Fabrications and Applications of Stimulus-Responsive Polymer Films and Patterns on Surfaces(Review)

* Author to whom correspondence should be addressed; E-Mail: changcj@.tw; Tel.: +886-4-2451-7250 (ext. 3678); Fax: +886-4-2451-0890. Received: 26 November 2013; in revised form: 10 January 2014 / Accepted: 16 January 2014 / Published: 28 January 2014
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Mother Nature shows us abundant examples of stimuli-responsive (or smart) materials. The leaves of Mimosa pudica collapse suddenly when touched, and those of the Venus flytrap snap shut on doomed insect prey; the leaflets of Codariocalyx motorius rotate, and sunflowers turn toward the sun; and chameleons change color according to their environment. At their most fundamental level, many of the most important substances in living systems are macromolecules with structures and behaviors that vary according to the conditions in the surrounding environment. Mimicking the functions of such organisms, scientists have made great efforts to synthesize stimuli-responsive polymers that have significance to science and promising applications. Incorporating multiple copies of functional groups that are readily amenable to a change in character (e.g., charge, polarity, and solvency) along a polymer backbone causes relatively minor changes in chemical structure to be synergistically amplified to bring about dramatic transformations in macroscopic material properties. Polymers such as proteins, polysaccharides, and nucleic acids are present as basic components in living organic systems. Synthetic polymers, which are designed to mimic these biopolymers, have been developed into a variety of functional forms to meet industrial and scientific applications. These synthetic polymers can be classified into different categories based on their chemical properties. Certain special types of polymers have emerged as very useful class of polymers having their own special chemical properties and applications in various areas. These “stimuli-responsive” polymers (SRPs) have been variously called stimuli-sensitive [1], intelligent [2], smart [3,4], or environmentally-sensitive polymers [5]. SRPs can rapidly change shape with respect to configuration or dimension under the influence of stimuli such as temperature [6], pH value [7,8], light [9], magnetic field [10], electricity [11], and solvent/water [12]. These polymers can also have different compositions and architecture, including not only homopolymers [13] but also statistical/block copolymers [14], graft copolymers, and molecular brushes. They can be also grafted on/from surfaces [15] or be used as chemically or physically cross-linked gels [16]. SRPs are usually capable of stimuli-induced conformational changes, reversible solubility control [17], and reversible self-assembly into polymeric micelles or vesicles. Given these unique properties, stimuli-responsive polymers are being developed for use in such fields as drug delivery, cell adhesion, sensors, actuator systems, releasing of encapsulated materials and trafficking of molecules through polymeric membranes [18–23]. The “response” of a polymer can be defined in various ways. SRPs in solution are typically classified as those that change their individual chain dimensions/size, secondary structure, solubility, or the degree of intermolecular association. In most cases, the physical or chemical event that causes these responses is limited to the formation or destruction of secondary forces (hydrogen bonding, hydrophobic effects, electrostatic interactions, etc.), simple reactions (e.g., acid-base reactions) of moieties pendant to the polymer backbone, and/or osmotic pressure differentials that result from such phenomena. In other systems, the definition of a response can be expanded to include more dramatic alterations in the polymeric structure. In the past decade, many breakthroughs have been made in developing SPRs with novel stimulus-active mechanisms. This article reviews the mechanisms and fabrication strategies of stimulus active polymers that are sensitive to heat, light, electrical field, magnetic field, and solvent/water. The wide applications of patterned SRPs are also summarized.
Materials 2014, 7, 805-875; doi:10.3390/ma7020805
OPEN ACCESS
materials
ISSN 1996-1944 /journal/materials Review
Fabrications and Applications of Stimulus-Responsive Polymer Films and Patterns on Surfaces: A Review
Jem-Kun Chen 1 and Chi-Jung Chang 2,*