📄 chemistry

Phase Evolution and Selective Barium Titanate Localization in Poly(vinylidene fluoride) and Epoxidized Natural Rubber Blends with Tunable Mechanical and Dielectric Properties

This study investigates non-vulcanized PVDF/ENR-50 blends with tunable mechanical and dielectric properties, revealing that phase inversion boundaries dictate morphology and performance while barium titanate particles selectively segregate into the ENR-50 phase, enlarging its domains without disrupting PVDF continuity.

Original authors: Subhan Salaeh, Philippe Cassagnau, Charoen Nakason

Published 2026-08-13

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Subhan Salaeh, Philippe Cassagnau, Charoen Nakason

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to build a super-material that is both tough like a plastic ruler and stretchy like a rubber band. In the world of materials science, this is a classic challenge. Most materials are either hard and stiff or soft and squishy, but rarely both. Scientists often try to solve this by mixing two different polymers (long chains of molecules) together, like mixing peanut butter and jelly. However, just like oil and water, many plastics and rubbers hate to mix; they separate into distinct blobs, which can make the final material weak or brittle. To fix this, scientists look for ways to make these "enemies" get along, or they add special ingredients to change how the mixture behaves. One such ingredient is a ceramic powder called barium titanate, which is famous for its ability to store electrical energy. The big question is: if you mix a stiff plastic, a stretchy rubber, and this magical powder, what happens? Does the powder just sit there, or does it change the way the plastic and rubber arrange themselves? This is the story of a new experiment that tries to find the perfect recipe for a material that can bend, stretch, and conduct electricity all at once.

The researchers behind this study decided to mix two specific ingredients: Poly(vinylidene fluoride), or PVDF, which is a stiff, semi-crystalline plastic known for holding a charge, and Epoxidized Natural Rubber (ENR-50), a stretchy, modified rubber. They didn't just mix them once; they created a whole library of recipes, changing the ratio from mostly plastic to mostly rubber. They found that as they added more rubber, the material didn't just get softer; it went through a dramatic transformation. At first, the rubber was just tiny islands floating in a sea of plastic. But as they added more rubber, those islands started touching and merging until, at a 50/50 mix, both the plastic and the rubber formed their own continuous, interlocking networks. It was like a maze where both the walls and the corridors were made of different materials, both stretching all the way through the block. This "co-continuous" state was the sweet spot, offering a balance of strength and flexibility.

But the real magic happened when they added the star ingredient: barium titanate (BT) particles. The researchers expected the particles to just act as a filler to boost electrical properties. Instead, they discovered that the BT particles were picky eaters; they refused to hang out in the plastic and chose to live exclusively inside the rubber phase. This preference had a surprising side effect. In the mix that was mostly plastic (80% plastic, 20% rubber), the BT particles made the rubber "islands" grow bigger, swelling from about 6.5 micrometers to 11.4 micrometers, but the plastic sea remained the main structure. However, in the 50/50 mix, the BT particles changed the entire game. By making the rubber phase "thicker" and more resistant to flow, the particles pushed the rubber to take over as the main continuous phase, turning the 50/50 mix from a balanced maze into a rubbery sea with plastic islands floating inside.

This shift in structure completely changed how the material behaved. The 80/20 mix with BT stayed stiff and strong, which is great if you need something that holds its shape. But the 50/50 mix with BT became incredibly stretchy, able to stretch up to 800% before breaking, though it lost some of its ability to hold a heavy load. The researchers also found that the BT particles made the material much better at storing electrical energy (dielectric permittivity), especially in the plastic-rich mix. However, they also noted that this electrical boost came with a trade-off: the material became a bit "lossy," meaning it wasted some energy as heat, particularly at low frequencies.

The study suggests that by carefully choosing how much plastic and rubber to use, and by letting the ceramic particles do their own thing by hiding in the rubber, scientists can tune a material to be exactly what they need. If you want a flexible sensor or a soft, stretchy liner, the rubber-rich mix with BT is the way to go. If you need a stiff, high-energy capacitor, the plastic-rich mix is better. The paper doesn't claim to have solved all the problems—these materials are still not chemically crosslinked, meaning they might not be durable enough for heavy-duty industrial use yet—but it proves that you can use filler particles not just to add a property, but to actively reshape the material's internal architecture. It's a reminder that in the world of mixing materials, sometimes the ingredient you add changes the whole recipe, not just the flavor.

Technical Summary: Phase Evolution and Selective Barium Titanate Localization in PVDF/ENR-50 Blends

Problem Statement
Polymer blending offers an economical route to combine properties difficult to achieve with single polymers, yet immiscible pairs like poly(vinylidene fluoride) (PVDF) and natural rubber derivatives often suffer from poor interfacial adhesion and phase separation. While PVDF possesses excellent dielectric and mechanical properties, its brittleness limits flexible applications. Conversely, epoxidized natural rubber (ENR) offers flexibility but lacks the stiffness and dielectric response of PVDF. Previous research has largely focused on limited compositions, compatibilized blends, or dynamically vulcanized systems. There is a need to systematically understand how composition, phase continuity, and the selective localization of high-permittivity fillers influence the morphology and properties of non-vulcanized PVDF/ENR blends to design materials with tunable mechanical and dielectric characteristics.

Methodology
The study investigated non-vulcanized blends of PVDF and epoxidized natural rubber containing 50 mol% epoxide (ENR-50) across a composition range of 80/20 to 20/80 wt%. Blends were prepared via melt blending at 180°C. To examine the effect of fillers, 5 vol% barium titanate (BT) was incorporated into the 80/20 (PVDF-rich) and 50/50 (equimass) blends.

Characterization techniques included:

Morphology: Scanning Electron Microscopy (SEM) with selective solvent extraction (toluene for ENR-50 removal in PVDF-rich blends; dimethylformamide for PVDF removal in ENR-rich blends) to identify phase continuity and domain sizes.
Mechanical Properties: Tensile testing, tension set, and Shore A hardness measurements.
Thermal Analysis: Differential Scanning Calorimetry (DSC) to determine crystallization temperature ( $T_c$ ), melting temperature ( $T_m$ ), and degree of crystallinity ( $X_c$ ).
Dynamic Mechanical Analysis (DMA): Measurement of storage modulus ( $E'$ ) and loss tangent ( $\tan \delta$ ) to assess stiffness and damping behavior.
Dielectric Properties: Broadband dielectric spectroscopy to measure real permittivity ( $\varepsilon'$ ) and dielectric loss ( $\varepsilon''$ ) over a frequency range of $10^{-1}$ to $10^7$ Hz.

Key Results

Phase Morphology and Inversion: The blends exhibited a clear evolution from a PVDF-continuous/ENR-50-dispersed structure (80/20) to an apparent co-continuous region (60/40–50/50), and finally to an ENR-50-continuous/PVDF-dispersed structure (20/80). Two phase-inversion boundaries were identified: the first between 70/30 and 60/40, and the second between 50/50 and 40/60.
Mechanical Behavior: Increasing ENR-50 content reduced stiffness and tensile stress while significantly increasing extensibility, with elongation at break reaching 1000–2200% in ENR-rich blends. The 60/40 and 50/50 compositions offered a balance of load-bearing capacity and flexibility characteristic of thermoplastic elastomers.
Crystallization: The addition of ENR-50 increased the PVDF crystallization temperature ( $T_c$ ) from 135.8°C (neat PVDF) to a maximum of 139.3°C at the 50/50 ratio, attributed to heterogeneous nucleation at the interface. However, PVDF-normalized crystallinity decreased in ENR-rich blends due to spatial confinement.
Dielectric Properties: Blends exhibited higher permittivity than neat components due to Maxwell–Wagner–Sillars interfacial polarization. The addition of BT significantly enhanced permittivity, with the 80/20 blend showing the highest values due to the continuous high-permittivity PVDF matrix.
Effect of BT Localization: BT particles preferentially segregated into the ENR-50 phase.
- In the 80/20 blend, BT increased the average ENR-50 domain size from 6.5 to 11.4 μm but preserved the PVDF-continuous matrix. Mechanical properties remained largely unchanged, while dielectric permittivity increased.
- In the 50/50 blend, the preferential localization of BT altered the rheological balance, transforming the morphology from apparent co-continuity to an ENR-50-continuous/PVDF-dispersed structure. This resulted in a sharp decrease in tensile stress and storage modulus but a substantial increase in extensibility (up to ~800%) and damping.

Significance and Claims
The authors claim the novelty of this work lies in the systematic identification of phase-inversion boundaries in non-vulcanized PVDF/ENR-50 blends and the demonstration that selectively localized BT acts not merely as a high-permittivity filler but as a morphology-controlling component.

The study establishes that BT localization can regulate the balance between stiffness, extensibility, damping, and dielectric response. Specifically:

Morphology Control: BT incorporation can shift phase inversion boundaries, as seen in the 50/50 blend where co-continuity was suppressed in favor of an ENR-continuous matrix.
Tunable Properties: By controlling composition and filler localization, materials can be tailored for specific applications: PVDF-rich BT-filled blends for flexible dielectric layers and sensors, and intermediate/ENR-rich blends for vibration damping and flexible liners.
Limitations: The authors note that the materials are non-vulcanized, meaning the ENR-50 phase lacks a permanent chemical network, limiting the materials to low-load applications. Future work is suggested to optimize BT loading, improve interfacial adhesion, and evaluate long-term durability and energy storage efficiency.

More like this