Dean Shi

Graphene-Enabled Superior and Tunable Photomechanical Actuation in Liquid Crystalline Elastomer Nanocomposites.

Programmable photoactuation enabled by graphene: Graphene sheets aligned in liquid crystalline elastomers are capable of absorbing near-infrared light. They thereafter act as nanoheaters and provide thermally conductive pathways to trigger the nematic-to-isotropic transition of elastomers, leading to macroscopic mechanical deformation of nanocomposites. Large strain, high actuation force, high initial sensitivity, fast reversible response, and long cyclability are concurrently achieved in nanocomposites.

Judicious selection of bifunctional molecules to chemically modify graphene for improving nanomechanical and thermal properties of polymer composites

Covalently-functionalised graphene (FG) was successfully obtained by grafting m-isopropenyl-α, α′-dimethyl benzyl isocyanate (m-TMI) to graphene oxide (GO) followed by the chemical and solvothermal reduction of GO. The FG sheets were hydrophobic and stable in polar solvents such as N,N-dimethylformamide. The reactive vinyl-benzyl groups of m-TMI attached to FG copolymerised with methyl methacrylate to produce graphene/poly(methyl methacrylate) (PMMA) composites. The FG sheets were well dispersed in PMMA and formed strong interfacial bonds with the matrix, contributing to large increases in elastic modulus (+72.9%) and indentation hardness (+51.2%) at 1% loading by weight. The incorporation of FG into PMMA changed its elastic-plastic behaviour; hence, a decrease in the plasticity index and an increase in recovery resistance were observed for the resulting composites due to the increased portion related to the elastic work. The onset decomposition temperature and glass transition temperature of neat PMMA increased by 100 °C and 12.7 °C, respectively, by the addition of 1 wt% FG. Herein, in situ copolymerisation of monomers and well-suspended FG promotes the exfoliation of graphene associated with strong chemical bonding with the polymer matrix. This report provides a promising and facile method for fabricating high-performance polymeric composites.

Core/shell rubber toughened polyamide 6: an effective way to get good balance between toughness and yield strength

We have recently shown that by adding 10 to 30 wt% core/shell toughener with a low density polyethylene (LDPE) core and a polybutadiene-g-maleic anhydride (PB-g-MAH) rubber shell to polyamide 6 (PA6), the impact strength of PA6 matrix can be significantly increased by 600–1000%. However, this is at the expense of quite large losses in elastic modulus of 10–25% and tensile yield strength of 30–55%, especially at high core/shell rubber loading (e.g., 30 wt%). In this study, we have redressed this problem by replacing the LDPE core with a polypropylene (PP) core, which has both higher elastic modulus and yield strength than that of LDPE, forming a new core/shell (PP/PB-g-MAH) toughener. When this core/shell toughener containing 5 wt% PB-g-MAH is blended with PA6 in the weight ratios of 10/90 and 30/70, the Izod impact strengths are 390 and 480 J m−1 (which are 330 and 550% increases compared to neat PA6), and the modulus are 2.37 and 2.13 GPa, and yield strength are 60.2 and 54 MPa, respectively (which represent only 6 and 15% loss of modulus, and 5 and 13% decrease in yield strength relative to neat PA6). These improved results confirm that although the decrease of tensile modulus cannot be avoided with increasing impact strength, increasing the elastic modulus and yield strength of the core material in the rigid core/soft rubber shell toughener is an effective way to obtain a good balance of elastic modulus, tensile yield strength and impact strength.

Adsorption Behavior of High Stable Zr-Based MOFs for the Removal of Acid Organic Dye from Water

Zirconium based metal organic frameworks (Zr-MOFs) have become popular in engineering studies due to their high mechanical stability, thermostability and chemical stability. In our work, by using a theoretical kinetic adsorption isotherm, we can exert MOFs to an acid dye adsorption process, experimentally exploring the adsorption of MOFs, their external behavior and internal mechanism. The results indicate their spontaneous and endothermic nature, and the maximum adsorption capacity of this material for acid orange 7 (AO7) could be up to 358 mg·g−1 at 318 K, estimated by the Langmuir isotherm model. This is ascribed to the presence of an open active metal site that significantly intensified the adsorption, by majorly increasing the interaction strength with the adsorbates. Additionally, the enhanced π delocalization and suitable pore size of UiO-66 gave rise to the highest host–guest interaction, which further improves both the adsorption capacity and separation selectivity at low concentrations. Furthermore, the stability of UiO-66 was actually verified for the first time, through comparing the structure of the samples before and after adsorption mainly by Powder X-ray diffraction and thermal gravimetric analysis.

Morphology Control and Stabilization in Immiscible Polypropylene and Polyamide 6 Blends with Organoclay

Abstract In the current study, 70/30 (w/w) polypropylene (PP)/polyamide 6 (PA6)/organoclay ternary blends were prepared by melt mixing in three different blending sequences, i. e., organoclay premixed with PA6 and then mixed with PP (S1 blending sequence), organoclay premixed with PP and then mixed with PA6 (S2 blending sequence), and organoclay, PA6 and PP mixed simultaneously (S3 blending sequence). The effects of organoclay on the phase morphologies, rheological properties and mechanical properties of the blends are examined to reveal the role of organoclay in these immiscible blends. First of all, the dispersion and distribution of organoclay is investigated using XRD and TEM techniques. The organoclay is exfoliated and distributed in the dispersed PA6 phase as well as at the interface between PA6 and PP. Interestingly, more organoclay sheets are observed at the interface when the S2 or S3 blending sequences are utilized. From the SEM images, it is clear that the domain size of the PA6 phase decreases remarkably after introducing organoclay into the PP/PA6 blends. Two different rheological protocols are applied to probe the effect of organoclay on the morphology of the blend by in-situ monitoring the morphological evolution. The rheological results reveal that the phase morphology of the PP/PA6 blends remains relatively stable during shear for a wide range of shear rates when 1.0 wt% organoclay has been added. For the blends with a relatively high clay loading (5.0 wt%), a characteristic and pronounced “plateau” is observed in the low frequency range of the G′-ω curves, which indicates the presence of a percolating network of clay nanosheets. From the mechanical measurements, we find that the tensile strength of the blends increases slightly first and then declines dramatically with increasing organoclay content. Moreover, the elongation at break drops sharply as the organoclay content increases. In summary, it is clear that the organoclay can effectively reduce the domain size of the dispersed PA6 phase and stabilize the phase morphology in shear flow. However, the mechanical properties of the blends are not really improved by clay addition, even though a cocontinuous morphology with a percolated clay network was generated.

Synthesis of amphiphilic poly(cyclooctene)-graft-poly(ethylene glycol) copolymersviaROMP and its surface properties

Macromonomer cyclooctene-poly(ethylene glycol) (cyclooctene-PEG) was first synthesized before being copolymerized with cyclooctene by ring opening metathesis polymerization (ROMP) to obtain an amphiphilic graft copolymer (poly(cyclooctene)-g-PEG) with polycyclooctene as the hydrophobic trunk chain and PEG as hydrophilic side chains. The structure of poly(cyclooctene)-g-PEG copolymer was characterized by FTIR and 1H-NMR. The surface properties of poly(cyclooctene)-g-PEG film were evaluated through water contact angle and X-ray photoelectron spectroscopy (XPS). Water contact angle decreased from 87.7° to 65.8° along with increasing the content of PEG. Protein adsorption results showed that poly(cyclooctene)-g-PEG copolymers had significant effect on preventing bovine serum albumin (BSA) from absorbing onto the polymer surface.

Effect of polyethylene glycol on the antibacterial properties of polyurethane/carbon nanotube electrospun nanofibers

The discovery of antibacterial functions for carbon nanotubes (CNT) has triggered great interest because of the excellent antibacterial properties of CNT. However, there are two obstacles, i.e., cell toxicity and CNT aggregation in a polymer matrix, which greatly limit the antibacterial application of CNT in medical devices. In this study, a facile, cost-effective, time-saving and environmentally friendly approach was proposed to impart the antibacterial property to thermoplastic polyurethane (TPU) electrospun nanofibers with CNT. The ultrasonication technique was explored to in situ anchor the CNT onto the TPU electrospun nanofibers to achieve the bactericidal property. This effectively circumvented the aggregation of CNT when the TPU/CNT electrospun nanofibers were prepared. In addition, the anchor preparation was efficient taking only 10 min to complete and it was also non-toxic because the green solvent ethanol was used as the dispersion solvent. PEG was chemically grafted onto the TPU (TPU-g-PEG) electrospun nanofibers through UV photo-graft polymerization. Although CNT exhibit a good bactericidal property, they could be toxic to human cells. Incorporation of PEG could not only effectively reduce the toxicity of CNT to the human cells but also decrease bacterial attachment. The TPU-g-PEG/CNT nanofibers exhibited excellent hemocompatibility, including suppression of red blood cell adhesion, and lower hemolysis ratios. Importantly, the as-prepared nanofibers had better antibacterial properties due to the bacterial resistance of the grafted PEG and the bactericidal effect of CNT. Our facile approach has significant potential for the infection-resistant wound dressing.

A Si-doped flexible self-supporting comb-like polyethylene glycol copolymer (Si-PEG) film as a polymer electrolyte for an all solid-state lithium-ion battery

Herein, a self-supporting comb-like Si-PEG copolymer with flexible Si–O–C bonds in the main chain and pending short PEG chains as the side chain was synthesized to improve the low temperature performance and overcome the quandary between good mechanical and electrochemical properties of the polymer electrolyte in lithium-ion batteries. The tensile strength of Si-PEG polymer electrolytes (SPH15) is 0.8 MPa at 30 °C, which is high enough to inhibit the growth of lithium dendrites. The ion conductivities of Si-PEG (SPH15) are 1.2 × 10−4 S cm−1 at 30 °C and 3.2 × 10−5 S cm−1 at 10 °C, which are one order of magnitude higher than those for PEG-based copolymer electrolytes without Si doping. The assembled LiFePO4/SPH15/Li half batteries can deliver the specific capacities of 84 mA h g−1 at 10 °C and present 75% capacity retention after 500 charge–discharge cycles at 0.5C.

Highly-effective Flame Retardancy of Poly(lactide) Composite Achieved Through Incorporation of Amorphous Nickel Phosphate Microparticle

In this study, amorphous nickel phosphate (NiPO) was prepared through urea-assisted hydrothermal process. The composition of NiPO was investigated via X-ray photoelectron spectrum (XPS). And the structure of NiPO was characterized by Fourier transform infrared spectrometer (FTIR) and X-ray diffraction measurement (XRD).Then poly(lactide) (PLA) was melt blended with the resulting NiPO to prepare flame retardant PLA composites. The flame retardant property of PLA composites was probed using limiting oxygen index test (LOI), UL-94 vertical burning test (UL-94), cone calorimeter test (CCT). And the thermal combustion property was analyzed through pyrolysis combustion flow calorimeter test (PCFC). In the meantime, the thermal stability of NiPO microparticles and PLA composites was analyzed through thermogravimetric analyzer (TGA) and integrated procedural degradation temperature (IPDT). In the meantime, the melting and crystallization property of PLA composites was investigated through DSC analysis. Results showed that NiHPO3 was the main component of NiPO. PLA composite with only 2 wt.% NiPO powder exhibited excellent flame retardancy (LOI = 27.5% and UL-94 V-0 rating). In the CCT and PCFC test, it showed that HRR of PLA composites was higher in the early stage of combustion and lower in the late stage of combustion than that of pure PLA. Moreover, a slightly increased CO production rate (COP) and obviously decreased total smoke production (TSP) were found in PLA composites containing 2 wt.% NiPO in CCT. In the DTG curve, the similar weight derivation trend to HRR in CCT and PCFC test was also observed. Additionally, the intrinsic thermal stability was enhanced significantly by 19°C with 2 wt.% NiPO into PLA composites. DSC results showed that NiPO could also improve the crystallization property of PLA composites.

Simultaneous polymerization enabled the facile fabrication of S-doped carbons with tunable mesoporosity for high-capacitance supercapacitors

A cationic polymerization of 2-thiophenemethanol (ThM) and a sol–gel polycondensation of tetraethylorthosilicate (TEOS) were simultaneously catalyzed by trifluoroacetic acid in a single process step to produce poly(2-thiophenemethanol)/silica (PThM/SiO2) composites. S-Doped mesoporous carbon (S-MC) materials were then achieved by high-temperature carbonization of PThM/SiO2 under an inert atmosphere and subsequent etching off SiO2 in hydrofluoric acid. This in situ crafting process allows us to tailor the porosity of S-MC in the range of 6 to 30 nm. The specific surface area (278–650 m2 g−1) and pore volume (0.15–0.67 cm3 g−1) increase with increasing the feed ratio of TEOS to ThM. Both the specific surface area and pore volume of S-MC are also higher than those of the un-doped mesoporous carbon (MC) materials using furfuryl alcohol as the starting monomer. The S-MC electrodes thus show larger specific capacitance (Cs) values (252 F g−1 at 25 mV s−1 and 125 F g−1 at 0.5 A g−1) compared to the un-doped MC electrode (203 F g−1 at 25 mV s−1 and 110 F g−1 at 0.5 A g−1). The retention of initial Cs for S-MC is 66%, higher than 53% for MC after a 20-fold increase in the scan rate. After 1000 charge/discharge cycles, the Cs retention for S-MC is 97%, also higher than that of MC (93%). As expected, the S-MC electrodes exhibit larger Cs, higher rate performance, and better cycling stability, compared to the MC counterparts and those fabricated in the absence of TEOS by identical experimental processes. Excellent performance can be contributed to the mesoporous morphology in combination with active doping of rich S heteroatoms.