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Softmatterworld.org has received generous funding from the National Science Foundation and continues to incorporate a science writing internship program for UC Merced undergrads.
“Morphology transition in lipid vesicles due to in-plane order and topological defects”
L.S. Hirst, A. Ossowski, M. Fraser, J. Geng, J.V. Selinger and R.L.B. Selinger, PROC. NATL. ACAD. SCI. 110 (9) 3242-3247 (2013) Link
“Tuning quantum dot organization in liquid crystal for robust photonics applications”
A.L. Rodarte, Z.S. Nuno, B.H. Cao, R. J. Pandolfi, M. Quint, S. Ghosh, J. Hein and L.S. Hirst, CHEM PHYS CHEM, , Issue 7, pages 1413–1421, (2014) Link
Mesogenic ligands have the potential to provide control over the dispersion and stabilization of nanoparticles in liquid crystal (LC) phases. The creation of such hybrid materials is an important goal for the creation of soft tunable photonic devices, such as the LC laser. Herein, we present a comparison of isotropic and mesogenic ligands attached to the surface of CdSe (core-only) and CdSe/ZnS (core/shell) quantum dots (QDs). The mesogenic ligand′s flexible arm structure enhances ligand alignment, with the local LC director promoting QD dispersion in the isotropic and nematic phases. To characterize QD dispersion on different length scales, we apply fluorescence microscopy, X-ray scattering, and scanning confocal photoluminescent imaging. These combined techniques demonstrate that the LC-modified QDs do not aggregate into the dense clusters observed for dots with simple isotropic ligands when dispersed in liquid crystal, but loosely associate in a fluid-like droplet with an average interparticle spacing >10 nm. Embedding the QDs in a cholesteric cavity, we observe comparable coupling effects to those reported for more closely packed isotropic ligands.
“Dye sensitized cholesteric liquid crystalline photonic luminescent solar concentrator”
A.L. Rodarte, F. Cisneros, L.S. Hirst and S. Ghosh, LIQUID CRYSTALS, DOI:10.1080/02678292.2014.924163, (2014) Link
We have developed organic dye-integrated thin-film liquid crystalline photonic luminescent solar concentrators (LSCs), where the chirality of the liquid crystal (LC) results in the formation of a one-dimensional photonic cavity. By varying the different LSC parameters, including dye concentration, spectral position of the photonic band-gap and the LC phase, and by using spectroscopic and electrical characterisation, we have systematically studied the effects of self-absorption, incident absorption and confinement of down-converted emission on optical efficiency. Our results demonstrate that the efficiency of our LSCs is significantly enhanced in the LC phase when the photonic band-gap is at long wavelengths (>600 nm), overcoming associated low incident absorption and higher self-absorption. We reach the significant conclusion that focusing on improving the confinement of dye-emitted photons, rather than on increasing incident absorption, is a more promising route to enhancing thin-film LC-based LSC performance.
Professor Hirst is the author of “Fundamentals of soft matter science” (Taylor and Francis, CRC Press) 2012
About the book
Soft materials such as liquid crystals, polymers, biomaterials, and colloidal systems touch every aspect of our lives. Not surprisingly, the rapid growth of these fields over the past few decades has resulted in an explosion of soft matter research groups worldwide. Fundamentals of Soft Matter Science introduces and explores the scientific study of soft matter and molecular self-assembly, covering the major classifications of materials, their structure and characteristics, and everyday applications.
Designed for beginners to the field with a basic scientific background, this readable book emphasizes conceptual understanding, minimizing detailed mathematical derivations. Each chapter is dedicated to a different group of soft materials, including liquid crystals, surfactants, polymers, colloids, and soft biomaterials. Each subject is broken down into the essential concepts: material structures and physical characteristics, some simple theoretical ideas, and important experimental methods. The book emphasizes commonly used experimental techniques and practical applications. Full color illustrations and photographs are incorporated throughout to help describe the systems and key concepts.
Purchase from CRC press or Amazon
Congratulations go to Dr Andrea Rodarte who passed her PhD defense in August.
“Dispersions of Semiconductor Nanoparticles in Thermotropic Liquid Crystal: From Optical Modiﬁcation to Assisted Self-Assembly”
Read the full version here
Andrea has now begun a postdoctoral position at UC SanDiego.
“Designing highly tunable semi-flexible filament networks”
R. Pandolfi, L. Edwards, D. Johnston, P. Becich and L.S. Hirst, PHYS. REV. E. 89, 062602(2013) Link
Semiflexible polymers can generate a range of filamentous networks significantly different in structure from those seen in conventional polymer solutions. Our coarse-grained simulations with an implicit cross-linker potential show that networks of branching bundles, knotted morphologies, and structural chirality can be generated by a generalized approach independent of specific cross-linkers. Network structure depends primarily on filament flexibility and separation, with significant connectivity increase after percolation. Results should guide the design of engineered semiflexible polymers