Nabil Kleinhenz

Ultrasound-induced ordering in poly(3-hexylthiophene): role of molecular and process parameters on morphology and charge transport.

Facile methods for controlling the microstructure of polymeric semiconductors are critical to the success of large area flexible electronics. Here we explore ultrasonic irradiation of solutions of poly(3-hexylthiophene) (P3HT) as a simple route to creating ordered molecular aggregates that result in a one to two order of magnitude improvement in field effect mobility. A detailed investigation of the ultrasound induced phenomenon, including the role of solvent, polymer regioregularity (RR) and film deposition method, is conducted. Absorption spectroscopy reveals that the development of low energy vibronic features is dependent on both the regioregularity as well as the solvent, with the latter especially influential on the intensity and shape of the band. Use of either higher regioregular polymer or ultrasonic irradiation of lower regioregular polymer solutions results in high field effect mobilities that are nearly independent of the dynamics of the film formation process. Surprisingly, no distinct correlation between thin-film morphology and macroscopic charge transport could be ascertained. The relationships between molecular and process parameters are very subtle: modulation of one effects changes in the others, which in turn impact charge transport on the macroscale. Our results provide insight into the degree of control that is required for the development of reproducible, robust materials and processes for advanced flexible electronics based on polymeric materials.

Photoinduced Anisotropic Assembly of Conjugated Polymers in Insulating Polymer Blends

Low-dose UV irradiation of poly(3-hexylthiophene) (P3HT)-insulating polymer (polystyrene (PS) or polyisobutylene (PIB)) blend solutions led to the formation of highly ordered P3HT nanofibrillar structures in solidified thin films. The P3HT nanofibers were effectively interconnected through P3HT islands phase-separated from insulating polymer regions in blend films comprising a relatively low fraction of P3HT. Films prepared with a P3HT content as low as 5 wt % exhibited excellent macroscopic charge transport characteristics. The impact of PS on P3HT intramolecular and intermolecular interactions was systematically investigated. The presence of PS chains appeared to assist in the UV irradiation process of the blend solutions to facilitate molecular interactions of the semiconductor component, and to enhance P3HT chain interactions during spin coating because of relatively unfavorable P3HT-PS chain interactions. However, P3HT lamellar packing was hindered in the presence of PS chains, because of favorable hydrophobic interactions between the P3HT hexyl substituents and the PS chains. As a result, the lamellar packing d-spacing increased, and the coherence length corresponding to the lamellar packing decreased, as the amount of PS in the blend films increased.

Conjugated Polymer Alignment: Synergisms Derived from Microfluidic Shear Design and UV Irradiation

Solution shearing has attracted great interest for the fabrication of robust and reliable, high performance organic electronic devices, owing to applicability of the method to large area and continuous fabrication, as well as its propensity to enhance semiconductor charge transport characteristics. To date, effects of the design of the blade shear features (especially the microfluidic shear design) and the prospect of synergistically combining the shear approach with an alternate process strategy have not been investigated. Here, a generic thin film fabrication concept that enhanced conjugated polymer intermolecular alignment and aggregation, improved orientation (both nanoscale and long-range), and narrowed the π-π stacking distance is demonstrated for the first time. The impact of the design of shearing blade microfluidic channels and synergistic effects of fluid shearing design with concomitant irradiation strategies were demonstrated, enabling fabrication of polymer-based devices with requisite morphologies for a range of applications.

Analyzing Public and State Reactions to Global Surveillance Disclosures: Using Ethical Frameworks to Gain Understanding

Secretive surveillance activities are carried out by government agencies in an effort to protect national security. Upon discovery, however, there can sometimes be significant ramifications on diplomatic relations, potentially impacting international cooperation and security. In the wake of the Snowden leaks, various levels of reaction have been observed from nation states and the public. This work attempts to understand the differences observed in reactions to recent intelligence leaks and explore theories around intelligence ethics. Ethical standards used by intelligence officials differ from those applied by the general public. Following the surveillance disclosures by Edward Snowden, the rhetoric among public officials was heated. Global opinions strongly view NSA surveillance activities of foreign citizens or heads of state as “unacceptable” (unless specifically targeting a terrorist). However, the magnitude of action taken by a nation-state in response to the leaks correlated with the level of public opposition to surveillance activity in that country.