Fully printable plasticized fluorinated terpolymers for mirror active morphing control

Copyright 2025 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited. Colin Lesenne, David Audigier, Pierre-Jean Cottinet and Jean-Fabien Capsal, "Fully printable plasticized fluorinated terpolymers for mirror active morphing control", Proc. SPIE 13431, Electroactive Polymer Actuators, Sensors, and Devices (EAPAD) 2025, 134310T (12 May 2025); https://doi.org/10.1117/12.3050308 Fully printable, plasticized fluorinated terpolymers for mirror active morphing control Colin Lesenne*a, David Audigiera, Pierre-Jean Cottineta, Jean-Fabien Capsal*a aINSA Lyon, LGEF, UR682, 69621 Villeurbanne, France ABSTRACT The use of plasticized P(VDF-TrFE-CFE), a relaxor ferroelectric polymer, has shown major improvements over the past few years. Dedicated to telescopes active optics actuators for the Live-Mirror project, the analysis of the plasticizer (here, DNOP) interaction with various polymer matrixes for high permittivity and softness is investigated here. The amount of termonomer not only leads to a low crystalline fraction but also increases the number of amorphous – crystalline interfaces where it can accumulate and get trapped. The obtention of large S33 of 2.5% at 30V/µm (here 6µm), measured by interferometry, vows great displacements for 4D-printed multilayer actuators. Keywords: Plasticized terpolymers, 4D-printing, active optics, P(VDF-TrFE-CFE), actuators. 1. INTRODUCTION The approach undertaken by Live-Mirror [1], a collaboration regrouping multiple research parties, is to establish the additive manufacturing process of an electroactive polymer (EAP)-based multilayer structure capable of locally curving a few-mm thick, 5m-wide mirror for active optics [2], [3]. EAPs have gain in interest during the past decades due to their wide range of applications, from artificial muscles and micro-pumps to sensors and actuators. Among them, the addition of a third monomer inside a P(VDF-TrFE) matrix, such as chlorotrifluoroethylene (CTFE) [4], [5] or chlorofluoroethylene (CFE) [6], has demonstrated conformation changes into a relaxor-ferroelectric with a minimized hysteresis. Recently, Capsal et. al reported major improvements in the electromechanical response of terpolymers thanks to the incorporation of phthalate plasticizers [7]. The addition of 15 wt.% of bis(2-ethylhexyl) phthalate (DEHP) has increased by up to 215x the mechanical energy and by 28x the electrostrictive coefficient. The addition of DINP, through various concentrations, also unveiled a 25% enhancement in strain for a same content as DEHP[8]. This originates from a boost in permittivity at low frequencies and a drop in Young’s modulus, leading to unprecedented strains related to Maxwell forces (eq.(1), expressed as : 𝑆!"#$%&& = 𝜀'𝜀(𝐸) 𝑌 (1) with e0 the vacuum permittivity, er the relative permittivity of the dielectric material, E the applied electric field. As compared to a neat terpolymer, while it has been demonstrated a 20x enhancement of the mechanical energy density for CTFE-based terpolymers, CFE-based ones underwent a 100x increase [9], leading this study to pursue with P(VDF-TrFECFE). The influence of terpolymer composition on plasticizer benefits has been studied for only a few CTFE contents. Although CTFE-based terpolymers are cheaper and more available, their molecular differences from CFE suggest they won't yield similar outcomes. This study aims to analyze various CFE-based terpolymers to reassess the impact of plasticizers on electromechanical performance. Identifying a candidate with high softness, permittivity, and stability for low-frequency actuation is crucial for the Live-Mirror project. *C. Lesenne : [email protected] ; +33 7 69 94 95 01 *J.-F. Capsal : [email protected] ; lgef.insa-lyon.fr Copyright 2025 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited. Colin Lesenne, David Audigier, Pierre-Jean Cottinet and Jean-Fabien Capsal, "Fully printable plasticized fluorinated terpolymers for mirror active morphing control", Proc. SPIE 13431, Electroactive Polymer Actuators, Sensors, and Devices (EAPAD) 2025, 134310T (12 May 2025); https://doi.org/10.1117/12.3050308 2. MATERIALS AND METHODS 2.1 Materials Poly(vinylidene-trifluoroethylene-chlorofluoroethylene), P(VDF-TrFE-CFE) powders were provided by Piezotech (Arkema group, France) with various VDF, TrFE and CFE contents. Each terpolymer is named after its VDF and CFE content as T(VDF:CFE). They were synthesized by suspension polymerization [10] and their composition is displayed in Table 1. Methyl-ethyl-ketone (MEK, AnalaR NORMAPUR® Reag. Ph.Eur., ACS, 100.0%) was supplied by VWR Chemicals, and Cyclopentanone (> 99%) by Carl-Roth®. Di-n-octyl phthalate (DNOP, > 98%, GC) plasticizer was supplied by Sigma-Aldrich, and the Durapore® 5µm PVDF membrane filters by Merck (Millipore). Table 1. Terpolymers compositions. Sample VDF/(VDF+TrFE) % CFE T(62:7) 0,67 7.0 T(61:8) 0,66 7.9 T(79:8) 0,86 8.2 T(54:9) 0,59 9.2 T(49:13) 0,57 12.9 T(79:13) 0,92 13.4 T(52:13) 0,60 13.5 2.2 Methods Each terpolymer was dissolved into a 60:40 MEK:Cyclopentanone mixture with a polymer-to-solvent mass fraction of 16 wt.%, followed by the addition of 10 wt.% (with respect to the terpolymer content) of DNOP plasticizer. Once formulated, a filtering step through a 5µm PVDF membrane allowed the removal of any residual gel from in-situ polymerization, improving the breakdown strength of the resulting EAP solution [11]. A Doctor Blade (elcometer® 3700) was used to cast 1mm-thick films onto glass substrates which were let for 2h at room temperature to allow the solvents evaporation (Figure 1). The films were introduced into an oven at 60°C for 2h and at 10 to 20°C below Tonset for 2h to ensure a homogeneous crystallization process for increased breakdown strength and permittivity, compliant with a median crystal fraction [12]. Figure 1. Illustration of film-making process. DSC measurements of raw terpolymers powders were performed with a DSC 131 EVO calorimeter from Seteram Instrumentation. The second run, erasing the thermal history, was analysed with Calisto Processing. The dielectric characterization of pure and plasticized EAP films was performed with Broadband Dielectric Spectroscopy (BDS). Dielectric properties (i.e, permittivity and tan delta) were measured with a Solartron 1280 connected to an AC generator and a Trek Amplifier 20/20. Electric field varying from 0V/µm to 20V/µm, according to the sample’s thickness, was applied with a frequency ranging from 20kHz to 10mHz. The direct measurement of the field-induced strain was obtained through an Agilent Keysight interferometer. A 4-layer structure was assembled with z-conductive tape and aluminium sheets [13], in order to multiply the total displacement. Data was recorded on a with the dedicated acquisition software. Copyright 2025 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited. Colin Lesenne, David Audigier, Pierre-Jean Cottinet and Jean-Fabien Capsal, "Fully printable plasticized fluorinated terpolymers for mirror active morphing control", Proc. SPIE 13431, Electroactive Polymer Actuators, Sensors, and Devices (EAPAD) 2025, 134310T (12 May 2025); https://doi.org/10.1117/12.3050308 3. RESULTS AND DISCUSSIONS 3.1 DSC results On Figure 2 (a) is displayed the thermograms associated to each terpolymer powder. As expected from the CFE/TrFE ratio, the melting temperature decreases from 130.4°C for T(62:7), to 113.4°C for T(52:13) and ultimately 102.7°C for T(79:13). The onset temperatures reported were used for the annealing temperature of the casted films. The inhomogeneous chain composition distribution of T(79:8) is revealed by its triple endothermic peak around its melting point, deconvoluted on Figure 2 (b). The degree of crystallinity (cc) of each terpolymer is calculated using the following expression: 𝜒!(%)=∆H" ∆H#$$ ×100 (2) with DH100 the enthalpy of fusion of a fully crystalline terpolymer, which value of 42.56 J/g has been determined by extrapolation of data acquired by J. Klein et. al [14]. The decreasing crystallinity with the CFE content, represented on Figure 2 (c), outlines the disrupting behaviour of the termonomer in the crystal. a) b) c) Figure 2. (a) Thermograms of terpolymer powders and (b) evolution of their enthalpy of fusion and crystallinity with %CFE. 3.2 Broadband Dielectric Spectroscopy (BDS) results On Figure 3 is compared the dielectric properties T(62:7) (a) and T(54:9) (b). For comparison, the pure terpolymers (in red) show high permittivity at 1kHz, with the highly crystalline T(62:7) displaying a permittivity of 56 whereas T(54:9) stands lower with 46. At low frequency (100mHz) and electric field (5V/µm), both plasticized terpolymers witness a significant gain in performance with eT(62:7) = 265 and eT(54:9) = 256. Triggered by the enhanced free volume brought by DNOP in constrained amorphous – crystalline interfaces, a 10 wt.% plasticizer concentration allows a higher frequencyshifted (characterized by tan(d)max) free carriers mobility [8]. a) b) Figure 3. Dielectric properties of pure (red) and plasticized (a) T(62:7) and (b) T(54:9) over 10mHz - 1kHz and 0 - 20V/µm. Copyright 2025 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited. Colin Lesenne, David Audigier, Pierre-Jean Cottinet and Jean-Fabien Capsal, "Fully printable plasticized fluorinated terpolymers for mirror active morphing control", Proc. SPIE 13431, Electroactive Polymer Actuators, Sensors, and Devices (EAPAD) 2025, 134310T (12 May 2025); https://doi.org/10.1117/12.3050308 3.3 Field-induced strain measurements Following the dielectric and mechanical characterizations, the realization of 4-layer actuators led to the direct measurement of the field-induced strain. As the structure involves conductive tape between metallized films, which mechanical properties (Young’s modulus or creep) are unknown, the observable residual strain might alter a quantitative interpretation. On Figure 4 is represented S33 of an optimized terpolymer calculated as the recorded displacement divided by the total thickness of EAP (therefore ignoring the tape’s thickness), with a 10mHz input solicitation. While a quadratic evolution with E, in accordance with eq.(1, can be noticed up to 25V/µm, a slight saturation appears at 30V/µm. This follows the observed evolution of permittivity of plasticized terpolymers at low frequency, as shown on Figure 3 (b). For a maximum strain of 2.5%, the total strain of this 4 EAP-layer structure led to a displacement of nearly 6µm. Greater inputs weren’t tested as many possible defects (between aluminum, tape and EAP), increased the probability of electrical breakdown. Figure 4 : (a) S33 at 10mHz and (b) its average value with E. 4. CONCLUSION The analysis of different P(VDF-TrFE-CFE) compositions revealed significant, sometimes neglected, differences with CTFE-based terpolymers. Similar dielectric properties were found between a highly crystalline T(62:7) and a soft T(54:9) due to its higher CFE retention, leading to a multiplicated electrostrictive coefficient. The resultant strain produced by an optimized terpolymer with 10 wt.% of DNOP led to S33 of 2.5% at 30V/µm, corresponding to a total displacement of nearly 6µm. The 4D-printing of multilayer actuators will be the next step for the development of lightweight, low-powered actuation for telescopes’ active optics. ACKNOWLEDGEMENTS This project has received funding from the European Union’s Horizon Europe Pathfinder under grant agreement n°101099220. C.L acknowledges the cooperation of Arkema for the delivery of tailored terpolymer powders. Copyright 2025 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. 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