37
increasing force between polymer chains and longer polymer chains, as well as the
following factors: crystallinity, degree of crosslinking, Mw, polar chains, side
groups, among others.
Other parameters influencing creep are fillers, stress and temperature. High temperatures and pressures can, for example, accelerate creep, and this is a negative
point for SMPs. In contrast, fillers can have a positive effect on SMPs, as they
restrict the movement of polymer chains, thus inhibiting creep of polymer materials.
3.4 Types and Applications of SMPs
3.4.1 Shape Memory Gels (SMGs)
In the 1950s, researchers began to explore the sensitivity of gels. Flory (1953) was
the first to study the swelling sensitivity of gels, while Scarpa et al. (1967) were the
first to report thermo-sensitive hydrogels based on poly(N-isopropyl acrylamide)
(PNIPAAm). Dušek and Patterson (1968) also predicted the volume change of the
gels, and ten years later, Tanaka (1978, 1981) and Tanaka et al. (1982) reported pHsensitive hydrogels made from poly(acrylamide) (PAAm). Thereafter, research on
the volume phase transition of gels and the critical phenomena associated with them
have been actively studied. Since then, a new field of research has been explored,
such as hydrogels sensitive to different environmental conditions (also called stimulating sensitive hydrogel).
SMGs are a novel type of smart polymeric materials, whose network is made up
of polymeric chains and solvent. As smart materials, SMGs could perceive small
changes from the external environment, such as electric field, light intensity, pH,
temperature, etc (Zarrintaj et al. 2019). After the change of shape, the physicochemical properties of these materials are altered, mainly volume phase transition
(VPT). SMGs could return to their original shape after the stimulus is gone. SMGs
can also have the ability to exchange energy and information, as a result, they can
be used as controlled drug release devices, material separation, sensors, among others.
3.4.1.1 Thermo-Responsive SMGs
The themo-sensitive SMGs have been studied since 1956. In this sense, Scarpa et al.
(1967) found that NIPAAm-based hydrogels have a phase transition between 30 and
40 ° C, thus indicating a lower critical solution temperature (LCST). Tanaka et al.
(1978) also prepared PNIPAAm gels and found their sensitivity to temperature and
concentration of solvents. Since then, themo-sensitive SMGs have been an intensively studied research field.
Hirai et al. (1992) reported a thermo-sensitive poly(vinyl alcohol) (PVA) hydrogel system obtained chemically via crosslinking, resulting in an elastic material in
3 Smart and Shape Memory Polymers
increasing force between polymer chains and longer polymer chains, as well as the
following factors: crystallinity, degree of crosslinking, Mw, polar chains, side
groups, among others.
Other parameters influencing creep are fillers, stress and temperature. High temperatures and pressures can, for example, accelerate creep, and this is a negative
point for SMPs. In contrast, fillers can have a positive effect on SMPs, as they
restrict the movement of polymer chains, thus inhibiting creep of polymer materials.
3.4 Types and Applications of SMPs
3.4.1 Shape Memory Gels (SMGs)
In the 1950s, researchers began to explore the sensitivity of gels. Flory (1953) was
the first to study the swelling sensitivity of gels, while Scarpa et al. (1967) were the
first to report thermo-sensitive hydrogels based on poly(N-isopropyl acrylamide)
(PNIPAAm). Dušek and Patterson (1968) also predicted the volume change of the
gels, and ten years later, Tanaka (1978, 1981) and Tanaka et al. (1982) reported pHsensitive hydrogels made from poly(acrylamide) (PAAm). Thereafter, research on
the volume phase transition of gels and the critical phenomena associated with them
have been actively studied. Since then, a new field of research has been explored,
such as hydrogels sensitive to different environmental conditions (also called stimulating sensitive hydrogel).
SMGs are a novel type of smart polymeric materials, whose network is made up
of polymeric chains and solvent. As smart materials, SMGs could perceive small
changes from the external environment, such as electric field, light intensity, pH,
temperature, etc (Zarrintaj et al. 2019). After the change of shape, the physicochemical properties of these materials are altered, mainly volume phase transition
(VPT). SMGs could return to their original shape after the stimulus is gone. SMGs
can also have the ability to exchange energy and information, as a result, they can
be used as controlled drug release devices, material separation, sensors, among others.
3.4.1.1 Thermo-Responsive SMGs
The themo-sensitive SMGs have been studied since 1956. In this sense, Scarpa et al.
(1967) found that NIPAAm-based hydrogels have a phase transition between 30 and
40 ° C, thus indicating a lower critical solution temperature (LCST). Tanaka et al.
(1978) also prepared PNIPAAm gels and found their sensitivity to temperature and
concentration of solvents. Since then, themo-sensitive SMGs have been an intensively studied research field.
Hirai et al. (1992) reported a thermo-sensitive poly(vinyl alcohol) (PVA) hydrogel system obtained chemically via crosslinking, resulting in an elastic material in
3 Smart and Shape Memory Polymers