Polymeric Sensors and Actuators

Chapter 14

Switchable Polymers

Some polymeric systems are rather abruptly changing their properties due to external influences. These systems are addressed as switchable. Besides simple tasks, such systems can also perform rather complicated challenges, e.g., in molecular electronics, which is an emerging and rapidly developing field (1–4). Types of switchable devices are summarized in Table 14.1.

Table 14.1 Stimuli in switchable devices (5–7)

Energy based	Chemical based
Magnetic field (8)	pH
Electric field (9)	Ionic strength
Light (10)	Solvents
Ultrasound	Metal ions
Temperature	Chemicals and Biochemicals (11)

There are two major mechanisms for switching a device by a biomolecule (5):

1. A stimulus may act on the surface to effect a change in the interfacial properties. This in turn alters the interactions between biomolecule and interface.

2. A stimulus interacts directly with a biomolecule to change its properties subsequent to interaction with the surface (12, 13).

Many polymers exhibit an ability to transition, however, Only a few show sharp transitions at moderate temperatures. These include poly(N-isopropyl acrylamide), poly(N,N-diethyl acrylamide), and poly(N-isopropyl acrylamide-co-2-carboxyisopropyl acrylamide) (5).

Electrodes modified with different signal-responsive materials have been designed as switchable electrochemical interfaces. These respond to a variety of physical an chemical signals.

Light-switchable electrodes are based on photoisomerizable ...