Effect of Ca2+ Ion and Temperature on Association of Thermally Sensitive PAA-b-PNIPAM Diblock Chains in Aqueous Solutions

Microstructural transition of poly(vinyl alcohol)-based aerogels in the presence of interpolymer complexes

Interpolymer interactions play a vital role of determining the microstructure and properties of polymer aerogels.

Quest for Thermoresponsive Block Copolymer Nanoparticles with Liquid-Crystalline Surfactant Cores

This work reports on the preparation and characterization of anisotropic composition nanoparticles based on the electrostatic binding of dodecyltrimethylammonium surfactant to poly(acrylic acid) blocks of diblock copolymers with poly(ethylene oxide) (PEO) and poly(N-isopropyl acrylamide) (PNIPAm). These nanoparticles form kinetically stable dispersions and display liquid-crystalline cores with a micellar cubic structure, as determined by small-angle X-ray scattering. Mixtures with different proportions of the two block copolymers and stoichiometric amounts of C₁₂TA⁺ were prepared and their behavior was compared with that of the parent nanoparticles. Upon heating, dilute dispersions (0.01 and 0.1 wt %) analyzed by dynamic light scattering display a slight decrease in the hydrodynamic radius, consistent with the dehydration of PNIPAm and mixed PNIPAm-PEO blocks at the shell. At higher concentrations, 2 wt %, the nanoparticles with pure PNIPAm shell undergo macroscopic phase separation above 32 °C. Nanoparticles with a pure PEO shell do not display temperature sensitivity. For the mixtures, no visual change is observed, but the dynamic light scattering results evidence the formation of clusters, whose size and reversibility depend on the PEO/PNIPAm proportion. This indicates the formation of mixed nanoparticles containing both PEO and PNIPAm blocks. Nuclear Overhauser enhancement spectroscopy NMR analyses of the mixtures do not show the correlation peak expected for PEO and PNIPAm blocks in close proximity, suggesting their segregation at the nanoparticle shell. On the basis of these results, we discuss the possibilities of the neutral blocks distribution on the shell of mixed nanoparticles. Overall, we have confirmed that these nanoparticles may display a temperature-controlled reversible aggregation while preserving their internal liquid-crystalline structures.

Molecular switching involving metastable states: molecular thermal hysteresis and sensing of environmental changes by chiral helicene oligomeric foldamers

Molecular switching is a phenomenon in which the molecular structure reversibly changes in response to external stimulation. It is crucial in biology and is used in various biological sensing applications and responses. In contrast to the well-studied molecular switching involving two or more thermodynamically stable states, switching involving metastable states exhibits notable non-equilibrium thermodynamic properties. Synthetic chiral helicene oligomeric foldamers that exhibit molecular thermal hysteresis in dilute solution are examples. Molecular switching can be used for sensing environmental changes, including temperature threshold, temperature decrease/increase, rate of temperature decrease, counting the numbers 1 and 2, and concentration increase.

Calcite nucleation on the surface of PNIPAM–PAAc micelles studied by time resolved in situ PXRD

Nanocrystalline calcite is formed under the influence of block copolymers containing thermoresponsive PNIPAM and a mineralization controlling block of poly(acrylic acid) and the nanocrystal formation kinetics studied by in situ X-ray diffraction.

Heating/cooling stimulus induces three-state molecular switching of pseudoenantiomeric aminomethylenehelicene oligomers: reversible nonequilibrium thermodynamic processes

A 1:1 mixture of pseudoenantiomeric aminomethylenehelicene (P)-tetramer and (M)-pentamer formed three states, namely, the heterodouble helices B and C and the random coil A. At high temperatures, A is the most stable. At low temperatures, C is the most stable, and the structural changes from A to the metastable state B to the product C occur, where B and C have pseudoenantiomeric helical structures. Heating then converts C to A. Essentially, all the molecules change their structure from A to B to C to A. Various nonequilibrium reversible thermodynamic responses appeared depending on thermal conditions: The metastable states A and B can be interconverted with thermal hysteresis without forming C in a far-from-equilibrium manner; three-state hysteresis occurs; states A and B can be frozen at low temperatures and defrosted by warming. An energy and population model for the three-state switching is given, involving inversion of thermodynamic stability and thermal hysteresis.

Bulk and solution properties of a thermo-responsive rod–coil block polymer based on poly(N-isopropylacrylamide)

Molecular weight dependence on thermoresponsive behaviors of rod–coil diblock copolymers (x indicates the DP of rod PHIPPVTA blocks).

Synthesis and characterization of well-defined PAA–PEG multi-responsive hydrogels by ATRP and click chemistry

Well-defined multi-responsive PAA–PEG hydrogels exhibit a unique swelling property at different pH and Ca²⁺ secondary crosslinking, and can potentially be used as stimuli responsive biomaterials.