Molecular mechanisms in compatibility and mechanical properties of Polyacrylamide/Polyvinyl alcohol blends

Prediction of the Glass Transition Temperature in Polyethylene Terephthalate/Polyethylene Vanillate (PET/PEV) Blends: A Molecular Dynamics Study

Polyethylene terephthalate (PET) is one of the most common polymers used in industries. However, its accumulation in the environment is a health risk to humans and animals. Polyethylene vanillate (PEV) is a bio-based material with topological, mechanical, and thermal properties similar to PET, allowing it to be used as a PET replacement or blending material. This study aimed to investigate some structural and dynamical properties as well as the estimated glass transition temperature (T_g) of PET/PEV blended polymers by molecular dynamics (MD) simulations with an all-atom force field model. Four blended systems of PET/PEV with different composition ratios (4/1, 3/2, 2/3, and 1/4) were investigated and compared to the parent polymers, PET and PEV. The results show that the polymers with all blended ratios have T_g values around 344–347 K, which are not significantly different from each other and are close to the T_g of PET at 345 K. Among all the ratios, the 3/2 blended polymer showed the highest number of contacting atoms and possible hydrogen bonds between the two chain types. Moreover, the radial distribution results suggested the proper interactions in this system, which indicates that this is the most suitable ratio model for further experimental studies of the PET/PEV polymer blend.

Functional Properties of Two-Component Hydrogel Systems Based on Gelatin and Polyvinyl Alcohol-Experimental Studies Supported by Computational Analysis

The presented research is focused on an investigation of the effect of the addition of polyvinyl alcohol (PVA) to a gelatin-based hydrogel on the functional properties of the resulting material. The main purpose was to experimentally determine and compare the properties of hydrogels differing from the content of PVA in the blend. Subsequently, the utility of these matrices for the production of an immobilized invertase preparation with improved operational stability was examined. We also propose a useful computational tool to predict the properties of the final material depending on the proportions of both components in order to design the feature range of the hydrogel blend desired for a strictly specified immobilization system (of enzyme/carrier type). Based on experimental research, it was found that an increase in the PVA content in gelatin hydrogels contributes to obtaining materials with a visibly higher packaging density, degree of swelling, and water absorption capacity. In the case of hydrolytic degradation and compressive strength, the opposite tendency was observed. The functionality studies of gelatin and gelatin/PVA hydrogels for enzyme immobilization indicate the very promising potential of invertase entrapped in a gelatin/PVA hydrogel matrix as a stable biocatalyst for industrial use. The molecular modeling analysis performed in this work provides qualitative information about the tendencies of the macroscopic parameters observed with the increase in the PVA and insight into the chemical nature of these dependencies.

Effect of amorphous cellulose on the deformation behavior of cellulose composites: molecular dynamics simulation

This study was aimed at predicting and enhancing the properties of the blend, as well as exploring the mechanism, of a polylactic acid (PLA)/amorphous cellulose composite system through molecular characterization. The static properties of the amorphous cellulose/PLA blend model and the mechanical response of the material under uniaxial tension were studied by molecular dynamics simulation to establish the structure-property relationship. PLA and cellulose showed poor miscibility, the change in the compatibility of the mixture can be attributed to the hydrogen bond interaction between the cellulose and PLA functional groups. The radius of gyration, interaction and free volume of the molecular chain in the blend were analyzed. The conformational changes under tensile deformation indicated that the load-bearing role of cellulose in the system was the main reason for increasing the strength of the material. The yield process was considered to be the infiltration of free volume caused by deformation.

Microstructural features, spectroscopic study and thermal analysis of potassium permanganate filled PVA-PVP blend films

Potassium permanganate (KMnO₄) filled polyvinyl alcohol (PVA)-polyvinylpyrrolidone (PVP) polymeric blend films have been prepared by solution casting technique, with filler levels (FL) varying from 0.01 up to 4.70 mass%. The microstructural features, thermal properties and spectroscopic properties of these films have been studied using powder XRD, AFM, Fe-SEM, DSC, TG and FTIR. FTIR spectra for filled samples indicated a major molecular structural modification, involving conversion of the hydroxyl (OH) group into ketones at higher FLs. The bands showed a clear distortion in the wide OH band especially at higher FLs of 3.80 mass% and 4.70 mass%. This is confirmed from the TG scans, whose thermal degradation signature reveals multiple stages of degradation for FL of 2.8 mass%, 3.8 mass% and 4.7 mass%. The DSC, TG and DTA curves revealed that value ofT_gwas found to decrease on addition of filler in the PVA-PVP blend, whereas the thermal stability of the filled samples was found to increase. The XRD results revealed that the incorporation of KMnO₄in PVA-PVP blend made the sample more amorphous. At low FLs, AFM and SEM micrographs show evidence for formation of nano-particles in the host polymeric material only at the lowest FL of 0.01 mass% with uniform dispersion of nano-structures, whereas at moderate FLs, there are micro-structures in the polymeric host, followed by agglomeration of filler induced chemical species as the FL increases beyond 2.8 mass%. Therefore, KMnO₄filled PVA-PVP blend films show desirable properties expected from a good solid polymeric electrolyte, for FLs below 1.5 mass%.

Towards real-life EEG applications: novel superporous hydrogel-based semi-dry EEG electrodes enabling automatically "charge-discharge" electrolyte

A novel polyacrylamide/polyvinyl alcohol superporous hydrogel (PAAm/PVA SPH)-based semi-dry electrode was constructed for capturing EEG signals at the hairy scalp, showing automatically "charge-discharge" electrolyte concept in EEG electrode development. In this regard, PAAm/PVA SPH was polymerized in-situ in the hollow electrode cavity by freezing polymerization, which acted as a dynamic reservoir of electrolyte fluid. The superporous hydrogel can be completely "charged" with electrolyte fluid, such as saline, in just a few seconds and can be "discharged" through a few tiny pillars into the scalp at a desirable rate. In this way, an ideal local skin hydration effect was achieved at electrode-skin contact sites, facilitating the bioelectrical signal pathway and significantly reducing electrode-skin impedance. Moreover, the electrode interface effectively avoids short circuit and inconvenient issues. The results show that the semi-dry electrode displayed low and stable contact impedance, showing non-polarization properties with low off-set potential and negligible potential drift. The average temporal cross-correlation coefficient between the semi-dry and conventional wet electrodes was 0.941. Frequency spectra also showed almost identical responses with anticipated neural electrophysiology responses. Considering prominent advantages such as a rapid setup, robust signal, and user-friendliness, the new concept of semi-dry electrodes shows excellent potential in emerging real-life EEG applications.

Efficient Polymer Pendant Approach toward High Stable Organic Fluorophore for Sensing Ultratrace Hg2+ with Improved Biological Compatibility and Cell Permeability

A convenient and efficient method to eliminate the aggregation effect of organic photoelectric sensing materials and to improve biological compatibility and cell permeability as well was developed by hanging organic fluorophores on a polymer chain, for example, fluorescein fluorophores had been controllably hung on polyacrylamide main chains with a 1:2 stoichiometric ratio by a simple copolymerization strategy. The results showed that introduction of water-soluble bioactive polyacrylamide main chains into fluorescein fluorophores via covalent bonds could effectively improve their optical stability by deteriorating π-π stack and charge-transfer interactions among different fluorophores. More importantly, the resultant materials possessed low toxicity and excellent cell permeability ten times larger than their precursor fluorescein fluorophore, which made it express an especially turn-on fluorescent response to ultratrace Hg²⁺ both in aqueous and living cells by forming stable 5-member-ring complexes with Hg²⁺ with a correlation coefficient of 0.997 and a low detection limit of 4.0 × 10^-10 mol·L^-1. This work provides promising insight into constructing some practical sensing materials for environmentally-friendly biological analyses.

Interfacial Adhesion of Polylactic Acid on Cellulose Surface: A Molecular Dynamics Study

Interfacial bonding and adhesion mechanisms are important in determining the final properties of the polymer composite. Molecular dynamics (MD) simulations have been used to characterize the interfacial structure and adhesion behavior of crystalline cellulose planes in contact with polylactic acid. The structure of the PLA at the interface exhibits a shape that can accommodate the structure of the cellulose surface. The adhesion between the PLA and the cellulose surface is affected by the polarity of the functional groups and the surface roughness. The improved adhesion is primarily due to hydrogen bonds formed between the cellulose and PLA molecular chains. Cellulose planes with higher molecular protrusions and greater surface roughness produce stronger adhesion to PLA due to enhanced hydrogen bonding. This study provides a basic insight into the interfacial mechanisms of PLA and cellulose surfaces at the molecular level.

The Mechanical Properties of Poly (Urea-Formaldehyde) Incorporated with Nano-SiO2 by Molecular Dynamics Simulation

Self-healing materials can promote the sustainable reuse of resources. Poly (urea-formaldehyde) (PUF) microcapsules can be incorporated into dielectric materials for self-healing. However, the mechanical properties of PUF microcapsules need to be improved due to insufficient hardness. In this paper, PUF models incorporated with nano-SiO₂ of different filler concentrations (0, 2.6, 3.7, 5.3, 6.7, 7.9 wt.%) were designed. The density, the fractional free volume, and the mechanical properties of the PUF-SiO₂ models were analyzed at an atomic level based on molecular dynamics simulation. The interfacial interaction model of PUF on the SiO₂ surface was also constructed to further investigate the interaction mechanisms. The results showed that the incorporation of nano-SiO₂ had a significant effect on the mechanical properties of PUF. Density increased, fractional free volume decreased, and mechanical properties of the PUF materials were gradually enhanced with the increase of nano-SiO₂ concentration. This trend was also confirmed by experimental tests. By analyzing the internal mechanism of the PUF–SiO₂ interfacial interaction, it was found that hydrogen bonds play a major role in the interaction between PUF and nano-SiO₂. Moreover, hydrogen bonds can be formed between the polar atoms of the PUF chain and the hydroxyl groups (–OH) as well as O atoms on the surface of SiO₂. Hydrogen bonds interactions are involved in adsorption of PUF chains on the SiO₂ surface, reducing the distance between PUF chains and making the system denser, thus enhancing the mechanical properties of PUF materials.

Evaluating the Effects of Nanosilica on Mechanical and Tribological Properties of Polyvinyl Alcohol/Polyacrylamide Polymer Composites for Artificial Cartilage from an Atomic Level

Due to the superior performances of nanosilica particles, this research has been designed to study their effects on the mechanical and trigological properties of a PVA/PAM polymer composite by a molecular dynamics simulation method. To realize the research objectives mentioned above, the molecular models of amorphous cells and sandwiched friction models for pure polyvinyl alcohol (PVA)/polyacrylamide (PAM) (component weight ratio is 1:1) and PVA/PAM/nanosilica (component weight ratio is 5.75:5.75:1) polymer composites were constructed and simulated, respectively. The simulation results of the mechanical properties show increases about 31.6% in the bulk modulus, 53.1% in the shear modulus, and 50.1% in the Young's modulus by incorporating a nanosilica particle into a pure PVA/PAM polymer composite. Meanwhile, the changes in Cauchy pressure, B/G ratio, and Poisson's ratio values indicate that incorporating a nanosilica particle into pure PVA/PAM weakened the ductility of the composite. Incorporating a nanosilica particle into a pure PVA/PAM composite also showed a decrease about 28.2% in the abrasion rates and relative concentration distributions of polymer molecules in the final friction models. Additionally, the binding energy and the pair correlation functions between a nanosilica particle and the polymer chains in a cubic cell demonstrate that incorporating nanosilica into PVA/PAM polymer composites improves the internal binding strength between different components through the forming hydrogen bonds. As a result, the mechanical and tribological properties of PVA/PAM polymer composites can be enhanced by incorporating nanosilica particles.

Computer simulation for the study of the liquid chromatographic separation of explosive molecules

The application of high performance liquid chromatography (HPLC) to separate explosive chemicals was investigated by molecular dynamics (MD) simulations. The explosive ingredients including NG, RDX, HMX and TNT were assigned as solutes, while methanol (CH₃OH) and acetonitrile (CH₃CN) were assigned as solvents in the solution system. The polymeric-molecular siloxanes (SiC8) and poly-1,2-methylenedioxy-4-propenyl benzene (PISAF) compounds were treated as stationary phase in the simulation. The simulation results showed that the different species of explosive ingredients were separated successfully in the solutions by each of the constructed stationary phase of SiC8 and PISAF after a total simulation time of 12.0 ps approximately, which were consistent with the experimental analysis of HPLC spectra. The origin for the separation was found due to the electrostatic interactions between polymer and explosives.

Triple network hydrogels (TN gels) prepared by a one-pot, two-step method with high mechanical properties

In this work, poly(vinyl alcohol) (PVA) was incorporated into the networks of polyacrylamide/polyacrylic acid (PAM/PAA) to prepare novel PAM/PAA/PVA Triple-network (TN) hydrogels by an in situ polymerization and repeated freezing-thawing (F-T) process. The TN hydrogels have not only high mechanical strength, but also a moderate swelling ability by varying the weight ratio of calcium chloride (CaCl2) and PVA and free shaping. The compressive stress of the as-prepared hydrogels could reach 11 MPa, and the highest stretching stress could reach 0.8 MPa. Upon mechanical loading, the coordination network between PAA and CaCl2 served as sacrificial bonds to efficiently dissipate energy. However, they can reform when the mechanical load is released, resulting from the fast coordination between PAA and Ca2+. Therefore, TN hydrogels have potential application in biomaterials.

Aggregation Behavior of Nano-Silica in Polyvinyl Alcohol/Polyacrylamide Hydrogels Based on Dissipative Particle Dynamics

Due to the aggregation behavior of nano-silica in aqueous solution, the use of nano-silica without surface modification for synthesizing hydrogels is still a challenging task. This paper presents our study on the use of dissipative particle dynamics simulations to discover the aggregation behavior of nano-silica in polyvinyl alcohol (PVA)/polyacrylamide (PAM) blended hydrogels. By simulations, we aimed at investigating the effects of such factors as nano-silica content, polymer component ratio, temperature and shear rate on the aggregation behavior of nano-silica in terms of the mesoscopic morphologies and the relative concentration distribution functions. Our results reveal that the dispersion of nano-silica is seen if the nano-silica content is increased to 1.5%, and the aggregation of nano-silica becomes noticeable in blended hydrogels with an increase in the nano-silica content. This finding agrees well with the experimental results obtained by means of scanning electron microscopy. Furthermore, it is also found that the dispersion of nano-silica becomes more uniform with an increase in PAM content, temperature and shear rate. These findings greatly enrich our understanding of the aggregation behavior of nano-silica in PVA/PAM blended hydrogels.

3D fabrication and characterization of phosphoric acid scaffold with a HA/β-TCP weight ratio of 60:40 for bone tissue engineering applications

A key requirement for three-dimensional printing (3-DP) at room temperature of medical implants depends on the availability of printable and biocompatible binder-powder systems. Different concentration polyvinyl alcohol (PVA) and phosphoric acid solutions were chosen as the binders to make the artificial stent biocompatible with sufficient compressive strength. In order to achieve an optimum balance between the bioceramic powder and binder solution, the biocompatibility and mechanical properties of these artificial stent samples were tested using two kinds of binder solutions. This study demonstrated the printable binder formulation at room temperature for the 3D artificial bone scaffolds. 0.6 wt% PVA solution was ejected easily via inkjet printing, with a supplementation of 0.25 wt% Tween 80 to reduce the surface tension of the polyvinyl alcohol solution. Compared with the polyvinyl alcohol scaffolds, the phosphoric acid scaffolds had better mechanical properties. Though both scaffolds supported the cell proliferation, the absorbance of the polyvinyl alcohol scaffolds was higher than that of the phosphoric acid scaffolds. The artificial stents with a hydroxyapatite/beta-tricalcium phosphate (HA/β-TCP) weight ratios of 60:40 depicted good biocompatibility for both scaffolds. Considering the scaffolds' mechanical and biocompatible properties, the phosphoric acid scaffolds with a HA/β-TCP weight ratio of 60:40 may be the best combination for bone tissue engineering applications.

Structural and water diffusion of poly(acryl amide)/poly(vinyl alcohol) blend films: Experiment and molecular dynamics simulations

To study the effects of composition ratios and temperature on the diffusion of water molecules in PVA/PAM blend films, five simulation models of PVA/PAM with ten water molecules at different composition ratios (4/0, 3/1, 2/2, 1/3, 0/4) were constructed and simulated by using a molecular dynamics (MD) simulation. The diffusion behavior of water molecules in blends were investigated from the aspects of the diffusion coefficient, free volume, pair correlation function (PCF) and trajectories of water molecules, respectively. And the hydrophilicity of blend composite was studied based on the contact angle and equilibrium water content (EWC) of the blend films. The simulation results show that the diffusion coefficient of water molecules and fractional free volume (FFV) of blend membranes increase with the addition of PAM, and a higher temperature can also improve the diffusion of water molecules. Additionally, the analysis of PCFs reveals the main reason why the diffusion coefficient of water in blend system increases with the addition of PAM. The measurement results of contact angle and EWC of blend films indicate that the hydrophilicity of blend films decreases with the addition of PAM, but the EWC of blends increases with the addition of PAM.