Decreasing the shear stress-induced in-plane molecular alignment by unprecedented stereolithographic delay in three-dimensional printing

Chakraborty, Patatri; Zhao, Guanglei; Zhou, Chi; Cheng, Chong; Chung, D.D.L.

doi:10.1007/s10853-018-3047-0

Cited by 7 publications

(6 citation statements)

References 24 publications

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“…The photopolymer in this work is a general-purpose ultraviolet (UV) curable resin from Formlabs (Somerville, MA). It contains methacrylated monomers, methacrylated oligomers, and photoinitiator, its viscosity is 2950 cP [9]. The specific chemical components in the resin are trade secrets.…”

Section: Methodsmentioning

confidence: 99%

“…Capacitance measurement has been previously reported for sensing voids in a 3D-printed metal structure that is simulated in the laboratory [5] and for sensing the stress in a 3D-printed polymer structure [6]. In addition, capacitance measurement has been used for characterization of the structure [7][8][9] and piezoelectric behavior [10] of 3D-printed polymers capacitance measurement has also been previously reported for sensing the voids and stress in monolithic steel [11,12] and cement paste [13,14], which are both not obtained by 3D-printing. Capacitance measurement has not been previously reported for sensing interlayer defects.…”

Section: Introductionmentioning

confidence: 99%

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Unprecedented sensing of interlayer defects in three-dimensionally printed polymer by capacitance measurement

Chakraborty

Zhao

Zhou

et al. 2018

Smart Mater. Struct.

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Interlayer defects in a three-dimensionally (3D) printed structure are expected from the residual stress and commonly observed warpage, but their detection has been challenging and elusive. They are to be distinguished from intralayer defects (e.g., discernible voids), which can be quite easily detected. Interlayer defects in the form of local inadequate interlayer bonding in a 3D-printed polymer structure have been unprecedentedly shown in this work to be detectible by capacitance measurement. The interlayer defects are artificially obtained and judiciously positioned. The printing involves conventional stereolithography, using an acrylate resin. Two coplanar electrical contacts are positioned on the exterior surface of the structure. The capacitance decreases monotonically with increasing number of defects at a given layer, and with decreasing N, where N is the number of layers above the defect, thus providing an effective indicator of the presence and location defects. However, the capacitance can be the same for different numbers of defects if N is different. This issue may be circumvented in future work by having additional electrical contacts at various layers. The maximum value of N that allows capacitance-based defect detection exceeds 210. The fractional decrease in capacitance due to the defects (relative to the case of no defect) increases monotonically with increasing number of defects at a given layer, but it essentially does not vary with N. Thus, the fractional decrease in capacitance indicates the presence of defects, but is not an effective indicator of the defect location. The capacitance increases with N, due to the larger depth of penetration of the current when N is higher. The greater is the number of defects at a layer, the more is the reduction in the depth of current penetration by these defects. The technique of this work may be extended to the detection of the 3D positions of defects by capacitance tomography.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Unprecedented sensing of interlayer defects in three-dimensionally printed polymer by capacitance measurement

Chakraborty

Zhao

Zhou

et al. 2018

Smart Mater. Struct.

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“…The more the platform is lowered, the more the resin is squeezed and the greater the shear stress encountered by the resin. As shown by shear stress analytical modeling (with consideration of the viscosity of the resin and the layer thickness) and measurement of the downward force exerted by the platform, the shear stress is large enough to align the monomer molecules [2]. The higher the viscosity of the resin, the greater the shear stress involved [2].…”

Section: Introductionmentioning

confidence: 99%

“…As shown by shear stress analytical modeling (with consideration of the viscosity of the resin and the layer thickness) and measurement of the downward force exerted by the platform, the shear stress is large enough to align the monomer molecules [2]. The higher the viscosity of the resin, the greater the shear stress involved [2]. The occurrence of in-plane molecular alignment is supported by the increase in the out-of-plane electric permittivity [1] beyond the value for the bulk polymer, which has no molecular alignment.…”

Section: Introductionmentioning

confidence: 99%

Enhancing the inherent piezoelectric behavior of a three-dimensionally printed acrylate polymer by electrical poling

Chakraborty

Zhou

Chung

2018

Smart Mater. Struct.

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A three-dimensionally (3D) printed acrylate polymer without filler, printed by stereolithography, has previously been shown to be inherently piezoelectric in the out-of-plane and in-plane directions in the absence of electrical poling. This work has shown that the longitudinal piezoelectric coupling coefficient d is increased by poling at an electric field of 2400 V m−1 by up to about 200%. The poling takes 60 min for either direction. The effect of in-plane poling on the in-plane piezoelectric effect is greater than the effect of out-of-plane poling on the out-of-plane piezoelectric effect. This is due to the lower piezoelectric coefficient without poling for the in-plane direction, consistent with the fact that the molecular alignment is 2D in the plane of the printed layers and the in-plane poling is conducted in a particular in-plane direction. Without poling, d is smaller for the in-plane direction than the out-of-plane direction. With poling, d is essentially equal for the two directions. This suggests that the in-plane poling possibly causes the in-plane molecular alignment to develop a slight degree (if any) of 1D molecular alignment. The natural depoling that occurs immediately after the completion of the poling takes as little as 60 min, with the depoling being faster in the out-of-plane direction than the in-plane direction. Due to the depoling, the inherent piezoelectric behavior without poling remains practically attractive.

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“…In the current issue, Chung et al take this work one step farther and demonstrate a method to control the degree of molecular alignment [6]. They achieve this by introducing a pause between the final motion of the print stage toward the tank bottom and the beginning of the photolithography.…”

mentioning

confidence: 99%

Controlling anisotropy in stereolithographically printed polymers

Huber

2018

J Mater Sci

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Decreasing the shear stress-induced in-plane molecular alignment by unprecedented stereolithographic delay in three-dimensional printing

Cited by 7 publications

References 24 publications

Unprecedented sensing of interlayer defects in three-dimensionally printed polymer by capacitance measurement

Unprecedented sensing of interlayer defects in three-dimensionally printed polymer by capacitance measurement

Enhancing the inherent piezoelectric behavior of a three-dimensionally printed acrylate polymer by electrical poling

Controlling anisotropy in stereolithographically printed polymers

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