figure 1 shows the impressions left behind by a Vickers indenter on the surface of glassy poly(ethylene terephthalate) (PET). A convenient measure of hardness,
H
, can be obtained by dividing the peak contact load,
P
, by the
projected area of indentation,
A
(
H
=
P
/
A
). This optical procedure is rather simple and allows for a rapid evaluation of the surface mechanical properties of a polymer material. Applied loads in the interval 0.049 – 1.96 N yield indentation depths in the micron range, which characterizes microhardness.
