Photonic Sintering of Aerosol Jet Printed Lead Zirconate Titanate (PZT) Thick Films

Lead Zirconate Titanate (PZT) is a commonly used piezoelectric material due to its high piezoelectric response. We demonstrate a new method of printing and sintering micro‐scale PZT films with low substrate temperature increase. Self‐prepared PZT ink was Aerosol‐Jet printed on stainless steel substrates. After drying for 2 h in vacuum at 200°C, the printed PZT films were divided into two groups. The first group was traditionally sintered, using a thermal process at 1000°C for 1 h in an Argon environment. The second group was photonically sintered using repetitive sub‐msec pulses of high intensity broad spectrum light in an atmospheric environment. The highest measured substrate temperature during photonic sintering was 170.7°C, enabling processing on low melting point substrates. Ferroelectric measurements were performed with a low‐frequency sinusoidal signal. The remanent polarization (P_r) and coercive field (E_c) for thermally sintered PZT film were 17.1 μC/cm² and 6.3 kV/cm, respectively. The photonically sintered film had 32.4 μC/cm² P_r and 6.7 kV/cm E_c. After poling the samples with 20 kV/cm electric field for 2 h at 150°C, the piezoelectric voltage constant (g₃₃) was measured for the two film groups yielding ?16.9 × 10^?3 (V·m)·N^?1 (thermally sintered) and ?17.9 × 10^?3 (V·m)·N^?1 (photonically sintered). Both factors indicate the PZT films were successfully sintered using both methods, with the photonically sintered material exhibiting superior electrical properties. To further validate photonic sintering of PZT on low melting point substrates, the process and measurements were repeated using a polyethylene terephthalate (PET) substrate. The measured P_r and E_c were 23.1 μC/cm² and 5.1 kV/cm, respectively. The g₃₃ was ?17.3 × 10^?3 (V·m)·N^?1. Photonic sintering of thick film PZT directly on low melting point substrates eliminates the need for complex layer transfer processes often associated with flexible PZT transducers.     

Sintering Behavior,Properties, and Applications of Co‐Fired Piezoelectric/Low Temperature Co‐Fired Ceramic (PZT‐SKN/LTCC) Multilayer Ceramics

Materials and processing conditions have been developed allowing co‐firing of fluxed PZT‐SKN materials with commercial low temperature co‐fired ceramic (LTCC) tapes. Previously, Pb(Zr_0.53, Ti_0.47)O₃–Sr(K_0.25, Nb_0.75)O₃ (PZT‐SKN) ceramics fluxed with 1 wt% LiBiO₂ and 1 wt% CuO addition were shown to sinter to high density at 900°C for 1 h, with a large d₃₃ piezoelectric coefficient of ~415 pm/V. Currently, the master sintering curve (MSC) approach has been used to study the densification behaviors of fluxed PZT‐SKN and LTCC tapes. Different sintering mechanisms for fluxed PZT‐SKN ceramics and LTCC materials are confirmed by analyzing the apparent activation energy (Q_a). Using knowledge gained from MSC results, an optimized sintering profile was developed. Multilayer PZT‐SKN/HL2000 (HeraLock^? Tape, Heraeus) stacks co‐fired at 900°C for 0.5 h maintain large piezoelectric coefficient (high field d₃₃ > 340 pm/V). EDS analysis reveal limited interdiffusion of Pb from PZT‐SKN layers in LTCC and the appearance of Al, Ca, and Si in the PZT‐SKN near the PZT‐SKN/LTCC interface. Further, elemental interdiffusion was not detected at the center of piezoelectric layer in PZT‐SKN/LTCC multilayer ceramics and no subsequent reduction in piezoelectric coefficient d₃₃ was observed. Finally, a piezoelectric microbalance with mass sensitivity of 150 kHz/mg was fabricated using the materials and methods developed.     

Matrix influence on the piezoelectric properties of piezoelectric ceramic/polymer composite exhibiting particle alignment

This study was addressed to the influence of an electric field strength applied at fabrication process and matrix properties, such as the dielectric constant and the Young's modulus, on “pseudo‐1‐3 piezoelectric ceramic/polymer composite” in order to further enhance the piezoelectricity of that. The pseudo‐1‐3 piezoelectric ceramic/polymer composite consists of linearly ordered piezoelectric ceramic particles in polymer material. Silicone gel, silicone rubber, urethane rubber, and poly‐methyl‐methacrylate, which exhibit different dielectric constants and Young's modulus, were used as matrices to evaluate the matrix influence. The piezoelectricity of the pseudo‐1‐3 piezoelectric ceramic/polymer composite was evaluated using the piezoelectric strain constant d₃₃. The d₃₃ is one of the indices of the piezoelectric properties for piezoelectric materials. As a result, it was confirmed that d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite increased with the increase of the electric filed strength applied at fabrication process, though, it reached a constant value at a certain strength value. Further it was confirmed that dielectric constant of the matrix had a small influence on d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite, however, in case of matrix of lower Young's modulus, d₃₃ was increase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41817.     

Piezoelectric Properties of Ink‐Jet–Printed Lead Zirconate Titanate Thick Films Confirmed by Piezoresponse Force Microscopy

An ink consisting of Pb(Zr_0.53Ti_0.47)O₃ (PZT) particles with a median size of 170 nm and a narrow size distribution, in a dispersion of water and glycerol, and with a low viscosity and surface tension, was used for the fabrication of thick films by piezoelectric ink‐jet printing. This study reports the printing conditions, the subsequent thermal treatment of the as‐deposited layers, and the properties of the sintered PZT thick film. The film, sintered at 1100°C, had a locally dense microstructure and consisted of grains that are a few 100 nm across, as revealed by scanning electron microscopy. A local piezoelectric response of 15 pm/V was measured in the ink‐jet–printed PZT thick film by piezoresponse force microscopy.     

Simultaneous Enhancement of Fracture Toughness and Unipolar Strain in Pb(Zr,Ti)O3‐ZrO2 Composites Through Composition Adjustment

The influence of second phase zirconia particles on the electrical properties and fracture behavior of various polycrystalline soft Pb(Zr_1?xTi_x)O₃ (PZT) compositions was investigated. PZT composites with yttria‐stabilized tetragonal zirconia particles exhibited enhanced crack resistance in comparison to monolithic compositions, regardless of the PZT composition. The addition of zirconia, however, was found to change the PZT composition through the diffusion of zirconium, resulting in variations in the observed piezoelectric and ferroelectric responses. Through the tailoring of the PZT matrix composition, the large electromechanical response and enhanced fracture toughness could be retained. The variation in both small and large signal properties is contrasted to fracture results and crystal structure changes, as determined by X‐ray diffraction.     

Rubber modification of unsaturated polyester resin with core–shell rubber particles: Effect of shell composition

Poly(butyl acrylate)/poly(vinyl acetate‐co‐methyl methacrylate) PBA/P(VAc‐co‐MMA) core–shell rubber particles with various shell compositions, i.e., VAc/MMA weight ratios, were used to toughen unsaturated polyester. The morphology and surface‐free energy of the rubber particles were determined by transmission electron microscopy (TEM) and contact angle measurements, respectively. The effect of shell structure on the dispersion state of rubber particles inside the unsaturated polyester resin was studied by scanning electron microscopy and TEM. Increasing MMA units in the shell changed the particle dispersion state from small agglomerates or globally well‐dispersed particles to large aggregates in the cured‐resin matrix. For the blends that contain 5 wt% rubber, the highest un‐notched impact toughness, stress‐intensity factor (K_IC), and fracture energy (G_IC) were observed for the blend containing PVAc shell particles. The results showed that by increasing the particle level from 5 to 10 wt%, the highest K_IC and G_IC values were obtained for the blend containing rubber particles with VAc/MMA (80/20 wt/wt) copolymer shell. The crack‐tip damage zone in the neat and rubber‐modified unsaturated polyester resins was observed by means of transmission optical microscopy. In addition, using PVAc shell particles exhibited a minimum reduction in the volume shrinkage and tensile properties of the rubber‐modified resin. POLYM. ENG. SCI., 52:1928–1937, 2012. © 2012 Society of Plastics Engineers     

Piezoelectric Properties of a Pioneering 3‐1 Type PZT/Epoxy Composites Based on Freeze‐Casting Processing

Lead zirconate titanate (PbZr_1 ? xTi_xO₃, PZT)/epoxy composites with one‐ dimensional epoxy in PZT matrix (called 3‐1 type piezocomposites) have been fabricated by tert‐butyl alcohol (TBA)‐based directional freeze casting of PZT matrix and afterward infiltration of epoxy. The composites with PZT volume fraction ranging from 0.36 to 0.69 were obtained by adjusting initial solid loading in freeze‐casting slurry. The effect of poling voltage on piezoelectric properties of the composites was studied for various volume fraction of PZT phase. With the increasing of PZT volume fraction, relative permittivity (ε_r) increased linearly and piezoelectric coefficient (d₃₃ and d₃₁) increased step by step. The resultant composites with 0.57 PZT volume fraction possessed the highest hydrostatic piezoelectric strain coefficient (d_h) value (184 pC/N), voltage coefficient (g_h) value (13.6 × 10^?3 V/m Pa), and hydrostatic figure of merit (HFOM) value (2168 × 10^?15 Pa^?1).     

Structural and piezoelectric properties of <001> textured PZT‐PZNN piezoelectric ceramics

Rhombohedral 0.69Pb(Zr_0.47Ti_0.53)‐0.31Pb(Zn_0.6Ni_0.4)NbO₃ (PZT‐PZNN) ceramics were textured using 10.0 vol. % BaTiO₃ (BT) platelets along the <001> direction at 950°C with a high Lotgering factor of 95.3%. BT platelets did not react with the PZT‐PZNN ceramics, and the textured PZT‐PZNN ceramic had a tetragonal structure. The PZT‐PZNN ceramics exhibited a strain of 0.174% with a piezoelectric strain constant (d*₃₃) of 580 pC/N at 3.0 kV/mm. The textured PZT‐PZNN ceramic showed an increased strain of 0.276% and d*₃₃ of 920 pC/N at 3.0 kV/mm, which can be explained by the domain rotation. However, the d₃₃ values of the textured specimens are smaller than those of the untextured specimens because of the small remanent polarization and relative dielectric constant of BT platelets. The textured PZT‐PZNN ceramic synthesized in this work can be used for piezoelectric multilayer actuators because of its large strain and low sintering temperature.     

A series of 0‐3 composites of lead zirconate titanate and ferroelectric nylon77: Preparation and electrical properties

A series of 0‐3 composites of lead zirconate titanate (PZT) and nylon77 was prepared with PZT volume fractions between 0.1 and 0.6 using the combined method of solvent casting and hot pressing. Depending upon the volume fraction of PZT, the relative permittivities of the composites were found to be in the range of 200–2000 when measured at the highest practically possible temperature of 200°C. As PZT volume fraction increases, both the relative permittivity and the piezoelectric constant d₃₃ increase. The best combination of electrical properties and flexibility was obtained in 0.5 PZT volume fraction composites. At this composition, the remanent polarization P_r of composites was up to 1000 mC/m² at the applied electric field of 40 MV/m and it increased with an increase in temperature. The highest piezoelectric strain coefficient d₃₃ was obtained at 17 pC/N in 0.6 PZT volume fraction composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fine‐Scaled Piezoelectric Ceramic/Polymer 2‐2 Composites for High‐Frequency Transducer

A novel technique was utilized to fabricate fine‐scaled piezoelectric ceramic/polymer 2‐2 composites for high‐frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape‐casted acetylene black tapes were used to define kerfs after sintering. A one‐directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72‐μm‐thick composite with an aspect ratio of ~3.6 exhibited a k_t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high‐frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse‐echo test. The center frequency was found to be 23.75 MHz, with ?6 dB bandwidth of 5.5 MHz.     

An experimental model for predicting the piezo and dielectric constant of PVDF-PZT nanocomposite fibers with 0–3 and 1–3 connectivity

Energy harvesting from mechanical energy around ambient by flexible nanogenerators is one of the most efficient ways to generate green and renewable energy. Lead zirconate titanate (PZT) particles were embedded into a polyvinylidene fluoride (PVDF) polymer matrix to prepare mixed 0–3 and 1–3 connectivity nanocomposite fibers by electrospinning method. Various theoretical models of Maxwell-Garnett, Rayleigh, and Tinga etc were presented at two different Classes to predict the dielectric constant of PVDF-PZT nanocomposite fibers and compared the predicted results with the experimental results. Also, the piezoelectric properties like the piezoelectric coefficient (d₃₃) and piezoelectric voltage coefficient (g₃₃) were predicted by the Furukawa model and the predicted values were compared with the experimental values. Finally, the experimental model was derived to predict the dielectric constant of binary composites with mixed 0–3 and 1–3 connectivity. Compared to well-known models, the proposed experimental model accurately predicted the dielectric constant of PVDF-PZT nanocomposite fibers. The highest and lowest difference between the theoretical and the experimental results were obtained 12.24% and 0.12% for PZT volume fractions 1.1 and 17, respectively. Also, due to the linear relationship between the dielectric constant and piezoelectric coefficients, this model was generalized to predict the piezoelectric coefficients.     

Porous PZT Ceramics with Aligned Pore Channels for Energy Harvesting Applications

In this study, aligned porous lead zirconate titanate (PZT) ceramics with high pyroelectric figures‐of‐merit were successfully manufactured by freeze casting using water‐based suspensions. The introduction of aligned pores was demonstrated to have a strong influence on the resultant porous ceramics, in terms of mechanical, dielectric, and pyroelectric properties. As the level of porosity was increased, the relative permittivity decreased, whereas the Curie temperature and dielectric loss increased. The aligned porous structure exhibited improvement in the compressive strength ranging from 19 to 35 MPa, leading to easier handling, better processability and wider applications for such type of porous material. Both types of pyroelectric harvesting figures‐of‐merit (F_E and F′_E) of the PZT ceramics with a porosity level of 25–45 vol% increased in all porous ceramics, for example, from 11.41 to 12.43 pJ/m³/K² and 1.94 to 6.57 pm³/J, respectively, at 25°C, which were shown to be higher than the dense PZT counterpart.     

Effect of heat treatment on the electrical properties of lead zirconate titanate/poly (vinylidene fluoride) composites

Ceramic/polymer composites are attracting increasing interest in materials research and practical applications due to the combination of excellent electric properties of piezoelectric ceramics and good flexibility of polymer matrices. In this case, the crystallization of the polymer has a significant effect on the electric properties of ceramic/polymer composites. Based on different heat treatment methods, the crystallization of poly(vinylidene fluoride) (PVDF) in composites of lead zirconate titanate (PZT) and PVDF can be controlled effectively. PZT/PVDF composites with various PVDF crystallizations exhibit distinctive dielectric and piezoelectric properties. When the crystallization of PVDF is 21%, the PZT/PVDF composites show a high dielectric constant (ε) of 165 and a low dielectric loss (tan δ) of 0.03 at 10³ Hz, and when the crystallization of PVDF reaches 34%, the piezoelectric coefficient (d₃₃) of PZT/PVDF composites can be up to ca 100 pC N^?1. By controlling the crystallization of PVDF, PZT/PVDF composites with excellent dielectric and piezoelectric properties were obtained, which can be employed as promising candidates in high‐efficiency capacitors and as novel piezoelectric materials. Copyright © 2010 Society of Chemical Industry     

Processing and electromechanical properties of lead zirconate titanate thick films by electrophoretic deposition

Electrophoretic deposition (EPD) was used for the fabrication of piezoelectric [lead zirconate titanate (PZT)] thick films on alumina substrates. The EPD was performed in constant current mode from an ethanol based suspension consisting of PZT and PbO particles. The influence of addition of ethyl cellulose (EC) and sintering temperature on the thickness, density, homogeneity and functional response of PZT thick films is studied. Results show that the highest electromechanical performance is obtained for the PZT thick films sintered at 900 or 950°C, with a thickness coupling factor k_t of 50%. The addition of EC influenced the thickness of the PZT thick films but had only minor effect on the porosity content for sintering temperatures over 900°C. Moreover, elastic constants of the thick films based on the suspension with EC were lower, which leads to lower acoustic impedance (15?MRa) while maintaining high (k_t) value. In this last case, a better acoustic matching can be expected with propagation media such as water or biological tissues for ultrasound medical imaging applications.     

Sol‐gel process of alkyltriethoxysilane in latex for alkylated silica formation in natural rubber

Sol‐gel process of alkyltriethoxysilanes that was dispersed in natural rubber latex was used to generate alkylated silica particles inside the rubber matrix. Three types of alkyltriethoxysilanes were chosen, i.e., vinyltriethoxysilane (VTOS), ethyltriethoxysilane (ETOS), and i‐butyltriethoxysilane (BTOS), as they differed in the type of one substituent group. Together with tetraethoxysilane (TEOS), a typical precursor for silica formation, all silanes were studied for their conversion to silica and subsequent reinforcement capabilities in sulfur‐vulcanized rubber. The in situ generated silicas were fine and well dispersed in the rubber matrix, as analyzed by SEM and TEM. Solid‐state ²⁹Si‐NMR technique was used to confirm the presence of alkyl substituents on the silica particles buried inside the rubber matrix. Tensile and tear properties of the in situ silica‐filled NR vulcanizates were higher than those of the vulcanizate prepared by conventional mixed method. Among the three alkyltriethoxysilanes used, only VTOS, when used as a mixture with TEOS, did not cause a reduction in silica formation. The resulting vinylated silica tended to enhance the tensile modulus and resistant to tear of the rubber vulcanizates. Cure characteristic and swelling behavior in toluene of the silica‐containing vulcanizates were also investigated. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Particle features of poly(vinyl chloride) resins prepared by a new heterogeneous polymerization process

The heterogeneous polymerization of vinyl chloride monomer (VCM), with n‐butane as the reaction medium, was used to prepare poly(vinyl chloride) (PVC) resins. The particle features of the resulting resins and the particle formation mechanism of the polymerization process were investigated. The PVC resins prepared by the new polymerization process had a volume‐average particle size comparable to that of suspension PVC resins and a lower number‐average particle size. From scanning electron micrographs, it could be seen that the new PVC resins had a regular particle shape and a smooth surface with no obvious skin. They also had a high porosity. The new PVC resins were composed of individual and loosely aggregated primary particles. The diameter of the primary particles in the top layer of the grains was smaller than that of the primary particles in the center part of the grains. On the basis of the particle features of these PVC resins, a particle formation mechanism for the new polymerization process was proposed. PVC chains precipitate from a VCM/n‐butane mixed medium to form primary aggregates at a very low conversion, and the primary aggregates of the PVC chains aggregate to form primary particles, which further aggregate to form grains. The primary particles and grains grow by the capture of newly formed PVC chains and their primary aggregates and by polymerization occurring inside the aggregates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 954–958, 2003     

Role of core‐shell rubber particle cavitation resistance on toughenability of epoxy resins

The role of rubber particle cavitation resistance on toughening of epoxy resins is still unresolved. In this research, the role of rubber particle cavitation resistance was exclusively studied. Two types of core‐shell rubber (CSR) particles with different cavitation resistances were utilized for modifying epoxy resin. Matrix crosslink density (XLD) was varied by using nonstoichiometric amounts of hardener. Fracture toughness values of neat and CSR‐modified epoxy samples decreased with lowering of XLD via deviation from stoichiometric point. It was resulted by higher modulus and lower elongation at break of the nonstoichiometric samples, and also antiplasticization of epoxy networks resulted from suppression of β‐transition relaxation motions. In all XLDs, the CSR particles with higher core T_g and modulus yielded higher fracture energy. Results showed that core properties such as T_g and modulus of CSR particles had a significant effect on toughening of the epoxy networks. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

High Electric‐Induced Strain and Temperature‐Dependent Piezoelectric Properties of 0.75BF–0.25BZT Lead‐Free Ceramics

0.75BiFeO₃–0.25Ba(Zr_xTi_1?x) + 0.6 wt% MnO₂ (0.75BF–0.25BZT) ceramics with Mn addition were prepared by the solid‐state reaction method. The high‐field strain and high‐temperature piezoelectric properties of 0.75BF–0.25BZT ceramics were studied. Introduction of Zr in the solid solutions decreased the Curie temperature slightly, and improved the dielectric and piezoelectric properties obviously. The piezoelectric properties of 0.75BZT–0.25BT ceramics reached the maximum at Zr content of 10 mol%. The Curie temperature T_c, dielectric constant ε and loss tanδ (1 kHz), piezoelectric constant d₃₃, and planner electromechanical coupling factor k_p of 0.75BF–0.25BZT ceramics with 10 mol% Zr were 456°C, 650, 5%, 138 pC/N, and 0.30, respectively. The high‐field bipolar and unipolar strain under an electric field of 100 kV/cm reached up to 0.55% and 0.265%, respectively, which were comparable to those of BiScO₃–PbTiO₃ and “soft” PZT‐based ceramics. The typical “butterfly”‐shaped bipolar strain and frequency‐dependent peak‐to‐peak strain indicated that the large high‐field‐induced strain may be due to non‐180° domain switching. Rayleigh analysis reflected that the improved piezoelectric properties resulted from the enhanced extrinsic contribution by Zr doping. The unipolar strain of 0.75BF‐0.25BZT ceramics with 10 mol% Zr was almost linear from RT to 200°C. These results indicated that 0.75BF–0.25BZT ceramics were promising candidates for high‐temperature and lead‐free piezoelectric actuators.     

A flexible piezoelectric pressure sensor based on PVDF nanocomposite fibers doped with PZT particles for energy harvesting applications

Flexible piezoelectric energy harvesters are a suitable choice for scavenging wasted mechanical energy because of the high demand for sustainable power sources. Flexible pressure sensors based on PVDF-PZT nanocomposite with different PZT volume fractions (0.011, 0.041, 0.096, 0.17, 0.3, and 0.37) were prepared in the form of fibers through an electrospinning method for piezoelectric energy harvesting application. According to the results, dielectric constant and piezoelectric coefficients (e.g. piezoelectric coefficient, and figure of merit) gradually increased with the doping of PZT particles into PVDF fibers. Dielectric constant (ϵ), piezoelectric coefficient (d), and figure of merit (d × g) for PVDF-PZT nanocomposite with 0.011 PZT volume fraction were 37.29, 10.51 pCN⁻¹, and 33.46 × 10⁻¹⁶ m²/N, respectively, and increased to 104.81, 22.93 pCN⁻¹, and 56.68 × 10⁻¹⁶ m²/N for PVDF-PZT nanocomposite fibers with a volume fraction of 0.37. As piezoelectric energy harvesters, piezoelectric sensitivity of PVDF-PZT nanocomposite fibers rose with increasing the PZT volume fraction. The generated output voltage was 184 mV under an applied force of 2.125 N with the piezoelectric sensitivity calculated as 173.507mV/Nμm for PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions which increased compared to pristine PVDF fibers (generated output voltage = 22 mV under applied force 2.4 N, piezoelectric sensitivity = 29.49 mV/Nμm). The achieved output power density of PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions was obtained 30.69μW cm⁻² higher than PVDF-PZT nanocomposite fibers with 0.011 PZT volume fractions (18.44μW cm⁻²).     

Deformation mechanism of polystyrene toughened with sub‐micrometer monodisperse rubber particles

Core–shell polybutadiene‐graft‐polystyrene (PB‐g‐PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core‐shell rubber particles were then blended with polystyrene to prepare PS/PB‐g‐PS blends with a constant rubber content of 20 wt%. PB‐g‐PS particles with a lower PB/PS ratio (≤70/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high‐impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1–3 µm rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub‐micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress‐whitening zone of blends with a PB/PS ratio of 70/30 in PB‐g‐PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation. Subsequently, a compression‐induced activation method was explored to compare the PS/PB‐g‐PS blends with commercial HIPS, and the result show that the toughening mechanisms of the two samples are different. Copyright © 2006 Society of Chemical Industry