Abstract

INTRODUCTION

COMPUTATIONAL METHODS

DPD Method

Drift-diffusion Model

RESULTS AND DISCUSSION

One-step Quench

Two-step Quench

Comparison with Existing Experimental Observations

CONCLUSIONS

REFERENCES

Abstract

     The mixing morphology control plays a crucial role in photovoltaic power generation, yet this specific effect on device performances remains elusive. Here, we employed computational approaches to delineate the photovoltaic properties of layered heterojunction polymer solar cells with tunable mixing morphologies. One-step quench and two-step quench strategies were proposed to adjust the mixing morphology by thermodynamic and kinetic effects. The computation for the one-step quench revealed that modulating interfacial widths and interfacial roughness could significantly promote the photovoltaic performance of layered heterojunction polymer solar cells. The two-step quench can provide a buffer at a lower temperature before the kinetic quenching, leading to the formation of small-length-scale islands connected to the interface and a further increase in photovoltaic performance. Our discoveries are supported by recent experimental evidence and are anticipated to guide the design of photovoltaic materials with optimal performance.

Introduction

     Polymer solar cells (PSCs) are a kind of potential clean-energy technology, which holds promise for manufacturing lightweight and highly flexible devices such as portable electronic products and building-integrated photovoltaics.[1−5] Although the power conversion efficiency was dramatically improved recently, it has not yet broken through the requirements of commercial markets due to the limitation on the mechanism of charge carrier generation and transport.[6,7] To date, a considerable effort has been devoted to creating novel π-conjugated polymers to improve photovoltaic performance. In contrast, understanding the morphology effect on PSC performance and formulating basic rules that guide morphology optimization need to be further enhanced.

     Optimizing the morphology is indispensable for the successful preparation of PSCs with outstanding performance.[8−12] The PSC performance can be quantitatively correlated with phase purity and Flory-Huggins parameters.[13] Insufficient phase separation in PSCs can lead to performance deteriorations. However, a larger repulsion between donors and acceptors can lead to over-purification of mixed domains and decreased PSC performance.[14] For example, Ade et al. observed that the average power conversion efficiency shows a substantial drop as the composition of the amorphous mixed domains is below the percolation threshold.[15] Ye et al. recently found that such a problem can be resolved by kinetically quenching the mixed domains to an optimal composition close to the percolation threshold.[16] Despite this, fundamental guidelines are still required to optimize PSC performances with optimal mixing morphologies. Combining thermodynamic effects and kinetic controls can assist the design of heterojunctions with varied mixing morphologies.[16] The thermodynamics can drive the phase separation of donors and acceptors in PSCs, and the quench by kinetic control can “lock-in” instantaneous phase-separated morphologies. Recent attention has been paid to the stability of such mixing morphologies.[17−20] However, little is known about the kinetic route to control mixing morphologies and the influence of mixing morphologies on PSC performances. Quantifying the impact of mixing morphology on device performance by developing kinetic control rules is the key to optimizing the heterojunction structure and promoting power conversion efficiency.

Conclusion

     The DPD method, coupled with the drift-diffusion model, was employed to study the mixing morphology effect on the photovoltaic performance of layered heterojunction PSCs. We performed an in silico layer inter-diffusion experiment and designed two quench approaches to regulating the mixing morphology of layered heterojunctions, that is, one-step quench and two-step quench. In the one-step quench, the layered heterojunction with intermediate interfacial width exhibits an optimal photovoltaic performance. We further enhanced the power conversion efficiency of the layered heterojunction by modulating the mixing morphology with a two-step quench method. We discovered that the interfacial width, interfacial roughness, and small-length-scale island structures formed within acceptor- and donor-rich domains combinedly affect the power conversion efficiency. Our work delineates the effect of quenching processes on photovoltaic performance, which could be beneficial to the design and quantitative optimization of active layers.

Abstract

     Synthesis and characterization of new polybutadiene-based polyurethane, graphene quantum dot-MnO2 nanoparticles, and relative nanocomposites were set as the aim of current artwork. For this purpose, a one-pot polymerization approach was employed in preparation of polyurethane through the reaction of amine polyol and toluene diisocyanate (TDI) in presence of DBTDL catalyst. Nanocomposites were synthesized using 1 to 3 incorporation percent of graphene quantum dot-MnO2 nanoparticles in polymer matrix. 1H-NMR and FT-IR spectroscopies confirmed successful synthesis of reaction products including graphene quantum dot-MnO2, polyurethane, and nanocomposites. UV-vis and PL spectrophotometry techniques were applied for achieving optical information of samples. Optical properties of nanocomposites were reserved properly with no great quenching. Thermal stabilities, degradation rates, and thermal characteristics of polyurethane and nanocomposites were investigated using TGA/DTG and DSC analysis. Thermal stability showed direct relationship to nanoparticle content, and 3%wt nanocomposite showed improved thermal behaviour in comparison with pure PU. SEM, XRD, and AFM techniques proved successful nanocomposite synthesis with detecting nanoparticle species and fine nanoparticle dispersion with improved topographic and morphologic characteristics making GQD-MnO2 polyurethane nanocomposites a good candidate for using in optical active and thermal stable coatings.

Introduction

     At a time when socioenvironmental problems of polluting industries are the focus of legislators, the general trend is toward the production of new products from recycled materials, especially waste materials. In the case of polybutadiene, because of most usage in tire production in crosslinked form with sulfur or carbon dioxide, it does not seem so reasonable to pay attention on polybutadiene recycling, at least until recognition of successful separation approaches. However, crude polybutadiene itself faced some issues of processability like high molecular weight, high viscosity, low solubility, and high molding that can be solved for usage in wide speared areas with chain modification [1–4].

      Based on a common belief in green chemistry, it is much more beneficial to produce high-performance polymers form existing low-use ones than new starting monomers. With this respect, chemical modification of polybutadiene chain could make possible goals like raising polymer applications, introducing high-performance polymers, and preventing overproduction of new polymers with optimistic perspective to polybutadiene recycling [5, 6].

     Double-bond scission of polybutadiene chain usually occurs through chain oxidation using hydrogen peroxide, metachloroperbenzoic acid, and dimethyl dioxirane. The molecular weight could be engineered by peracid/double-bond unit ratio [7, 8]. Carbonyl functionalized polybutadiene derived from chain cutting down process is an attractive procedure for polyurea and polyurethane synthesis [9, 10].

Conclusion

     At the beginning of this research, graphene quantum dot was successfully prepared by hydrothermal method and coprecipitation approach in order to have GQD-MnO2 nanoparticle synthesis. GQD and GQD-MnO2 nanoparticle accurate synthesis approved by FT-IR spectroscopy, and optical properties of nanoparticles were investigated with UV-vis and PL techniques. In the following, PU-GQD-MnO2 nanocomposite was prepared through an in situ polymerization reaction of synthesized polyol and TDI diisocyanate in presence of different GQD-MnO2 nanoparticle percent. PU-GQD-MnO2 nanocomposite synthesis was confirmed using FT-IR technique. Also, it was resulted from UV-vis and PL analysis that nanocomposites excellently reserved their optical characteristics. Thermal property improvement of nanocomposites was observed using TGA/DTG and DSC methods. Finally, SEM, XRD, and AFM investigations resulted satisfying nanocomposite synthesis, fine nanoparticle distribution, and morphologic and topographic property improvement in nanocomposites in comparison with pure PU.

Highlights

Abstract

Graphical abstract

Keywords

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusions

Declaration of Competing Interest

Acknowledgement

Declaration of Competing Interest

Data Availability

Appendix A. Supplementary material

References

Abstract

Ring-opening polymerization of benzoxazine monomers is a complex process and various chemical structures including N,O-acetal structures, phenolic Mannich structures and arylamine Mannich structures are formed in polybenzoxazines. To understand the polymerization mechanism, the effects of temperature, time and solvent polarity on the polymerization routes, chemical structures and thermal properties were studied. It was discovered that the N,O-acetal structures and the phenoxy structures can be obtained in a low-polarity solvent like dichloromethane at low temperature (−20 °C) with the aid of PCl5, while the arylamine Mannich structures can be readily generated in polar solvent like N,N-Dimethylformamide at high temperature (>80 °C) in the presence of PCl5. However, the phenolic Mannich structures can be directly formed at high temperature (>180 °C) without any catalysts. Upon prolonging the reaction time or elevating the temperature, the phenoxy structures easily rearranged into the N,O-acetal structures or the arylamine Mannich structures. Further increasing the temperature will cause the arylamine Mannich structures to rearrange into the phenolic Mannich structures and even the phenolic methylene structures. Therefore, both phenoxy structures and N,O-acetal structures showed poor thermal stability; while the arylamine Mannich structures possessed lower initial decomposition temperature but higher char yield compared with the phenolic Mannich structures because of the formation of thermally unstable iminium ions and the anchoring of dangling aniline moieties.

1. Introduction

Polybenzoxazines (PBzs) are formed by the ring-opening polymerization (ROP) of nitrogen and oxygen containing six-membered heterocyclic compounds, 3,4-dihydro-2H-1,3-benzoxazines. They are labeled as a kind of new high-performance thermosetting resins that possess good properties similar to or even higher than phenolic resins and satisfactory processability resembling epoxy resins [1–6]. Polybenzoxazines have aroused high research enthusiasm in academic communities and drawn much attention from industries because of their well-known merits: high strength, high modulus, good thermal stability, flame retardance, good dielectric properties, good dimensional stability, low water uptake, outstanding processability and tremendous design flexibility [7–12]. More recently, polybenzoxaiznes have found many functional applications such as shape memory, self-healing, catalyst support, pollution treatment, super capacitor, CO2 absorption and corrosion prevention [13–19]. Additionally, polybenzoxazines are of great potential in the future application as the fossil resources are decreasing rapidly but the amines and phenols that can be used to synthesize benzoxazine monomers are abundant and reproducible in nature [20–24].

Abstract

Keywords

1. Introduction

2. Experimental methods

3. Results and discussion

4. Conclusions

Declaration of Competing Interest

Acknowledgements

References

Further Reading

Abstract

Strontium silicate nanoparticles were filled in the organic matrix of poly ethylene glycol, polyvinyl alcohol and polyvinyl pyrrolidone polymers. Different weight percentages were selected for the preparation of thin films on the glass substrate using spin coating technique. Prepared polymer nanocomposite films were characterized for their structural analysis and compositional details using powder X-ray diffraction. Amorphous polymer films with intense diffraction peaks at around 43.8° and 73° exhibited the crystalline phase when doped with strontium silicate in polymer blend matrix. Structural information shows the stable existence of crystalline nanoparticles in the polymer matrix. Dielectric and electrical properties of these samples were studied in the frequency range from 100 Hz to 5500 Hz. Dielectric constant decreased with increase in frequency and changed to different values based on the loading of different weight percentage of nanoparticles. With increase in frequency, the dipolar ordering of polymer-polymer decreased and strengthens the polymer-nanoparticles interaction. Polyvinyl alcohol with 3- wt% of poly ethylene glycol showed the low dielectric constant and dielectric loss as less than 0.03 confirms their improved dielectric properties. Hence, this composition can be used as a better insulating polymeric nanodielectric material which finds application in packaging of nanoscale electronic devises to have better electromagnetic shielding.

1. Introduction

There is a huge demand for the Multifunctional materials to meet the fast growing technological needs [1–7] Silicates (SiO2) based nanomaterials (NMs) [8–10] have showed better role in the fields of optoelectronics [11,12], electrical insulation [13,14], advance battery [15,16], and fuel cells [17] applications because of their physical and chemical stability. Further, silicates are cheap and available in enormous; further in nano-regime, different properties exhibited were because of increased surface to volume ratio and the quantum confinement effects. Because of their ability to convert near IR-light into strong visible light [18], they can be used in phosphor based lamps [19], Solar cells [20], Biological imaging and Medical-Dosimetry [21]. Thin films of nanocomposites (NCs) blended with both organic and inorganic compounds are in demand for the effective insulation of small-scale devices during packaging. Inorganic and organic materials based polymer nanocomposite (PNC) films where the polymer matrix filled with NMs significantly changes the strength, morphology etc helps in tailoring the various requirements in the fields of automobile, coatings, packaging materials, electronics and optical devices, aerospace, EMI shielding, drug delivery, sensors, medical and consumer devices etc. [22].

Highlights

Abstract

Keywords

1. Introduction

2. Experimental details

3. Results and discussion

4. Health hazards of ethylene acrylic acid co-polymer

5. Conclusion

Declaration of Competing Interest

Acknowledgements

References

Abstract

Bleached cotton fabric and a water-based polymer coating solution made from ethylene acrylic acid co-polymer which is multifunctional polymer material is used in this experimental study to increase the bending and thermal properties of cotton fabrics. Roller coating and Exhaust methods is used to apply ethylene acrylic acid co-polymer solution on the cotton fabric surface. The coated fabric surface is then cured and dried at a temperature of 60–90 °C using a laboratory oven. The developed fabric samples are then taken for testing for its bending and thermal properties using a fabric stiffness tester and DSC thermal analyzer. The chemical composition and its chemical group finger print analysis is also ascertained using FTIR spectra. The fabric stiffness results of coated fabrics show increased bending properties and the thermal property results from DSC and plotted graphs prove its robustness and resistance to heat. However, Roller coating method seems to be more efficient than exhaust method with respect to the application method employed for coating ethylene acrylic acid co-polymer.

1. Introduction

A water-based polymer coating solution, namely ethylene acrylic acid co-polymer which is multifunctional in nature is coated on bleached cotton fabric with an objective to enhance its bending and thermal properties in this study. The bleached cotton fabric is coated with ethylene acrylic acid by padding and exhaust bath process. In this experimental study, small soft rollers are used for padding the cotton fabrics using ethylene acrylic acid solution. Ethylene acrylic acid is multifunctional co-polymer and is mainly used for textile fabric coatings and many other applications which are of medicinal value, including packaging substrates. This liquid forms a thin film and binds uniformly to the substrate when applied on the surface externally. The liquid also finds many applications in cosmetics and commercial polymer thin film products. The liquid is colorless, with no foul odor and hence is used in many textiles and non-woven textiles. The solution has excellent sealing, adhesion properties coupled with its flexibility and special hardness [1].

Coating formulation and its application on fabrics is a complicated process. Many chemicals and polymer additives are used for coating, since adhesion and durability properties are also important for a coated fabrics. The quality of coating is also determined by the coating method and machinery used for coating. There are many techniques of coating that are used in finishing process. Some of them are done using knife-over-roller method, particularly used for polymer coatings that are solvent based, dip-coating for variety of water-based polymers and fabric treatments [11,12,18]. The chemical formulations are based on the functional properties that is desired and the level of ethylene acrylic acid is also determined keeping the health hazard parameters that ethylene acrylic acid can cause to human skin [13,14].

Abstract

Keywords

1. Introduction

2. Polymeric materials used in AM industry

3. Drug delivery

4. Automotive industry

5. Fashion and fabric industry

6. Impact of using polymeric materials

7. Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

References

Abstract

Polymers are the greatest innovation of the millennium. Due to their low price, ease of manufacture, resistance to water and versatility, polymers have several applications in different domestic and industrial sectors. Digital fabrication technology which is also referred to as 3D printing or additive Manufacturing (AM) is used for creating physical components from a geometrical representation by step-by-step addition of materials. This review paper elaborates on the use of polymers for Rapid Manufacturing. One such material used is Shape Memory Polymers that have been analyzed as Smart Materials (4D Printing Materials). Polymers such as Thermoplastics, elastomers, thermosets, and polymers with integrated fillers, bio-polymers, and polymers blended with biological materials come under the range of other polymeric materials used in AM. The quality evaluations that are performed are based on mechanical properties, part density and temperature stability. Polycarbonates (PC), acrylonitrile butadiene styrene (ABS), polyether-ester ketone (PEEK), polyetherimide (ULTEM) and Nylon are usually utilized polymers in measures which need thermoplastics, or plastics treated by warming to a semi-fluid state and near the softening point.

1. Introduction

Additive manufacturing (AM) is basically 3D printing. Rather than simply using conventional machining techniques which include wastage of materials by removing unwanted fragments, additive manufacturing causes fusion of materials to bind them and create objects. It is comparatively a flexible technology that subtractive manufacturing. Since technology is advancing day by day, new materials are being created to have the right properties that can be applied to the right functions. This review paper mainly focuses on the characteristics of polymeric materials that had been produced and used by the AM industry and the impact on the market of AM. Since several kinds of polymeric materials are available, the manufacturer of the product would prefer the polymer with the optimum conditions for the required purpose. Mechanical properties for example, optimum strength for manufacturing and prototyping is required.

High elasticity is required for garment industry. A high thermal resistivity is required for insulation. Use of light weight polymers are for aerospace applications. Greater amount of ductility is required for wiring and circuitries. Increased toughness is required for supporting materials. An optimum melting point is essential for temperature-dependent environmental factors that are experienced by the polymeric substance used. A proper amount of flexibility is required for better portability of the material. A property called Shape memory has been exhibited by certain polymeric materials which have been discussed in this review which can be used for bridge structures and heat exchangers. Degradability of a material for an allocated period of time is required for the extended use of the material considering fatigue strength of the material. Chemical resistance is an important factor needed for manufacturing of apparatus in chemical industries

Abstract

Keywords

1. Introduction

2. Filler materials

3. Thermal properties of polymer composites

4. Summary

CRediT authorship contribution statement

Declaration of Competing Interest

References

Abstract

Polymer composites are commonly used in industry and are used in various fields such as the aircraft industry, automobile industry, electronic industry and packaging industry, etc. due to their diverse versatility, low cost, light weight, and outstanding chemical consistency. For new technologies, especially in aerospace and aeronautics, thermal properties have become a significant parameter. A reference to a number of research studies is made in this paper and the role of fillers in polymers is studied. The main purpose of this analysis is to identify any possible patterns that control and dictate the thermal properties in polymeric composites.

1. Introduction

There is an increasing demand and development in the field of material science since the last two decades and to fit the requirements of the out-dated products available in the market, material scientists have evolved the polymer composites to outperform their original functions that is being rigid and not buckling. Polymer composite has a large variety of industrial applications due to its many desirable properties ranging from high thermal conductivity to excellent chemical resistance. Polymer composites are mostly anisotropic in nature, these results in them having good mechanical, electrical and thermal properties. Compared to isotropic materials composite materials are much more effective and efficient.

There are many conventional filler materials that are using as a filler material in polymer composites for different applications [1–5]. The ever-alarming concern about the environment can also be put to rest by using the construction, industrial and animal waste as filler which is reinforced with the polymer matrix and enhances the mechanical, physical and thermal properties. However, epoxy polymeric composite despite having so many industrial applications, possess poor mechanical properties. Silica is one of the most ideal inorganic compounds that can be used as reinforcement material along with other inorganic materials. Research also indicates that plant fibres are often used as fillers because of their renewability and high availability. The main sources of natural fibres are both inexhaustible and nonsustainable for example sisal, palm oil and flax. These are then used to make composite material.

Presently the composites that are used in thermal fillers do not provide any electrical properties. Carbon Nanotubes (CNTs) and Graphene Nanotubes (GNTs) have excellent mechanical, thermal and electrical properties. CNTs and GNTs have a strong lattice which gives them good physical and thermal properties [6–8].

With these polymer composite materials integrating into the electronics industry, the developments in thermal properties, especially thermal dissipation heavily influences the performance, reliability and lifetime of these devices. Hence thermal conductivity of these polymer composite materials plays a huge role in a lot of industries. Exhaust heat affects the functioning and the properties of the equipment. A good thermal management system is necessary to protect the equipment from any heat related damages

1- Introduction

2- Experimental

3- Results

4- Discussion

5- Conclusions

References

Abstract

The influence of the microstructure of carbon fibre reinforced polymers (CFRPs) with epoxy matrix (E-CFRP) and nylon matrix (T-CFRP) on the galvanic behaviour of DP590 steel, 6022-aluminium alloy, 1040-steel and AZ31-magnesium alloy was investigated in the GMW14872 solution. The E-CFRP/metal couples were initially more galvanic corrosion resistant, but their galvanic corrosion gradually became more severe than the T-CFRP/metal couples. The effective micro-defects in the surface polymer layer of the CFRP samples critically determined the galvanic corrosion. A detailed surface layer model was proposed, the electrochemical processes through the surface polymer layers during galvanic corrosion were discussed. A better understanding on the microstructure of CFRP determined by composites manufacture process can be obtained.

Introduction

Due to their high strength, high modulus, high corrosion resistance and especially light weight, carbon fibre reinforced polymers (CFRP) have been regarded as a promising material to replace some traditional high strength metals. For example, the use of CFRPs in car body can lead to obvious weight reduction, improved mileage, and eventually reduced carbon dioxide emission [1]. The high strength and corrosion resistance [2–4] have also made CFRPs one of the durable materials in infrastructure, such as the highways, oil and gas production facilities, chemical refineries, water and wastewater treatment systems. They have even been successfully used to strengthen the elements of concrete bridge structures [5]. However, because of the high fabrication cost, most important applications of CFRPs today are mainly limited to military and aerospace industries [6,7]. There is no doubt that CFRPs will find more applications in various industries after they become affordable. Currently, CFRPs are usually used together with metallic engineering materials, such as steels and aluminium alloys.

Fiber Reinforced Polymer (FRP) anchors are an effective method to increase the bond strength and/or ensure load path continuity between FRP materials and the concrete substrate when FRP materials are used as Externally Bonded Reinforcement (EBR) to strengthen and/or repair existing structures. While advances in developing a design methodology have been made on the fiber rupture and concrete cone failure modes for FRP anchors, the FRP-to-FRP bond behavior has received limited research attention. In an effort to develop design equations to calculate FRP-to-FRP bond capacity to be used by engineers, an extensive experimental program was undertaken to characterize the behavior of adhesively bonded FRP-to-FRP lap joints. Two force-based models to calculate the FRP-to-FRP bond capacity were proposed considering the influence of the critical bond length on lap joint behavior. A study to characterize the statistical properties of the experimental data was undertaken, and 95 and 99.87 percentile models were developed based on the statistical distribution of the experimental data set. Main conclusions inferred from the study and ideas for future work are also presented.

Introduction

Externally Bonded Fiber Reinforced Polymer (EBR-FRP) systems are widely used as a method for strengthening of existing structures. FRP materials feature a high strength to weight ratio, which is one of the main advantages of using FRP materials to improve the capacity of existing structures. FRP sheets, consisting of a varying number of fiber tows interweaved together, are one of the most commonly used products in EBR-FRP systems. The sheets are saturated with epoxy resins to form a composite matrix and then adhered to the external surface of the structure, but premature debonding of the FRP sheets from the concrete substrate is one of the main drawbacks of EBR-FRP systems [1]. Another common problem is the obstructions caused by structural or nonstructural elements that prevent the complete wrapping of the structure. Both of these problems limit the FRP design strain that the engineers can use when implementing EBR-FRP systems. The use of FRP anchors has been identified as one possible method to minimize premature FRP-to-concrete debonding [2,3], by transferring load from the FRP sheet directly into the RC structure. FRP anchors (as shown in Fig. 1 [4]) consist of a bundle of fibers splayed in a fan shape and bonded onto the FRP sheet at one end, with the bundle of fibers being embedded into the structure at the other end. FRP anchors typically feature a high concentration of stresses at the section where the fan transitions into the dowel, commonly known as the key portion of the anchor.

1- Introduction

2- Experimental section

3- Results and discussion

4- Conclusion

References

Abstract

A series of hemiphasmidic luminescent liquid crystalline polymers, in which the hemiphasmidic mesogen containing cyanostilbene were linked to the polymethacrylate main-chains via flexible spacers with different lengths, named poly {(Z)-m-(4-(1-cyano-2-(3,4,5-tris(octyloxy)phenyl)vinyl)phenoxy)alkyl methacrylate} (donated as Pr-m, m = 2, 4, 6, 8, 10) were synthesized via free radical polymerization. The phase structures and photophysical properties of Pr-m were investigated in detail by a combination of techniques including differential scanning calorimetry (DSC), polarizing optical microscopy (POM), small-angle X-ray scattering (SAXS), UV–Vis absorption spectra (UV–Vis spectra), photoluminescence spectra (PL spectra) and particle size analyzer. The results revealed that the phase structures of Pr-m transformed from hexagonal columnar phase (m = 2, 4) to smectic A phase (m = 6, 8, 10) with the increasing of flexible spacer length. All of the polymers featured similar AIEE properties, however, the solid state quantum yields of Pr-m decreased with the increasing flexible spacer length, and the solid quantum yields of Pr-m decreased from 8.55 (Pr-2) to 3.71 (Pr-10) with the increasing flexible spacer length.

Introduction

Over the past few decades, liquid crystals (LCs) have been widely studied as a type of functional material [1-9]. A substantial number of LCs have been synthesized, and their physical and chemistry properties have been investigated because the LCs show excellent anisotropic physical properties that can be used in many classical fields, such as stimuli-responsive [10-12], information storage [3, 4], and photomechanical materials [13, 14] etc. Among various applications of LCs, display materials is always the most important application direction of LCs. However, the conventional liquid crystal materials are non-self-luminescent, so that a backlight needs to be added in the liquid crystal display device, which violates the development trend of energy saving and thinning of liquid crystal display device [15]. Therefore, new strategy toward more efficient liquid crystal display device is highly desirable. Luminescent liquid crystals (LLCs), which combines optoelectronic characteristics of luminescent materials with the unique properties of anisotropic fluids, is expected to be an effective way to solve those problems mentioned above. LLCs can overcome the shortcomings of traditional liquid crystals as display materials and enjoy tremendous advantages for the construction of linear or circular polarized light emitting materials [16, 17]. In view of the traditional luminogens, researchers have tried to construct fluorescent liquid crystal materials [18-20]. However, due to the aggregation caused quenching (ACQ) effect, these fluorescent liquid crystal materials usually emit strong fluorescence only in dilute solution while hardly emit light in aggregate state, which makes the preparation of LLCs with excellent performance intractable [21-24].

The flexural properties and impact resistance of the composites with bamboo cellulosic fiber (BF) weight fractions ranging from 4% to 16% was investigated using a universal testing machine and a full instrumented drop weight impact system, respectively. The effect of addition of BF on the flexural properties and impact resistance of the composites was estimated according to max flexural strength, fracture toughness, the contact force, failure pattern and absorbed energy. On the basis of the above results, the impact behaviour of the specimens with 12 wt% BF was examined from the point of view of the impact energy change, the deformation feedback and the absorbed energy. Additionally, impact damage morphology and extent were analyzed using the digital camera and an industrial microfocus computed tomography (CT) system. The results show that BF reinforced cement based composites have higher fracture toughness and impact energy absorbility, the fracture toughness and absorbed energy of the specimens with 4–16 wt% BF are higher by 2.7–45.9 times and 2–24 times than that of the control specimen, respectively. However, due to fibers agglomeration resulted from fibers addition beyond certain content, max flexural strength and impact resistant of the composites no further increase. Furthermore, the different impact energy leads to the different failure patterns and energy absorption modes: at low impact energy, the main energy absorption modes are the debonding between fiber and the matrix; with the increase of the impact energy, the main energy absorption modes are delamination and BF breakage.

Introduction

In recent years, utilization of natural fibers in cement based composites has attracted increasing attentions, due to their many advantages over traditional fibers, such as biodegradability, economical and eco-friendly, etc. [1–5]. And natural fibers have already been considered as potential alternatives to traditional fibers (steel fiber, polymer fibers, glass fiber) [6]. Many studies in previous references have reported the influence of natural fibers on the properties of cement based composites, such as flexural properties [7–9], crack resistance [10,11], durability [12–14] and impact resistance [15–17], and the results show addition of the natural fibers can remarkably improve the toughness of the cementitious materials. Generally, the capacity of absorption energy of the composites is defined as ‘‘toughness”, which is very important for evaluating the service behavior of composite materials under actual conditions when fibers reinforced composites are subjected to static, dynamic or fatigue loading [15]. It is well known that the impact test is a method to evaluate the toughness and ductility of cement based materials [18], while the impact strength is a specific parameter to measure the toughness of materials under dynamic impact loading.