Molecular Segments Research Articles

High Water Resistance and Enhanced Mechanical Properties of Bio-Based Waterborne Polyurethane Enabled by in-situ Construction of Interpenetrating Polymer Network

In this study, acrylic acid was used as a neutralizer to prepare bio-based WPU with an interpenetrating polymer network structure by thermally induced free radical emulsion polymerization. The effects of the content of acrylic acid on the properties of the resulting waterborne polyurethane-poly (acrylic acid) (WPU-PAA) dispersion and the films were systematically investigated. The results showed that the cross-linking density of the interpenetrating network polymers was increased and the interlocking structure of the soft and hard phase dislocations in the molecular segments of the double networks was tailored with increasing the content of acrylic acid, leading to enhancement of the mechanical properties and water resistance of WPU-PAA films. Notably, with the increase in content of acrylic acid, the tensile strength, Young’s modulus, and toughness of the WPU-PAA-110 film increased by 3 times, and 8 times, and 2.4 times compared with WPU-PAA-80, respectively. The WPU-PAA-100 film showed the best water resistance, and the water absorption rate at 96 h was only 3.27%. This work provided a new design scheme for constructing bio-based WPU materials with excellent properties.

Preparation and structure–property relationship of flexible aramid films with enhanced strength by introducing asymmetric and symmetric aromatic ether bond structures

The flexible molecular segments and aggregated structures of MAPB–PMIA and PAPB–PMIA endow polymers with soft properties with high extension and low modulus.

Facile preparation of Cross-linked polyester composite rubber with excellent mechanical strength and high toughness by loading adjustable Low-cost clay

Preparing polymeric elastomer materials with high strength, high toughness yet low energy dissipation has been a long-standing challenge. In this work, we report a dual synergistic strengthening strategy, based on building a vulcanized cross-linked network and regulating nano clay loading, for preparing a novel butyl phenyl polyester nano clay composite rubber. The molecular monomers 2-hydroxyethyl acrylate (HEA) and acrylonitrile (AN) were grafted on the rubber molecular chains, which facilitated the optimization of the crosslinking of the flexible segments. Meanwhile, a rigid unit-flexible chain segment network structure is constructed by regulating the grafting of functionally modified ball clay (BC) in the molecular chain segments. This cross-linking and filling structure provides maximum resistance to energy loss and reinforces the mechanical properties of the composite rubber. Experiments confirmed that BC strengthens the intermolecular forces through Si-O bond and Si-N bond on the macromolecular chain. Compared with raw rubber, the composite rubber with BC loading of 20 wt% has a 327.3% increase in tensile strength and a 249.5% increase in toughness, and presents huge advantages in fatigue resistance and environmental stability, yet the BC filler has extremely low cost. This work provides a new insight in creating rubber/nano clay composites with excellent mechanical strength and dynamic properties, showing high potential for industrialization.

Curing Degree Dependence of Dielectric Properties of Bisphenol-A-Based Epoxy Resin Cured With Methyl Hexahydrophthalic Anhydride

The dielectric properties of epoxy resin mainly depend on its microstructures, especially the curing degree. In this article, the reaction process of diglycidyl ether of bisphenol A (DGEBA)/methyl hexahydrophthalic anhydride (MHHPA) system is studied by differential scanning calorimetry, and samples with different curing degrees are prepared by regulating the curing temperature and time. The evolution of microstructure during epoxy resin crosslinking is simulated by molecular dynamics simulation. It is found that the effect of the curing degree on dielectric properties can be attributed to the distribution of polar groups and the mobility of chain segments, while the contribution of free volume is insignificant. With the increase of the curing degree, the epoxy group at the chain end is transformed into an ester group with weaker polarity, as well as the epoxy molecular segments are combined more closely and the mobility of molecules decreases, resulting in an improvement in the dielectric properties of the epoxy resin.

Finite Element Solution for Dynamic Mechanical Parameter Influence on Underwater Sound Absorption of Polyurethane-Based Composite

Underwater noise pollution, mainly emitted by shipping and ocean infrastructure development of human activities, has produced severe environmental impacts on marine species and seabed habitats. In recent years, a polyurethane-based (PU-based) composite with excellent damping performance has been increasingly utilized as underwater sound absorption material by attaching it to equipment surfaces. As one of the key parameters of damping materials, dynamic mechanical parameters are of vital importance to evaluating the viscoelastic damping property and thus influencing the sound absorption performance. Nevertheless, lots of researchers have not checked thoroughly the relationship and the mechanism of the material dynamic mechanical parameters and its sound absorption performance. In this work, a finite element model was fabricated and verified effectively using acoustic pulse tube tests to investigate the aforementioned issues. The influence of the dynamic mechanical parameters on underwater sound absorption performance was systematically studied with the frequency domain to reveal the mechanism and the relationship between damping properties and the sound absorption of the PU-based composite. The results indicate that the internal friction of the molecular segments and the structure stiffness were the two main contributors of the PU-based composite's consumption of sound energy, and the sound absorption peak and the sound absorption coefficient could be clearly changed by adjusting the dynamic mechanical parameters of the composite. This study will provide helpful guidance to develop the fabrication and engineering applications of the PU-based composite with outstanding underwater sound absorption performance.

Target-oriented design of helical nanotube molecules for rolled incommensurate bilayers

Incommensurate double-wall carbon nanotubes give rise to unique stereochemistry originating from twisted stacks of hexagon arrays. However, atomic-level studies on such unique systems have rarely been performed, even though syntheses of molecular segments of carbon nanotubes have been extensively explored. The design of cylindrical molecules with chirality, particularly, in pairs provides synthetic challenges, because relationships between diameters specified with chiral indices and structures of arylene panels have not been investigated in a systematic manner. Here we show that a molecular version of incommensurate double-wall carbon nanotubes can be designed through the development of an atlas for the top-down design of cylindrical molecules. A large-bore cylindrical molecule with a diameter of 1.77 nm was synthesized using a readily available pigment and encapsulated a small-bore cylindrical molecule with a diameter of 1.04 nm. The large- and small-bore molecules possessed helicity in atomic arrangements, and their coaxial assembly proceeded in nonstereoselective manner to give both heterohelical and homohelical combinations.

Preparation of laminated safety glass based on high strength polyurethane film by solution annealing

AbstractCompared with the traditional polyvinyl butyral (PVB) laminated glass, the polyurethane (PU) based laminated glass has the advantages of higher impact strength and longer service life. Thus, aromatic polyurethane films have attracted more attentions in recent years due to their high light transmittance, adhesion and functionality. In this paper, the tensile strength of polyurethane films based on bis(4‐isocyanatocyclohexyl)‐methane (HMDI) have been increased from 27 to 51 MPa and their elongation at break have been increased from 330% to 525% after solvent annealing in toluene. It is attributed to molecular segments with high crystallization and hydrogen bond formation of PU, which are confirmed by FT‐IR and XRD characterization. Based on this, laminated glasses with higher impact strength based on the thermoplastic polyurethane films are constructed successfully.

Pluronic-F127 and Click chemistry-based injectable biodegradable hydrogels with controlled mechanical properties for cell encapsulation

A new class of dual-crosslinked hydrogels comprising thermoresponsive Pluronic-F127 (coded as TIC) and the covalently-linked molecular segment (coded as NIC) forming through the Michael-type addition reaction of vinyl sulfone-modified dextran (Dex-VS) and thiolated-poly(ethylene glycol) was introduced. Dextrans with two different molecular weights were first modified with divinyl sulfone and then thoroughly characterized. Subsequently, the in situ-forming hydrogels with weight ratios of TIC and NIC components varied from 0/100 to 50/50 were prepared with and without chondrocytes. The stiffness of the resultant hydrogels fell in the range of 3.1 to 25.9 kPa. The physicochemical properties of the hydrogels, e.g., pore structure, degradability, and swellability, were thoroughly assessed as a function of incubation time in culture media, alongside their influence on the viability and growth of cells encapsulated in the hydrogels. Interestingly, using a higher molecular weight of Dex-VS altered the physicochemical property of hydrogel and improved cellular activity. The leaching profiles of TIC segments from the hydrogels were also investigated using fluorescently tagged Pluronic-F127. Notably, both TIC and NIC segments concurrently degraded over time. The developed biodegradable hydrogels with controlled mechanical properties had the potential to be used in cartilage tissue engineering and other regenerative medicine applications.

Towards Nematic Phases in Ionic Liquid Crystals - A Simulation Study.

Ionic liquid crystals (ILCs) are soft matter materials with broad liquid crystalline phases and intrinsic electric conductivity. They typically consist of a rod-shaped mesogenic ion and a smaller spherical counter-ion. Their mesomorphic properties can be easily tuned by exchanging the counter ion. ILCs show a strong tendency to form smectic A phases due to the segregation of ionic and the non-ionic molecular segments. Nematic phases are therefore extremely rare in ILCs and the question of why nematic phases are so exceptional in existing ILCs, and how nematic ILCs might be obtained in the future is of vital interest for both the fundamental understanding and the potential applications of ILCs. Here, we present the result of a simulation study, which highlights the crucial role of the location of the ionic charge on the rod-like mesogenic ions in the phase behaviour of ILCs. We find that shifting the charge from the ends towards the centre of the mesogenic ion destabilizes the liquid crystalline state and induces a change from smectic A to nematic phases.

Evolution of Charge Trapping and Insulating Performances of Epoxy Materials Containing Hydrolyzable Chlorine During Hygrothermal Aging

Hydrolyzable chlorine is a well-known residue issued from the synthesis of epoxy resin, which may impart specific dielectric properties. In this work, the changes in distributed energy levels and charge trap depths of the molecule containing such defects are investigated using quantum chemical calculations. These changes are analyzed from the microscopic perspectives of electron energy structure and electron cloud offset. The charge transport and charge injection behavior in epoxy materials before and after the hydrolysis are predicted using the analysis results. The volume resistivities and space charges of epoxy materials with three different hydrolyzable chlorine contents are tested at different hygrothermal aging times, which are consistent with the previous predictions. These results are used to explain the ac breakdown strength of these epoxy materials at different hygrothermal aging times. It is indicated that the structural changes (electronegativity and atomic position changes) of the molecule containing hydrolyzable chlorine before and after hydrolysis change the spatial distribution of electron cloud density between and on valence bonds, and in turn, change the energy levels of different molecular segments. This results in a large increase in the overall electron trap depth and a small decrease in the overall hole trap depth of the molecule after hydrolysis.

Application of Nanocomposite Energy Storage Materials in Green Building Design.

In order to solve the problem of the application of composite phase change heat storage materials in building energy conservation, the author proposes the application of nanocomposite energy storage materials in green building design. Modified carbon nanotubes were prepared by mixed acid oxidation and ball milling, and composited with stearic acid to prepare phase change heat storage materials. Modified carbon nanotubes were prepared by mixed acid oxidation and ball milling and composited with stearic acid to prepare phase change heat storage materials. Experimental results show that acidified carbon nanotubes have a hindering effect on the thermal diffusion of stearic acid molecular segments so that the thermal conductivity of carbon nanotubes added with a mass fraction of 1% is only 1.3 times higher than that of pure stearic acid. Conclusion. Nanocomposite energy storage materials have excellent application prospects in green building design.

Molecular mechanics-based design of high-modulus epoxy to enhance composite compressive properties

The performance of carbon fiber reinforced composites has been shown to be constrained by the low compression to tensile strength ratio, which blocks its lightweight application. Designing and preparing high-strength, high-modulus resins has become a popular direction in the field of synthetic materials and increasing resin modulus has become one of the key goals for improving composite compression properties. This study improves the interactions between molecular segments and reduces chain motility by introducing polar groups into resin molecules and increasing the reactive functionality. Four typical polar epoxy resins with high purity were synthesized, with a modulus of 6500 MPa and a tensile strength of 86 MPa when cured. Hydrogen bonds are detected and the complex process of group changes as a function of temperature is investigated using in-situ IR. The compression properties of the composites made with the newly synthesized resins were significantly improved, which suggests the significance of high-performance resin design in lightweight carbon fiber composite materials.

Preparation of size-tunable sub-200 nm PLGA-based nanoparticles with a wide size range using a microfluidic platform.

The realization of poly (lactic-co-glycolic acid) nanoparticles (PLGA NPs) from laboratory to clinical applications remains slow, partly because of the lack of precise control of each condition in the preparation process and the rich selectivity of nanoparticles with diverse characteristics. Employing PLGA NPs to establish a large range of size-controlled drug delivery systems and achieve size-selective drug delivery targeting remains a challenge for therapeutic development for different diseases. In this study, we employed a microfluidic device to control the size of PLGA NPs. PLGA, poly (ethylene glycol)-methyl ether block poly (lactic-co-glycolide) (PEG-PLGA), and blend (PLGA + PEG-PLGA) NPs were engineered with defined sizes. Blend NPs exhibit the widest size range (40–114 nm) by simply changing the flow rate conditions without changing the precursor (polymer molecular weight, concentration, and chain segment composition). A model hydrophobic drug, paclitaxel (PTX), was encapsulated in the NPs, and the PTX-loaded NPs maintained a large range of controllable NP sizes. Furthermore, size-controlled NPs were used to investigate the effect of particle size of sub-200 nm NPs on tumor cell growth. The 52 nm NPs showed higher cell growth inhibition than 109 nm NPs. Our method allows the preparation of biodegradable NPs with a large size range without changing polymer precursors as well as the nondemanding fluid conditions. In addition, our model can be applied to elucidate the role of particle sizes of sub-200 nm particles in various biomedical applications, which may help develop suitable drugs for different diseases.

Ultra-high-strength self-healing supramolecular polyurethane based on successive loose hydrogen-bonded hard segment structures

Solving the weak toughness and strength of self-healing materials seems to be a mountain that is difficult to get over. Although some studies have reported high-strength self-healing materials, human intervention and long heal time are needed as compensation to self-heal. The balance between mechanical properties and self-healing efficiency is still challenging. Here, a high-strength self-healing supramolecular polyurethane is constructed based on a continuous loose hard segment structure. The polyurethane exhibits a maximum tensile strength greater than 45 MPa, maximum elongation at break of 850 %, and a tear strength of up to 118.776 KJ/m3, a self-healing efficiency of 95 %, which can effectively prolong the service life of the material. Strong soft segments and high-density loose hydrogen bond arrays are the source of strong mechanical strength. The asymmetric alicyclic loose hard segment structure ensures sufficient mobility of the molecular segments to complete hydrogen bond recombination in a short time. At the same time, its research as a conductive polymer matrix has been verified to restore 90 % of the conductivity, showing great application potential in the field of self-healing conductive composite material.

Mechanical Properties of High Temperature Resistant Energy Storage Dielectric Materials and Radiation Scintillation Detection Composite Materials in Bridge Construction

With the rapid development and utilization of energy by human beings, the preparation of high-efficiency energy storage materials has become a current hot spot. This article mainly studies the mechanical properties of high temperature resistant energy storage dielectric materials and radiation scintillation detection composite materials in bridge construction. In this paper, the dispersion conditions of PBI on carbon nanomaterials were optimized, and PBI derivatives with different chemical structures were synthesized to enhance the interface force between them and carbon nanomaterials. By means of physical blending and chemical reaction grafting, the non-covalent modification or covalent modification of the surface of CNTs and graphene by the polymer was realized. In this paper, FTIR can be used to characterize the molecular structure and segment conformation (crystal phase) of PVDF-based polymers. The attenuated total reflection (ATR) mode of the E55 + FRA106 instrument was used to directly test the polymer film. In this paper, MCNP is used to simulate the interaction between Y-rays and crystal, and the structure of the detector probe is designed, including the selection of crystal material, the design of crystal size, and the requirements of structural packaging. A self-made plastic light cone is used for the coupling between the scintillator and the transmission fiber. With the increase of TPU content, the breakdown strength of the composite film showed a trend of first increasing and then decreasing. TPUs with three hardnesses all showed the highest breakdown field strength at a content of 3 vol%. The results show that changing the direct connection between the scintillator and the PMT to the light guide connection can effectively improve the light collection efficiency of the detection system. Under the simulation conditions in this article, the increase is about 30%, which is considerable and has a certain energy resolution capability.

Topological bio-scaling analysis as a universal measure of protein folding.

Scaling relationships for polymeric molecules establish power law dependencies between the number of molecular segments and linear dimensions, such as the radius of gyration. They also establish spatial topological properties of the chains, such as their dimensionality. In the spatial domain, power exponents α = 1 (linear stretched molecule), α = 0.5 (the ideal chain) and α = 0.333 (compact globule) are significant. During folding, the molecule undergoes the transition from the one-dimensional linear to the three-dimensional globular state within a very short time. However, intermediate states with fractional dimensions can be stabilized by modifying the solubility (e.g. by changing the solution temperature). Topological properties, such as dimension, correlate with the interaction energy, and thus by tuning the solubility one can control molecular interaction. We investigate these correlations using the example of a well-studied short model of Trp-cage protein. The radius of gyration is used to estimate the fractal dimension of the chain at different stages of folding. It is expected that the same principle is applicable to much larger molecules and that topological (dimensional) characteristics can provide insights into molecular folding and interactions.

Shape memory performance of PETG 4D printed parts under compression in cold, warm, and hot programming

The main novelty of this paper is the use of poly-ethylene terephthalate glycol (PETG) as a new shape memory polymer with excellent shape memory effect (SME) and printability. In addition, for the first time, the effect of programming temperature on PETG 4D printed samples has been studied. The amorphous nature of the PETG necessitates that molecular entanglements function as net points, which makes the role of programming temperature critical. SME comprehensively was conducted under compression loading for three programming conditions as well as various pre-strains. Significant results were obtained that summarized the gross differences exhibiting that the hot, cold, and warm programmed samples had the highest shape fixity, shape recovery, and stress recovery, respectively. The recovery and fixity ratios fell and rose, respectively, as the programming temperature increased. This effect intensified in hot programmed samples as the applied strain (loading time) expanded. So, the recovery ratio dropped from 68% to 50% by raising the pre-strain from 20% to 80%. The maximum stress recovery was 16 MPa, suggesting the fantastic benefit of warm programming conditions in PETG 4D printed parts. The locking mechanism (recovery force storage) for cold and hot programming is quite different. The dominant mechanism in cold programming is increasing internal energy by potential energy level enhancement. Contrary to this, in hot programming, the entropy reduction applies to the majority of the molecular segments, playing this role. By cooling, the state of the material changes from rubbery to glassy, and with this phase change, the oriented conformation of the deformed polymer chains is maintained under deformation. The results of this research can be used for various applications that require high shape fixity, recovery, or stress recovery.

Mechanism of matrix influencing the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite

This study focuses on the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite (CFRP) unidirectional laminate, and the cryogenic evolution mechanism is discussed from the microstructural perspective of resin free volume and intermolecular forces. The primary transition temperature (147 °C) and the secondary transition temperature (−25 °C) is identified through dynamic mechanical analysis. As the cryogenic condition (−196 °C) is significantly lower than the temperature of main-chain segmental and micro-structure unit motion, the resin molecular segments are frozen, free volume fraction and resin toughness are reduced, thus the brittleness increases. These effects reduce the cryogenic failure strain of CFRP at break by 43.7% compared to room temperature, resulting in a smoother fracture surface morphology. Resin molecules under cryogenic condition have higher packing density, stronger intermolecular forces, which increase the strength and modulus of both resin and CFRP.

Enhance the mechanical properties of epoxy resin reinforced with functionalized graphene oxide nanocomposites prepared by atom transfer radical polymerization

AbstractInspired by the strengthening effect of nanoparticles and the toughening effect of block polymers, we prepared a block polymer filler with graphene oxide (GO) as the main body by surface initiate atom transfer radical polymerization (SI‐ATRP). In the side groups of the main molecular segment of this block polymer, glycidyl methacrylate (GMA) fragment and N‐(3,4‐bis([tert‐butyldimethylsilyl]oxy)phenethyl)methacrylamide (DOPAmTBDMS) fragment can promote dispersion and toughening respectively. The molecular structure was characterized by Fourier transform infrared and X‐ray photoelectron spectroscopy. After the modified GO was added to the epoxy composite, the mechanical properties of the composite could be significantly improved. The toughness of epoxy composites was enhanced by crack deflection of the matrix. When the added amount of modified GO was 0.25 wt%, the flexural strength reached 151 MPa, which was 37.27% higher than pure epoxy composite. The tensile strength and izod impact strength were increased by 50.56% and 69.89%, respectively. These are attributed to the strengthening and toughening effects of GO and the side groups on it. This research had potential application value in the field of resin fillers and in combination with carbon fiber, metal and other materials.

Influence of the Chemical Structure on the Flame Retardant Mechanism and Mechanical Properties of Flame‐Retardant Epoxy Resin Thermosets

AbstractTwo types of isomeric bi‐DOPO（9,10‐dihydro‐9‐oxa‐10‐phosphaphenan threne‐10‐oxide） flame retardants named DHK（6,6’‐((4,6’‐dihydroxy‐[1,1’‐biphenyl]‐3,3’‐diyl)bis(propane‐3,1‐diyl))bis(dibenzo[c,e][1,2] oxaphosphinine 6‐oxide)） and DMG (6,6’‐((6,6’‐dihydroxy‐[1,1’‐biphenyl]‐3,3’‐diyl) bis (propane‐3,1‐diyl)) bis (dibenzo [c,e][1,2] oxaphosphinine 6‐oxide)） are successfully prepared and their flame retardant properties are investigated. Although they have the same phosphorus content, the corresponding thermoset DHK/Epoxy resins (EP) and DMG/EP show different flame retardancy. The flame retardant mechanism is compared by thermal analysis coupled with Fourier transform infrared (TG‐FTIR), residue FTIR, elemental analysis, Raman spectra, scanning electron microscopy (SEM), and cone calorimetry. More phosphorus remains in the residue of DHK/EP which suggests better‐condensed phase flame retardancy than that of DMG/EP. However, DMG shows a better flame inhibition effect than that of DHK. The results of mean square displacement, free volume fraction, and cohesive energy density in molecular dynamics simulations show that the weakening of the movement ability of the DMG/EP molecular segments should be the reason for the increase in toughness. This shows that although flame retardants possess the same composition, their structure will also affect their flame retardant mechanism and properties, which provide a guide for the design and preparation of high‐efficiency flame retardants.