Polymer Interactions Research Articles

Understanding the Role of Polymer Interactions within Binders in Composite Lithium-Ion Anodes

Understanding the Role of Polymer Interactions within Binders in Composite Lithium-Ion Anodes

Symmetry-breaking in patch formation on triangular gold nanoparticles by asymmetric polymer grafting

Synthesizing patchy particles with predictive control over patch size, shape, placement and number has been highly sought-after for nanoparticle assembly research, but is fraught with challenges. Here we show that polymers can be designed to selectively adsorb onto nanoparticle surfaces already partially coated by other chains to drive the formation of patchy nanoparticles with broken symmetry. In our model system of triangular gold nanoparticles and polystyrene-b-polyacrylic acid patch, single- and double-patch nanoparticles are produced at high yield. These asymmetric single-patch nanoparticles are shown to assemble into self-limited patch‒patch connected bowties exhibiting intriguing plasmonic properties. To unveil the mechanism of symmetry-breaking patch formation, we develop a theory that accurately predicts our experimental observations at all scales—from patch patterning on nanoparticles, to the size/shape of the patches, to the particle assemblies driven by patch‒patch interactions. Both the experimental strategy and theoretical prediction extend to nanoparticles of other shapes such as octahedra and bipyramids. Our work provides an approach to leverage polymer interactions with nanoscale curved surfaces for asymmetric grafting in nanomaterials engineering.

Flexible polymeric tail for micro robot drag reduction bioinspired by the nature microorganisms

In nature, most microorganisms have flexible micro/nanostructure tails, which help them create propulsion, reduce drag, or search for food. Previous studies investigated these flexible structures mostly from the propulsion creation perspective. However, the drag reduction and the underlying physical mechanisms of such tails are less known. This scientific gap is more significant when multi-polymeric/hierarchical structures are used. To fill the gap, we use the dissipative particle dynamics (DPD) method as a powerful fluid–polymer interaction technique to study the flexible tails' influences on drag reduction. Note that the flow regime for these microorganisms is in the range of laminar low Reynolds number; hence, the effects of both pressure and viscous drag forces are crucial. On the other hand, in the DPD method, only the total drag force is obtained. Therefore, this paper first proposes a way to determine the contribution of viscous and pressure drags and then investigates their effects on the body of the micro-robot separately. As a bioinspired-templated micro-robot simulation, the flow over a circular cylinder with an attached flexible tail is investigated. The problem is carried out for the Reynolds numbers from 10 to 25 for different polymer lengths (single/multi) and hierarchical structure tails. Our results show that long polymer tails strongly affect pressure drag, such that the longer polymeric tails (single/multi), the more drag reduction, particularly the pressure drag. Moreover, the hierarchical structures (containing short and long tails) caused the total drag reduction mainly by decreasing the viscous drag rather than the pressure one.

Comparison of synergistic interactions of yellow mustard gum with locust bean gum or κ-carrageenan

Yellow mustard gum (YMG), a plant mucilage, has been investigated as a natural stabilizer for improving the texture, quality, and shelf life of food products. To expand its applications, synergistic polysaccharide-polysaccharide interactions were examined with two classical gums: κ-carrageenan and locust bean gum (LBG), which have been widely used in food, pharmaceutical and medicinal industries. A rheological approach was used to evaluate gelation characteristics of the two types of binary polysaccharide mixtures during the gelling process. Both types of mixtures demonstrated significant synergisms by forming stronger hydrogels at an equivalent total gum concentration (1% w/v) as their individual gums; however, their gel characteristics and gelation behaviors were different. YMG-κ-carrageenan mixtures formed a firm and elastic gel, but the synergistic effect only occurred at the blending ratio 3 to 7. YMG-LBG mixtures synergistically interacted to form an adhesive and paste-like gel. The gelation of YMG-κ-carrageenan began on cooling and continued during holding at 22 °C while YMG-LBG gel formed quickly after heated mixing at 80 °C and behaved stable regardless of temperature. The synergistic gelation mechanism of YMG-κ-carrageenan was proposed for the first time and illustrated as a result of polymer interactions (both association and segregation) and ion effects. Although further confirmation of the mechanisms is needed, this proposed mechanism would be useful for guiding the use of the synergistic gums regarding their applications in specific processing conditions. Either κ-carrageenan or LBG can be mixed with YMG to act as texturizers, thickeners, stabilizers, gelling agents in food products at an economic concentration.

Structural Optimization of Platinum Drugs to Improve the Drug-Loading and Antitumor Efficacy of PLGA Nanoparticles.

Currently, molecular dynamics simulation is being widely applied to predict drug-polymer interaction, and to optimize drug delivery systems. Our study describes a combination of in silico and in vitro approaches aimed at improvement in polymer-based nanoparticle design for cancer treatment. We applied the PASS service to predict the biological activity of novel carboplatin derivatives. Subsequent molecular dynamics simulations revealed the dependence between the drug-polymer binding energy along with encapsulation efficacy, drug release profile, and the derivatives' chemical structure. We applied ICP-MS analysis, the MTT test, and hemolytic activity assay to evaluate drug loading, antitumor activity, and hemocompatibility of the formulated nanoparticles. The drug encapsulation efficacy varied from 0.2% to 1% and correlated with in silico modelling results. The PLGA nanoparticles revealed higher antitumor activity against A549 human non-small-cell lung carcinoma cells compared to non-encapsulated carboplatin derivatives with IC50 values of 1.40-23.20 µM and 7.32-79.30 µM, respectively; the similar cytotoxicity profiles were observed against H69 and MCF-7 cells. The nanoparticles efficiently induced apoptosis in A549 cells. Thus, nanoparticles loaded with novel carboplatin derivatives demonstrated high application potential for anticancer therapy due to their efficacy and high hemocompatibility. Our results demonstrated the combination of in silico and in vitro methods applicability for the optimization of encapsulation and antitumor efficacy in novel drug delivery systems design.

Turning a polystyrene microsphere into a multimode light source by laser irradiation

Abstract Polystyrene (PS) is generally considered as a passive optical material that is transparent to light with wavelengths longer than 300 nm. In practice, PS micro- and nanospheres with uniform sizes are usually used to build photonic crystals based on self-assembly mechanism. Here, we demonstrate experimentally that PS microspheres supporting whispery gallery modes can be transformed into multimode light sources by laser irradiation. We show that a PS microsphere placed on a silica substrate can be lighted up when it is consecutively irradiated by using a 488-nm continuous wave laser beam with a pumping power above a threshold. Broadband luminescence emitted from the PS microsphere increases rapidly to a maximum value and decreases gradually with increasing irradiation time, implying the generation and degradation of a certain luminescent material upon laser irradiation. However, the PS microsphere is found to be damaged by high temperature based on morphology examination. By replacing the silica substrate with a thin silver film, the threshold laser power for lighting up a PS microsphere is dramatically reduced. More importantly, we can see enhanced luminescence intensities from the whispery gallery modes supported by the PS microsphere, which becomes an efficient multimode light source. Interestingly, the threshold laser power can be further lowered by inserting a molybdenum disulfide monolayer in between the PS microsphere and the silver film. As a result, the PS microsphere remains nearly unchanged except the formation of the luminescence material. Our findings open a new horizon for the interaction of polymer with laser light by exploiting the optical resonances supported by micro- and nanoparticles and pave the way for constructing photonic devices based on laser-induced luminescent materials in polymers.

Molecular modeling and in vitro studies to assess solubility enhancement of nevirapine by solid dispersion technique

Aim of this study was to improve nevirapine solubility using solid dispersion technique and applying molecular modeling to assess drug-polymer interactions.Solid dispersions were prepared usingEudragit S100 and HPMC K4M by solvent evaporation. Schrodinger 2021-3 softwarewas used to compute solubility parameters and drug polymer interactions. Spectral and thermal studies were used to evaluate interaction of nevirapine with polymers. Saturation solubility and dissolution studies were performed. FTIR and PXRD investigations revealed amorphization of NVP in solid dispersions. DSC thermograms further confirmed this. NVP-HPMC K4M solid dispersion displayed significantly higher solubility than with Eudragit S100 (ES100). Hansen and Hildebrand solubility parameters revealed greater affinity of NVP with HPMC K4M than with ES100. Interaction studies revealedgreater number of hydrogen bonds between NVP and HPMC K4M than with ES 100. In vitro and molecular modeling studies thus revealed that NVP showed higher solubility with HPMC K4M than with ES100.

Heterogeneous Percolation in Poly(methylvinylsiloxane)/Silica Nanocomposites: The Role of Polymer–Particle Interaction

Agglomeration and linking of nanoparticles or aggregates lead to the formation of percolated particle networks and alter the mechanical enhancement in polymer nanocomposites. Although critical behaviors have been widely studied, the solidlike behavior is only well described under the condition of the uniform dispersion of nanoparticles. In this work, we illustrate the role of particle–polymer interaction in the uniformity of particle dispersion and mechanical enhancement. Two types of silica with different interfacial adhesion energies with poly(methylvinylsiloxane) were adopted, resulting in different uniformities of particle dispersion. The critical percolation concentrations from the yield shear stress and yield first normal stress difference are identical. A lower interfacial adhesion energy leads to a higher critical concentration. The preshear stress only affects the critical concentration but does not change the critical exponents, which rely on the particle–polymer interaction. The mechanical enhancement, expressed as the power-law dependence of the yield stresses on the filler content, exhibits extraordinarily large power-law exponents for nanocomposites with lower interfacial adhesion energy, seriously deviating from the theoretical prediction in homogeneous dispersion systems. Based on the structural information from small-angle X-ray scattering (SAXS)/ultrasmall-angle X-ray scattering (USAXS) and transmission electron microscopy (TEM), we propose a model describing the heterogeneous percolation of loose aggregates in the presence of compact aggregates. This model shows that the heterogeneity of aggregates, including the fraction of compact aggregates and their fractal dimension, is the key factor in the scaling relationship between the yield stress and the particle volume fraction.

Antibacterial, Antifungal and Antiviral Polymeric Food Packaging in Post-COVID-19 Era.

Consumers are now more concerned about food safety and hygiene following the COVID-19 pandemic. Antimicrobial packaging has attracted increased interest by reducing contamination of food surfaces to deliver quality and safe food while maintaining shelf life. Active packaging materials to reduce contamination or inhibit viral activity in packaged foods and on packaging surfaces are mostly prepared using solvent casting, but very few materials demonstrate antiviral activity on foods of animal origin, which are important in the human diet. Incorporation of silver nanoparticles, essential oils and natural plant extracts as antimicrobial agents in/on polymeric matrices provides improved antifungal, antibacterial and antiviral properties. This paper reviews recent developments in antifungal, antibacterial and antiviral packaging incorporating natural or synthetic compounds using preparation methods including extrusion, solvent casting and surface modification treatment for surface coating and their applications in several foods (i.e., bakery products, fruits and vegetables, meat and meat products, fish and seafood and milk and dairy foods). Findings showed that antimicrobial material as films, coated films, coating and pouches exhibited efficient antimicrobial activity in vitro but lower activity in real food systems. Antimicrobial activity depends on (i) polar or non-polar food components, (ii) interactions between antimicrobial compounds and the polymer materials and (iii) interactions between environmental conditions and active films (i.e., relative humidity, oxygen and water vapor permeability and temperature) that impact the migration or diffusion of active compounds in foods. Knowledge gained from the plethora of existing studies on antimicrobial polymers can be effectively utilized to develop multifunctional antimicrobial materials that can protect food products and packaging surfaces from SARS-CoV-2 contamination.

Insight into non-covalent interactions in 1D Gd-based coordination polymer for solid-state self-assembly through a new supramolecular synthon

In solid-state, different non-covalent interactions between different parts of molecules play a key role in the formation of supramolecular architecture through the molecular assembly. Choice of the appropriate ligand is very crucial for such a solid. In this work, 5-phenyl-1,3,4-oxadiazole-propionate ligand and water form a one-dimensional polymer with the help of Gd(III) metal ion. Each Gd center of the polymer has a polarized amphiphilic environment. It has three water molecules on one side and a hydrophobic aromatic ligand is on a different side. This unique feature of ligand distribution help to recognize another part of the second 1D chain of the same polymer. In this way, such 1D polymer chains are self-assembled together and form an infinite 2D sheet. The hydrogen bonding between water ligands and 1,3,4-oxadiazole nitrogen of the organic ligand of two consecutive polymeric chains is the main binding force in the self-assembly process. These interactions bring aromatic rings together to form infinitely long π-staking interactions along the chain axis. These 1D chains create a 2C1 type of topology in the solid which was found, in some cases, in the metal-organic framework, with small organic, and inorganic molecules.

Structural Characterization of Cis- and Trans-Pt(NH3)2Cl2 Conjugations with Chitosan Nanoparticles.

The conjugation of chitosan 15 and 100 KD with anticancer drugs cis– and trans–Pt (NH3)2Cl2 (abbreviated cis–Pt and trans–Pt) were studied at pH 5–6. Using multiple spectroscopic methods and thermodynamic analysis to characterize the nature of drug–chitosan interactions and the potential application of chitosan nanoparticles in drug delivery. Analysis showed that both hydrophobic and hydrophilic contacts are involved in drug–polymer interactions, while chitosan size and charge play a major role in the stability of drug–polymer complexes. The overall binding constants are Kch–15–cis–Pt = 1.44 (±0.6) × 105 M−1, Kch–100–cis–Pt = 1.89 (±0.9) × 105 M−1 and Kch–15–trans–Pt = 9.84 (±0.5) × 104 M−1, and Kch–100–trans–Pt = 1.15 (±0.6) × 105 M−1. More stable complexes were formed with cis–Pt than with trans–Pt–chitosan adducts, while stronger binding was observed for chitosan 100 in comparison to chitosan 15 KD. This study indicates that polymer chitosan 100 is a stronger drug carrier than chitosan 15 KD in vitro.

Study of Nanoparticle-Polymer Interactions via the Mechanical Stretching of Surface-Enhanced Raman Scattering Substrates.

It is shown that the aligned electrospun fibers are a convenient platform for studying the mechanical effects on nanomaterials, particularly when using surface-enhanced Raman scattering as a sensitive tool of monitoring. The ligands on the surface of the embedded Au nanoparticles fall off easily with the shear force from the stretching, in contrast to the counterparts protected by polymer/silica shells. Upon stretching, the chains of Au nanoparticles will reversibly break, as revealed by the dramatic changes in the longitudinal plasmon absorption. It is believed that such a platform will open a window for understanding mechanical effects at the nanoscale, and also a new means for synthetic control.

Nitrogen and oxygen-codoped microporous carbon derived from acid-base interaction of carboxylic acid polymers and urea for enhanced CO2 capture

Nitrogen and oxygen-codoped microporous carbon was prepared using carboxylic acid polymer (PDVH) with urea as precursor. Due to the acid-base interaction, urea was trapped on the surface of the precursor, enhancing of the specific surface area, the nitrogen content and pore volume of the porous carbon after carbonization. Among these materials, the PDVH-NC-2.0 obtained an uptake of CO2 to 3.05 mmol g-1 at 25 ℃ and 1 atm. Meanwhile, the CO2 adsorption selectivity of these PDVH-NC-X ranged from 21.3 to 30.4 (CO2/N2 =85:15) based on the IAST adsorbed solution theory, resulting from the increased amount of the pyrrolic-N and oxidized-N, which enhanced the adsorption selectivity of CO2. Furthermore, the weak interaction involving N sites with CO2 should be responsible for the improvement of the uptake of CO2 through electrostatic potential mapping (ESP) and interaction region indicator (IRI). Finally, the CO2 uptake of the PDVH-NC-2.0 was still maintained after five cycles of reuse, which meant this porous carbon would be superior alternative for CO2 capture.

The effect of nanoparticle softness on the interfacial dynamics of a model polymer nanocomposite.

The introduction of soft organic nanoparticles (NPs) into polymer melts has recently expanded the material design space for polymer nanocomposites, compared to traditional nanocomposites that utilize rigid NPs, such as silica, metallic NPs, and other inorganic NPs. Despite advances in the fabrication and characterization of this new class of materials, the effect of NP stiffness on the polymer structure and dynamics has not been systematically investigated. Here, we use molecular dynamics to investigate the segmental dynamics of the polymer interfacial region of isolated NPs of variable stiffness in a polymer matrix. When the NP-polymer interactions are stronger than the polymer-polymer interactions, we find that the slowing of segmental dynamics in the interfacial region is more pronounced for stiff NPs. In contrast, when the NP-polymer interaction strength is smaller than the matrix interaction, the NP stiffness has relatively little impact on the changes in the polymer interfacial dynamics. We also find that the segmental relaxation time τα of segments in the NP interfacial region changes from values lower than to higher than the bulk material when the NP-polymer interaction strength is increased beyond a "critical" strength, reminiscent of a binding-unbinding transition. Both the NP stiffness and the polymer-surface interaction strength can thus greatly influence the relative segmental relaxation and interfacial mobility in comparison to the bulk material.

New Development in Understanding Drug-Polymer Interactions in Pharmaceutical Amorphous Solid Dispersions from Solid-State Nuclear Magnetic Resonance.

Pharmaceutical amorphous solid dispersions (ASDs) represent a widely used technology to increase the bioavailability of active pharmaceutical ingredients (APIs). ASDs are based on an amorphous API dispersed in a polymer, and their stability is driven by the presence of strong intermolecular interactions between these two species (e.g., hydrogen bond, electrostatic interactions, etc.). The understanding of these interactions at the atomic level is therefore crucial, and solid-state nuclear magnetic resonance (NMR) has demonstrated itself as a very powerful technique for probing API-polymer interactions. Other reviews have also reported exciting approaches to study the structures and dynamic properties of ASDs and largely focused on the study of API-polymer miscibility and on the identification of API-polymer interactions. Considering the increased use of NMR in the field, the aim of this Review is to specifically highlight recent experimental strategies used to identify API-polymer interactions and report promising recent examples using one-dimensional (1D) and two-dimensional (2D) experiments by exploiting the following emerging approaches of very-high magnetic field and ultrafast magic angle spinning (MAS). A range of different ASDs spanning APIs and polymers with varied structural motifs is targeted to illustrate new ways to understand the mechanism of stability of ASDs to enable the design of new dispersions.

Synergistic Effect of Cerium Oxide for Improving the Fire-Retardant, Mechanical and Ultraviolet-Blocking Properties of EVA/Magnesium Hydroxide Composites.

Rare earth oxide particles have received important attention in recent years, and due to the wide diversity of promising applications, the need for this kind of material is predicted to expand as the requirements to use the current resources become more demanding. In this work, cerium oxide (CeO2) was introduced into ethylene-vinyl acetate (EVA)/magnesium hydroxide (MDH) composites for enhancing the flame retardancy, mechanical properties and anti-ultraviolet aging performance. The target EVA/MDH/CeO2 composites were prepared by extrusion and injection molding, and the effects of the addition of the CeO2 were explored by thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), limiting oxygen index (LOI), UL-94, cone calorimetry test, and anti-ultraviolet aging test. Typically, the incorporation of the CeO2 allows a significant increase of the elongation at break and Young’s modulus compared with EVA/MDH by 52.25% and 6.85%, respectively. The pHRR remarkably decreased from 490.6 kW/m2 for EVA/MDH to 354.4 kW/m2 for EVA/MDH/CeO2 composite. It was found that the CeO2 presents excellent synergism with MDH in the composites for the anti-UV properties in terms of mechanical properties preservation. Notably, the combination of CeO2 with MDH is a novel and simple method to improve the filler–polymer interaction and dispersion, which resulted in the improvement of the mechanical properties, flame retardancy and the anti-ultraviolet aging performance of the composites.

Hydrophilic Polymer-Guided Polycatecholamine Assembly and Surface Deposition.

Mussel-inspired surface chemistry based on polycatecholamines and polyphenols has been widely applied as a facile and universal method for modifying surfaces. Specifically, the catecholamine-assisted codeposition as a one-step strategy is a versatile strategy used to impart surface functionalities. Despite successful incorporation of numerous functional agents, very little understanding has emerged over the years regarding the mechanism behind their coassembly and codeposition. Here, we employed six different ultrahigh molecular weight hydrophilic polymers of diverse chemistry and architecture and three catecholamines and a polyphenol for investigating the coassembly and codeposition process. The chemistry of the polymers is found to influence the strength of the interaction between the polycatecholamine and the hydrophilic polymers, thus playing an important role in the aqueous self-assembly in solution to nanoaggregates, its formation kinetics, steric stabilization, and surface deposition. Additionally, the codeposition method was used as a platform for developing antifouling and antibiofilm coatings and evaluating their efficiency. Both the chemistry of hydrophilic polymers and the type of the catecholamine influence the antibiofilm properties of the coating. Our studies demonstrated that significant opportunities exist to further define the surface coating process and polycatecholamine self-assembly process by altering the polycatecholamine-hydrophilic polymer interactions.

Impact of Polydopamine Nanoparticle Surface Pattern and Roughness on Interactions with Poly(ethylene glycol) in Aqueous Solution: A Multiscale Modeling and Simulation Study.

A significant research effort in the past few years has been devoted to engineering synthetic mimics of naturally occurring eumelanin. One such effort has involved the assembly of oligomers of 5,6-dihydroxyindole (DHI), a synthetic precursor of polydopamine (PDA), into melanin-mimicking nanoparticles for use in a variety of applications with desired optical, photonic, thermal, and electrical properties. In many of these applications, the PDA nanoparticles are mixed with other polymers or oligomers, thus motivating this specific study to understand how the surface characteristics of the assembled PDA-nanoparticles affect their interaction with poly(ethylene glycol) (PEG) chains in aqueous solution. We use molecular dynamics (MD) simulations to study the interaction of linear 20-mer PEG chains with different PDA-nanoparticles assembled using four types of oligomers of 5,6-DHI: two isomers of 5,6-DHI 2-mers with the monomers bonding either at the 2-2' position (A-type isomer) or 7-7' position (B-type isomer), denoted as A:2-mer and B:2-mer, respectively, and a 4-mer and an 8-mer of B-type chemistry denoted as B:4-mer and B:8-mer, respectively. Using explicit-solvent atomistic MD simulations, we find that PDA-nanoparticle surfaces assembled from B:8-mer exhibit smaller density fluctuations of water molecules and, as a result, are relatively more hydrophilic than the PDA-nanoparticle surfaces assembled from A:2-mer, B:2-mer, and B:4-mer. The surface composition of PDA-nanoparticles assembled from A:2-mer contains relatively fewer hydroxyl (-OH) groups compared to PDA-nanoparticles assembled from a B:2-mer, B:4-mer, or B:8-mer, yet the sample of PEG chains show more collapsed and adsorbed conformations on A:2-mer nanoparticles' surface. To explain the atomistically observed behavior of PEG chains on the nanoparticles' surfaces, we use coarse-grained (CG) MD simulations and explain the roles of the pattern formed by the attractive sites (e.g.,-OH groups) exposed on the surface and the roughness of the surface on interactions with a genric PEG-like copolymer chain. By comparing atomistic and CG MD simulation results, we confirm that the -OH groups' pattern on the surface of the PDA-nanoparticle assembled from A:2-mer is patchier than the random or string-like patterns on the PDA-nanoparticle assembled from B:2-mer, B:4-mer, or B:8-mer, and it is this -OH groups' surface pattern that dictates the PEG chain conformations and adsorption on the PDA-nanoparticle surface. Overall, these results guide the design of chemically and physically heterogeneous nanoparticle surfaces for the desired polymer interaction and conformations.

Hierarchical Amine-Functionalized ZIF-8 Mixed-Matrix Membranes with an Engineered Interface and Transport Pathway for Efficient Gas Separation

Herein, we report a facile approach to engineer a metal–organic framework (MOF) structure and polymer–MOF interface in a mixed-matrix membrane (MMM) to achieve high gas separation performance and plasticization resistance. Hierarchical ZIF-8-NH2 nanoparticles with a relatively small concentration of amine functionality (∼5 mol %) were prepared. The hierarchical MOF structure provides fast molecular transport pathways because of the MOF–MOF percolated network and high MOF packing density. Moreover, the interfacial interaction between the 6FDA-DAM:DABA(3:2) polyimide and the amine-functionalized MOF enhances the chemical stability and polymer chain rigidity. The hierarchical ZIF-8-NH2 MMMs exhibit a significantly improved gas permeability because of the accelerated molecular diffusion through the direction-oriented MOF pathway. For example, the ZIF-8-NH2 30 wt % MMM showed ∼6- and ∼4-fold enhanced H2 (761.7 Barrer) and CO2 (552.4 Barrer) permeabilities when compared to those of a pure polyimide film, with an H2/CH4 selectivity of 35.7 and CO2/CH4 selectivity of 25.9. Additionally, the MMM exhibits an improved plasticization resistance due to the connected MOF structure and MOF–polymer interaction. This strategy provides remarkable insight into the rational design of the polymer and MOF constituents in the MMM system.

The unusual rheological behaviors of poly(acrylamide-co-acrylonitrile)s with UCST features in aqueous solutions

The polymer with the upper critical solution temperature (UCST) in aqueous solution exhibits temperature sensitivity, whose solvation is more sensitive to temperature than that of ordinary polymer in aqueous solution. However, the rheological behavior of UCST-type polymer in aqueous solution with temperature has not been definitively concluded. In this work, the rheological behaviors of poly(acrylamide-co-acrylonitrile) with UCST features in dilute and semi-dilute aqueous solutions at different temperatures were investigated. Our results showed that the viscosities of both the dilute and semi-dilute aqueous solutions increase when temperature rises. To understand this unusual observation of rheological behavior, related dynamic and thermodynamic properties were studied. The intrinsic viscosity ([η]), viscometric radius (Rη), hydrodynamic size (Rh), friction coefficient (ζ), relaxation time(τ) and correlation length(▪) of the solution were quantitatively investigated at different temperatures. Based on experimental data, the theta temperature was determined, and the change rate of excluded volume with temperature was also obtained. The interaction parameter χ and intermolecular interactions of polymer were analyzed at different temperatures. The unusual rheological behavior of UCST-type polymer in aqueous solution is analyzed according to classical polymer physics based upon our experimental observations. We envisage that this work will provide an insight and benefit for the design of thermoviscosifying UCST-type polymers which is urgently needed in both petroleum and chemical industries.