@article{wang_xiao_siddika_shamsi_frey_qian_bai_brendan t. o'connor_dickey_2024, title={Glassy gels toughened by solvent}, volume={6}, ISSN={["1476-4687"]}, url={https://doi.org/10.1038/s41586-024-07564-0}, DOI={10.1038/s41586-024-07564-0}, journal={NATURE}, author={Wang, Meixiang and Xiao, Xun and Siddika, Salma and Shamsi, Mohammad and Frey, Ethan and Qian, Wen and Bai, Wubin and Brendan T. O'Connor and Dickey, Michael D.}, year={2024}, month={Jun} }
 @article{siddika_peng_balar_dong_zhong_you_ade_oconnor_2023, title={Molecular interactions that drive morphological and mechanical stabilities in organic solar cells}, volume={7}, ISSN={["2542-4351"]}, DOI={10.1016/j.joule.2023.06.002}, abstractNote={Morphological and mechanical stabilities of organic solar cells (OSCs) are of paramount importance to ensure long-lived devices. However, the fundamental drivers of these stability metrics and their competing relationship have yet to be well defined. Here, several high-performance polymers and small molecule acceptors (SMAs) are considered to assist in the development of a comprehensive view of the molecular drivers of, and interrelationships between, morphological and mechanical stabilities. We find that the SMAs drive much of the embrittlement and diffusion characteristics in the blend films. However, the heterointeraction of the SMA and polymer, probed through dynamic mechanical analysis, is a key contributing factor to the film toughness. The heterointeraction energy is ideally maximally negative (i.e., repulsive), deviating from the geometric mean of the homointeraction energy. These findings assist in introducing a framework to understand the active layer stability and highlight material properties that lead to morphologically stable and physically robust OSCs.}, number={7}, journal={JOULE}, author={Siddika, Salma and Peng, Zhengxing and Balar, Nrup and Dong, Xinyun and Zhong, Xiaowei and You, Wei and Ade, Harald and OConnor, Brendan T.}, year={2023}, month={Jul}, pages={1593–1608} }
 @article{shanahan_oh_son_siddika_pendleton_brendan t. o'connor_you_2023, title={Strategic Incorporation of Cleavable Side Chains Improves Thermal Stability of PffBT-T4-Based Polymer Solar Cells}, volume={35}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.3c02181}, abstractNote={Thermal degradation by intrinsic morphological change and extrinsic oxidation remain outstanding challenges for bulk heterojunction (BHJ)-based polymer solar cells (PSCs). Postprocessing thermocleavage of side chains on the donor conjugated polymers using ester pyrolysis is a proven method to kinetically trap the morphology via increased glass transition temperature (Tg) and improved thermal oxidation resistance. We previously showed that having a certain fraction of thermocleavable side chains (TCS) incorporated into the archetypical polymer P3HT, achieved through the copolymerization of a TCS-functionalized thiophene monomer, can offer high thermal stability to its BHJ devices without compromising significant performance metrics. This work expands the concept of using the copolymerized TCS monomer unit to balance the stability with efficiency into the state-of-the-art PSC system PffBT-T4-OD:PCBM, where the original octyl–decyl (OD) branched side chains are partially replaced with TCS in 50–70 mol % in the copolymers. Structural differences of the fully cleavable PffBT-T4-TCS polymer and P3ET polymers disclose that increasing backbone rigidity and alkyl chain length can increase the temperature of eliminating alkyl chains by up to 20 °C in the solid state. Dynamic mechanical analysis shows the cleaved PffBT-T4-TCS polymer has significantly increased thermal relaxation temperatures and high storage modulus over a large temperature range. Thermal stability testing at 100 °C in air reveals that increasing the TCS content drastically increases the polymer resistance to oxidation. PSCs made with the fully cleavable PffBT-T4-TCS polymer offer only a meager efficiency of 0.2%, while the copolymer with 60 mol % TCS can deliver a PCE of 3.2% with its BHJ device, double the previous highest reported efficiency for TCS-containing polymer-based PSCs. Importantly, the copolymer with the 60 mol % TCS-based device is stable, retaining 80% of the initial performance after accelerated aging tests (100 °C, 2 weeks). Together with our previous works, these new findings demonstrate that using partial cleavage of side chains could be a general strategy to gain both efficiency and stability for conjugated polymer-based PSCs.}, number={23}, journal={CHEMISTRY OF MATERIALS}, author={Shanahan, Jordan and Oh, Jiyeon and Son, Sung Yun and Siddika, Salma and Pendleton, David and Brendan T. O'Connor and You, Wei}, year={2023}, month={Nov}, pages={10139–10149} }
 @article{booth_khanna_schrickx_siddika_al shafe_brendan t. o'connor_2022, title={Electrothermally Actuated Semitransparent Shape Memory Polymer Composite with Application as a Wearable Touch Sensor}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.2c10290}, abstractNote={A semitransparent shape memory polymer (SMP):silver nanowire (AgNW) composite is demonstrated to be capable of low-temperature actuation, thus making it attractive for wearable electronics applications that require intimate contact with the human body. We demonstrate that the SMP:AgNW composite has tunable electrical and optical transparency through variation of the AgNW loading and that the AgNW loading did not significantly change the mechanical behavior of the SMP. The SMP composite is also capable of electrical actuation through Joule heating, where applying a 4 V bias across the AgNWs resulted in full shape recovery. The SMP was found to have high strain sensitivity at both small (<1%) and large (over 10%) applied strain. The SMP could sense strains as low as 0.6% with a gauge factor of 8.2. The SMP composite was then utilized as a touch sensor, able to sense and differentiate tapping and pressing. Finally, the composite was applied as a wearable ring that was thermally actuated to conformably fit onto a finger as a touch sensor. The ring sensor was able to sense finger tapping, pressing, and bending with high signal-to-noise ratios. These results demonstrate that SMP:AgNW composites are a promising design approach for application in wearable electronics.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Booth, Ronald E. and Khanna, Chetna and Schrickx, Harry M. and Siddika, Salma and Al Shafe, Abdullah and Brendan T. O'Connor}, year={2022}, month={Nov} }
 @article{siddika_sharif_hasan_2021, title={Effect of Areca and Waste Nylon Fiber Hybridization on the Properties of Recycled Polypropylene Composites}, ISSN={["1544-046X"]}, DOI={10.1080/15440478.2021.1929651}, abstractNote={ABSTRACT Present research investigated the effect of areca and waste nylon fiber hybridization on the properties of areca and waste nylon fiber-reinforced hybrid recycled polypropylene composites. The impact of fiber surface modification was also investigated by the alkali treatment of natural areca fiber. Composites were manufactured using hot press machine by creating an alternative layer of fiber matrix lamellae arrangement at four levels of fiber loading (10, 15, 20, and 25 wt%). Areca and waste nylon fiber ratio were varied at 1:3, 2:3, 3:2, and 3:1 for 20 wt% fiber-loaded composites. Tensile, flexural and hardness tests, scanning electron microscopic, and Fourier transform infrared spectroscopic analysis were conducted for characterization of the composites. Fourier transform infrared spectroscopic analysis of the composites indicated decrease of hemicelluloses and lignin content and corresponding improved mechanical interlocking with alkali treatment of areca fiber. Treated fiber-reinforced composite showed better mechanical properties in comparison with the untreated ones. Tensile test of composites showed a decreasing trend of tensile strength after 10 wt% fiber loading. Whereas Young’s modulus, flexural strength, flexural modulus, and hardness values were found to be increased with the increase in fiber loading. Only tensile strength value was higher in higher areca fiber-reinforced composite. All other properties were peaked on highest waste nylon fiber-reinforced one. Scanning electron microscopic analysis indicated more uniform distribution of fibers in treated fiber-reinforced composite, while fiber agglomeration increased in higher fiber-loaded composites.}, journal={JOURNAL OF NATURAL FIBERS}, author={Siddika, Salma and Sharif, Ahmed and Hasan, Mahbub}, year={2021}, month={Jun} }
 @article{balar_rech_siddika_song_schrickx_sheikh_ye_bonilla_awartani_ade_et al._2021, title={Resolving the Molecular Origin of Mechanical Relaxations in Donor-Acceptor Polymer Semiconductors}, volume={32}, ISSN={["1616-3028"]}, url={https://doi.org/10.1002/adfm.202105597}, DOI={10.1002/adfm.202105597}, abstractNote={AbstractThe thermomechanical behavior of polymer semiconductors plays an important role in the processing, morphology, and stability of organic electronic devices. However, donor–acceptor‐based copolymers exhibit complex thermal relaxation behavior that is not well understood. This study uses dynamic mechanical analysis (DMA) to probe thermal relaxations of a systematic set of polymers based around the benzodithiophene (BDT) moiety. The loss tangent curves are resolved by fitting Gaussian functions to assign and distinguish different relaxations. Three prominent transitions are observed that correspond to: i) localized relaxations driven primarily by the side chains (γ ), ii) relaxations along the polymer backbone (β  ), and iii) relaxations associated with aggregates (α  ). The side chains are found to play a clear role in dictating Tγ, and that mixing the side chain chemistry of the monomer to include alkyl and oligo(ethylene glycol) moieties results in splitting the γ ‐relaxation. The β relaxations are shown to be associated with backbone elements along with the monomer. In addition, through processing, it is shown that the α‐relaxation is due to aggregate formation. Finally, it is demonstrated that the thermal relaxation behavior correlates well with the stress–strain behavior of the polymers, including hysteresis and permanent set in cyclically stretched films.}, number={4}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={Balar, Nrup and Rech, Jeromy James and Siddika, Salma and Song, Runqiao and Schrickx, Harry M. and Sheikh, Nadeem and Ye, Long and Bonilla, Anthony Megret and Awartani, Omar and Ade, Harald and et al.}, year={2021}, month={Oct} }
 @article{son_samson_siddika_brendan t. o'connor_you_2021, title={Thermocleavage of Partial Side Chains in Polythiophenes Offers Appreciable Photovoltaic Efficiency and Significant Morphological Stability}, volume={33}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.1c01305}, abstractNote={The intrinsic degradation of conjugated polymer (CP) based solar cells (PSCs) due to morphological change by heat is an outstanding challenge. Increasing the glass transition temperature (Tg) of the materials used in PSCs can largely mitigate the thermal instability, yet most CPs used in high-efficiency PSCs only show low Tg values, mainly due to the long and bulky side chains needed for solution processing of such polymers. Thermally removing cleavable side chains is an effective approach to regain the high Tg of CPs after the film formation, thereby achieving higher stability; however, previous results using polythiophenes only achieved moderate efficiency (0.8% with PC61BM) after a high temperature (300 °C) treatment to remove all side chains. To better understand and utilize thermocleavable side chains (TCSs), we explore a series of regioregular polythiophenes having TCSs and hexyl side chains by varying the ratio of different side chains, from 0 mol % TCSs to 100 mol % TCSs at an increment of 20 mol %. Through a systematic investigation, we find that the polymers with more TCSs than hexyl side chains exhibit sufficient stability under a rather harsh condition (100 °C, in air and under continuous ambient light). While a complete removal of alkyl chains might offer a higher stability, the device efficiency was very low (∼0.14%); by contrast, the polymer having ∼70 mol % of TCSs achieved the highest efficiency (∼1.5%) after alkyl chain cleavage at 200 °C and significant morphological stability. Under our stability test (150 °C, 24 h and ambient light), these specific polymer:PC61BM based solar cells were able to retain 90% of the original efficiency. These key findings, together with mechanistic understanding of the thermocleavage process, provide valuable insight into the impact of TCS and present a new design rationale to achieve PSCs with both high efficiency and improved stability.}, number={12}, journal={CHEMISTRY OF MATERIALS}, author={Son, Sung Yun and Samson, Stephanie and Siddika, Salma and Brendan T. O'Connor and You, Wei}, year={2021}, month={Jun}, pages={4745–4756} }
 @article{balar_siddika_kashani_peng_rech_ye_you_ade_brendan t. o'conner_2020, title={Role of Secondary Thermal Relaxations in Conjugated Polymer Film Toughness}, volume={32}, ISSN={["1520-5002"]}, url={https://publons.com/wos-op/publon/35208553/}, DOI={10.1021/acs.chemmater.0c01910}, abstractNote={Conjugated polymers have proven to be an important class of materials for flexible and stretchable electronics. To ensure long term thermal and mechanical stability of associated devices, there is ...}, number={15}, journal={CHEMISTRY OF MATERIALS}, author={Balar, Nrup and Siddika, Salma and Kashani, Somayeh and Peng, Zhengxing and Rech, Jeromy James and Ye, Long and You, Wei and Ade, Harald and Brendan T. O'Conner}, year={2020}, month={Aug}, pages={6540–6549} }