@article{zhao_zikry_2017, title={Oxidation-induced failure in semi-crystalline organic thin films}, volume={109}, ISSN={["1879-2146"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85009488974&partnerID=MN8TOARS}, DOI={10.1016/j.ijsolstr.2017.01.008}, abstractNote={Polymer oxidation is a major degradation mechanism in organic solar cells. However, microstructural details of diffusion-reaction processes and oxidation-induced failure in structured semi-crystalline active layers are difficult to be predicted or measured, due to material heterogeneities, such as different material phases, crystallinities, nano-film thickness. Hence, a diffusion-reaction process has been coupled to a crystalline-amorphous material model and fracture algorithm within a nonlinear microstructurally-based finite element (FEM) framework to investigate and predict heterogeneous oxidative degradation and embrittlement failure in semi-crystalline organic thin films due to the interrelated effects of diffusion, reaction, stress accumulations, and crystalline packing order. The edge-on packing oriented film was more susceptible to oxidation than the face-on oriented packing film due to higher local stresses and reaction accumulations that resulted in higher decrease of local toughness and extensive film cracking in the amorphous phase. The coupled effects of mechanical stresses and oxygen diffusion-reaction accelerated degradation mechanisms and resulted in film cracking and delamination occurring at lower nominal strains in comparison with the case without oxidation embrittlement. Degradation was dominated by the reaction process and exposure time, as opposed to the diffusion process due to the nano-sized films. This predictive framework can be used to understand fundamental local oxidative degradation mechanisms and the morphological effects on long term durability of semi-crystalline organic thin films.}, journal={INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES}, author={Zhao, Bingxiao and Zikry, M. A.}, year={2017}, month={Mar}, pages={72–83} }
 @article{zhao_awartani_o'connor_zikry_2016, title={A direct correlation of x-ray diffraction orientation distributions to the in-plane stiffness of semi-crystalline organic semiconducting films}, volume={108}, ISSN={["1077-3118"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84968866659&partnerID=MN8TOARS}, DOI={10.1063/1.4948533}, abstractNote={Large charge mobilities of semi-crystalline organic semiconducting films could be obtained by mechanically aligning the material phases of the film with the loading axis. A key element is to utilize the inherent stiffness of the material for optimal or desired alignment. However, experimentally determining the moduli of semi-crystalline organic thin films for different loading directions is difficult, if not impossible, due to film thickness and material anisotropy. In this paper, we address these challenges by presenting an approach based on combining a composite mechanics stiffness orientation formulation with a Gaussian statistical distribution to directly estimate the in-plane stiffness (transverse isotropy) of aligned semi-crystalline polymer films based on crystalline orientation distributions obtained by X-ray diffraction experimentally at different applied strains. Our predicted results indicate that the in-plane stiffness of an annealing film was initially isotropic, and then it evolved to transv...}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Zhao, Bingxiao and Awartani, Omar and O'Connor, Brendan and Zikry, Mohammed A.}, year={2016}, month={May} }
 @article{awartani_zhao_currie_kline_zikry_brendan t. o'connor_2016, title={Anisotropic Elastic Modulus of Oriented Regioregular Poly(3-hexylthiophene) Films}, volume={49}, ISSN={["1520-5835"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84954288748&partnerID=MN8TOARS}, DOI={10.1021/acs.macromol.5b02680}, abstractNote={Specific morphological features of polymer semiconductors are often promoted in devices to optimize optoelectronic behavior. Less studied is the role of morphology on the mechanical properties of the film, such as elastic modulus, which is an important property for the development of flexible and stretchable devices. To gain insight into the morphological origin of elasticity in polymer semiconductors and its relationship to charge transport, we study the anisotropic in-plane elastic modulus of strain-aligned regioregular poly(3-hexylthiophene) (P3HT) films and compare the results to previously measured field effect charge mobility. The film morphology is varied through the amount of applied strain and post strain thermal annealing. Morphological characterization includes UV–vis optical spectroscopy and X-ray diffraction. The elastic modulus is measured using a buckling-based measurement technique. The elastic modulus of the film is found to decrease as the film is plastically strained. Thermally annealin...}, number={1}, journal={MACROMOLECULES}, author={Awartani, Omar M. and Zhao, Bingxiao and Currie, Tyler and Kline, R. Joseph and Zikry, Mohammed A. and Brendan T. O'Connor}, year={2016}, month={Jan}, pages={327–333} }
 @article{zhao_awartani_o'connor_zikry_2016, title={Microstructural Behavior and Failure Mechanisms of Organic Semicrystalline Thin Film Blends}, volume={54}, ISSN={["1099-0488"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84954289843&partnerID=MN8TOARS}, DOI={10.1002/polb.23991}, abstractNote={Organic thin film blends of P3HT semiconducting polymers and PCBM fullerenes have enabled large-scale semiconductor fabrication pertaining to flexible and stretchable electronics. However, molecular packing and film morphologies can significantly alter mechanical stability and failure behavior. To further understand and identify the fundamental mechanisms affecting failure, a multiphase microstructurally based formulation and nonlinear finite-element fracture methodology were used to investigate the heterogeneous deformation and failure modes of organic semicrystalline thin film blends. The multiphase formulation accounts for the crystalline and amorphous behavior, polymer tie-chains, and the PCBM aggregates. Face-on packing orientations resulted in extensive inelastic deformation and crystalline rotation, and this was characterized by ductile failure modes and interfacial delamination. For edge-on packing orientations, brittle failure modes and film cracking were due to lower inelastic deformation and higher film stress in comparison with the face-on orientations. The higher crystallinity of P3HT and larger PCBM aggregates associated with larger domain sizes, strengthened the film and resulted in extensive film cracking. These predictions of ductile and brittle failure are consistent with experimental observations for P3HT:PCBM films. The proposed predictive framework can be used to improve organic film ductility and strength through the control of molecular packing orientations and microstructural mechanisms. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 896–907}, number={9}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Zhao, Bingxiao and Awartani, Omar and O'Connor, Brendan and Zikry, Mohammed A.}, year={2016}, month={May}, pages={896–907} }
 @article{zhao_zikry_2015, title={The effects of structural disorders and microstructural mechanisms on semi-crystalline P3HT behavior}, volume={57}, ISSN={["1873-2291"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84920446650&partnerID=MN8TOARS}, DOI={10.1016/j.polymer.2014.12.003}, abstractNote={Semiconducting conjugated polymers, such as P3HT, have applications for photovoltaic and flexible electronics. However, charge transport is sensitive to the mechanical behavior of the donor P3HT. A computational framework has, therefore, been used to identify the microstructural mechanisms, at different physical scales, that affect behavior. The approach accounts for the microstructure as an interrelated three-phase model that is physically representative of crystalline domains, an amorphous interphase, and tie-chain bridging regions. Based on our predictions, the face-on packing crystalline orientations had higher toughness in comparison with the edge-on packing orientations that had higher strengths due to local dislocation-density interaction mechanisms. The higher inelastic deformation, associated with face-on orientations, disrupted the conjugation structure in the crystalline phase, and this could affect charge. These predictions indicate that the behavior of P3HT polymers can be optimized by controlling the packing orientations, the crystallinity, the entangled chain density, and the tie chain interconnectivity.}, journal={POLYMER}, author={Zhao, Bingxiao and Zikry, M. A.}, year={2015}, month={Jan}, pages={1–11} }