Suppressing the phase transition of ZrP_(2)O_(7), by defect and entropy regulation for high-temperature wave-transparent material application

ZrP_(2)O_(7) is a promising wave-transparent material due to its low dielectric constant and low dielectric loss,but its inherent phase transition characteristic at approximately 300℃ limits its high-temperature application.Therefore,suppressing the phase transition is necessary for ZrP_(2)O_(7),to serve in extremely harsh environments.In this work,introducing Ti and Hf into ZrP_(2)O_(7) causes significant lattice distortion and an increase in entropy,both of which synergistically limit the crystal structure transformation.In addition,enhanced phonon scattering by mismatch of atomic mass and local distortion leads to a reduction in the thermal conductivity.Lattice distortions also cause changes in both bond length and tilting angle,so that(Ti_(1/3)Zr_(1/3)Hf_(1/3))P_(2)O_(7) does not undergo sudden expansion as does ZrP_(2)O_(7).(Ti_(1/3)Zr_(1/3)Hf_(1/3))ZrP_(2)O_(7) maintains excellent dielectric properties,which highlights it as a promising high-temperature wave-transparent material.

PBO fibers/fluorine-containing liquid crystal compound modified cyanate ester wave-transparent laminated composites with excellent mechanical and flame retardance properties

Bisphenol A dicyanate ester resins modified by fluorine-containing liquid crystal compound(LCFE)are applied as polymer matrix(LCFE-BADCy),poly(p-phenylene-2,6-benzobisoxazole)(PBO)fibers as rein-forcements,and fluorine/adamantane PBO precursor(pre FABPBO)as interfacial compatibilizer to prepare the corresponding PBO fibers/FABPBO/LCFE-BADCy wave-transparent laminated composites.LCFE could improve the order degree of BADCy cured network,in favor of enhancing the wave-transparent perfor-mance,mechanical properties,and intrinsic thermal conductivity.The dielectric constant and dielectric loss of PBO fibers/FABPBO/LCFE-BADCy composites are highly temperature(25–200℃)and frequency(10^(4)–10^(7) Hz and 8.2–12.4 GHz)stable with the value of 2.49 and 0.003 under 10^(6) Hz at 25℃,and the corresponding wave transmission efficiency is 95.0%,higher than that of 92.5%for PBO fibers/BADCy com-posites.The interlamellar shear strength and flexural strength are respectively 50.7 MPa and 682.5 MPa,38.1%and 16.2%higher than those of PBO fibers/BADCy composites.Besides,the volume resistivity,breakdown voltage,heat resistance index,glass transition temperature,flame retardant grade,and ul-timate oxygen index of PBO fibers/FABPBO/LCFE-BADCy composites are respectively 5.3×10^(15)Ωcm,29.75 kV/mm,217.2℃,245.7℃,V-1 grade,and 33.6%,expected to be performed as a new generation of“lightweight/loading/wave-transparent”electromagnetic window materials in advanced military weapons and civil communication base station.

Branched Fluorine/Adamantane Interfacial Compatibilizer for PBO Fibers/Cyanate Ester Wave-Transparent Laminated Composites

Comprehensive Summary Branched fluorine/adamantane PBO precursor(preFABPBO),synthesized via random co-condensation between 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoro propane,1,3-adamantanedicarbonyl dichloride,and trimesoyl chloride,is performed as interfacial compatibilizer,bisphenol A dicyanate ester(BADCy)resin as polymer matrix,and poly(p-phenylene-2,6-benzobisoxazole)(PBO)fibers as reinforcements to prepare PBO fibers/FABPBO-BADCy wave-transparent laminated composites by high temperature molding.The mechanical properties,wave-transparent performances,and heat resistances of PBO fibers/BADCy composites are simultaneously improved by the addition of preFABPBO.The interlaminar shear strength(ILSS)and flexural strength of PBO fibers/FABPBO-BADCy composites are 48.9 and 665.3 MPa,respectively,increased by 33.2%and 13.3%compared to those of PBO fibers/BADCy composites(36.7 and 587.4 MPa).The dielectric constant and dielectric loss values at 106 Hz are 2.53 and 0.003,respectively,lower than those of PBO fibers/BADCy composites(3.06 and 0.006),and the corresponding wave transmission efficiency is 94.8%,which also presents excellent stability over the wide temperature(25-200℃)and frequency range(103-107 Hz and 8.2-12.4 GHz).Meanwhile,the heat resistance index and glass transition temperature are 229.9℃and 247.5℃,also better than those of PBO fibers/BADCy composites(229.6℃and 247.1℃).

Block copolymer functionalized quartz fibers/cyanate ester wave-transparent laminated composites

A block copolymer of PDMS-b-PGMA is synthesized by polymerizing glycidyl methacrylate(GMA)via reversible addition-fragmentation chain transfer(RAFT)polymerization applying a polydimethylsiloxane(PDMS)based macro-RAFT agent,which is then performed to functionalize the quartz fibers(QFs@PDMS-b-PGMA)via a simple coating process.Finally,the QFs@PDMS-b-PGMA/bisphenol A dicyanate ester(BADCy)wave-transparent laminated composites are fabricated by high-temperature molding.Nuclear magnetic resonance(NMR)spectroscopy,Fourier transform infrared(FT-IR)spectroscopy and size ex-clusion chromatography(SEC)demonstrate the successful preparation of PDMS-b-PGMA with expected structure.When the molar mass and coating amount of PDMS-b-PGMA are respectively 8100 g/mol and 2.0 wt.%,QFs@PDMS-b-PGMA/BADCy wave-transparent laminated composites present optimal mechan-ical properties and wave-transparent performance.The interlaminar shear strength(ILSS)and flexural strength are 53.6 and 552.0 MPa,respectively.Meanwhile,the dielectric constant and dielectric loss val-ues are 2.61 and 0.0028 at 1 MHz(wave transmittance of 93.8%),showing good stability at different frequencies(102-106 Hz and 8.4-12.4 GHz)and temperatures(25-250℃).

Polymer matrix wave-transparent composites:A review

With the rapid development of electronic information technology,antenna systems in the fields of aviation,aerospace,transportation,and 5 G communication services are becoming more and more intensive and accurate.Polymer matrix wave-transparent composites with lightweight,low dielectric constant(∈)and dielectric loss tangent(tanδ),high temperature resistance,and excellent mechanical properties are urgently needed in order to ensure high-fidelity transmission of electromagnetic wave and protect antenna systems from external interference.This review introduces the wave transmission mechanism,key compositions(polymer matrix&reinforced fibers),and several typical testing methods for dielectric properties of polymer matrix wave-transparent composites,mainly elaborates the latest research progress and achievements of polymer matrix wave-transparent composites from polymer matrix,reinforced fibers and their surface functionalization methods,and presents the key scientific and technical problems that need to be solved urgently in the application of polymer matrix wave-transparent composites in the antenna systems.Finally,the future development trends and application prospects of the polymer matrix wave-transparent composites are also proposed.

High-strength super-hydrophobic double-layered PBO nanofiberpolytetrafluoroethylene nanocomposite paper for high-performance wave-transparent applications

Poly(p-phenylene-2,6-benzobisoxazole)nanofiber(PNF)paper is facing unprecedented challenges in enhancing the interaction between the PNFs and improving its hydrophobicity.In this work,a sol–gel film transformation approach was developed to fabricate high-strength PNF paper.Iron ions formed coordination bonds between PNFs to obtain a preforming three-dimensional,interconnective nanofiber network.Subsequently,polytetrafluoroethylene(PTFE)particles were sprayed onto the surface of the paper,followed by thermal treatment to obtain double-layered PTFE-P/PNF nanocomposite paper.The nanocomposite paper presents incredible tensile strength(271.6 MPa,increased by 52.9%),folding endurance,super-hydrophobicity,and self-cleaning performances.Moreover,it exhibits low dielectric constant(2.06)and dielectric loss tangent(0.0133)values.According to the wave-transparent model for a doublelayered dielectric established by Maxwell’s equations,the wave-transparent coefficients of electromagnetic waves incident from both sides of the paper are 97.6%(PNF side)and 96.0%(PTFE/P(S-co-BCB-coMMA)side),respectively.The PTFE-P/PNF nanocomposite paper possesses great potential in the fields of wave-transparent applications.

Effects of oxidation treatment on properties of SiO_(2f)/SiO_2-BN composites

The silica fiber reinforced silica and boron nitride-based composites （SiO2f/SiO2-BN） were prepared firstly via the sol-gel method and then the urea route, and the effects of oxidation treatment on the component, structure, mechanical and dielectric properties of the composites were investigated. The results show that the oxidation treatment at 450 ℃ will not impair the structure of boron nitride, and carbon is the main impurity with the excessive urea. The density of SiO2f/SiO2-BN composites is 1.81 g/cm3, and the flexural strength and elastic modulus are 113.9 MPa and 36.5 GPa, respectively. After oxidation treatment, the density varies to 1.80 g/cm3, and the flexural strength and elastic modulus are decreased to 58.9 MPa and 9.4 GPa, respectively. The mechanical properties of the composites are severely damaged, but they still exhibit a good toughness. The composites show excellent dielectric properties with the dielectric constant and loss tangent being 3.22 and 0.003 9, respectively, which indicates that the oxidation treatment is ineffective to improve the dielectric properties of SiOzf/SiO2-BN composites.

Polysilsesquioxane‑PBO Wave‑Transparent Composite Paper with Excellent Mechanical Properties and Ultraviolet Aging Resistance

The rapid development of radar antenna systems to meet requirements for high integration and precision places stringent requirements on the dielectric properties,mechanical properties and heat resistance of wave-transparent composite paper.In this paper,poly(p-phenylene-2,6-benzobisoxazole)(PBO)fibers are first dissolved by trifluoroacetic acid/methyl sulfonic acid to obtain PBO nanofibers(PNF),and the amino polysilsesquioxane(NH_(2)-POSS)is dispersed uniformly inside the PNF via ultrasonic-assisted and deprotonation.The POSS-PNF composite paper is fabricated by the method of“suction filtration and hot-pressing”.Because of the uniformly dispersion of NH_(2)-POSS,the POSS-PNF composite paper has a low dielectric constant(ε,2.08)and dielectric loss tangent(tanδ,0.0047),and the wave-transparent coefficient(|T|2)is 96.7%(1 MHz),which is higher than that of PNF paper(95.5%,1 MHz).Additionally,the POSS-PNF composite paper possesses excellent tensile strength of 163.3 MPa,tensile modulus of 6.9 GPa,toughness of 9.1 MJ/m^(3),outstanding flame retardancy and excellent UV aging resistance.According to a simulation of the radome honeycomb panel,POSS-PNF composite paper has low loss and reflections of electromagnetic waves in the X-band(8.4~12.4 GHz),and wide angle of incidence(0°-80°),which favor high|T|2.The results indicate that the POSS-PNF composite paper has excellent potential for applications in the fields of aerospace,wearable flexible electronic devices and 5G communication.

Hybrid Polymer Membrane Functionalized PBO Fibers/Cyanate Esters Wave‑Transparent Laminated Composites

Hybrid polymer membrane(TA-APTES),synthesized by tannic acid(TA)and aminopropyl trethoxysilane(APTES)based on the Schif’s base and Michael addition reaction,is deposited on the surface of poly(p-phenylene-2,6-benzobisoxazole)(PBO)fbers,and then grafted with epoxy-terminated polysesquisiloxane(POSS)to obtain POSS-g-PBO@TA-APTES fbers.The POSS-g-PBO@TA-APTES fbers reinforced bisphenol A dicyanate ester(BADCy)resins(POSS-g-PBO@TAAPTES fbers/BADCy)wave-transparent laminated composites are prepared.The interlaminar shear strength and fexural strength of POSS-g-PBO@TA-APTES fbers/BADCy composites are respectively enhanced from 36.7 and 587.4 MPa to 42.8 and 645.8 MPa,increased by 16.6%and 9.9%compared with those of PBO fbers/BADCy composites.At 1 MHz,the corresponding dielectric constant and dielectric loss are reduced to 2.85 and 0.0047,respectively,lower than those of PBO fbers/BADCy(3.06 and 0.006)composites.Meanwhile,the simulated wave transmittance rate of POSS-g-PBO@TA-APTES fbers/BADCy composites with the thicknesses of 1.5–3.5 mm is higher than 86.2%at 0.3–40 GHz.The volume resistivity and breakdown strength of POSS-g-PBO@TA-APTES fbers/BADCy composites are 2.8×10^(15)Ω·cm and 19.80 kV/mm,higher than PBO fbers/BADCy composites(2.2×10^(15)Ω·cm and 17.69 kV/mm),respectively.And the corresponding heat resistant index is 221.5℃,lower than PBO fbers/BADCy composites(229.6℃).