Ghodratollah Hashemi Motlagh

1. Conductive polymer composites (CPCs) are pivotal to the ongoing shift toward lightweight, flexible, and low-cost alternatives to metals for energy storage, sensing, and electromagnetic interfere...

This research focuses on toughening epoxy (EP) resins by blending with ethylene vinyl acetate (EVA) copolymer, addressing their inherent immiscibility through chemical modification. EVA was partially hydrolyzed (hEVA) to introduce hydroxyl groups and subsequently grafted with (3‐glycidyloxypropyl) trimethoxysilane (GPTMS) to create silane‐functionalized derivatives (gEVA and hgEVA). Materials included Diglycidyl ether of bisphenol A (DGEBA) epoxy, Jeffamine D230 curing agent, neopentyl glycol diglycidyl ether (NGDE) reactive diluent, Decylamine (DA) co‐curing agent, and EVA (19% vinyl acetate). Blends were prepared via melt‐mixing at 150°C, followed by co‐curing. Characterization methods such as scanning electron microscopy (SEM), optical microscopy, and Fourier transform infrared (FTIR) were employed to analyze morphology, phase behavior, and chemical interactions. SEM revealed finer dispersions with modified EVAs, indicating enhanced interfacial adhesion. FTIR confirmed successful modifications and suggested new bond formations between EP and modified EVA. The study systematically investigated EP/EVA blends at varying compositions (2–10 wt% EVA, 5 wt% modified EVA) and characterized their thermal properties and mechanical performance (tensile testing). Notably, the EP/hgEVA blend demonstrated a significant increase in impact strength (~100%) while largely retaining EP's flexural and tensile strength, highlighting the effectiveness of the compatibilization strategy for advanced coating applications.

In this study, we used electrical impedance spectroscopy (EIS) to analyze dispersion and distribution states of CNT conductive nanoparticles in poly(butylene adipate-co-terephthalate) PBAT. We also used field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and rheology along with EIS, to investigate how CNT surface chemistry affects dispersion and electrical response in PBAT/CNT nanocomposites. PBAT nanocomposites containing 1.5 vol% of pristine CNTs, hydroxylated CNTs (CNT-OH), or carboxylated CNTs (CNT-COOH) were prepared by melt mixing. FE-SEM and Raman analyses showed considerably better dispersion for the PBAT/CNT-COOH sample. Rheological measurements further supported this observation; the rheological Cole–Cole plots of the PBAT/CNT-COOH composite exhibited a pronounced tail at low frequencies, indicative of strong CNT–polymer interactions and the formation of a bound polymer layer. The EIS results revealed a cutoff frequency of 70 Hz for PBAT/CNT-COOH, compared to 403 Hz for the other samples which implies that CNT interparticle distance is larger in the former. Fitting the Nyquist data with a modified Randles circuit yielded a parallel resistance of 694 Ω for PBAT/CNT-COOH, whereas the other two composites exhibited a considerably lower resistance of approximately 70 Ω. We attribute these electrical and rheological signatures to stronger interactions between COOH groups of CNT and ester groups of PBAT, which promote the adsorption of a bound polymer layer around the nanotubes. This interfacial layer effectively increases the average interparticle distance and polymer interlayer thickness, leading to higher electrical resistance and reduced capacitance. These findings of EIS are applied to the behavior of the whole bulk of the nanocomposite while other methods such as SEM only characterize tiny limited areas of the samples. The dispersion state, interparticle distance, bond polymer layer on CNTs and several electrical properties are detectable by EIS which all are the bulk characteristics of conductive polymer nanocomposites.

High density polyethylene is susceptible to Slow Crack Growth (SCG), which may cause premature failures. In this work, masterbatches of chemically reduced graphene oxide (CRGO), amino‐functionalized CRGO (FCRGO), and carbon black (CB) were used. Polyethylene grafted maleic anhydride (PE‐g‐MA) was used as a compatibilizer. RGO Masterbatches were prepared using solvent‐mixing and compared with the CB industrial masterbatch. Final nanocomposites produced by melt‐mixing (upon 2 wt.% of nanoparticles). Tensile modulus of all composites increased up to 17%. Elongation at break decreased 90% for CRGO composite, but slightly by CB and FCRGO composites (20%) loading. Tensile strength remained almost constant by adding FCRGO and CB, but decreased 60% with CRGO loading. Notched constant tensile loading (NCTL) test results showed improvement in the SCG resistance by adding 1.5 wt.% of FCRGO for more than 50%, but dis‐improvement in the SCG resistance of CB and CRGO composites. Strain hardening modulus (SHM) of FCRGO composites were 7% higher than HDPE, supporting the NCTL results. OLM and SEM macroscopic images showed that FCRGO nanocomposite has better dispersion than the non‐functionalized ones. All tests revealed a strong interaction between FCRGO nanoparticles and the matrix. Thus, FCRGO has a high potential to enhance long‐term properties of HDPE particularly for pipe grade PE.

This study investigates how carbon black (CB) distribution in co-continuous polypropylene (PP)/poly(ethylene-co-vinyl acetate) (EVA) blends affects electrical impedance spectroscopy (EIS) properties. PP:CB and EVA:CB masterbatches with 1, 2, or 3 vol% CB were prepared by the melt-mixing method. PP:CB and EVA:CB masterbatches with different CB volume fractions were mixed together to form PP/EVA blends (40/60 vol%) with CB distributions of 1/3, 2/2, or 3/1 vol%. A 60/40 vol% PP/EVA blend with 2/2 vol% CB was also prepared to study morphology effects. Samples were characterized using EIS, scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, and dynamic rheometry. SEM and AFM confirmed co-continuous morphology in all samples. EIS revealed that uneven CB distribution, particularly in the PP:CB 3 vol%/EVA:CB 1 vol% blend, reduced the real part of impedance and increased the frequency cut-off (fc), indicating higher capacitance in Nyquist plots. The 60/40 vol% PP/EVA blend with 2/2 vol% CB exhibited a 38-fold capacitance increase compared to the 40/60 vol% blend, attributed to lower impedance in the PP:CB phase. These findings demonstrate that tailoring CB distribution optimizes electrical energy storage performance and establishes EIS as a robust tool for characterizing conductive particle distribution in immiscible polymer blends.

Despite the widespread use of conductive composites with a binary blend matrix in electrical applications, computational studies examining the effects of conductive particle localization within individual phases and at their interface on conductance and the percolation threshold remain limited. To address this gap, we employ a simple cubic lattice model to simulate the localization of conductive sites within individual phases and at the interface between them. Our results show that exclusive localization of conductive sites within a single phase lowers the percolation threshold and enhances conductance, especially near the percolation threshold, whereas localization at the interface further reduces the threshold. When all conductive sites are exclusively localized in one phase, the percolation threshold can be expressed in two ways: first, as the fraction of conductive sites calculated relative to the total number of sites, denoted as Π; and second, as the fraction calculated relative to the available sites in that phase, denoted as Π _f . In this situation, the second phase effectively acts as an excluded volume, reducing the number of available sites. At a constant concentration of the excluded-volume phase, increasing the size of this phase causes the percolation threshold to first decrease and then converge to a constant value. The constant value corresponds to a state in which the structure of conductive sites within the available volume is similar to that of a homogeneous system. In this case, the percolation threshold expressed relative to the available sites is given by Π _f = Π _homogen , which equals 0.31 in the case of a simple cubic lattice; additionally, the percolation threshold relative to all sites is given by Π = (1 − φ _A )Π _homogen , where φ _A is the fraction of the excluded-volume phase. We also studied situations in which particles are distributed between the two phases with different probabilities. In such cases, the percolation threshold lies between the two extreme cases: a fully homogeneous system and a fully segregated system in which one phase acts as an excluded volume.

Due to limited research on interfacial shear stress (ISS) and critical fiber length (Lc) in rubber-based composites, this study systematically investigates how fiber length, orientation, and bonding agents influence the mechanical properties of NBR/PA6 composites, focusing on evaluating ISS and Lc. Composite samples with fibers of varying lengths (1–12 mm) were produced, incorporating different bonding agents. Preparation involved internal mixing followed by processing on a two-roll mill to induce fiber orientation. Tests, including tensile, fiber pull-out, FTIR analysis, SEM imaging, and dynamic mechanical thermal analysis, were conducted to assess the composites’ mechanical properties and micromechanics. The addition of bonding agents significantly reduced the critical fiber length, a result attributed to increased ISS. This improved fiber-matrix interaction was confirmed by decreased void content and FTIR analysis, which showed covalent and hydrogen bonds between fibers and the matrix. However, excessive bonding agent (beyond 5 phr for epoxy resin) caused phase separation and overplasticization, while high fiber content led to aggregation and hindered interfacial bonding, lowering ISS. Tensile strength increased with fiber length up to 9 mm but decreased afterward due to fiber entanglement and uneven dispersion, reducing reinforcement efficiency. Evaluation of theoretical models showed decreased accuracy at high fiber aspect ratios. These findings suggest that optimizing fiber-reinforced rubber composites involves maintaining fiber lengths above the critical length, using moderate fiber content, and applying suitable interfacial adhesion strategies.

Incorporating graphene oxide (GO) with controlled localization into poly(butylene adipate‐co‐terephthalate) (PBAT) blends with poly(ethylene vinyl alcohol) (EVOH) aimed to improve barrier properties, biodegradability, and mechanical strength of PBAT. The PBAT/EVOH/GO nanocomposites containing 0 to 1 wt% of GO were prepared by a reactive mixing process in internal mixer. Microscopic images confirmed that the GO nanoplatelets are mainly localized in PBAT phase and then at the interface, contrary to the thermodynamic affinity of GO toward EVOH. The reactive nature of PBAT/EVOH/GO nanocomposites was confirmed via time‐sweep rheological studies where specific changes were observed in melt viscosity over time. The results of microscopic studies, rheometry, tensile test, and dynamic mechanical thermal analysis (DMTA) confirmed that localizing GO at the interface establishes strong interactions between PBAT and EVOH. By the addition of 0.75 wt% GO, tensile and yield strength were improved by 19% and 45%, respectively. Increasing GO significantly increased the hydrolysis degradation rate of the nanocomposites. Furthermore, the addition of GO considerably decreased the oxygen and water vapor permeability of the blends by up to 40% at 1 wt% GO.