Kevin G. Yager

Brookhaven National Laboratory

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Gregory S. Doerk

Brookhaven National Laboratory

Alamgir Karim

University of Houston

Masafumi Fukuto

Brookhaven National Laboratory

Paweł W. Majewski

University of Warsaw

Charles T. Black

Brookhaven National Laboratory

Chinedum O. Osuji

University of Pennsylvania

Christopher J. Barrett

McGill University

Marcus M. Noack

Lawrence Berkeley National Laboratory

Oleg Gang

Brookhaven National Laboratory

Gurpreet Singh

Punjab Engineering College

Cooperative Institutions

Brookhaven National Laboratory

136

Stony Brook University

National Institute of Standards and Technology

Argonne National Laboratory

Lawrence Berkeley National Laboratory

Columbia University

Chinese Academy of Sciences

National Synchrotron Light Source II

Stanford Synchrotron Radiation Lightsource

Oak Ridge National Laboratory

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Suppression of target patterns in domain aligned cold-zone annealed block copolymer films with immobilized film-spanning nanoparticles

Soft Matter (2014)

Xiaohua Zhang Kevin G. Yager Jack F. Douglas Alamgir Karim

We examine the effect of a moving in-plane temperature gradient on the ordering of cylinder-forming block-copolymers (BCP) in films containing immobilized nanoparticles that span the film thickness. In a previous paper, we reported the effect of static step oven-annealing of these films above the glass transition temperature Tg for a long period before ordering the BCP film at a much higher temperature. In the dynamic film annealing method of the present work, termed cold zone annealing (CZA), the material is continuously raised to a temperature somewhat above the glass transition temperature and then well above it, with a control of the heating time and thermal gradient. Oven annealing before ordering has been found to relieve residual stresses in the film associated with large thermal expansion of the film upon heating, eliminating the large scale target patterns induced by stresses effects associated with residual solvent and thermal expansion. By comparison, CZA naturally suppresses undesirable target patterning with enhanced ordering kinetics created through this thermal history.

Temperature Gradient

10.1039/c4sm00238e

Cite

Citations (6)

Improved Anisotropic Thermoelectric Behavior of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) via Magnetophoresis

ACS Omega (2018)

Vera Zarubin Tai‐De Li Sunita Humagain Haojie Ji Kevin G. Yager

There is strong demand for achieving morphological control of conducting polymers in its many potential applications, from energy harvesting to spintronics. Here, the static magnetic-field-induced alignment of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) particles is demonstrated. PEDOT:PSS thin films cast under modest mT-level magnetic fields exhibit a fourfold increase in the Seebeck coefficient and doubled electrical conductivity. Atomic force microscopy measurements confirm the presence of conducting islands that exhibit a 10-fold increase in the local charge carrier mobility and threshold behavior that is associated with phase separation. High-resolution scanning electron microscopy identifies a consistent structural coil-to-rod transition, and three-dimensional time-of-flight secondary-ion mass spectrometry imaging shows that the rodlike structures coincide with PEDOT domains that generally align with the magnetic field and cluster on the outer surface. Grazing-incidence small-angle X-ray scattering, Raman spectra, electron paramagnetic resonance, and circular dichroism spectroscopy point to the physical nature of the magnetophoretic alignment, which is expected to occur via magnetic coupling of PEDOT domains with polaron modes. Because casting under mT-level magnetic fields increases the electrical conductivity and Seebeck coefficient of PEDOT:PSS thin films without additional dopants that commonly limit the thermoelectric performance, our research reveals that low-field magnetophoresis significantly influences the structure and corresponding physical properties of PEDOT:PSS. Our results also point to concerns that the presence of small external magnetic fields in laboratory settings may appreciably and inadvertently influence the PEDOT:PSS morphology during settling, drying, or annealing processes.

Poly(N-isopropylacrylamide)

10.1021/acsomega.8b00999

Cite

Citations (9)

Responsive blends of block copolymers stabilize the hexagonally perforated lamellae morphology

Soft Matter (2023)

Samantha R. Nowak Nikhil Tiwale Gregory S. Doerk Chang‐Yong Nam Charles T. Black

Blends of block copolymers can form phases and exhibit features distinct from the constituent materials. We study thin film blends of cylinder-forming and lamellar-forming block copolymers across a range of substrate surface energies. Blend materials are responsive to interfacial energy, allowing selection of pure or coexisting phases based on surface chemistry. Blending stabilizes certain motifs that are typically metastable, and can be used to generate pure hexagonally perforated lamellar thin films across a range of film thicknesses and surface energies. This tolerant behavior is ascribed to the ability of blend materials to redistribute chains to stabilize otherwise high-energy defect structures. The blend responsiveness allows the morphology to be spatially defined through multi-tone chemical surface patterns.

Morphology

10.1039/d3sm00142c

Cite

Citations (6)

Self-Assembly beyond 2D – Interactions in Multi-Layered Arrays of Block Copolymer Films

Bulletin of the American Physical Society (2018)

Arkadiusz A. Leniart Andrzej Sitkiewicz Kevin G. Yager Paweł W. Majewski

Source

Cite

Citations (0)

Control of all‐conjugated block copolymer crystallization via thermal and solvent annealing

Journal of Polymer Science Part B Polymer Physics (2014)

Kendall Smith Bridget Stewart Kevin G. Yager Joseph Strzalka Rafael Verduzco

ABSTRACT Control of the crystallization of conjugated polymers is of critical importance to the performance of organic electronics, such as organic photovoltaic devices, due to the effect on charge separation and transport, particularly for all‐polymer devices. The block copolymer poly(3‐dodecylthiophene)‐ block ‐poly(9,9‐dioctylfluorene) (P3DDT‐ b ‐PF), which has matched crystallization temperatures for each block, is used to study the effects of processing history on resulting crystallization. For longer annealing times and rapid quenching to room temperature, P3DDT crystals are preferred whereas for shorter annealing times and slower quenching, PF crystals are preferred. Both crystal forms are evidenced for long annealing time and slow quenching. Additionally, for room temperature annealing in the presence of a chloroform vapor, PF crystals are found in the PF β phase with the predominant crystal peak oriented perpendicular to the thermally annealed case. These results will provide guidance for optimizing annealing strategies for future donor/acceptor block copolymer photovoltaic devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52 , 900–906

10.1002/polb.23506

Cite

Citations (10)

Diffusion-based clustering analysis of coherent X-ray scattering patterns of self-assembled nanoparticles

Hao Huang Shinjae Yoo Konstantine Kaznatcheev Kevin G. Yager Lu Fang

Coherent X-ray scattering is an emerging technique for measuring structure at the nanoscale. Data management and analysis is becoming a bottleneck in this technique. We present an unsupervised method which can sort and cluster the scattering snapshots, uncovering patterns inherent in the data. Our algorithm operates without resorting to templates, specific noise models, or user-directed learning. We test our methods using scattering images of two-dimensional nanoparticle assemblies. The experimental results show the effectiveness of our algorithm on real world scientific data.

Template

10.1145/2554850.2554914

Cite

Citations (3)

Thermally Reversible Surface Morphology Transition in Thin Diblock Copolymer Films

ACS Nano (2010)

Xiaohua Zhang Kevin G. Yager Nathaniel J. Fredin Hyun Wook Ro Ronald L. Jones

Many phase transitions exhibit ordering transitions at the boundary of the material that are distinct from its interior where intermolecular interactions can be significantly different. The present work considers the existence of a surface thermodynamic order−order transition between two distinct morphologies in thin block copolymer (BCP) films that are of interest in nanomanufacturing applications. Specifically, we find a thermally reversible interfacial transition between sphere-like structures and cylinders in flow-coated films of poly(styrene-block-methyl methacrylate) (PS-b-PMMA), where the BCP forms a cylinder microphase in the bulk. We present direct evidence from atomic force microscopy (AFM) of ion-etched films and grazing-incidence small-angle X-ray scattering (GISAXS) on films without etching, which shows that the order−order transition is restricted to the outer layer of the film, while the film interior remains in the cylinder state. Moreover, we find this order−order transition to be insensitive to film thickness over the range investigated (40−170 nm). This morphological transition is of importance in characterizing the thermodynamics and dynamics of thin BCP films used as templates in nanomanufacturing applications.

Morphology

10.1021/nn9016586

Cite

Citations (14)

Linking Group Influences Charge Separation and Recombination in All‐Conjugated Block Copolymer Photovoltaics

Advanced Functional Materials (2015)

Jorge Mok Yen‐Hao Lin Kevin G. Yager Aditya D. Mohite Wanyi Nie

All‐conjugated block copolymers bring together hole‐ and electron‐conductive polymers and can be used as the active layer of solution‐processed photovoltaic devices, but it remains unclear how molecular structure, morphology, and electronic properties influence performance. Here, the role of the chemical linker is investigated through analysis of two donor–linker–acceptor block copolymers that differ in the chemistry of the linking group. Device studies show that power conversion efficiencies differ by a factor of 40 between the two polymers, and ultrafast transient absorption measurements reveal charge separation only in block copolymers that contain a wide bandgap monomer at the donor–acceptor interface. Optical measurements reveal the formation of a low‐energy excited state when donor and acceptor blocks are directly linked without this wide bandgap monomer. For both samples studied, it is found that the rate of charge recombination in these systems is faster than in polymer–polymer and polymer–fullerene blends. This work demonstrates that the linking group chemistry influences charge separation in all‐conjugated block copolymer systems, and further improvement of photovoltaic performance may be possible through optimization of the linking group. These results also suggest that all‐conjugated block copolymers can be used as model systems for the donor–acceptor interface in bulk heterojunction blends.

Acceptor

Electron acceptor

Photoinduced charge separation

10.1002/adfm.201502623

Cite

Citations (39)

11-BM Complex Materials Scattering (CMS) - A New SAXS/WAXS Beamline at NSLS II

Bulletin of the American Physical Society (2018)

Masafumi Fukuto Ruipeng Li Kevin G. Yager

Small-angle X-ray scattering

Source

Cite

Citations (0)

Azobenzene Polymers as Photomechanical and Multifunctional Smart Materials

The Royal Society of Chemistry eBooks (2007)

Kevin G. Yager Christopher J. Barrett

Among the many classes of novel advanced materials now being researched worldwide are photofunctional and photoresponsive materials. The advantages of materials that respond to light are numerous: natural light is a plentiful and effectively unlimited energy source, light is correlated to many every...

Azobenzene

Smart polymer

Smart material

10.1039/9781847558008-00424

Cite

Citations (11)