Polymer-based smart materials, also known as stimuli-responsive polymers or intelligent polymers, are materials that can undergo significant changes in their properties, such as shape, size, or solubility, in response to external stimuli like temperature, pH, light, electric or magnetic fields, and specific chemical or biological agents. The mechanism behind the responsiveness of these materials lies in their unique molecular structure and the interactions between their constituent molecules.The responsiveness of polymer-based smart materials can be attributed to the following factors:1. Molecular structure: The molecular structure of the polymer plays a crucial role in determining its responsiveness to external stimuli. Polymers with specific functional groups, such as hydrophilic or hydrophobic moieties, can exhibit a change in their properties upon exposure to certain stimuli. For example, temperature-sensitive polymers like poly N-isopropylacrylamide PNIPAM have a lower critical solution temperature LCST , above which they become hydrophobic and collapse, while below the LCST, they are hydrophilic and soluble in water.2. Inter- and intra-molecular interactions: The interactions between polymer chains or within a single polymer chain can significantly influence the responsiveness of the material. Hydrogen bonding, van der Waals forces, and electrostatic interactions can be affected by external stimuli, leading to changes in the polymer's properties. For instance, pH-sensitive polymers can undergo protonation or deprotonation of their functional groups, altering the electrostatic interactions and causing the polymer to swell or shrink.3. Crosslinking: Crosslinked polymers have covalent or non-covalent bonds connecting their chains, which can provide additional responsiveness to external stimuli. For example, hydrogels are crosslinked polymer networks that can swell or shrink in response to changes in temperature, pH, or ionic strength.Utilization of polymer-based smart materials in novel applications:The unique responsiveness of polymer-based smart materials has led to their use in a wide range of applications, including:1. Drug delivery: Stimuli-responsive polymers can be used to develop targeted drug delivery systems that release their payload upon exposure to specific stimuli, such as changes in pH, temperature, or the presence of specific enzymes. This can improve the efficacy and reduce the side effects of the drugs.2. Tissue engineering and regenerative medicine: Smart polymers can be used as scaffolds for cell growth and tissue regeneration, with their properties being tuned to match the requirements of specific tissues. Additionally, their responsiveness to external stimuli can be used to control cell behavior and promote tissue repair.3. Sensors and actuators: Polymer-based smart materials can be used to develop sensors that change their properties in response to specific stimuli, such as changes in temperature, pH, or the presence of specific chemicals. These materials can also be used to create actuators that convert external stimuli into mechanical motion, such as artificial muscles or soft robots.4. Environmental applications: Stimuli-responsive polymers can be used for environmental remediation, such as the removal of pollutants from water or air. For example, temperature- or pH-responsive polymers can be used to selectively capture and release contaminants, enabling their efficient removal and recovery.5. Adaptive and self-healing materials: Smart polymers can be used to develop materials that can adapt their properties in response to external stimuli, such as self-healing materials that can repair themselves upon exposure to specific triggers.In conclusion, the mechanism behind the responsiveness of polymer-based smart materials lies in their molecular structure and the interactions between their constituent molecules. This responsiveness can be harnessed for the development of novel applications in various fields, such as drug delivery, tissue engineering, sensors and actuators, environmental remediation, and adaptive materials.