Daniel P. Armstrong
North Carolina State University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Daniel P. Armstrong.
Advanced Materials | 2017
Mohammad Vatankhah-Varnoosfaderani; William F. M. Daniel; Alexandr P. Zhushma; Qiaoxi Li; Benjamin J. Morgan; Krzysztof Matyjaszewski; Daniel P. Armstrong; Richard J. Spontak; Andrey V. Dobrynin; Sergei S. Sheiko
Freestanding, single-component dielectric actuators are designed based on bottlebrush elastomers that enable giant reversible strokes at relatively low electric fields and altogether avoid preactuation mechanical manipulation. This materials design platform allows for independent tuning of actuator rigidity and elasticity over broad ranges without changing chemical composition, which opens new opportunities in soft-matter robotics.
Nature Communications | 2016
David J. Lunn; Oliver E. C. Gould; George R. Whittell; Daniel P. Armstrong; Kenneth P. Mineart; Mitchell A. Winnik; Richard J. Spontak; Paul G. Pringle; Ian Manners
Anisotropic nanoparticles prepared from block copolymers are of growing importance as building blocks for the creation of synthetic hierarchical materials. However, the assembly of these structural units is generally limited to the use of amphiphilic interactions. Here we report a simple, reversible coordination-driven hierarchical self-assembly strategy for the preparation of micron-scale fibres and macroscopic films based on monodisperse cylindrical block copolymer micelles. Coordination of Pd(0) metal centres to phosphine ligands immobilized within the soluble coronas of block copolymer micelles is found to induce intermicelle crosslinking, affording stable linear fibres comprised of micelle subunits in a staggered arrangement. The mean length of the fibres can be varied by altering the micelle concentration, reaction stoichiometry or aspect ratio of the micelle building blocks. Furthermore, the fibres aggregate on drying to form robust, self-supporting macroscopic micelle-based thin films with useful mechanical properties that are analogous to crosslinked polymer networks, but on a longer length scale.
Proceedings of SPIE | 2017
Mohammad Vatankhah-Varnosfaderani; William F. M. Daniel; Alexandr P. Zhushma; Qiaoxi Li; Benjamin J. Morgan; Krzysztof Matyjaszewski; Daniel P. Armstrong; Andrey V. Dobrynin; Sergei S. Sheyko; Richard J. Spontak
Electroactive polymers (EAPs) refer to a broad range of relatively soft materials that change size and/or shape upon application of an electrical stimulus. Of these, dielectric elastomers (DEs) generated from either chemically- or physically-crosslinked polymer networks afford the highest levels of electroactuation strain, thereby making this class of EAPs the leading technology for artificial-muscle applications. While mechanically prestraining elastic networks remarkably enhances DEs electroactuation, external prestrain protocols severely limit both actuator performance and device implementation due to gradual DE stress relaxation and the presence of a cumbersome load frame. These drawbacks have persisted with surprisingly minimal advances in the actuation of single-component elastomers since the dawn of the “pre-strain era” introduced by Pelrine et al. (Science, 2000). In this work, we present a bottom-up, molecular-based strategy for the design of prestrain-free (freestanding) DEs derived from covalently-crosslinked bottlebrush polymers. This architecture, wherein design factors such as crosslink density, graft density and graft length can all be independently controlled, yields inherently strained polymer networks that can be readily adapted to a variety of chemistries. To validate the use of these molecularly-tunable materials as DEs, we have synthesized a series of bottlebrush silicone elastomers in as-cast shapes. Examination of these materials reveals that they undergo giant electroactuation strains (>300%) at relatively low fields (<10 V/m), thereby outperforming all commercial DEs to date and opening new opportunities in responsive soft-material technologies (e.g., robotics). The molecular design approach to controlling (electro)mechanical developed here is independent of chemistry and permits access to an unprecedented range of actuation properties from elastomeric materials with traditionally modest electroactuation performance (e.g., polydimethylsiloxane, PDMS). Experimental results obtained here compare favorably with theoretical predictions and demonstrate that the unique behavior of these materials is a direct consequence of the molecular architecture.
Proceedings of SPIE | 2016
Richard J. Spontak; Krishna B. Subramani; Daniel P. Armstrong; Enes Cakmak; Tushar K. Ghosh
Several reports have appeared on the topic of anisotropic actuation in dielectric elastomers. Most of these, including our own published in Advanced Materials (2014), incorporate aligned microfibers into the VHB adhesive. In all these studies, the results have been quite promising, demonstrating that anisotropic actuation is achieved primarily in the direction normal to the fiber axis. We have previously explored this phenomenon in detail using polyurethane and carbon fibers. In the present study, we shall use these results to set the stage for our ongoing studies that employ our unique thermoplastic elastomer gel (TPEG) design, which provides much more versatility than VHB. These results allow us to decouple the roles of dielectric constant and mechanical modulus in actuation development.
Advanced Functional Materials | 2017
Christopher B. Cooper; Kuralamudhan Arutselvan; Ying Liu; Daniel P. Armstrong; Yiliang Lin; Mohammad Rashed Khan; Jan Genzer; Michael D. Dickey
Journal of Polymer Science Part B | 2017
Heba A. Al-Mohsin; Kenneth P. Mineart; Daniel P. Armstrong; Richard J. Spontak
Solar RRL | 2018
Heba A. Al-Mohsin; Kenneth P. Mineart; Daniel P. Armstrong; Ahmed El-Shafei; Richard J. Spontak
Rubber Chemistry and Technology | 2017
Daniel P. Armstrong; Richard J. Spontak
ACS Macro Letters | 2016
Daniel P. Armstrong; Kenneth P. Mineart; Byeongdu Lee; Richard J. Spontak
Advanced Functional Materials | 2018
Daniel P. Armstrong; Richard J. Spontak