Chapter 7
A Primer on Gels (with an Emphasis
on Molecular Gels)
Richard G. Weiss
Abstract This chapter describes structural, kinetic, thermodynamic and viscoelastic
aspects of how dispersions of small molecules (essentially 0-dimensional objects)
aggregate into thermally reversible or thixotropic networks that immobilize large
volumes of a liquid. When possible, the different properties of these molecular gels
are correlated. The data are considered at different time and distance scales during
the lives of the gels. A short history of molecular gels and challenges to advancing the
field are also presented. The properties of some molecular gels with simple gelator
structures, including long n-alkanes and derivatives of them, are described as well.
Keywords Hansen parameters · Schröder-van Laar equation · Ostwald ripening ·
Storage and loss modulus · Viscoelasticity · Critical gelator concentration ·
Avrami equation
7.1 Introduction: General Classifications
Gels are a part of almost all aspects of our materials world [1]. The processes by
which gels form from particle structures are only one type of self-assembly. Others
lead to a myriad of different phases which will not be discussed here, although
each type depends on the relative magnitudes of enthalpic and entropic factors that
are time-dependent [2]. Examples of hydrogels (i.e., gels based on aqueous liquid
components) include aggregates of collagen (the most abundant protein in our bodies;
when denatured, it can take the form of aspic or, as sold commercially with different
additives in the US and elsewhere, Jell-O ©), amyloids (that have been linked to
Alzheimer’s disease), and other protein-based gels with actin, clathrin, and tubulin
as the non-aqueous component. Other common hydrogels are in human and other
mammalian bodies and jelly fish, and in jellied sand worms. Many types of toothpaste,
deodorants, cosmetics, soaps, pharmaceutical delivery agents, and foods [3] are gels,
as are many non-edible materials such as silly-putty, paints, inks, dental materials
R. G. Weiss (B)
240 Reiss Science Building, Georgetown University, Washington, DC 20057-1227, USA
e-mail: weissr@georgetown.edu
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
X.-Y. Liu (ed.), Frontiers and Progress of Current Soft Matter Research,
Soft and Biological Matter, https://doi.org/10.1007/978-981-15-9297-3_7
299
A Primer on Gels (with an Emphasis
on Molecular Gels)
Richard G. Weiss
Abstract This chapter describes structural, kinetic, thermodynamic and viscoelastic
aspects of how dispersions of small molecules (essentially 0-dimensional objects)
aggregate into thermally reversible or thixotropic networks that immobilize large
volumes of a liquid. When possible, the different properties of these molecular gels
are correlated. The data are considered at different time and distance scales during
the lives of the gels. A short history of molecular gels and challenges to advancing the
field are also presented. The properties of some molecular gels with simple gelator
structures, including long n-alkanes and derivatives of them, are described as well.
Keywords Hansen parameters · Schröder-van Laar equation · Ostwald ripening ·
Storage and loss modulus · Viscoelasticity · Critical gelator concentration ·
Avrami equation
7.1 Introduction: General Classifications
Gels are a part of almost all aspects of our materials world [1]. The processes by
which gels form from particle structures are only one type of self-assembly. Others
lead to a myriad of different phases which will not be discussed here, although
each type depends on the relative magnitudes of enthalpic and entropic factors that
are time-dependent [2]. Examples of hydrogels (i.e., gels based on aqueous liquid
components) include aggregates of collagen (the most abundant protein in our bodies;
when denatured, it can take the form of aspic or, as sold commercially with different
additives in the US and elsewhere, Jell-O ©), amyloids (that have been linked to
Alzheimer’s disease), and other protein-based gels with actin, clathrin, and tubulin
as the non-aqueous component. Other common hydrogels are in human and other
mammalian bodies and jelly fish, and in jellied sand worms. Many types of toothpaste,
deodorants, cosmetics, soaps, pharmaceutical delivery agents, and foods [3] are gels,
as are many non-edible materials such as silly-putty, paints, inks, dental materials
R. G. Weiss (B)
240 Reiss Science Building, Georgetown University, Washington, DC 20057-1227, USA
e-mail: weissr@georgetown.edu
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
X.-Y. Liu (ed.), Frontiers and Progress of Current Soft Matter Research,
Soft and Biological Matter, https://doi.org/10.1007/978-981-15-9297-3_7
299