Poly(N-isopropylacrylamide): experiment, theory and application

Hydrogels for tissue engineering.

A review of stimuli-responsive nanocarriers for drug and gene delivery

Chemical sensors respond to the presence of a specific analyte in a variety of ways. One of the most convenient is a change in optical properties, and in particular a visually perceptible colour change. Here we report the preparation of a material that changes colour in response to a chemical signal by means of a change in diffraction (rather than absorption) properties. Our material is a crystalline colloidal array of polymer spheres (roughly 100 nm diameter) polymerized within a hydrogel that swells and shrinks reversibly in the presence of certain analytes (here metal ions and glucose). The crystalline colloidal array diffracts light at (visible) wavelengths determined by the lattice spacing, which gives rise to an intense colour. The hydrogel contains either a molecular-recognition group that binds the analyte selectively (crown ethers for metal ions), or a molecular-recognition agent that reacts with the analyte selectively. These recognition events cause the gel to swell owing to an increased osmotic pressure, which increases the mean separation between the colloidal spheres and so shifts the Bragg peak of the diffracted light to longer wavelengths. We anticipate that this strategy can be used to prepare 'intelligent' materials responsive to a wide range of analytes, including viruses.

Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials

Temperature-sensitive aqueous microgels.

Aqueous solutions of poly(N-isopropyl acrylamide) show a lower critical solution temperature. The thermodynamic properties of the system have been evaluated from the phase diagram and the heat absorbed during phase separation and the phenomenon is ascribed to be primarily due to an entropy effect. From viscosity, sedimentation, and light-scattering studies of solutions close to conditions of phase separation, it appears that aggregation due to formation of nonpolar and intermolecular hydrogen bonds is important. In addition, a weakening of the ordering effect of the water-amide hydrogen bonds as the temperature is raised contributes to the stability of the two-phase system.

Solution Properties of Poly(N-isopropylacrylamide)

Study of Polymer-Solute Interactions by Gas Chromatography

As a result of the experimental work summarized in this review the value of the gas chromatographic method for studying polymers seems to be well established. Surface and bulk properties of polymers can be measured both from a thermodynamic and kinetic point of view. Because of its simplicity and precision it should become the method of choice for the study of thermodynamic interactions of small molecule “probes” or solutes in systems where the polymer is the major phase. Further advances in the kinetic theory of the GC process should provide even more reliable data about time dependent processes such as diffusion, adsorption, complex formation and possibly even chemical reaction.

Study of polymers by inverse gas chromatography

A Gas Chromatographic Method for the Study of Sorption on Polymers

Recent experiments in our laboratories [1–31], have shown that the technique of gas chromatography may be utilized to obtain extensive information about polymer structure and interactions in the solid phase. Although it might appear logical to apply the name “gas chromatography of polymers” to such experiments, the terminology is misleading in that the polymer is obviously not in the gas phase, nor is it undergoing a chromatographic separation. The terms GLC (gas-liquid chromatography) and GSC (gassolid chromatography) appear to be equally inapplicable for similar reasons. In fact, the nature of the experiment has more in common with the molecular beam technique for gaseous reactions and we prefer therefore to refer to these as studies on polymers using “molecular probes.”

J. E. Guillet

Papers

Solution Properties of Poly(N-isopropylacrylamide)

Study of Polymer-Solute Interactions by Gas Chromatography

Study of polymers by inverse gas chromatography

A Gas Chromatographic Method for the Study of Sorption on Polymers

Molecular Probes in the Study of Polymer Structure