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Polymers
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Mechanics of Emerging Polymers with Unprecedented Networks
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Mechanics of Emerging Polymers with Unprecedented Networks

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Physics and Theory".

Deadline for manuscript submissions: closed (15 June 2018) | Viewed by 78051

Special Issue Editors

Dr. Ying Li

E-Mail Website
Guest Editor
Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA
Interests: multiscale modeling; computational materials design; mechanics and physics of soft matter; materials by design
Special Issues, Collections and Topics in MDPI journals
Dr. Qiming Wang

E-Mail Website
Guest Editor
Sonny Astani Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA, USA
Interests: mechanics of materials and structures; constitutive modeling; multiphysics coupling; mechanical instability; fracture and adhesion; electromagnetoactive polymers; mechanochromic materials; stimuli-sensitive hydrogels
Special Issues, Collections and Topics in MDPI journals
Dr. Franck Vernerey

E-Mail Website
Guest Editor
Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA
Interests: solid mechanics; soft matter; theoretical and computational mechanics; dynamic and active networks
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Polymeric materials have been extensively used in aerospace, petrochemical, environment and energy industries. Comparing to classical metallic materials, polymers demonstrate some interesting and unique mechanical properties. In particular, polymers with dynamic bonds have shown great capability in adapting their environment and exhibiting unprecedented properties, such as high-toughness, self-healing, and mechanochromism. In this emerging field, dynamic bonds, including reversible covalent bonds and non-covalent bonds (such as ionic bonds, hydrogen bonds, metal–ligand coordinations and hydrophobic interactions), have been utilized to program macroscopic responses of polymers by regulating their molecular architectures. From a fundamental perspective, development of predictive models that connect the macroscopic mechanical behavior of these polymers to the corresponding molecular mechanisms is a challenging endeavor. This Special Issue will address recent experimental, computational and theoretical advances in this burgeoning field. Topics of particular interest include: (a) tough hydrogels and elastomers; (b) self-healing polymers; (c) mechanochemically responsive polymers; (d) covalently adaptable polymers; (e) photoresponsive polymers; and (f) electromagnetically responsive polymers. The goal of this Special Issue is to bring together researchers with a variety of backgrounds to exchange ideas, identify and address grand challenges, and to initiate new areas of research.

Dr. Ying Li
Dr. Qiming Wang
Dr. Franck Vernerey
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • polymers
    mechanics
  • dynamic bond
  • dynamic network
  • hydrogels
  • elastomers
  • self-healing polymers
  • mechanochemically responsive polymers
  • covalently adaptable polymers
  • photoresponsive polymers
  • electromagnetically responsive polymers

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Published Papers (15 papers)

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Research

12 pages, 2239 KiB  
Article
Tough and Self-Healable Nanocomposite Hydrogels for Repeatable Water Treatment
by Kunhao Yu, Di Wang and Qiming Wang
Polymers 2018, 10(8), 880; https://doi.org/10.3390/polym10080880 - 07 Aug 2018
Cited by 24 | Viewed by 4328
Abstract
Nanomaterials with ultrahigh specific surface areas are promising adsorbents for water-pollutants such as dyes and heavy metal ions. However, an ongoing challenge is that the dispersed nanomaterials can easily flow into the water stream and induce secondary pollution. To address this challenge, we [...] Read more.
Nanomaterials with ultrahigh specific surface areas are promising adsorbents for water-pollutants such as dyes and heavy metal ions. However, an ongoing challenge is that the dispersed nanomaterials can easily flow into the water stream and induce secondary pollution. To address this challenge, we employed nanomaterials to bridge hydrogel networks to form a nanocomposite hydrogel as an alternative water-pollutant adsorbent. While most of the existing hydrogels that are used to treat wastewater are weak and non-healable, we present a tough TiO2 nanocomposite hydrogel that can be activated by ultraviolet (UV) light to demonstrate highly efficient self-healing, heavy metal adsorption, and repeatable dye degradation. The high toughness of the nanocomposite hydrogel is induced by the sequential detachment of polymer chains from the nanoparticle crosslinkers to dissipate the stored strain energy within the polymer network. The self-healing behavior is enabled by the UV-assisted rebinding of the reversible bonds between the polymer chains and nanoparticle surfaces. Also, the UV-induced free radicals on the TiO2 nanoparticle can facilitate the binding of heavy metal ions and repeated degradation of dye molecules. We expect this self-healable, photo-responsive, tough hydrogel to open various avenues for resilient and reusable wastewater treatment materials. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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17 pages, 2600 KiB  
Article
The Chain Distribution Tensor: Linking Nonlinear Rheology and Chain Anisotropy in Transient Polymers
by Shankar Lalitha Sridhar and Franck J. Vernerey
Polymers 2018, 10(8), 848; https://doi.org/10.3390/polym10080848 - 01 Aug 2018
Cited by 20 | Viewed by 5523
Abstract
Transient polymer networks are ubiquitous in natural and engineered materials and contain cross-links that can reversibly break and re-form. The dynamic nature of these bonds allows for interesting mechanical behavior, some of which include nonlinear rheological phenomena such as shear thickening and shear [...] Read more.
Transient polymer networks are ubiquitous in natural and engineered materials and contain cross-links that can reversibly break and re-form. The dynamic nature of these bonds allows for interesting mechanical behavior, some of which include nonlinear rheological phenomena such as shear thickening and shear thinning. Specifically, physically cross-linked networks with reversible bonds are typically observed to have viscosities that depend nonlinearly on shear rate and can be characterized by three flow regimes. In slow shear, they behave like Newtonian fluids with a constant viscosity. With further increase in shear rate, the viscosity increases nonlinearly to subsequently reach a maximum value at the critical shear rate. At this point, network fracture occurs followed by a reduction in viscosity (shear-thinning) with a further increase in shear rate. The underlying mechanism of shear thickening in this process is still unclear with debates between a conversion of intra-chain to inter-chain cross-linking and nonlinear chain stretch under high tension. In this paper, we provide a new framework to describe the nonlinear rheology of transient polymer networks with the so-called chain distribution tensor using recent advances from the transient network theory. This tensor contains quantitatively and statistical information of the chain alignment and possible anisotropy that affect network behavior and mechanics. We investigate shear thickening as a primary result of non-Gaussian chain behavior and derive a relationship for the nonlinear viscosity in terms of the non-dimensional Weissenberg number. We further address the criterion for network fracture at the critical shear rate by introducing a critical chain force when bond dissociation is suddenly accelerated. Finally, we discuss the role of cross-linker density on viscosity using a “sticky” reptation mechanism in the context of previous studies on metallo-supramolecular networks with reversible cross-linkers. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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15 pages, 3200 KiB  
Article
Characterization and Research on Mechanical Properties of Bamboo Plastic Composites
by Yu Xian, Dongjuan Ma, Cuicui Wang, Ge Wang, Leemiller Smith and Haitao Cheng
Polymers 2018, 10(8), 814; https://doi.org/10.3390/polym10080814 - 25 Jul 2018
Cited by 12 | Viewed by 4607
Abstract
The focus of this study was to observe the mechanical properties of bamboo plastic composites (BPCs) with bamboo pulp fiber (BPF) or white mud (WM). The essential work of fracture (EWF) methodology was used to characterize the impact toughness of BPCs. The results [...] Read more.
The focus of this study was to observe the mechanical properties of bamboo plastic composites (BPCs) with bamboo pulp fiber (BPF) or white mud (WM). The essential work of fracture (EWF) methodology was used to characterize the impact toughness of BPCs. The results revealed an increase in flexural, tensile and impact properties, when adding the BPF in the BPCs. While the flexural properties of WM-reinforced BPCs revealed increasing, there was a decrease in tensile and impact strength. In an impact strength analysis study, BPF-filled BPCs showed excellent impact property over WM-filled BPCs; scanning electron microscopy (SEM) helps to explain impact fracture behavior of BPCs. EWF analysis of impact results showed that the specific essential work of fracture (we) increased significantly with the amount of BPF used in BPCs but decreased with the increase of WM in the BPCs. There was similar variation for the non-essential plastic work (βwp) of BPCs. This result indicates that the fracture initiation and fracture propagation of BPCs are different. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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15 pages, 6458 KiB  
Article
Rheology, Non-Isothermal Crystallization Behavior, Mechanical and Thermal Properties of PMMA-Modified Carbon Fiber-Reinforced Poly(Ethylene Terephthalate) Composites
by Guoliang Lin, Dongwei Li, Minyi Liu, Xiaoyi Zhang and Yuying Zheng
Polymers 2018, 10(6), 594; https://doi.org/10.3390/polym10060594 - 29 May 2018
Cited by 12 | Viewed by 3629
Abstract
Poly(ethylene terephthalate) (PET) composites containing carbon fiber (CF) or polymethyl methacrylate (PMMA)-grafted carbon fiber (PMMA-g-CF) were prepared by melt compounding. The rheology, non-isothermal crystallization behavior, and mechanical and thermal properties of pure PET, PET/CF and PET/PMMA-g-CF composites were investigated. The results show that [...] Read more.
Poly(ethylene terephthalate) (PET) composites containing carbon fiber (CF) or polymethyl methacrylate (PMMA)-grafted carbon fiber (PMMA-g-CF) were prepared by melt compounding. The rheology, non-isothermal crystallization behavior, and mechanical and thermal properties of pure PET, PET/CF and PET/PMMA-g-CF composites were investigated. The results show that the addition of CF or PMMA-g-CF significantly increases the storage modulus (G′), loss modulus (G″), and complex viscosity (η*) of the composites at low frequency. The Cole-Cole plots confirm that the surface modification of CF leads to a better interaction between the CF and PET, and then decreases the heterogeneity of the polymeric systems, which is confirmed by the SEM observation on the tensile fracture surface of the composites. Non-isothermal crystallization analysis shows that the CF or PMMA-g-CF could serve as nucleation agent to accelerate the crystallization rate of the composites, and the effect of PMMA-g-CF is stronger than that of CF. The result is further confirmed by the analysis of the crystallization activation energy for all composites calculated by the Flynn-Wall-Ozawa method. Moreover, the tensile and impact strength and the thermal stability of the composites are improved by CF, while the incorporation of PMMA-g-CF further enhances the tensile and impact strength and thermal stability. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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11 pages, 1997 KiB  
Article
Hyaluronan-Chondroitin Sulfate Anomalous Crosslinking Due to Temperature Changes
by Tomasz Andrysiak, Piotr Bełdowski, Jacek Siódmiak, Piotr Weber and Damian Ledziński
Polymers 2018, 10(5), 560; https://doi.org/10.3390/polym10050560 - 22 May 2018
Cited by 10 | Viewed by 5055
Abstract
Glycosaminoglycans are a wide class of biopolymers showing great lubricating properties due to their structure and high affinity to water. Two of them, hyaluronic acid and chondroitin sulfate, play an important role in articular cartilage lubrication. In this work, we present results of [...] Read more.
Glycosaminoglycans are a wide class of biopolymers showing great lubricating properties due to their structure and high affinity to water. Two of them, hyaluronic acid and chondroitin sulfate, play an important role in articular cartilage lubrication. In this work, we present results of the all-atom molecular dynamics simulations of both molecules placed in water-based solution. To mimic changes of the physiological conditions, especially temperature, of the synovial fluid in joints under successive load (e.g., walking, jogging, jumping), simulations have been performed at different physiological temperatures in the range of 300 to 320 Kelvin (normal intra-articular temperature is 305 K). The stability of the biopolymeric network at equilibrium (isothermal and isobaric) conditions has been studied. To understand the process of physical crosslinking, the dynamics of intra- and intermolecular hydrogen bonds forming and breaking have been studied. The results show that following addition of chondroitin sulfate, hyaluronan creates more intermolecular hydrogen bonds than when in homogeneous solution. The presence of chondroitin in a hyaluronan network is beneficial as it may increase its stability. Presented data show hyaluronic acid and chondroitin sulfate as viscosity modifiers related to their crosslinking properties in different physicochemical conditions. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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25 pages, 4064 KiB  
Article
Optimization of Mechanical Properties for Polyoxymethylene/Glass Fiber/Polytetrafluoroethylene Composites Using Response Surface Methodology
by Jasbir Singh Kunnan Singh, Yern Chee Ching, Luqman Chuah Abdullah, Kuan Yong Ching, Shaifulazuar Razali and Seng Neon Gan
Polymers 2018, 10(3), 338; https://doi.org/10.3390/polym10030338 - 20 Mar 2018
Cited by 28 | Viewed by 6044
Abstract
This paper investigated the effects of polytetrafluoroethylene (PTFE) micro-particles on mechanical properties of polyoxymethylene (POM) composites. Since PTFE is immiscible with most polymers, the surface was etched using sodium naphthalene salt in tetrahydrofuran to increase its surface energy. The effects of two variables, [...] Read more.
This paper investigated the effects of polytetrafluoroethylene (PTFE) micro-particles on mechanical properties of polyoxymethylene (POM) composites. Since PTFE is immiscible with most polymers, the surface was etched using sodium naphthalene salt in tetrahydrofuran to increase its surface energy. The effects of two variables, namely PTFE content and PTFE etch time, on the mechanical properties of the composite were studied. Experiments were designed in accordance to response surface methodology (RSM) using central composite design (CCD). Samples were prepared with different compositions of PTFE (1.7, 4.0, 9.5, 15.0, or 17.3 wt %) at different PTFE etch times (2.9, 5.0, 10.0, 15.0, or 17.1 min). Four mechanical properties of the POM/GF/PTFE composites, that is, strength, stiffness, toughness, and hardness, were characterized as a function of two studied variables. The dependency of these mechanical properties on the PTFE etch conditions was analyzed using analysis of variance (ANOVA). Overall desirability, D global index, was computed based on the combination of these mechanical properties for POM/GF/PTFE composites. The D global index was found to be 87.5%, when PTFE content and PTFE etch time were 6.5% and 10 min, respectively. Good correlation between experimental and RSM models was obtained using normal probability plots. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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10 pages, 2066 KiB  
Article
Mechanical Properties of Rice Husk Biochar Reinforced High Density Polyethylene Composites
by Qingfa Zhang, Weiming Yi, Zhihe Li, Lihong Wang and Hongzhen Cai
Polymers 2018, 10(3), 286; https://doi.org/10.3390/polym10030286 - 08 Mar 2018
Cited by 72 | Viewed by 8623
Abstract
Rice husk biochar was utilized to reinforce high-density polyethylene (HDPE) and to prepare biochar/plastic composites (BPC) by the extrusion method. Morphologies, non-isothermal crystallization behavior, and mechanical properties of the composites were investigated. The SEM (scanning electron microscope) showed that HDPE was embedded into [...] Read more.
Rice husk biochar was utilized to reinforce high-density polyethylene (HDPE) and to prepare biochar/plastic composites (BPC) by the extrusion method. Morphologies, non-isothermal crystallization behavior, and mechanical properties of the composites were investigated. The SEM (scanning electron microscope) showed that HDPE was embedded into the holes of the rice husk biochar. The DSC (differential scanning calorimeter) showed that biochar could reduce the crystallization rate and the higher the content of rice husk biochar, the slower the crystallization rate. Significantly, the bending and tensile strength of BPC could reach 53.7 and 20 MPa, far beyond WPC (wood plastic composites). With the increase of filler content, BPC were still stronger than WPC, although the impact strength of BPC and WPC all showed a general decline in the trend. The strong interaction was achieved by the utilization of rice husk biochar to reinforce HDPE. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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12 pages, 4110 KiB  
Article
Morphological Structure, Rheological Behavior, Mechanical Properties and Sound Insulation Performance of Thermoplastic Rubber Composites Reinforced by Different Inorganic Fillers
by Yanpei Fei, Wei Fang, Mingqiang Zhong, Jiangming Jin, Pin Fan, Jingtao Yang, Zhengdong Fei, Feng Chen and Tairong Kuang
Polymers 2018, 10(3), 276; https://doi.org/10.3390/polym10030276 - 07 Mar 2018
Cited by 37 | Viewed by 6614
Abstract
The application area of a sound insulation material is highly dependent on the technology adopted for its processing. In this study, thermoplastic rubber (TPR, polypropylene/ethylene propylene diene monomer) composites were simply prepared via an extrusion method. Two microscale particles, CaCO3 and hollow [...] Read more.
The application area of a sound insulation material is highly dependent on the technology adopted for its processing. In this study, thermoplastic rubber (TPR, polypropylene/ethylene propylene diene monomer) composites were simply prepared via an extrusion method. Two microscale particles, CaCO3 and hollow glass microspheres (HGW) were chosen to not only enhance the sound insulation but also reinforced the mechanical properties. Meanwhile, the processing capability of composites was confirmed. SEM images showed that the CaCO3 was uniformly dispersed in TPR matrix with ~3 μm scale aggregates, while the HGM was slightly aggregated to ~13 μm scale. The heterogeneous dispersion of micro-scale fillers strongly affected the sound transmission loss (STL) value of composites. The STL values of TPR composites with 40 wt % CaCO3 and 20 wt % HGM composites were about 12 dB and 7 dB higher than that of pure TPR sample, respectively. The improved sound insulation performances of the composites have been attributed to the enhanced reflection and dissipate sound energy in the heterogeneous composite. Moreover, the mechanical properties were also enhanced. The discontinued sound impedance and reinforced stiffness were considered as crucial for the sound insulation. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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11 pages, 4288 KiB  
Article
The Anomalies of Hyaluronan Structures in Presence of Surface Active Phospholipids—Molecular Mass Dependence
by Piotr Bełdowski, Tomasz Andrysiak, Aleksandra Mreła, Zenon Pawlak, Wayne K. Augé II and Adam Gadomski
Polymers 2018, 10(3), 273; https://doi.org/10.3390/polym10030273 - 06 Mar 2018
Cited by 8 | Viewed by 3608
Abstract
Interactions between hyaluronan (A-) and phospholipids play a key role in many systems in the human body. One example is the articular cartilage system, where the synergistic effect of such interactions supports nanoscale lubrication. A molecular dynamics simulation has been performed to understand [...] Read more.
Interactions between hyaluronan (A-) and phospholipids play a key role in many systems in the human body. One example is the articular cartilage system, where the synergistic effect of such interactions supports nanoscale lubrication. A molecular dynamics simulation has been performed to understand the process of formation of hydrogen bonds inside the hyaluronan network, both in the presence and absence of phospholipids. Additionally, the effect of the molecular mass of (A-) was analyzed. The main finding of this work is a robust demonstration of the optimal parameters (H-bond energy, molecular mass) influencing the facilitated lubrication mechanism of the articular cartilage system. Simulation results show that the presence of phospholipids has the greatest influence on hyaluronan at low molecular mass. We also show the specific sites of H-bonding between chains. Simulation results can help to understand how hyaluronan and phospholipids interact at several levels of articular cartilage system functioning. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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12 pages, 2821 KiB  
Article
Humidity Induces Changes in the Dimensions of Hydrogel-Coated Wool Yarns
by Lanlan Wang, Artur Cavaco-Paulo, Bo Xu and Madalena Martins
Polymers 2018, 10(3), 260; https://doi.org/10.3390/polym10030260 - 02 Mar 2018
Cited by 9 | Viewed by 4771
Abstract
Polymeric hydrogel based on acrylic acid (AA) and N,N-dimethylacrylamide (DMAA) was prepared by photopolymerization reaction, using nano-alumina as the inorganic crosslinker. Hydrogel-coated wool yarns determine their dimensional changes under humidity conditions. Surface morphology of the hydrogel-coated wool yarns was carried [...] Read more.
Polymeric hydrogel based on acrylic acid (AA) and N,N-dimethylacrylamide (DMAA) was prepared by photopolymerization reaction, using nano-alumina as the inorganic crosslinker. Hydrogel-coated wool yarns determine their dimensional changes under humidity conditions. Surface morphology of the hydrogel-coated wool yarns was carried out using SEM microscopy. The hydrogel was further characterized by Fourier transformer infrared spectrum (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG). This contribution showed that UV-initiated polymerization coating wool yarns can change the functional properties of wool fibers. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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14 pages, 4148 KiB  
Article
Mechanism Analysis of Selective Adsorption and Specific Recognition by Molecularly Imprinted Polymers of Ginsenoside Re
by Wei Zhang, Qian Li, Jingxiang Cong, Bofeng Wei and Shaoyan Wang
Polymers 2018, 10(2), 216; https://doi.org/10.3390/polym10020216 - 22 Feb 2018
Cited by 19 | Viewed by 4396
Abstract
In this article, the molecularly imprinted polymers (MIPs) of ginsenoside Re (Re) were synthesized by suspension polymerization with Re as the template molecule, methacrylic acid (MAA) as the functional monomers, and ethyl glycol dimethacrylate (EGDMA) as the crosslinker. The MIPs were characterized by [...] Read more.
In this article, the molecularly imprinted polymers (MIPs) of ginsenoside Re (Re) were synthesized by suspension polymerization with Re as the template molecule, methacrylic acid (MAA) as the functional monomers, and ethyl glycol dimethacrylate (EGDMA) as the crosslinker. The MIPs were characterized by Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), and surface porosity detector, and the selective adsorption and specific recognition of MIPs were analyzed using the theory of kinetics and thermodynamics. The experimental results showed that compared with non-imprinted polymers (NIPs), MIPs had a larger specific surface area and special pore structure and that different from the Langmuir model of NIPs, the static adsorption isotherm of MIPs for Re was in good agreement with the Freundlich model based on the two adsorption properties of MIPs. The curves of the adsorption dynamics and the lines of kinetic correlation indicate that there was a fast and selective adsorption equilibrium for Re because of the affinity of MIPs to the template rather than its analogue of ginsenoside Rg1 (Rg1). The study of thermodynamics indicate that the adsorption was controlled by enthalpy and that MIPs had higher enthalpy and entropy than NIPs, which contributed to the specific recognition of MIPs. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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12 pages, 8415 KiB  
Article
Investigation of Mechanical Properties of Silicone/Phosphor Composite Used in Light Emitting Diodes Package
by Yongjun Pan, Fulong Zhu, Jiajie Fan, Jiaquan Tao, Xinxin Lin, Fengren Wang and Lang Shi
Polymers 2018, 10(2), 195; https://doi.org/10.3390/polym10020195 - 15 Feb 2018
Cited by 20 | Viewed by 5049
Abstract
Mass fraction of phosphor in silicone and aging time play important roles in the optics and mechanical performance of the silicone that is used in the light emitting diode (LED) package. In this paper, the mechanical properties of silicone/phosphor composites are investigated experimentally [...] Read more.
Mass fraction of phosphor in silicone and aging time play important roles in the optics and mechanical performance of the silicone that is used in the light emitting diode (LED) package. In this paper, the mechanical properties of silicone/phosphor composites are investigated experimentally by separate tensile and compression tests. Distribution of the phosphors is observed by scanning electron microscopy (SEM) to ensure the homogeneity of the samples. Different loading rates are applied to study the silicone material’s rate-dependent properties. The experimental results of the tensile and compression test show that the Young’s modulus increases with the mass fraction of phosphor in silicone. Longer aging time stiffens the silicone composite and weakens the ductility of the materials. A three-dimensional model used cohesive zone material (CZM) between the interface of the phosphor particles, and matrix silicone is built up to study the degradation mechanism at a micro-scale level. The simulation results indicate that the diameter of particles in silicone also impacts its interface debonding and crack growth. The theoretical results concerning the mass fraction of phosphor are in good agreement with the experiments. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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16 pages, 3134 KiB  
Article
Rheological Behavior of Amino-Functionalized Multi-Walled Carbon Nanotube/Polyacrylonitrile Concentrated Solutions and Crystal Structure of Composite Fibers
by Hailong Zhang, Ling Quan, Fengjun Shi, Changqing Li, Huanqiang Liu and Lianghua Xu
Polymers 2018, 10(2), 186; https://doi.org/10.3390/polym10020186 - 14 Feb 2018
Cited by 24 | Viewed by 5682
Abstract
The rheological behavior of amino-functionalized multi-walled carbon nanotubes (amino-CNTs)/polyacrylonitrile (PAN) concentrated solutions in the dimethyl sulphoxide solvent and the effects of the amino-CNTs on the PAN precursor fibers by wet-spinning method were investigated. The amino-CNT/PAN concentrated solutions prepared by in situ solution polymerization [...] Read more.
The rheological behavior of amino-functionalized multi-walled carbon nanotubes (amino-CNTs)/polyacrylonitrile (PAN) concentrated solutions in the dimethyl sulphoxide solvent and the effects of the amino-CNTs on the PAN precursor fibers by wet-spinning method were investigated. The amino-CNT/PAN concentrated solutions prepared by in situ solution polymerization with homogeneous dispersion of amino-CNTs have higher complex viscosity, storage modulus and loss modulus as compared to the control PAN concentrated solutions containing 22% PAN polymer by mass. The composite fibers with amino-CNTs of 1 wt % have lower degree of crystallization, crystal size and crystal region orientation compared to the control PAN precursor fibers. However, the amino-CNT/PAN composite fibers with diameter of about 10.5 μm exhibit higher mechanical properties than the control PAN precursor fibers with diameter of about 8.0 μm. Differential scanning calorimetry analysis demonstrated that the cyclization reaction in composite fibers have broad exothermic temperature range and low exothermic rate. These results indicate that the addition of amino-CNTs into PAN precursor fibers is beneficial to controlling the process of thermal stabilization and obtaining the higher performance of composite fibers. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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10 pages, 9142 KiB  
Article
Study about Mechanical Property and Machinability of Polyimide
by Shijun Ji, Jilong Yang, Ji Zhao, Yanjuan Hu and Hong Gao
Polymers 2018, 10(2), 173; https://doi.org/10.3390/polym10020173 - 11 Feb 2018
Cited by 19 | Viewed by 4602
Abstract
Polyimide (PI) is a kind of polymer material with properties of high heat-resistance and good mechanical strength. As a special engineering material, it has been widely used in the fields of aviation, nanotechnology, etc. PI has been regarded as one of the most [...] Read more.
Polyimide (PI) is a kind of polymer material with properties of high heat-resistance and good mechanical strength. As a special engineering material, it has been widely used in the fields of aviation, nanotechnology, etc. PI has been regarded as one of the most promising engineering plastics in the future. Therefore, further research must be made on its mechanical properties and machinability of the PI, especially in ultra-precision machining. In this paper, both of the mechanical properties and machinability have been studied respectively. Through the nanoindentation experiment, the nanoindentation hardness and elastic modulus of PI are analyzed. Also, the single point diamond turning (SPDT) experiment is conducted to show that the form accuracy and surface roughness of PI surface can reach a submicron degree in peak-to-valley (PV) and a nanometer scale in surface roughness (Ra) respectively. The results demonstrate that the PI possesses good mechanical properties and machinability. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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11 pages, 14441 KiB  
Article
Influence of Temperature on the Mechanical Properties and Reactive Behavior of Al-PTFE under Quasi-Static Compression
by Huai-Xi Wang, Xiang Fang, Bin Feng, Zhen-Ru Gao, Shuang-Zhang Wu and Yu-Chun Li
Polymers 2018, 10(1), 56; https://doi.org/10.3390/polym10010056 - 10 Jan 2018
Cited by 12 | Viewed by 4703
Abstract
Al-PTFE (aluminum-polytetrafluoroethylene) is a typical kind of Reactive Material (RM), which has a variety of potential applications in weapon systems. In this paper, quasi-static compression experiments were carried out for a pressed and sintered mixture of Al and PTFE powders using a microcomputer-controlled [...] Read more.
Al-PTFE (aluminum-polytetrafluoroethylene) is a typical kind of Reactive Material (RM), which has a variety of potential applications in weapon systems. In this paper, quasi-static compression experiments were carried out for a pressed and sintered mixture of Al and PTFE powders using a microcomputer-controlled electronic universal testing machine. The results show that both the mechanical property and reactive behavior of Al-PTFE are strongly temperature-dependent. The material undergoes a brittle-ductile transition associated with a temperature-induced crystalline phase transformation of the PTFE matrix. At low temperatures (−18, 0, and 16 °C), samples of Al-PTFE failed with shear crack and no reaction was observed. As the temperature increased (22, 35, and 80 °C), Al-PTFE exhibited a high toughness and violent reaction occurred in all of the tested samples. Scanning electron microscope observations showed different fracture mechanisms of the PTFE matrix and the increase in toughness was due to the formation of PTFE fibrils which could dissipate energy and bridge crack plane during plastic deformation. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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