thawing of the frozen sample. The nature of gel precursors, their concentration in
the initial feed, and the conditions of each of the stages affect the physicochemical
properties and porous morphology of the resulting cryogels. Certain specific effects
are inherent in the processes of cryotropic gel formation, namely, apparent decrease
in the critical concentration of gelation, acceleration of gel formation over a certain
range of negative temperatures, a bell-shaped temperature dependence of the
cryotropic gelation efficiency, and generation of the specific porosity peculiar to
cryogels. This chapter presents the basic principles of cryotropic gelation processes
and also discusses the factors influencing the properties of various types of
cryogels.
Keywords Cryotropic gelation • Unfrozen liquid microphase • Freezing • Frozen
storage • Defrosting
Abbreviations
CCG
Critical concentration of gelation
CTAB
Cetyltrimethylammonium bromide
DMSO
Dimethylsulfoxide
GuAr
Gum arabic
LCST
Lower critical solution temperature
NMR
Nuclear magnetic resonance
PVA
Poly(vinyl alcohol)
SEM
Scanning electron microscopy
UCST
Upper critical solution temperature
UFLMP Unfrozen liquid microphase
VA
Vinyl alcohol
VAc
Vinyl acetate
1 Introduction
As described in the previous chapter of this volume [1], studies on the gel formation
processes in moderately frozen solutions or colloidal dispersions containing the
necessary precursors started at the beginning of 1970s, although empirical observations of freeze–thaw-caused gelation were made long before. The experimental
data obtained during the past four decades in this field have resulted in a sum of
knowledge on the general aspects of cryotropic gelation, which is the subject of the
present chapter. Before starting the discussion, the terminology will be defined in
order to clarify what each specialized term means.
50
V.I. Lozinsky and O. Okay
the initial feed, and the conditions of each of the stages affect the physicochemical
properties and porous morphology of the resulting cryogels. Certain specific effects
are inherent in the processes of cryotropic gel formation, namely, apparent decrease
in the critical concentration of gelation, acceleration of gel formation over a certain
range of negative temperatures, a bell-shaped temperature dependence of the
cryotropic gelation efficiency, and generation of the specific porosity peculiar to
cryogels. This chapter presents the basic principles of cryotropic gelation processes
and also discusses the factors influencing the properties of various types of
cryogels.
Keywords Cryotropic gelation • Unfrozen liquid microphase • Freezing • Frozen
storage • Defrosting
Abbreviations
CCG
Critical concentration of gelation
CTAB
Cetyltrimethylammonium bromide
DMSO
Dimethylsulfoxide
GuAr
Gum arabic
LCST
Lower critical solution temperature
NMR
Nuclear magnetic resonance
PVA
Poly(vinyl alcohol)
SEM
Scanning electron microscopy
UCST
Upper critical solution temperature
UFLMP Unfrozen liquid microphase
VA
Vinyl alcohol
VAc
Vinyl acetate
1 Introduction
As described in the previous chapter of this volume [1], studies on the gel formation
processes in moderately frozen solutions or colloidal dispersions containing the
necessary precursors started at the beginning of 1970s, although empirical observations of freeze–thaw-caused gelation were made long before. The experimental
data obtained during the past four decades in this field have resulted in a sum of
knowledge on the general aspects of cryotropic gelation, which is the subject of the
present chapter. Before starting the discussion, the terminology will be defined in
order to clarify what each specialized term means.
50
V.I. Lozinsky and O. Okay