Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

Zhang, Chi

doi:10.1177/0003702817708321

Cited by 44 publications

(41 citation statements)

References 184 publications

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“…To be able to evaluate the intensity of C–H vibrations without the interfering broad bands from O–H stretching vibrations, we have made use of the properties of the time-asymmetric visible pulse in our SFG spectrometer. 43 , 44 The short-lived O–H vibrations outlast less than 100 fs, 45 whereas the dephasing and life times of C–H vibrations are typically in the order of several picoseconds.…”

Section: Resultsmentioning

confidence: 99%

Effects of Ca²⁺ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces

2018

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The structure of poly(sodium 4-styrenesulfonate) (NaPSS) polyelectrolytes at air–water interfaces was investigated with tensiometry, ellipsometry, and vibrational sum-frequency generation (SFG) in the presence of low and high CaCl2 concentrations. In addition, we have studied the foaming behavior of 20 mM NaPSS solutions to relate the PSS molecular structure at air–water interfaces to foam properties. PSS polyelectrolytes without additional salt exhibited significant surface activity, which can be tuned further by additions of CaCl2. The hydrophobicity of the backbone due to incomplete sulfonation during synthesis is one origin, whereas the effective charge of the polyelectrolyte chain is shown to play another major role. At low salt concentrations, we propose that the polyelectrolyte is forming a layered structure. The hydrophobic parts are likely to be located directly at the interface in loops, whereas the hydrophilic parts are at low concentrations stretched out into near-interface regions in tails. Increasing the Ca2+ concentration leads to ion condensation, a collapse of the tails, and likely to Ca2+ intra- and intermolecular bridges between polyelectrolytes at the interface. The increase in both surface excess and foam stability originates from changes in the polyelectrolyte’s hydrophobicity due to Ca2+ condensation onto the PSS polyanions. Consequently, charge screening at the interface is enhanced and repulsive electrostatic interactions are reduced. Furthermore, SFG spectra of O–H stretching bands reveal a decrease in intensity of the low-frequency branch when c(Ca2+) is increased whereas the high-frequency branch of O–H stretching modes persists even for 1 M CaCl2. This originates from the remaining net charge of the PSS polyanions at the air–water interface that is not fully compensated by condensation of Ca2+ ions and leads to electric-field-induced contributions to the SFG spectra of interfacial H2O. A charge reversal of the PSS net charge at the air–water interface is not observed and is consistent with bulk electrophoretic mobility measurements.

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Section: Resultsmentioning

confidence: 99%

Effects of Ca²⁺ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces

2018

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“…Therefore, the detected signals are generated only at interfaces, and the SFG vibrational spectroscopy could in principle identify and quantify the surface composition, thus shedding light on interfacial segregation of a component. This issue of interfacial segregation of additives has already been extensively investigated by SFG spectroscopy for non-conjugated polymers (Lu et al, 2017; Zhang, 2017), but not really explored for conjugated polymers and blends.…”

Section: Interfacial Morphologymentioning

confidence: 99%

Polymer Solar Cells—Interfacial Processes Related to Performance Issues

2019

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Harnessing solar energy with solar cells based on organic materials (in particular polymeric solar cells) is an attractive alternative to silicon-based solar cells due to the advantages of lower weight, flexibility, lower manufacturing costs, easier integration with other products, low environmental impact during manufacturing and operations and short energy payback times. However, even with the latest efficiencies reported up to 17%, the reproducibility of these efficiencies is not up to par, with a significant variation in the efficiencies reported across the literature. Since these devices are based on ultrathin multilayer organic films, interfaces play a major role in their operation and performance. This review gives a concise account of the major interfacial issues that are responsible for influencing the device performance, with emphasis on their physical mechanisms. After an introduction to the basic principles of polymeric solar cells, it briefly discusses charge generation and recombination occurring at the donor-acceptor bulk heterojunction interface. It then discusses interfacial morphology for the active layer and how it affects the performance and stability of these devices. Next, the formation of injection and extraction barriers and their role in the device performance is discussed. Finally, it addresses the most common approaches to change these barriers for improving the solar cell efficiency, including the use of interface dipoles. These issues are interrelated to each other and give a clear and concise understanding of the problem of the underperformance due to interfacial phenomena occurring within the device. This review not only discusses some of the implemented approaches that have been adopted in order to address these problems, but also highlights interfacial issues that are yet to be fully understood in organic solar cells.

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“…The basic theory of SFG-VS can be found in numerous reviews [7][8][9][10][11] evidencing the importance of this powerful and versatile tool for surface-and interface-sensitive studies. In the following, a short introduction of the physical background is given.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Sum-Frequency Generation Vibrational Spectroscopy Investigations of Phosphonic Acids on Anodic Aluminum Oxide Films

2018

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Self-assembled monolayers of alkyl phosphonic acids on anodic aluminum oxide (AlOx) surfaces are important as dielectric layers in thin film electronic devices. Assessing the properties and quality of these monolayers on amorphous AlOx is limited to a few surface-sensitive methods. In this work, we study using nonlinear optical measurements the molecular ordering in n-alkyl phosphonic acids with various alkyl chain lengths (6 to 18 carbons) deposited on AlOx and show the influence of temperature on stability and conformational order. The results demonstrate that the octadecylphosphonic acid has fewest defects in the chain orientation. A detailed comparison of the longest and the shortest alkyl chain revealed different behavior in conformational ordering upon annealing.

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Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

Cited by 44 publications

References 184 publications

Effects of Ca²⁺ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces

Effects of Ca²⁺ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces

Polymer Solar Cells—Interfacial Processes Related to Performance Issues

Sum-Frequency Generation Vibrational Spectroscopy Investigations of Phosphonic Acids on Anodic Aluminum Oxide Films

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Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

Cited by 44 publications

References 184 publications

Effects of Ca2+ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces

Effects of Ca2+ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces

Polymer Solar Cells—Interfacial Processes Related to Performance Issues

Sum-Frequency Generation Vibrational Spectroscopy Investigations of Phosphonic Acids on Anodic Aluminum Oxide Films

Contact Info

Product

Resources

About

Effects of Ca²⁺ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces

Effects of Ca²⁺ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air–Water Interfaces