Fabrication and Structural Characterization of Module-Assembled Amphiphilic Conetwork Gels

Dynamic Covalent Amphiphilic Polymer Conetworks Based on End-Linked Pluronic F108: Preparation, Characterization, and Evaluation as Matrices for Gel Polymer Electrolytes

We present the development of a platform of well-defined, dynamic covalent amphiphilic polymer conetworks (APCN) based on an α,ω-dibenzaldehyde end-functionalized linear amphiphilic poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEG-b-PPG-b-PEG, Pluronic) copolymer end-linked with a triacylhydrazide oligo(ethylene glycol) triarmed star cross-linker. The developed APCNs were characterized in terms of their rheological (increase in the storage modulus by a factor of 2 with increase in temperature from 10 to 50 °C), self-healing, self-assembling, and mechanical properties and evaluated as a matrix for gel polymer electrolytes (GPEs) in both the stretched and unstretched states. Our results show that water-loaded APCNs almost completely self-mend, self-organize at room temperature into a body-centered cubic structure with long-range order exhibiting an aggregation number of around 80, and display an exceptional room temperature stretchability of ∼2400%. Furthermore, ionic liquid-loaded APCNs could serve as gel polymer electrolytes (GPEs), displaying a substantial ion conductivity in the unstretched state, which was gradually reduced upon elongation up to a strain of 4, above which it gradually increased. Finally, it was found that recycled (dissolved and re-formed) ionic liquid-loaded APCNs could be reused as GPEs preserving 50-70% of their original ion conductivity.

Star polymer networks: a toolbox for cross-linked polymers with controlled structure

The synthesis of precisely controlled polymer networks has been a long-cherished dream of polymer scientists. Traditional random cross-linking strategies often lead to uncontrolled networks with various kinds of defects. Recent...

Synthesis and properties of a temperature-sensitive hydrogel based on physical crosslinking via stereocomplexation of PLLA-PDLA

A synthetic route to amphiphilic conetwork (APCN) gels was developed and involved (1) a ring-opening polymerization (ROP) synthesis of the macromonomer HEMA-PLLA/PDLA, and (2) a radical polymerization of a stereocomplex of the synthesized macromonomers with P(MEO₂MA-co-OEGMA) to form the APCN gels. The structure of the gel was successfully verified using X-ray diffraction. Thermal analysis and differential scanning calorimetry data showed that the thermal behaviors of the gels were greatly improved compared with that of polylactic acid (PLA). The mechanical properties of the gels were measured by using a dynamic viscometer, and the results indicated a greater mechanical strength before swelling than afterwards, and an increasing strength of the gels with increasing amount of PLA stereocomplex. Gels placed in different aqueous phases at different temperatures showed different swelling ratio (SR) values. Specifically, the SR gradually decreased as the temperature was increased, indicating a temperature sensitivity of the gels. In addition, the gels placed in the aqueous and organic phases presented as hydrogels and hydrophobic gels, respectively, and their SR values were relatively low. These results indicated the amphiphilic nature of the gel, and indicated great application prospects for the gel in biomedicine.

A synthetic route to amphiphilic conetwork (APCN) gels was developed and involved (1) ring-opening polymerization synthesis of the macromonomer, and (2) radical polymerization of stereocomplex of the synthesized macromonomers with MEO₂MA, OEGMA to form the APCN gels.

Thermodynamic control over energy dissipation modes in dual-network hydrogels based on metal-ligand coordination

Modern polymeric hydrogels use reversible bonds to mimic biological functionalities. However, true biological materials benefit from several supramolecular elements and deliver multiple functions at the same time. To approach similar creation and control of multiple different functional elements in a synthetic soft material, we develop a model dual-network hydrogel in which multiple energy dissipating modes are formed by metal-ligand coordination and regulated by their association thermodynamics. This idea is realized by using linear and tetra-arm poly(ethylene glycol) (PEG) precursors with complementary reactive end groups. The former also carries terpyridine ligands on both ends, which form metallo-supramolecular bonds upon addition of metal ions. Multiple relaxation modes are provided by a combination of different metal ions. The timescale and amplitude of energy dissipating elements are characterized by oscillatory shear deformation. These studies suggest that the composition of metal ions controls the contribution of the corresponding relaxation modes in a linear fashion. A molecular-level confirmation is provided by following the UV-vis absorbance of the linear precursor in combination with mixtures of metal ions, accompanied by a theoretical study on the kinetics of the reversible association process. These results show that the linearity of the aforementioned dependence holds for such systems in which the utilized combination of metal ions and ligands exclusively form stable bis-complexes. By contrast, in many other cases, especially when the ions may compete to form mono-, bis-, or tris-complexes with the ligand, deviation from linearity is expected.

Self-organization of gel networks formed by block copolymer stars

The equilibrium properties of block copolymer star networks (BCS) are studied via computer simulations. We employ both molecular dynamics and multiparticle collisional dynamics simulations to investigate the self-organization of BCS with f = 9 functionalized arms close to their overlap concentrations under conditions of different fractions of functionalization and varying attraction strength. We find three distinct macroscopic self-organized states depending on fraction of attractive end-monomers and the strength of the attraction. At weak attractions, ergodic, diffusive liquids result, with short-lived bonds between the stars. As the attraction strength grows, the whole system forms a percolating cluster, while at the same time the individual molecules are diffusive. Finally, arrested gels emerge when the attractions become strong. The conformation of the BCS in these solutions is found to be strongly affected by the concentration, with the stars assuming typically spherical, open configurations in seeking to maximize inter-star associations as opposed to the inter-star collapse that results at infinite dilution, giving rise to strongly aspherical shapes and reduced sizes.

Model Amphiphilic Polymer Conetworks in Water: Prediction of Their Ability for Oil Solubilization

In this work, we computationally explored the ability of water-swollen, model ionizable ABA triblock copolymer-based amphiphilic polymer conetworks (APCNs) to solubilize a water-immiscible organic solvent (oil), via Gibbs free energy minimization. This was done as a function of the conetwork hydrophobe (A-blocks) mol fraction and the degree of ionization of the hydrophilic B-blocks. Expectedly, highest oil solubilization capacities were calculated for the most hydrophobic and least ionized APCNs, which could absorb up to 6.4 times more oil than water and exhibited a lamellar morphology. Our results also included a phase diagram, which indicated transitions from spheres to cylinders, lamellae, and unimers in oil, as the hydrophobe content increased and the degree of ionization decreased. All of these transitions were accompanied by discontinuous changes in the degrees of swelling in the aqueous and oil nanophases, discontinuous changes in the asymmetry ratios (for the anisotropic morphologies), and discontinuous changes in the oil solubilization capacities. This is the first time that a dual discontinuous volume phase transition is reported within a polymer gel.

QUOKKA, the pinhole small-angle neutron scattering instrument at the OPAL Research Reactor, Australia: design, performance, operation and scientific highlights

QUOKKA is a 40 m pinhole small-angle neutron scattering instrument in routine user operation at the OPAL research reactor at the Australian Nuclear Science and Technology Organisation. Operating with a neutron velocity selector enabling variable wavelength, QUOKKA has an adjustable collimation system providing source–sample distances of up to 20 m. Following the large-area sample position, a two-dimensional 1 m2position-sensitive detector measures neutrons scattered from the sample over a secondary flight path of up to 20 m. Also offering incident beam polarization and analysis capability as well as lens focusing optics, QUOKKA has been designed as a general purpose SANS instrument to conduct research across a broad range of scientific disciplines, from structural biology to magnetism. As it has recently generated its first 100 publications through serving the needs of the domestic and international user communities, it is timely to detail a description of its as-built design, performance and operation as well as its scientific highlights. Scientific examples presented here reflect the Australian context, as do the industrial applications, many combined with innovative and unique sample environments.