Fast-thermoresponsive carboxylated carbon nanotube/chitosan aerogels with switchable wettability for oil/water separation

Graft copolymers with brush-type architectures are explored containing poly(ethylene glycol) methacrylates copolymerized with “thermoresponsive” monomers which impart lower critical solution temperatures to the polymer. Initially, the chemical structure of the thermoresponsive polymer is explored, synthesizing materials containing N-isopropyl acrylamide, N,N-diethyl acrylamide and diethylene glycol methyl ether methacrylate. Thermoresponsive graft-copolymers containing di(ethylene glycol) methyl ether methacrylate (DEGMA) exhibited phase transition temperature close to physiological conditions (ca 30 °C). The effect of polymer composition was explored, including molecular weight, PEG-methacrylate (PEGMA) terminal functionality and PEGMA/DEGMA ratios. Molecular weight exhibited complex relationships with phase behavior, where lower molecular weight systems appeared more stable above lower critical solution temperatures (LCST), but a lower limit was identified. PEGMA/DEGMA feed was able to control transition temperature, with higher PEGMA ratios elevating thermal transition. It was found that PEGMA terminated with methoxy functionality formed stable colloidal structures above LCST, whereas those the hydroxy termini generally formed two-phase sedimented systems when heated. Two thermoresponsive DEGMA-based graft polymers, poly(PEGMA7-ran-DEGMA170) and poly(PEGMA1-ran-DEGMA38), gave interesting temperature-dependent rheology, transitioning to a viscous state upon heating. These materials may find application in forming thermothickening systems which modify rheology upon exposure to the body’s heat.

Plenty of oily wastewater discharged from industrial and domestic sewage has deteriorated the environment severely, so stimuli‐responsive membranes with switchable wettability have been of considerable attraction for its potential application in oil/water separation. In this work, a novel pH‐dependent thermoresponsive membrane fabricated by grafting the poly[2‐(diethylamino)ethyl acrylamide] (PDEAEAM) from the poly(vinylidene fluoride) (PVDF) membrane via surface‐initiated atom transfer radical polymerization is explored to achieve the oil/water separation. The PDEAEAM‐g‐PVDF membrane shows hydrophilicity at room temperature under neutral condition while hydrophobicity at 50°C under alkaline condition. Wettability of the membrane at different temperatures is dominated by the lower critical solution temperature (LCST) of PDEAEAM, and the LCST of PDEAEAM is pH dependent. Due to the LCST of PDEAEAM, the membrane shows a variation of separation efficiency for separating hexadecane/water emulsion with temperature and pH. Typical separation efficiencies are 97.10% at 25°C under neutral condition and 30.26% at 50°C under alkaline condition.

Thermo-responsive brush copolymers with structure-tunable LCST and switchable surface wettability

Water‐soluble polymers with tunable temperature sensitivity: Solution behavior

Here we have obtained a temperature responsive melamine sponge with a controllable wettability between superhydrophilicity and superhydrophobicity by grafting the octadecyltrichlorosilane and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) onto the surface of melamine sponge skeletons. The whole process included the silanization in which step the rough surface with low surface energy and the NH2 were provided, and the atom transfer radical polymerization which ensured the successful grafting of PNIPAAm onto the skeleton's surface. The product exhibits a good reversible switch between superhydrophilicity and superhydrophobicity by changing the temperature below or above the lower critical solution temperature (LCST, about 32 °C) of PNIPAAm, and the modified sponge still retains a good responsiveness after undergoing two temperature switches for 20 cycles. Simultaneously, the functionalized sponges could be used to absorb the oil under water at 37 °C, and they released the absorbed oil in various ways under water at 20 °C, showing wide potential applications including oil/water separation.

Multifunctional carboxylated cellulose nanofibers/exfoliated bentonite/Ti3C2 aerogel for efficient oil adsorption and recovery: The dual effect of exfoliated bentonite and MXene

There exists a huge demand for efficient, reliable and safe technologies for oily water treatment and/or oil recovery. Among many techniques, absorbent-based technology shows the possibility of full removal and reclaim of oils from water, while bringing little adverse effects to the environment [1]. In spite of their promises, the issues pertaining to the recycling and regenerating of saturated absorbents have been less-explored [1, 2]. In this work, we demonstrate a conjugated polymer mesh as oil absorbent capable of in situ self-regeneration via wettability switch during electrochemical oxidation and reduction. We fabricate the absorbent through electropolymerization of polypyrrole-dodecylbenzenesulfonate (PPy(DBS)) on the surfaces of carbon nanotubes (CNTs) grown out of the surface of a stainless steel (SS) mesh. The PPy(DBS)-coated mesh shows oleophilic property when electrochemically oxidized, allowing the mesh to absorb oils (i.e., oils stick to the polymer surface; oils are trapped within the micro-pores of mesh). Under reduction, the surface switches to oleophobic (i.e., oils do not stick to the polymer surface), which allows trapped-oils by the mesh to be released, while in situ self-regenerating the polymer surface. We also observe that this switchable adhesion property is further enhanced incorporating CNTs into the structure. Using this approach, in situ absorbing and releasing of dichloromethane (DCM) in aqueous solution is demonstrated using a rolled-up absorbent mesh. We further demonstrate the wettability switch performance (characterizing the retention force when oxidized and switch time when reduced) of the absorbent during 250 redox cycles. In addition, the potential usage of this oil absorbent for oil/water separation is demonstrated by transporting DCM from one vial to another. Together, this novel adsorbent shows great promise towards high-efficient continuous oil/water separation applications. [1] J. Ge, H. Zhao, H. Zhu, J. Huang, L. Shi, and S. Yu, “Advanced sorbents for oil-spill cleanup: recent advances and future perspectives,” Advanced Materials, 28 (47), 10459–10490, (2016). [2] Z. Chu, Y. Feng, and S. Seeger, “Oil/water separation with selective superantiwetting/superwetting surface materials,” Angewandte Chemie - International Edition, 54 (8), 2328–2338, (2015).

Ultra-Strong, Ultra-Tough, Transparent, and Sustainable Nanocomposite Films for Plastic Substitute

Adjusting the low critical solution temperature of poly(N-isopropyl acrylamide) solutions by salts, ionic surfactants and solvents: A rheological study

With the increasing attention of indoor air pollutant, high adsorption performance materials are widely used to deal with formaldehyde. However, the mechanical properties and adsorption efficiency usually limited their applications. In this study, amine-functionalized graphene/fiber composite paper with nacre-inspired structure and high mechanical strength is fabricated through vacuum filtration-induced self-assembly process via a environmentally friendly synthesis route. By the interaction between amine-functional graphene oxide and pine pulp fiber, the formaldehyde adsorption composite paper has been successfully achieved, having high mechanical properties for tensile strength, tear strength and elongation and good adsorption performance. The good physical and adsorption performance of our composite paper provides a new insight into the design and fabrication of advanced photocatalytic materials.

Poly(N-isopropylacrylamide) (pNIPAm) undergoes a hydrophilicity/hydrophobicity change around its lower critical solution temperature (LCST). Therefore, pNIPAm-based polymer nanoparticles (NPs) shrink above their LCST and swell below their LCST. Although temperature responsiveness is an important characteristic of synthetic polymers in drug and gene delivery, few studies have investigated the temperature-responsive catch and release of low-molecular-weight drugs (LMWDs) as their affinity to the target changes. Since LMWDs have only a few functional groups, preparation of NPs with high affinity for LMWDs is hard compared with that for peptides and proteins. However, LMWDs such as anticancer drugs often have a stronger effect than peptides and proteins. Therefore, the development of NPs that can load and release LMWDs is needed for drug delivery. Here, we engineered pNIPAm-based NPs that capture paclitaxel (PTX), an anticancer LMWD that inhibits microtubules, above their LCST and release it below their LCST. The swelling transition of the NPs depended on their hydrophobic monomer structure. NPs with swelling ratios (=NP size at 25 °C/NP size at 37 °C) exceeding 1.90 released captured PTX when cooled to below their LCST by changing the affinity for PTX. On the other hand, NPs with a swelling ratio of only 1.14 released melittin. Therefore, optimizing the functional monomers of temperature-responsive NPs is essential for the catch and release of the target in a temperature-dependent manner. These results can guide the design of stimuli-responsive polymers that catch and release their target molecules.

Folate-conjugated and thermo-responsive poly((N-isopropylacrylamide)-co- acrylamide-co-(octadecyl acrylate)-co-(folate-(polyethylene glycol)-(acrylic acid))) (P(NIPA-co-AAm-co-ODA-co-FPA)) micelles with mean diameter of about 60 nm and lower critical solution temperature (LCST) of about 39°C were synthesized by free radical random copolymerization. Single-factor tests of acrylamide and octadecyl acrylate were carried out to modulate micelles' LCST and diameter, respectively. LCST, diameter, and morphology of micelles were determined by UV-vis spectrophotometer, laser particle size analyzer, and transmittance electron microscope (TEM), respectively. Fluorescein was then used as a model drug to investigate the drug loading content of micelles. Micelles with maximum amount of octadecyl acrylate (180 mg) were found to yield drug loading content of 10.48%. Near infrared dye No.10 was chosen as the tracer to monitor micelles in vivo. The targeting behaviors of micelles in folate receptor positive Bel-7402 tumor bearing nude mice were assessed by a self-constructed near infrared imaging system. Results showed satisfactory targeting capability of the thermo-responsive micelles toward Bel-7402 tumors, and targeting accumulation could last for more than 96 h, enabling P(NIPA-co-AAm-co-ODA-co-FPA) micelles to function as a diagnostic reagent as well as a targeted tumor therapy.

The development of intelligent, environmentally responsive oil-water separation membranes with reversible wettability presents a promising strategy for controllable emulsion separation and the advanced treatment of complex oily wastewater. Wastewater. In this study, a novel thermally responsive membrane with switchable wettability between superhydrophilic and superhydrophobic states was fabricated via in situ growth of bimetallic metal-organic frameworks (CoZn-ZIF) on electrospun poly(vinylidene fluoride)/poly(N-isopropylacrylamide) (PVDF/PNIPAM) nanofiber membranes. The resulting PVDF/PNIPAM@CoZn-ZIF membrane leverages the thermally induced reversible conformational transition of PNIPAM to exhibit underwater superoleophobicity below its lower critical solution temperature (LCST) and under-oil superhydrophobicity above LCST. This switchable wettability enabled efficient on-demand separation of both oil-in-water (O/W) and water-in-oil (W/O) emulsions, achieving water permeation fluxes exceeding 1900 L·m-2·h-1 and oil permeation fluxes over 1150 L·m-2·h-1, with separation efficiencies above 99.00% and 99.60%, respectively. Moreover, the embedded Co1Zn3-ZIF served as a catalyst to activate peroxymonosulfate (PMS), generating reactive oxygen species (·OH and·SO4-) and enabling rapid degradation of methylene blue, with a removal efficiency of 99.92% within 15 min. This study presents a multifunctional composite membrane as an intelligent, efficient platform for integrated oil-water emulsion separation and organic pollutant remediation.

The adhesion and mechanical properties of hydrogels used for vascular wound repair often deteriorate dramatically on wet surfaces, resulting in ineffective repair. In this work, a poly(N-isopropyl acrylamide-co-dopamine methacrylamide) nanogel with dopamine groups was synthesized and introduced into a polyacrylamide (PAAm) hydrogel to produce temperature-responsive hydrogels, which greatly improved mechanical and adhesive properties of PAAm hydrogels. Nanogel-reinforced PAAm (NR-PAAm hydrogel) can adhere to the surface of various solid materials and biological tissues through special physical interactions, which exhibited different mechanical and adhesion properties as temperature changes below or above the lower critical solution temperature (LCST). The maximum adhesion of the NR-PAAm hydrogel on the aluminum surface was 78 kPa. In addition, the NR-PAAm hydrogel exhibited sufficient mechanical properties with a fracture stress of 103.6 kPa at a fracture strain of 1800%. The NR-PAAm hydrogel has good adhesion on wet surfaces and could adhere for 600 s at a pressure difference of 30 mmHg. Hence, the obtained temperature-responsive hydrogels have excellent tunable mechanical properties and adhesion properties, which provides a theoretical basis for the development of vascular repair materials in the future.

The conformational collapse of polymers in mixtures of two individually good solvents is an intriguing yet puzzling phenomenon termed cononsolvency. In this paper, the concept of the preferential adsorption of the cosolvent is combined with mean-field approaches to elaborate the cononsolvency effect of dimethylformamide (DMF) on the thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels in aqueous solutions. We give a quantitative description concerning the effects of DMF preferential adsorption and partitioning on the reentrant transition of PNIPAM microgels below the lower critical solution temperature (LCST) of PNIPAM. While the DMF cononsolvency incurs the conformational collapse, the affinity of DMF molecules to PNIPAM chains becomes increasingly stronger, which reveals that the conformational collapse is decoupled from the solvent quality of DMF-water mixtures. Considering the chain elasticity, spatial constraints, and surface charge of microgels, we explore the cononsolvency effect on the persistence length quantifying the PNIPAM flexibility. Our analysis elucidates that, depending on chain length and temperature, the DMF cononsolvency-induced collapse of PNIPAM microgels leads to a remarkable increase in the persistent length below LCST, which is comparable to the experimental data regarding suspension mechanical properties of PNIPAM microgels in water above LCST.