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. 2025 Dec 5;6(1):203–213. doi: 10.1021/acspolymersau.5c00113

Formulation and 3D Printing of PVDF-Containing Photocurable Resins for Digital Light Processing

Megan McGeehan †, Étienne Durand-Laberge †, Matthieu Gervais ‡, Sébastien Roland ‡, Audrey Laventure †,*
PMCID: PMC12903459  PMID: 41693839

Abstract

Additive manufacturing of electroactive polymers offers transformative potential for flexible electronics and smart devices, yet preserving the microstructure responsible for the electroactive property during processing remains a challenge. Here, we report a digital light processing (DLP) approach formulated without any volatile organic solvent to prepare poly­(vinylidene fluoride) (PVDF)-based composites under ambient conditions, employing 1,6-hexanediol dimethacrylate (HDDMA) as a polymerizable matrix and phenylbis­(2,4,6-trimethylbenzoyl)­phosphine oxide (BAPO) as an efficient visible-light photoinitiator. Unlike conventional solvent-based methods relying on PVDF dissolution, this formulation enables direct dispersion of PVDF particles in the photocurable resin without the use of organic solvents that are typically used in the processing of PVDF. Formulation optimization enabled stable suspensions of PVDF up to 35 wt %, with rheological and optical properties leading to high-fidelity DLP printed samples. Atomic force microscopy (AFM) of cross sections of the 3D printed sample revealed uniform dispersion of PVDF-rich domains. Comprehensive characterization of the 3D printed sample using differential scanning calorimetry (DSC), infrared spectroscopy (IR), and X-ray diffraction confirmed the retention of the pristine PVDF’s semicrystalline phases postprocessing. Preprinting modification of the PVDF and postprinting modifications of the 3D printed composite were conducted to confirm this observation. For instance, solvent-precipitated PVDF with enhanced β phase fraction, which is often associated with electroactivity, was used in the formulation without phase degradation during photopolymerization and postprint annealing of the 3D printed composite provided additional phase tuning, underscoring the versatility of this approach. This work establishes DLP as a robust platform for the additive manufacturing PVDF-based composites, allowing for precise control and retention over crystalline phase content and complex architectures, potentially relevant for electroactive applications in next-generation flexible electronics.

Keywords: PVDF, Digital light processing, Photopolymerization, Additive manufacturing, Microstructure, Formulation

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Introduction

Additive manufacturing (AM) has transformed the fabrication of advanced materials, enabling precise voxel-by-voxel and layer-by-layer construction of complex three-dimensional (3D) structures, with resolutions reaching as small as 100 nm depending on the AM technology used. − Such capabilities have sparked considerable interest in integrating functionalities to these 3D structures owing to the speed, design flexibility, and cost-effectiveness they offer over conventional processing methods. To do so, various functional materials have already been successfully printed using AM techniques, including biodegradable polymers for tissue engineering, , shape-memory alloys, thermochromic materials, and magnetically responsive composites. Electroactive materials have increasingly been integrated into additive manufacturing platforms, such as semiconducting polymers, liquid crystal elastomers for soft actuators, and ionic hydrogels used in bioelectronics. These benefits are particularly appealing for the development of flexible electronic devices, including those intended for wearable technologies.

While traditional electroactive materials like lead zirconate titanate (PZT) and barium titanate (BaTiO3) offer high piezoelectric coefficients, they are rigid and brittle, limiting their utility in applications demanding flexibility. Electroactive polymers (EAPs) present a soft-matter alternative, combining intrinsic flexibility, stretchability, and conformability with irregular or dynamic surfaces. This makes them ideal for portable energy harvesters, pressure sensors, and soft robotics. ,, Although their piezoelectric coefficients are generally lower, EAPs d33 can reach −30 pC.N–1 compared to 200 pC.N–1 for PZT, , their low weight, nontoxicity, and processability offer a compelling compromise between performance and versatility for applications necessitating flexibility.

Among EAPs, poly­(vinylidene fluoride) (PVDF) and its copolymers, such as poly­(vinylidene fluoride-trifluoroethylene) (P­(VDF-TrFE)), poly­(vinylidene fluoride-hexafluoropropylene) (P­(VDF-HFP)), and terpolymers like poly­(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P­(VDF-TrFE-CTFE)), stand out for their favorable electromechanical properties. PVDF, in particular, exhibits notable piezoelectric activity when crystallized in its β phase, which is characterized by an all-trans (TTTT) conformation that promotes optimal dipole alignment. The fraction of the electroactive β phase can be enhanced through processing techniques such as solvent casting, annealing, mechanical stretching, and, more rarely, UV treatment, which promotes dipole alignment by reorienting the fluorine atoms along the polymer chain. Additionally, additives, including carbon nanotubes and other polymers such as poly­(methyl methacrylate) (PMMA), , can act as nucleating agents in specific conditions, further promoting β phase formation.

However, despite their desirable properties, EAPs like PVDF present significant challenges in AM. They are often insoluble in common solvents or prone to thermal degradation, limiting their compatibility with popular printing methods such as direct ink writing (DIW) or fused filament fabrication (FFF). Both methods typically rely on solvent-based formulations or high-temperature extrusion, which are poorly suited for PVDF and its derivatives. In addition, the thermal, chemical, and mechanical conditions imposed during these processes can significantly influence the polymer’s crystalline phase distribution and microstructure, factors that are critical to preserving structural features that may be associated with electroactive properties. ,,

Digital Light Processing (DLP) emerges as a compelling alternative to extrusion-based AM techniques. This vat photopolymerization technique selectively cures photosensitive resins using patterned UV or visible light, achieving high spatial resolution (down to 10 μm) and smooth surface finishes without the need for extrusion, elevated temperatures, or solvents. As such, DLP is particularly advantageous for processing electroactive polymers, where ambient conditions and minimal mechanical constraints are critical to preserving crystallinity and functional phase content. Furthermore, the ability to design complex geometries with submillimeter features opens new possibilities for tailoring the mechanical response of the architectures, potentially optimizing electromechanical performance of electroactive 3D printed structures. For example, Kowalchik et al. demonstrated that pore structure optimization in 3D-printed barium titanate-poly­(vinylidene fluoride) (BT-PVDF) piezoelectric scaffolds led to a 7-fold increase in output voltage.

To date, most DLP work on piezoelectric materials has focused on ceramic composites, , with limited success reported for polymer-based systems. Song et al. printed PVDF-HFP via DLP, but required organic solvents and substantial hardware modifications, including in situ poling. Chen et al. fabricated PVDF structures using stereolithography (SLA), yet also relied on solvents and platform adjustments. These examples highlight the absence of a formulation approach enabling DLP printing of PVDF without the use of volatile organic solvents or hardware modification.

Here, we report a DLP fabrication strategy formulated without volatile organic solvent for the preparation of PVDF composites under ambient conditions. Using a 1,6-hexanediol dimethacrylate (HDDMA) matrix, we preserve PVDF’s crystalline phases during printing. In this system, HDDMA can be compared to a reactive diluent as it is incorporated in the final samples. We investigate the influence of resin composition and processing techniques on phase stability, demonstrating that DLP can deliver high-resolution architectures without phase degradation. Additionally, we investigate preprinting and postprinting treatments, such as solvent precipitation and annealing, on the PVDF and on the 3D printed composite, respectively, to deliberately tune the crystalline. Collectively, these results position DLP as a practical and versatile platform for manufacturing flexible, wearable devices from PVDF-based polymers, potentially suitable for electroactive applications.

Materials and Methods

Preparation of Formulation

Poly­(vinylidene fluoride) (PVDF, M w = 530 000 g/mol; Scientific Polymer Products, Inc.) was dispersed in 1,6-hexanediol dimethacrylate (HDDMA; TCI America) along with 1 wt % of photoinitiator, either phenylbis­(2,4,6-trimethylbenzoyl)­phosphine oxide (BAPO; Sigma-Aldrich), or diphenyl­(2,4,6-trimethylbenzoyl)­phosphine oxide (TPO; Sigma-Aldrich), as specified. It is important that the PVDF is a fine powder to allow stable dispersion in the HDDMA matrix. The PVDF concentration varied from 0 to 35 wt %. The resulting mixtures were sonicated in an ultrasonic bath for 10 min to promote uniform dispersion of the components. Attempts were made to disperse PVDF in formulations containing methyl methacrylate (MMA; Sigma-Aldrich) and of ethylene glycol dimethacrylate (EGDMA; Sigma-Aldrich).

PVDF β-Phase Enrichment via Solvent-Precipitation

PVDF (10 g) was dissolved in a minimal volume of dimethylformamide (DMF) and heated at 80 °C for 2 h until fully dissolved. The solution was then precipitated by dropwise addition into a stirred methanol bath cooled to 4 °C. The resulting precipitate was recovered via Büchner filtration, air-dried for 1 h, and further dried under vacuum at 80 °C for 3 h to remove any residual solvent.

Cure Depth Measurements

The curing behavior of the formulations under UV exposure was evaluated using Jacob’s working curve, derived from the Beer–Lambert law:

Cd=Dpln(EEc) 1

where Cd represents the cure depth for a given exposure E, Dp is the penetration depth of the irradiation at the specified wavelength, and Ec corresponds to the critical exposure required to initiate polymerization.

To establish this curve, ∼ 2 mL of each formulation was deposited in a custom irradiation vat (see Supporting Information (SI), Figure S1). Samples were exposed to a constant light intensity of 2.2 mW/cm2, with exposure times ranging from 10 to 60 s. After curing, the samples were rinsed with isopropanol and dried with compressed air. The thickness of the cured layers was measured using a digital caliper. Each measurement was performed three times for each exposure time.

Viscosity Measurements

Rheology measurements were performed using an MARS60 rheometer (Thermo Fisher Scientific) equipped with a 40 mm diameter parallel plate geometry. Measurements were conducted isothermally at 25 °C over a frequency of 0.1 to 1000 Hz.

DLP 3D Printing

3D printing was performed using a Prusa SL1S printer equipped with a 405 nm light source (intensity: 2.2 mW/cm2). A layer thickness of 25 μm was selected to optimize print resolution. Exposure times were adjusted between 2 and 15 s based on cure depth data obtained.

Thermal Analysis

Differential scanning calorimetry (DSC) was performed using a DSC-Q2000 instrument (TA Instruments). Samples (2–4 mg) were sealed in aluminum pans and subjected to two heating–cooling cycles between 0 and 180 °C at a rate of 10 °C/min under nitrogen flow (50 mL/min). Calibration was performed using an indium standard.

Infrared spectroscopy

Fourier-transform infrared (IR) spectra were collected using a Nicolet iS50 spectrometer (Thermo Fisher Scientific) equipped with a DTGS detector and ATR accessory. A background of 60 scans was recorded, followed by 40 scans of each sample, over the range of 4000–650 cm–1.

X-ray Diffraction

X-ray diffraction (XRD) patterns were acquired using a Malvern Panalytical Empyrean 3 diffractometer in reflection mode with Cu Kα radiation (λ = 1.54 Å). Data were collected over a 2θ range of 4–40° in continuous scan mode with a total acquisition time of 10 min.

Atomic Force Microscopy

AFM imaging was performed in PeakForce QNM with a Bruker Dimension ICON FastScan microscope. The measurement was performed in air at room temperature. AFM-IR measurements were performed on a Nano-IR2 system (Anasys Instruments, USA) in contact mode, with a rate line of 0.7 Hz, using a gold-plated silicon nitride probe with an elastic constant of about 0.5 N m–1 and nominal radius of 10 nm. The IR spectrum was collected directly on sample surfaces, within the 1900–912 cm–1 range (QCL laser) at a spectral resolution of 2 cm–1 and The chemical images were recorded at a scan rate of 1 Hz, a resolution of 450 × 450 pixels, and 128 coaverages, at a laser power limit within 1–5% and at a frequency of 170–220 Hz. For cross-section measurements, the printed F20H80 objects are placed in a mold to be cross-linked in an epoxy block. The epoxy block containing the cross-section of the object that shows up upon slicing with a rotary microtome Leica HistoCore Nanocut R is then used for AFM-IR measurements.

Mechanical Properties

Mechanical tests were performed using an Instron series 5565 at room temperature. A cured dogbone prepared from the formulated mixture was mounted between pneumatic grips. The dogbone was obtained by curing the F20H80 formulation for 30 min in a silicone mold with a thickness of 1.7 mm, a length of 30 mm, and a width of 5 mm. The mechanical properties are summarized in the Table S2. The samples were stretched at a rate of 3 mm/min.

Results and Discussion

Resin Formulation

To enable high-resolution 3D printing of PVDF-based composites via digital light processing (DLP), the resin formulation was optimized with a focus on photopolymerization efficiency, compatibility with PVDF, and preservation of its crystalline structure. Three core components are essential to formulate the resin: a photoinitiator responsive to visible light, a monomer and PVDF as the functional filler. All formulations were prepared under ambient conditions and without the use of any additional volatile organic solvents, minimizing any processing-induced disruption of PVDF’s phase composition.

Initially, methyl methacrylate (MMA) was considered as a monomer due to its favorable dielectric properties. However, MMA contains only one reactive acrylate group per molecule, which proved insufficient to form a cross-linked network capable of sustaining DLP printing. Consequently, when irradiated, MMA-based mixtures did not produce any printed object. Attempts to improve network formation by adding ethylene glycol dimethacrylate (EGDMA) as a cross-linker were also unsuccessful, the cured samples resulted in brittle objects unsuitable for printing, likely due to overcross-linking of the network; details of these tests are provided in Table S1 in the Supporting Information. In contrast, 1,6-hexanediol dimethacrylate (HDDMA) emerged as an ideal matrix. HDDMA has already been reported in the literature for the preparation of PVDF-based composites by 3D printing, demonstrating good compatibility with this polymer. In addition, unlike MMA, HDDMA contains two acrylate groups, which promote efficient cross-linking during photopolymerization. The flexible hexanediol spacer between the acrylate groups provides additional network stability, eliminating the need for supplementary cross-linkers such as EGDMA.

To identify the most effective photoinitiator with HDDMA, cure depth experiments were conducted using formulations containing 20 wt % PVDF and 80 wt % HDDMA, with 1 wt % of either phenylbis­(2,4,6-trimethylbenzoyl)­phosphine oxide (BAPO) or diphenyl­(2,4,6-trimethylbenzoyl)­phosphine oxide (TPO) as 1 wt % is a common quantity reported in literature. BAPO demonstrated superior curing efficiency and print integrity, requiring only 7.5 s of irradiation to cure a 25 μm layer, compared to 13 s for TPO (see SI, Figure S2). This enhanced performance of BAPO is attributed to its higher molar absorptivity than TPO at 405 nm and its dual P–C bond cleavage mechanism, which enhances radical generation and thus polymerization kinetics.

The final formulation, consisting of HDDMA and 1 wt % BAPO, served as a stable and photoreactive base for PVDF loadings ranging from 5 to 35 wt %. The chemical structures of HDDMA, BAPO and the distinct crystalline conformations of PVDF (α, β, and γ) are shown in Figure , while chemical structures of MMA, EGDMA, and TPO are provided in the Supporting Information (Figure S3). Formulations were labeled FxHy where ‘x’ and ‘y’ represent the weight percent of PVDF (F) and HDDMA (H) respectively.

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Chemical structures of the components used in the formulation: (A) 1,6-hexanediol dimethacrylate (HDDMA), the reactive monomer; and (B) phenylbis­(2,4,6-trimethylbenzoyl)­phosphine oxide (BAPO), the photoinitiator. (C) Representative chain conformations of the α, β, and γ crystalline phases of poly­(vinylidene fluoride) (PVDF).

To the best of our knowledge, this is the first demonstration of DLP printing of PVDF composites using a HDDMA-based photopolymer resin under ambient conditions.

Rheological and Optical Properties of the Formulations

The incorporation of PVDF into the resin formulation significantly influenced key parameters related to the printability of the formulation, such as viscosity, light penetration, and dispersion stability. These factors are particularly critical in Digital Light Processing, where maintaining a homogeneous suspension of fillers over time remains a known challenge due to sedimentation tendencies in static vat systems. Despite this, the presence of PVDF in the resin did not result in major printability issues during the fabrication process. A concentration range of 5 to 40 wt % PVDF in HDDMA was initially tested to evaluate the solubility and temporal stability of the mixtures. Across all concentrations, visible sedimentation of PVDF was observed within 48 h, indicating poor long-term miscibility. At concentrations above 35 wt %, the resin could no longer adequately disperse the polymer, rather than forming a homogeneous suspension, the PVDF particles agglomerated due to insufficient interaction with the HDDMA matrix. Incorporation beyond this threshold therefore required the addition of organic cosolvents, such as N,N-dimethylformamide (DMF), methyl ethyl ketone (MEK), or dimethyl sulfoxide (DMSO). Consequently, subsequent analyses focused on formulations containing 5 to 35 wt % PVDF, using BAPO (1 wt %) as the photoinitiator. To ensure optimal dispersion prior to further characterization, all formulations were subjected to 5 min of ultrasonication.

This sedimentation behavior is closely linked to the viscosity of the formulation, which plays a central role in stabilizing particle dispersions and ensuring consistent layer formation during DLP printing. In vat photopolymerization systems, low-viscosity resins (η* < 0.1 Pa·s) promote rapid recoating but are more prone to phase separation and particle settling over time, compromising print fidelity. Conversely, excessively high viscosities (η*>10 Pa·s) can hinder flow and light penetration, reducing both resolution and curing efficiency. As shown in Figure , all tested formulations remained below the recommended upper viscosity limit of 10 Pa·s, with the 35 wt % PVDF formulation reaching approximately 2 Pa·s at an oscillation frequency of 0.1 Hz. However, for formulations containing 5 and 10 wt % PVDF, the average complex viscosity was around 0.03 Pa·s, suggesting that these lower-viscosity resins are more prone to sedimentation and may exhibit poor print fidelity as a result.

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Complex viscosity of the resin with concentrations of PVDF ranging from 0 to 35 wt %.

To assess the effect of PVDF on photopolymerization behavior, Jacobs working curves were constructed for formulations containing 5 to 30 wt % PVDF (Figure ). The derived penetration depth (Dp) and critical exposure energy (Ec) values, calculated using eq , are summarized in Table . A clear trend is observed, both in Figure and in Table and the curves for concentrations up to 10 wt % are remarkably different to those above 20 wt %. As the PVDF concentration increases, Dp decreases from 1.2 mm to 0.38 mm. This reduction suggests that PVDF interferes with light propagation through the resin, likely via two mechanisms. First, PVDF may scatter incoming light due to its refractive index contrast with HDDMA and the formation of microdomains, , thus reducing the intensity of light reaching deeper layers. Second, the increased viscosity associated with higher PVDF loadings (Figure ) may hinder the diffusion of reactive species, further limiting the extent of polymerization in depth.

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Representative cure depth measurement for varying concentrations of PVDF, from 5 to 30 wt %.

1. Optical Parameters Extracted from Jacobs Working Curve for Photopolymer Resins Containing Varying Weight Percentages of PVDF.

Weight Percent of PVDF Ec (mJ·cm–2) Dp (mm) R2
5% 21.6 1.2 ± 0.1 0.971
10% 19.4 1.12 ± 0.07 0.989
20% 15.3 0.52 ± 0.08 0.933
30% 9.40 0.38 ± 0.03 0.981
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Interestingly, while Dp decreases with PVDF content, the critical exposure energy (Ec) also declines, from 21.6 to 9.30 mJ·cm–2, illustrated by the intersection of the curves. This counterintuitive result suggests that although PVDF scatters light, it does not significantly absorb it and thus does not compete with BAPO for photon absorption. Instead, the scattered light may remain trapped within the reactive zone, contributing to radical generation and enhancing the efficiency of initiation. This could explain the reduced energy required to achieve polymerization at higher PVDF loadings.

Together, these findings demonstrate that despite increased scattering and viscosity, the PVDF-containing formulations remain within printable optical and rheological ranges for DLP. This opens the possibility of printing PVDF-based materials without requiring the addition of volatile organic solvents or phase-disrupting thermal treatments.

Print Fidelity and Morphology of Printed Structures

Given the limited temporal stability of the liquid formulations, the distribution of PVDF within the cured materials was investigated using stereomicroscopy. As shown in the stereomicroscopy images in Figure , a clear difference emerges between samples containing 10 and 30 wt % PVDF, particularly in the number, size and distribution of the visible PVDF-rich domains. These domains, appearing as aggregates homogeneously dispersed throughout the cured matrix, confirm that PVDF is not solubilized in HDDMA but rather suspended, leading to the retention of aggregates upon solidification. Similar behavior has been reported in other photopolymer systems where nonreactive additives demix during the curing process. Further characterization of the surface topography and cross-section microstructure is conducted for the 3D printed samples to access the effects on print fidelity (vide infra).

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Images obtained by stereomicroscopy of 3D printed samples using formulations containing (A) 10 wt % PVDF and (B) 30 wt % PVDF.

Jacobs working curves, established for formulations containing 5 to 30 wt % PVDF, were used to determine the optimal exposure dose required to achieve a target curing depth for each resin (Figure ). Based on the results of the cure depth measurements and viscosity analyses, 3D printing trials were carried out using a formulation containing 20 wt % PVDF in HDDMA (Figure ). Exposure times of 7 and 10 s per layer were selected based on the derived working curve equation, which indicated that an irradiation time of approximately 7.5 s would be required to fully cure a 25 μm layer. These exposure times were chosen to assess potential under and over curing effects. Compared to typical values reported in 3d printing forums for acrylate-based DLP resins, which often range from 2 to 20 s per layer depending on formulation and light intensity, these durations are within range and could be optimized using light absorbing additives.

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Evaluation of print fidelity for F20H80 composites. (A) Computer-aided design (CAD) model of the test structure. (B) Printed object obtained with a 7 s exposure time. (C) Printed pyramid with a 7 s exposure time. (D) Printed object obtained with a 10 s exposure time. In all cases, the scale bars correspond to 5 mm.

To evaluate print fidelity, stereomicroscopy measurements were performed on printed test structures of varying light exposures and compared to their corresponding computer-aided design (CAD) model (Figure A). Printed objects were obtained for both 7 and 10 s exposures (Figure B and D). The object cured for 7 s exhibited some defects, although fine details remained visible and well-defined. Its measured feature length, intended to be 10 mm, was 10.212 mm, representing a dimensional deviation of +2.12%. These defects could be attributed to the low viscosity of the resin or the presence of PVDF aggregates. In contrast, the 10 s exposure yielded a defect-free surface; however, some fine details were obscured, and signs of polymer “bleeding” were observed, consistent with overexposure. The measured feature length in this case was 10.253 mm, corresponding to a deviation of +2.53%. Although both exposure conditions produced dimensions close to the intended size, the 7 s exposure provided better preservation of fine details, while the 10 s exposure resulted in a slight dimensional overshoot and reduced feature resolution. To further demonstrate the printability and resolution of the formulation, a small pyramid structure was printed using the F20H80 formulation and an exposure time of 7 s (Figure C). The printed pyramid exhibits well-defined steps (0.5 mm height) and arch-like features (0.5 mm height and 0.9 mm width) at the apex, confirming the ability of the formulation to reproduce fine details and complex geometries.

Further insights into the microstructure of the printed PVDF-HDDMA composites were obtained through atomic force microscopy (AFM), performed on a cross-sectional slice taken from the center of the 3D-printed object (Figure ). These measurements are complemented by AFM surface-level observations (see SI, Figure S4), which showed higher surface roughness than that of the cross-section, likely due to resin flow or layer interface effects. In contrast, the cross-sectional AFM images in Figure revealed a more uniform morphology within the bulk, supporting the conclusion that PVDF is well-distributed throughout the printed material.

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Surface morphology, chemical mapping and adhesion contrast of the F20H80 printed object analyzed by AFM and AFM-IR. (A) AFM height image of the cross-section of the printed structure. The red and green boxes indicate the regions analyzed in (B) and (C), respectively. (B) AFM height (top) and adhesion (bottom) images of the lighter region (red box), exhibiting a root-mean-square (RMS) roughness of 165 nm. (C) AFM height (top) and adhesion (bottom) images of the darker region (green box), with an RMS roughness of 89 nm. (D) AFM-IR chemical mapping at 1732 cm–1 associated with HDDMA.

The AFM height image (Figure A) confirms the presence of PVDF-rich domains embedded in the photopolymer matrix. Regions of different contrasts, highlighted by the red and green boxes, were further analyzed to assess local roughness and adhesion (Figure B and C). The lighter region (B) exhibited a root-mean-square (RMS) roughness of 165 nm, while the darker region (C) had a smoother profile with an RMS of 89 nm. These variations are indicative of partial phase separation between PVDF and HDDMA, likely leading to mechanical and adhesive heterogeneity at the nanoscale. AFM-IR chemical mapping further confirms this phase separation and uniform dispersion of PVDF domains within the HDDMA matrix (Figure D). These measurements were used to confirm the phase composition of the printed object (Figure B). Since PVDF does not exhibit distinguishable absorption bands within the accessible AFM-IR range (1800–900 cm–1), the carbonyl stretching vibration of HDDMA at 1732 cm–1 was used to identify the matrix. The blue regions in the AFM-IR image correspond to HDDMA poor regions and thus can be identified as small aggregates of PVDF, which are homogeneously distributed throughout the matrix at an estimated content of approximately 20%, consistent with the formulation. Importantly, the presence of PVDF aggregates throughout the internal volume does not appear to disrupt printing fidelity or mechanical integrity, as previously hypothesized based on stereomicroscopy observations (Figure ). On the contrary, the embedded domains may contribute to mechanical reinforcement or energy dissipation, potentially enhancing durability. This observation is consistent with the tensile measurements (see SI, Figure S5 and Table S2), conducted on the cured F20H80 composite. These results indicate that the material maintains robust mechanical properties despite the inclusion of PVDF, confirming that the microstructural features observed by AFM do not compromise its overall integrity.

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Phase composition analysis of PVDF-containing formulations as a function of concentration and processing method. (A–C) Thermal and structural characterization of samples with increasing PVDF content (0 to 35 wt %) using (A) Differential Scanning Calorimetry (DSC) first heating curve, (B) Infrared Spectroscopy (IR), and (C) X-ray Diffraction (XRD). (D–F) Comparison of phase composition for samples processed by photocuring and 3D printing, using (D) DSC, (E) IR, and (F) XRD.

This result also highlights a key advantage of the DLP process: room-temperature photopolymerization preserves the initial crystalline phase of PVDF while ensuring high printing fidelity. AFM analysis further confirms that the microstructure remains homogeneous and unchanged by the printing process, suggesting that the processing method does not significantly disrupt the crystalline organization within the aggregates.

PVDF Crystalline Phase Characterization

To evaluate the impact of blending PVDF with HDDMA on both the degree of crystallinity and the preservation of PVDF’s characteristic crystalline phases during photopolymerization, a combination of differential scanning calorimetry (DSC), infrared spectroscopy (IR), and X-ray diffraction (XRD) analyses was performed on formulations containing 5 to 35 wt % PVDF. Both photocured disc and 3D-printed samples were characterized to assess potential differences in crystalline behavior due to the printing process.

As shown in Figure A, DSC analysis of pristine PVDF revealed a distinct melting peak around 157 °C, characteristic of its semicrystalline nature. Upon incorporation into the HDDMA matrix and subsequent photopolymerization, the presence of a distinct melting peak was retained, indicating that PVDF maintains its semicrystalline nature following DLP printing.

A slight increase in melting temperature, to approximately 164 °C, was also observed in all formulations containing HDDMA. This shift may be attributed to the formation of a cross-linked network that imposes spatial constraints on the PVDF domains, thereby requiring a higher thermal energy to disrupt their organization. These findings suggest that the printing process and resin formulation do not inhibit crystallization but rather support the stabilization of crystalline domains within the polymer matrix.

The degree of crystallinity (X c) of PVDF was calculated using eq :

Xc=ΔHfΔHf* 2

where ΔHf is the melting enthalpy of the sample and ΔHf* is the melting enthalpy for 100% crystalline PVDF (104.7 J/g).

The pristine PVDF exhibited a crystallinity of approximately 37%, which is slightly lower than the approximately 50% typically reported for commercial samples (M w = 530,000 g·mol–1), likely due to processing differences. In composite formulations, the corrected crystallinity values, normalized to PVDF content, ranged from 9% at 5 wt % to 14% at 35 wt % (see SI, Table S3). This percentage is lower than that of the pristine PVDF incorporated in the formulation, indicating that a partial solubilization of the PVDF might occur upon its blending within the HDDMA formulation. However, this partial solubilization does not disrupt drastically the phases in presence in the pristine PVDF. The crystalline phase content increases with the PVDF content supporting the hypothesis that less solubilization occurs upon the addition of PVDF. This trend further supports the retention of crystallinity in the photopolymerized system.

The cooling cycle analysis (see SI, Figure S6) provided additional insight into the crystallization behavior of PVDF in the presence of HDDMA. The crystallization temperature of PVDF increased in the composite formulations (ca. 137 °C) compared to pristine PVDF (ca. 120 °C), under identical cooling conditions. This shift may be explained by the presence of the cross-linked HDDMA network, which could serve as a structural scaffold promoting nucleation and growth of PVDF crystals by lowering the energy barrier for crystallization. ,, This would account for the higher crystallization temperatures observed in these networks compared to that observed for the pristine PVDF.

Infrared spectroscopy (IR) was used to evaluate the crystalline phase composition of PVDF within HDDMA-based formulations. This technique is particularly effective for identifying the α phase of PVDF, which is characterized by distinct absorption bands at 489, 614, 766, 795, 855, and 976 cm–1. , In contrast, the β and γ phases, due to their similar chain conformations, display overlapping absorption bands, in the range of 512 and 840 cm–1, making them more challenging to differentiate solely by IR.

As shown in Figure B, the IR spectrum of pure PVDF displays the characteristic α phase bands. While some peaks from HDDMA overlap with those of PVDF (around 820, 980, and 1150 cm–1), several key α phase markers, such as those at 614 and 766, cm–1, remain clearly distinguishable in all composite formulations. Notably, even at PVDF contents up to 35 wt %, no substantial changes in the IR spectral features were observed, indicating that the presence of the HDDMA matrix does not significantly alter the crystalline phase composition of PVDF, even though it modifies the degree of crystallinity. This result stands in contrast to previous studies involving PMMA thermoplastic matrices processed from the melt, ,, where partial miscibility and H-bonding between −CH2 groups of PVDF and carbonyl groups of PMMA, stabilize the all-trans conformation of PVDF chains, shift the α→β crystal transition to lower cooling rates and promote β phase formation. In our room-temperature DLP conditions, PVDF remains as solid particulates within a cross-linked HDDMA network; the absence of a melt-cooling step, combined with the immobility of ester groups within the cured network and the lack of molecular-scale miscibility, could prevent the chain rearrangements and interfacial interactions effects responsible for β phase promotion.

To further validate these findings, X-ray diffraction (XRD) analysis was conducted. XRD is particularly useful for distinguishing between PVDF’s α and β phases. Both α and β phases exhibit strong reflections near 2θ = 20°, but the α phase also shows additional peaks near 2θ = 18° and a distinct reflection at 26.56°, while the β phase presents a secondary reflection at 36.03°.

As shown in Figure C, all PVDF-HDDMA formulations displayed diffraction patterns consistent with the α-phase. However, HDDMA contributes a broad amorphous halo centered near 2θ = 19°, which overlaps with PVDF peaks at 18.03° and 20.26°, particularly in formulations with less than 10 wt % PVDF. This overlap leads to broadening of the β phase-associated peaks, especially at 20.26°, complicating phase identification at lower PVDF loadings.

Despite this diffractogram overlap, no new diffraction peaks or significant peak shifts were observed, suggesting that the printing process and the resin composition do not induce phase transitions in PVDF. The absence of emerging β phase signatures or loss of α phase reflections further supports the conclusion that the DLP process preserves the intrinsic crystalline structure of PVDF.

To confirm that the printing process does not impact the phase composition of PVDF, comparative analyses were carried out between a film polymerized by continuous light irradiation (using the same instrumental setup as the cure depth measurements), herein referred to as photocured sample, and a 3D object obtained via DLP printing, referred to as 3D printed sample. The former involves constant irradiation through the entire thickness, whereas DLP polymerizes the formulation layer-by-layer with uniform dosing, potentially influencing polymerization kinetics and component distribution.

In Figure D, DSC analyses revealed a slight shift in the melting peak. The photocured object exhibited a melting temperature approximately 5 °C lower than that of the printed object, along with a decrease in melting enthalpy (from 4.90 J/g to 4.77 J/g), which may indicate a slight reduction in overall crystallinity. Despite this thermal variation, XRD diffractograms showed no significant differences between the phases in presence in the two samples, confirming the stability of the α, β, and γ phase composition (Figure C). Complementary IR analyses, conducted using an attenuated total reflectance accessory probing the surface of the sample, revealed more intense absorption bands in the printed object, possibly due to migration of the PVDF toward the irradiated surface layers. Despite these minor differences, the α and β phase crystallinity remained comparable between the two processes indicating that the printing method does not induce any significant transformation of the crystalline structure of PVDF.

PVDF Phase Engineering before and after Printing

We demonstrated that DLP printing preserves the crystalline phase composition of PVDF, making it a suitable fabrication method when the phase content has been intentionally modified beforehand or requires adjustment after printing. This demonstration opens the possibility of controlling the β phase fraction independently of the printing process. To explore this, we assessed PVDF phase engineering both prior to and following printing.

To increase the fraction of β phase prior to printing, PVDF was subjected to a solvent-precipitation treatment in a highly polar medium, similar to the precipitation technique used by Sodano et al. IR analysis of the resulting powder (referred to as pPVDF) revealed a significant increase in β phase content, as evidenced by the stronger intensity of the absorption band at ∼ 840 cm–1 and the reduced intensity of α phase bands at ∼614 and 766 cm–1 (Figure A). Quantitative analysis of the peak intensities indicates that the β to α phase ratio in pPVDF is approximately 3 times higher than in pristine PVDF. XRD diffractograms (Figure B) confirmed this observation, showing more intense β phase peaks at 2θ = 20.26° and 36.03° compared to α-phase peaks at 2θ = 18° and 26.56°, with a β to α intensity ratio about 1.7 times higher than that of pristine PVDF. These results confirm that the precipitation treatment effectively enhances β phase content.

8.

8

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Phase composition analysis of PVDF-containing formulations as a function of treatment method. (A,B) Structural characterization of PVDF after solvent-precipitation (pPVDF) and after photopolymerization at 20 wt % (pPVDF-print) using (A) Infrared Spectroscopy (IR) and (B) X-ray Diffraction (XRD). (C,D) Comparison of phase composition for samples containing 30 wt % PVDF subjected to postprinting annealing (F30H70-a) using (C) IR and (D) XRD.

The pPVDF was then incorporated into HDDMA at 20 wt % and sonicated for 10 min. Due to the larger particle size resulting from precipitation, sedimentation occurred more rapidly than with the untreated powder, with visible settling within minutes. The formulation, containing BAPO as the photoinitiator, was photocured. Consistent with earlier results (Figure E), IR spectra of the cured composite (pPVDF-print) showed less pronounced PVDF bands relative to HDDMA, likely due to less homogeneous surface dispersion (Figure A). However, XRD patterns of pPVDF and pPVDF-print were identical, both showing a high β phase content, with a β to α intensity ratio about 1.4 times higher than that of pristine PVDF. These findings demonstrate that preprocessing PVDF to enrich its β phase does not result in phase composition changes during DLP printing.

Additive manufacturing enables the fabrication of complex geometries, but postprint treatments may be required to further tailor functional properties of the active fillers. Thermal annealing is a well-established method for promoting β phase crystallization, with optimal temperatures typically ranging between 70 and 110 °C depending on the matrix, solvent, and fillers. −

To investigate postprint modification, a HDDMA/PVDF print containing 30 wt % PVDF (F30H70-a) was annealed at 90 °C for 5 h and cooled under ambient conditions. IR and XRD analyses (Figure C and D) revealed a small increase in β phase content compared to the nonannealed sample, as indicated by slightly enhanced β phase peaks and a β to α intensity ratio around 1.1 times higher. However, the magnitude of this increase was lower than that achieved through the preprint solvent-precipitation method. While this procedure confirmed the feasibility of phase transformation after printing, optimization of annealing temperature and duration will be required to make this approach efficient and practically relevant. Alternative postprint techniques, such as UV or plasma treatment, could also be explored as they can enhance phase content without altering the geometry of the printed object, unlike mechanical methods such as stretching or rolling.

Conclusion

In this work, we have demonstrated an ambient-condition digital light processing (DLP) strategy for fabricating poly­(vinylidene fluoride) (PVDF)-based composites with high print fidelity and preserved crystalline phase integrity. By optimizing resin formulation, specifically using 1,6-hexanediol dimethacrylate (HDDMA) as the photopolymerizable matrix and phenylbis­(2,4,6-trimethylbenzoyl)­phosphine oxide (BAPO) as the photoinitiator, we achieved stable suspensions of PVDF particles up to 35 wt % and efficient photopolymerization without phase degradation.

Rheological and optical analyses confirmed the printability of the formulations, while microscopic and AFM characterizations revealed homogeneous PVDF dispersion with retained microstructural integrity. Comprehensive phase characterization by DSC, IR, and XRD showed that the intrinsic semicrystalline phases of PVDF remains stable throughout both photopolymerization and 3D printing. Moreover, phase modification prior to printing via solvent-precipitation successfully enhanced the β phase without loss during printing, and postprint thermal annealing offered further phase tuning. These results position DLP as a practical and versatile additive manufacturing platform for PVDF-based polymer devices, potentially suitable for electroactive applications, enabling tailored phase content and complex geometries without compromising structural or functional properties.

Supplementary Material

lg5c00113_si_001.pdf (1.4MB, pdf)

Acknowledgments

MMG acknowledges the financial support from Fonds de recherche du Québec secteur Nature et Technologie (FRQNT) (10.69777/351107). AL acknowledges the Canada Research Chair program, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canada Foundation for Innovation (CFI). The authors would also like to thank Jean-François Myre from the mechanical engineering workshop for the fabrication of the cure measurement setup as well as Daniel Chartrand for the XRD measurements. The authors would like to thank Jiayi Chen and Anthony Jolly for their help with the AFM-IR and tensile test measurements.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acspolymersau.5c00113.

  • Instrumental setup of the cure depth measurement technique as well as the results and molecular structure of tested molecules; characterization of the morphology and crystallinity of the printed samples containing PVDF (PDF)

CRediT: Megan Jane McGeehan conceptualization, data curation, formal analysis, investigation, methodology; Étienne Durand-Laberge data curation, formal analysis; Matthieu Gervais conceptualization, writing - review & editing; Sébastien Roland conceptualization, writing - review & editing; Audrey Laventure conceptualization, funding acquisition, methodology, project administration, resources, supervision, validation, writing - original draft, writing - review & editing.

The authors declare no competing financial interest.

Published as part of ACS Polymers Au special issue “2025 Rising Stars in Polymers”.

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Supplementary Materials

lg5c00113_si_001.pdf (1.4MB, pdf)

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