Energetics of LCST transition of poly(ethylene oxide) in aqueous solutions

Ionizing Radiation Synthesis of Hydrogel Nanoparticles of Gelatin and Polyethylene Glycol at High Temperature

Nanohydrogel particles of polyethylene glycol (PEG), gelatin (GEL), and PEG-GEL mixtures (MIXs) were synthesized with a high electron beam and 60Co gamma-ray radiation. The relatively novel technique of Asymmetrical Flow Field Flow Fractionation (AF4 or AFFFF) coupled to a Multi-Angle Laser Light Scattering (MALLS) detector was mainly used to determine the hydrodynamic diameter (Dh) of the radiation-synthesized PEG, GEL, and PEG-GEL nanohydrogel particles. Our approach to achieving nanohydrogel particles is to enhance the intracrosslinking reactions and decrease the intercrosslinking reactions of the C-centered radicals of the PEG and GEL. The intracrosslinking reactions of these free radicals were enhanced via irradiation at temperatures of 77-80 °C and using a high dose rate and pulsed irradiation. The shorter average distance between the C-centered free radicals on the backbone of the thermally collapsed PEG and GEL chain, due to the destruction of hydrogen bonds, enhances the intracrosslinking reactions. It was observed that increasing the dose and dose rate decreased the Dh. DLS results lined up with AF4 measurements. This study provides researchers with a clean method to produce GEL-PEG hydrogels without the use of toxic reagents. Particle size can be tuned with dose, dose rate, and temperature as demonstrated in this work. This is ideal for medical applications as the use of ionizing radiation eliminates toxicity concerns and provides simultaneous sterilization of the material.

Structure and Thermodynamics of Linear, Ring, and Catenane Polymers in Solutions and at Liquid-Liquid Interfaces

In recent decades, advances in the syntheses of mechanically interlocked macromolecules, such as catenanes, have led to much greater interest in the applications of these complexes, from molecular motors and actuators to nanoscale computational memory and nanoswitches. Much remains to be understood, however, regarding how catenated ring compounds behave as a result of the effects of different solvents as well as the effects of solvent/solvent interfaces. In this work, we have investigated, using molecular dynamics simulations, the effects of solvation of poly(ethylene oxide) chains of different topologies─linear, ring, and [2]catenane─in two solvents both considered favorable toward PEO (water, toluene) and at the water/toluene interface. Compared to ring and [2]catenane molecules, the linear PEO chain showed the largest increase in size at the water/toluene interface compared to bulk water or bulk toluene. Perhaps surprisingly, observations indicate that the tendency of all three topologies to extend at the water/toluene interface may have more to do with screening the interaction between the two solvents than with optimizing specific solvent-polymer contacts.

Missing Piece in Colloidal Stability─Morphological Factor of Hydrophobic Nanoparticles

Hydrophobic nanoparticles (NPs) in water were considered unstable because they lack the repulsive electrostatic interaction and steric effect to prevent aggregation. In this study, porous hydrophobic NPs of two star-shaped giant molecules, POSS-(R)₈, were found to be stable in water and able to retain their kinetic stability in a wide range of temperatures, pH values, and ionic strengths. Unlike the solid hydrophobic NPs that aggregate even with the negative zeta potential (ζ) induced by surface-structured hydrogen-bonded (SHB) water, the porous morphology of POSS-(R)₈ NPs reduces the entropically driven hydrophobic effect to prevent aggregation. With the porous morphology, the hydrophobic NPs are stable without the hydrophilic or charged surface functional groups and demonstrate good encapsulation capability. The morphological factor of colloids is thus one of the missing pieces in the theory of colloidal stability that extends our understanding of colloidal science.

Flow behavior of thermo-thickening associative polymers in porous media: effects of associative content, salinity, time, velocity, and temperature

Abstract

Above a critical temperature, thermo-thickening associative polymers (TAPs) have a superior ability to decrease the mobility of the water phase, compared to traditional polymers for enhanced oil recovery. The ability to decrease the mobility, will be amplified at low flow velocities, and by the presence of salt, and is much higher in porous media than would be expected from bulk viscosity. In this work, we have examined TAPs ability to reduce the mobility, i.e., to increase the resistance factor. We have studied the effect of increasing the associative content, changing the porous media, changing the salinity, and scaling up the size of the porous media. How the resistance factor evolved, was studied as a function of temperature, velocity, and time. We found that a critical associative content or critical concentration of polymer was needed to achieve thermo-thickening in the porous media. As expected, thermo-thickening increased by increasing the salinity. For the relative homogenous clastic porose media investigated here, ranging from ~ 1Darcy sandstone to multidarcy sand, type of porous media did not seem to have a significant impact on the resistance factor. Time and amount of polymer injected is a critical factor: The buildup of thermo-thickening is delayed compared to the polymer front. For our tests with the weaker systems, we also observed a breakdown of the associative network at very low injection rates, possibly caused by the formation of intramolecular association.

Article highlights

Key findings from our tests of thermo-thickening associative polymer for enhance oil recovery operations: