Biomedical Engineering Reference
In-Depth Information
1
Introduction
A number of high polymer systems can assemble to form networks and gels and this
assembly can occur by a variety of mechanisms. Some of these involve chemical treat-
ments and processes, others are largely physical in nature
it is on the latter that this
volume is focused. In this introductory chapter we consider the nature of polymer gels
and networks, the processes of assembly, their characterization by physical methods and
the coverage of succeeding chapters.
-
1.1
Gels from colloidal and polymer networks: a brief survey
Traditional colloidal gels were
first investigated by Thomas Graham in the Philosophical
Transactions of the Royal Society (Graham,
1861
). Graham proposed a de
nition of
substances according to their diffusive power. Colloidal substances (from the Greek
κολλα
,
'
glue
'
) are slowly diffusing substances, held together in solution by what he
termed
cation of these substances Graham included
hydrated silicic acid, hydrated alumina, starch, gelatin, albumen and gum.
Graham continued his discourse, saying
'
feeble forces
'
. In the classi
opposed to the colloidal, is the crystalline
condition, the distinction is no doubt of one of intimate molecular constitution
'
, although
the means of characterizing the latter were not available at that time. This very profound
introduction to the colloidal state also includes this following intuitive statement:
'
'
another eminently characteristic quality of colloids is their mutability
'
, that is to say
their ability to change. He writes:
, i.e. again
capable of change, which immediately points towards the current fully accepted diffi-
'
Their existence is a continued metastasis
'
-
culties in characterizing this particular state of the matter. He was also the
rst to
recognize the speci
city of the colloidal state and even went as far as suggesting that
'
revealing the mystery of life!
Efforts to analyse the colloidal state appear again in 1899, in a paper by W. B. Hardy
with the subtitle
it is the source of vitality
'
'
The Structure of Colloidal Matter and the Mechanism of Setting and of
'
Coagulation
. He addressed in particular the question of the effect of the
fixing reagents
used in cell observation:
I would start the discussion with no statement as to the nature of cell-protoplasm other than that it is,
as Dujardin described it,
'
glutinous
'
. Now this glutinous character is a special characteristic of that
state of matter to which Graham applied the word
'
colloidal
'
. This statement holds without
modification whether the initial stage, that is the soluble colloid, be entirely fluid (colloidal
