Dispersions of Two-Dimensional Titanium Carbide MXene in Organic Solvents

Maleski, Kathleen,Mochalin, Vadym N.,Gogotsi, Yury American Chemical Society 2017 Chemistry of materials Vol.29 No.4

<P>Two-dimensional titanium carbide (Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB>) MXene has attracted a great deal of attention in the research community and has already showed promise in numerous applications, but only its dispersions in aqueous solutions have previously been available. Here we show that Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB> can be dispersed in many polar organic solvents, but the best dispersions were achieved in <I>N</I>,<I>N</I>-dimethylformamide, <I>N</I>-methyl-2-pyrrolidone, dimethyl sulfoxide, propylene carbonate, and ethanol. The dispersions were examined by measuring the concentration and absorbance spectra of MXene in organic solvents as well as correlating the concentration to solvent physical properties, such as surface tension, boiling point, and polarity index. Hildebrand and Hansen solubility parameters were additionally used to provide an initial understanding of how Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB> MXene behaves in organic media and potentially develop quantitative correlations to select solvents and their combinations that can disperse Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB> and other MXenes. Using this analysis, we have outlined a range of organic solvents, which can disperse Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB>, expanding the opportunities for processing techniques, such as mixing MXenes with other nanomaterials or polymers to form composites, preparing inks for printing, and deposition requiring solution processable materials, allowing the use of Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB> in a multitude of applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2017/cmatex.2017.29.issue-4/acs.chemmater.6b04830/production/images/medium/cm-2016-048307_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm6b04830'>ACS Electronic Supporting Info</A></P>

Out of the Gray: The Impact of Provincial Institutions on Business Formalization in Vietnam

Edmund Malesky,Markus Taussig 동아시아연구원 2009 Journal of East Asian Studies Vol.9 No.2

Scholars have long argued that institutional context significantly influences business strategy and economic performance. Research on the relationship between institutions and business strategy, however, has overwhelmingly focused on the decisions of larger, established corporations, mostly neglecting the strategic thinking of smaller, more entrepreneurial ventures. This article seeks to correct this bias by focusing the analysis directly on the critical decision of small-scale entrepreneurs to move from the informal and largely unregulated sector into operation as formal companies. Using a unique dataset and ranking of provincial governance institutions from Vietnam, the authors show that improvements in institutions make firms more likely to choose the formal sector from the start and, for those who do not, to spend less time in the informal sector. The study also finds that property rights have a more salient impact on formalization than other types of institutions.

Star Search: Do Elections Help Nondemocratic Regimes Identify New Leaders?

Edmund Malesky,Paul Schuler 동아시아연구원 2013 Journal of East Asian Studies Vol.13 No.1

A commonly proffered theory to explain the use of elections in authoritarian regimes is that they help identify talented young leaders who can be groomed for leadership positions. Unfortunately, due to the difficulties of obtaining data in authoritarian settings, this hypothesis has not been tested satisfactorily. We examine candidate-level data from the 2007 Vietnamese National Assembly (VNA) election and subsequent selection of candidates for top positions within the VNA and for top ministry positions. We find no evidence that vote share is associated with promotion to leadership positions in the VNA and only limited evidence for vote share association with ministerial posts. Instead, the results indicate that leadership selection takes place within the party rather than through elections. Furthermore, behavior within the assembly suggests that those who were chosen may have been selected based on their loyalty or at least pliancy to the party elites.

Single-party Incumbency Advantage in Vietnam: A Conjoint Survey Analysis of Public Electoral Support

Edmund Malesky,Paul Schuler 동아시아연구원 2020 Journal of East Asian Studies Vol.20 No.1

Why do voters in single-party regimes express support for the ruling party in such large numbers? Scholars offer three sets of explanations: 1) Support is manipulated by regime leaders or falsified by frightened voters; 2) Support is due to genuine popularity or “performance legitimacy”; 3) The incumbent party holds an extreme incumbency advantage due to voters’ certainty about their candidates’ policy positions or access to state resources. Despite the impressive theoretical development in this literature, these arguments have not been subjected to a research design capable of examining the relative importance of each of these factors. We use a unique survey experiment on nearly 42,000 Vietnamese citizens over three years that reduces the threat of preference falsification and allows us to isolate voter's true preferences as much as possible. While we find some evidence for all three explanations, we find substantial support for incumbency bias. An important subset of Vietnamese voters—those inclined to vote for non-party candidates—sincerely favor the party under conditions of uncertainty about the candidates’ policy stances or experience in the legislature.

Guidelines for Synthesis and Processing of Two-Dimensional Titanium Carbide (Ti₃C₂T_<i>x</i> MXene)

Alhabeb, Mohamed,Maleski, Kathleen,Anasori, Babak,Lelyukh, Pavel,Clark, Leah,Sin, Saleesha,Gogotsi, Yury American Chemical Society 2017 Chemistry of materials Vol.29 No.18

<P>Two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides (MXenes) were discovered in 2011. Since the original discovery, more than 20 different compositions have been synthesized by the selective etching of MAX phase and other precursors and many more theoretically predicted. They offer a variety of different properties, making the family promising candidates in a wide range of applications, such as energy storage, electromagnetic interference shielding, water purification, electrocatalysis, and medicine. These solution-processable materials have the potential to be highly scalable, deposited by spin, spray, or dip coating, painted or printed, or fabricated in a variety of ways. Due to this promise, the amount of research on MXenes has been increasing, and methods of synthesis and processing are expanding quickly. The fast evolution of the material can also be noticed in the wide range of synthesis and processing protocols that determine the yield of delamination, as well as the quality of the 2D flakes produced. Here we describe the experimental methods and best practices we use to synthesize the most studied MXene, titanium carbide (Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB>), using different etchants and delamination methods. We also explain effects of synthesis parameters on the size and quality of Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB> and suggest the optimal processes for the desired application.</P> [FIG OMISSION]</BR>

Flexibility and non-destructive conductivity measurements of Ag nanowire based transparent conductive films via terahertz time domain spectroscopy

Hwang, Gyujeong,Balci, Soner,Gü,ngö,rdü,, M. Zeki,Maleski, Alex,Waters, Joseph,Lee, Sunjong,Choi, Sangjun,Kim, Kyoungkook,Cho, Soohaeng,Kim, Seongsin M. The Optical Society 2017 Optics express Vol.25 No.4

Metallic Ti₃C₂T_<i>x</i> MXene Gas Sensors with Ultrahigh Signal-to-Noise Ratio

Kim, Seon Joon,Koh, Hyeong-Jun,Ren, Chang E.,Kwon, Ohmin,Maleski, Kathleen,Cho, Soo-Yeon,Anasori, Babak,Kim, Choong-Ki,Choi, Yang-Kyu,Kim, Jihan,Gogotsi, Yury,Jung, Hee-Tae American Chemical Society 2018 ACS NANO Vol.12 No.2

<P>Achieving high sensitivity in solid-state gas sensors can allow the precise detection of chemical agents. In particular, detection of volatile organic compounds (VOCs) at the parts per billion (ppb) level is critical for the early diagnosis of diseases. To obtain high sensitivity, two requirements need to be simultaneously satisfied: (i) low electrical noise and (ii) strong signal, which existing sensor materials cannot meet. Here, we demonstrate that 2D metal carbide MXenes, which possess high metallic conductivity for low noise and a fully functionalized surface for a strong signal, greatly outperform the sensitivity of conventional semiconductor channel materials. Ti<SUB>3</SUB>C<SUB>2</SUB>T<SUB><I>x</I></SUB> MXene gas sensors exhibited a very low limit of detection of 50–100 ppb for VOC gases at room temperature. Also, the extremely low noise led to a signal-to-noise ratio 2 orders of magnitude higher than that of other 2D materials, surpassing the best sensors known. Our results provide insight in utilizing highly functionalized metallic sensing channels for developing highly sensitive sensors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2018/ancac3.2018.12.issue-2/acsnano.7b07460/production/images/medium/nn-2017-07460z_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn7b07460'>ACS Electronic Supporting Info</A></P>