Chuanshen Du

Iowa State University

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i-10 index

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Martin Thuo

North Carolina State University

Andrew Martin

North Carolina State University

Alana M. Pauls

North Carolina State University

Julia J. Chang

North Carolina State University

Boyce S. Chang

Iowa State University

Paul R. Gregory

Iowa State University

E. Johan Foster

University of British Columbia

Aaron J. Rossini

Iowa State University

Jiahao Chen

Changzhou University

Rick W. Dorn

Iowa State University

Cooperative Institutions

Iowa State University

North Carolina State University

Ames National Laboratory

Bissell (United States)

Chongqing Technology and Business University

Boston University

Chinese Academy of Sciences

Lawrence Berkeley National Laboratory

Shenyang Institute of Automation

University of Chinese Academy of Sciences

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Role of Nanoscale Roughness and Polarity in Odd–Even Effect of Self‐Assembled Monolayers

Angewandte Chemie International Edition (2022)

Chuanshen Du Zhengjia Wang Jiahao Chen Andrew Martin Dhruv Raturi

The dependency of substrate roughness on wetting properties of self-assembled monolayers (SAMs) has been studied extensively, but most previous studies used limited selection of probing liquid and range of surface roughness. These studies disregarded the limit to observation of sub-nanometer odd-even parity effect, hence are inconclusive. In this work we report the role of solvent polarity on the roughness-dependency of wetting behavior of SAMs by studying static con-tact angle of a variety of probing liquids, with different polarities, on SAMs formed on Ag-based substrate with different surface morphology. By overlapping the roughness ranges with previous studies on Au, the limitation of surface roughness (RMS=1 nm) to observation of the odd-even effect using water as probing liquid was confirmed, but other probing liquid yielded different roughness-dependent behaviors, with more polar solvent showing more roughness-dependent behavior. Based on these observations, we concluded that there exists a phase-transition like behavior in SAMs due to substrate roughness and molecule chain length, but whose determination is dependent on the probing liquid.

Wetting transition

Self-assembled monolayer

Nanometre

10.1002/anie.202205251

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Citations (13)

Substrate Roughness and Tilt Angle Dependence of Sum-Frequency Generation Odd–Even Effects in Self-Assembled Monolayers

The Journal of Physical Chemistry C (2022)

Chuanshen Du Richard S. Andino Matthew C. Rotondaro Shane W. Devlin Shyamsunder Erramilli

Role of substrate type, gold or silver, and surface roughness on the parity odd–even effect in n-alkanethiolate (n = 10–16) self-assembled monolayers (SAMs), materials of potential importance to molecular scale electronics, is studied using vibrational sum-frequency generation (SFG) spectroscopy. An inverted odd–even effect is observed for SAMs on Ag substrates relative to SAMs on Au. The metal-specific SFG spectra in the methyl and methylene stretching regions provide a sensitive probe of the in situ cant angle and molecular twist dependence of the interfacial group orientation. Within the precision of these measurements, disorder due to gauche defects is not evident in this spectral analysis. SFG methyl vibrational frequencies and line widths show parity and substrate dependence. Metal substrate roughness, an under-reported experimental parameter, affects the extent of odd–even methyl orientation anisotropy. Parity-dependent methyl orientation effects are seen on Ag beyond the roughness limit established by hydrophobicity data on Au. The SFG analysis predicts an ∼2.8 nm rms roughness limit for odd–even effects on Ag substrates. These SFG results further confirm the role competing pairwise short-range dispersive (∝1/r6) and longer range polar (∝1/r to 1/r4) interactions play in controlling the observed odd–even wetting behavior of SAMs on metal substrates as a function of surface roughness.

Self-assembled monolayer

10.1021/acs.jpcc.2c01109

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Cover Picture: Stabilization of Undercooled Metals via Passivating Oxide Layers (Angew. Chem. Int. Ed. 11/2021)

Angewandte Chemie International Edition (2021)

Andrew Martin Boyce S. Chang Alana M. Pauls Chuanshen Du Martin Thuo

Cool frustration. Engineering composition across a thin surface oxide layer of a metal particle, and stabilizing it with appropriate ligands, leads to a sharp surface stress that frustrates solidification. Chemical potential gradients from compositional variation and ligand inductive effects all contribute to stabilization of a metastable state. An undercooled liquid metal particle is formed, highlighting a new paradigm in engineering energy landscape of a material using thin surface layer, as described by Martin Thuo et al. in their Research Article on page 5928.

Metastability

Particle (ecology)

10.1002/anie.202100679

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Frontispiece: Tunable Hydrophobicity via Dimensionally Confined Polymerization of Organometallic Adducts

Angewandte Chemie International Edition (2021)

Julia J. Chang Chuanshen Du Alana M. Pauls Martin Thuo

Polymerization By restricting polymerization in native pores of undercooled particles, organometallic adducts were generated by Martin Thuo et al. in their Research Article on page 13929.

10.1002/anie.202182562

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PREPARATION OF THREE NOVEL IONIC LIQUIDS FOR THE DISSOLUTION OF CELLULOSE

Chuanshen Du S. N. Walford Bice S. Martincigh

The full potential of sugarcane bagasse has not been fully exploited, with the main usage in South Africa being for providing energy in sugar mill operations, and portions being utilised for paper products, animal feed and furfural production. The dissolution and subsequent reactions of cellulose from sugarcane bagasse is a possible future application of ionic liquids (ILs), which are more environmentally-friendly solvents that can also be used as reaction media. Such use of ILs is aimed at the production of value-added products from the abundant bagasse substrate. This work describes the synthesis of a starting compound (1-allyl-3methylimidazolium bromide) and subsequent preparation and characterisation of three novel organic ILs (1-allyl-3-methylimidazolium lactate, 1-allyl-3-methylimidazolium acetate and 1allyl-3-methylimidazolium salicylate) because of their potential for cellulose dissolution. Preliminary tests showed that, although the ILs are able to dissolve cellulose, the presence of water limited cellulose dissolution.

Bagasse

Environmentally Friendly

Source

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Introduction: biopolymers and biocomposites

Physical Sciences Reviews (2021)

Paul R. Gregory Souvik Banerjee Chuanshen Du Martin Thuo

Abstract Biopolymers and biocomposites are an exciting class of ubiquitous materials. Interest in these materials has been driven in part by their biocompatibility/biodegradability, sustainability, potentially low-cost, renewability, being environmental benign, among other properties. These fascinating materials come in a range of forms from the DNA and RNA that is essential to life to the cellulose and collagen that mechanically reinforce tissues and as hybrid organic–inorganic composites like teeth. Herein, we summarize some aspects of the two classes of materials biopolymer and biocomposites, exploring specific examples while pointing to potential monomer sources, neoteric post-extraction modification and processing conditions. This lays the foundation to the following more specific chapters while illustrating the breadth of these material classes.

Biopolymer

Biocompatibility

Biocompatible material

10.1515/psr-2020-0065

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Spatially Directed Pyrolysis via Thermally Morphing Surface Adducts

Angewandte Chemie International Edition (2023)

Chuanshen Du Paul R. Gregory Dhanush U. Jamadgni Alana M. Pauls Julia J. Chang

Combustion is often difficult to spatially direct or tune associated kinetics-hence a run-away reaction. Coupling pyrolytic chemical transformation to mass transport and reaction rates (Damköhler number), however, we spatially directed ignition with concomitant switch from combustion to pyrolysis (low oxidant). A 'surface-then-core' order in ignition, with concomitant change in burning rate,is therefore established. Herein, alkysilanes grafted onto cellulose fibers are pyrolyzed into non-flammable SiO2 terminating surface ignition propagation, hence stalling flame propagating. Sustaining high temperatures, however, triggers ignition in the bulk of the fibers but under restricted gas flow (oxidant and/or waste) hence significantly low rate of ignition propagation and pyrolysis compared to open flame (Liñán's equation). This leads to inside-out thermal degradation and, with felicitous choice of conditions, formation of graphitic tubes. Given the temperature dependence, imbibing fibers with an exothermically oxidizing synthon (MnCl2 ) or a heat sink (KCl) abets or inhibits pyrolysis leading to tuneable wall thickness. We apply this approach to create magnetic, paramagnetic, or oxide containing carbon fibers. Given the surface sensitivity, we illustrate fabrication of nm- and μm-diameter tubes from appropriately sized fibers.

Morphing

10.1002/anie.202308822

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Citations (3)

Spatially Directed Pyrolysis via Thermally Morphing Surface Adducts

Angewandte Chemie (2023)

Chuanshen Du Paul R. Gregory Dhanush U. Jamadgni Alana M. Pauls Julia J. Chang

Abstract Combustion is often difficult to spatially direct or tune associated kinetics—hence a run‐away reaction. Coupling pyrolytic chemical transformation to mass transport and reaction rates (Damköhler number), however, we spatially directed ignition with concomitant switch from combustion to pyrolysis (low oxidant). A ‘surface‐then‐core’ order in ignition, with concomitant change in burning rate,is therefore established. Herein, alkysilanes grafted onto cellulose fibers are pyrolyzed into non‐flammable SiO 2 terminating surface ignition propagation, hence stalling flame propagating. Sustaining high temperatures, however, triggers ignition in the bulk of the fibers but under restricted gas flow (oxidant and/or waste) hence significantly low rate of ignition propagation and pyrolysis compared to open flame (Liñán's equation). This leads to inside‐out thermal degradation and, with felicitous choice of conditions, formation of graphitic tubes. Given the temperature dependence, imbibing fibers with an exothermically oxidizing synthon (MnCl 2 ) or a heat sink (KCl) abets or inhibits pyrolysis leading to tuneable wall thickness. We apply this approach to create magnetic, paramagnetic, or oxide containing carbon fibers. Given the surface sensitivity, we illustrate fabrication of nm‐ and μm‐diameter tubes from appropriately sized fibers.

Oxidizing agent

Burn rate (chemistry)

10.1002/ange.202308822

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Stabilization of Undercooled Metals via Passivating Oxide Layers

Angewandte Chemie (2020)

Andrew Martin Boyce S. Chang Alana M. Pauls Chuanshen Du Martin Thuo

Abstract Undercooling metals relies on frustration of liquid–solid transition mainly by an increase in activation energy. Passivating oxide layers are a way to isolate the core from heterogenous nucleants (physical barrier) while also raising the activation energy (thermodynamic/kinetic barrier) needed for solidification. The latter is due to composition gradients (speciation) that establishes a sharp chemical potential gradient across the thin (0.7–5 nm) oxide shell, slowing homogeneous nucleation. When this speciation is properly tuned, the oxide layer presents a previously unaccounted for interfacial tension in the overall energy landscape of the relaxing material. We demonstrate that 1) the integrity of the passivation oxide is critical in stabilizing undercooled particle, a key tenet in developing heat‐free solders, 2) inductive effects play a critical role in undercooling, and 3) the magnitude of the influence of the passivating oxide can be larger than size effects in undercooling.

Supercooling

Passivation

10.1002/ange.202013489

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Citations (3)

Frontispiz: Spatially Directed Pyrolysis via Thermally Morphing Surface Adducts

Angewandte Chemie (2023)

Chuanshen Du Paul R. Gregory Dhanush U. Jamadgni Alana M. Pauls Julia J. Chang

Carbon Materials. Spatially directed pyrolysis via thermally morphing surface adducts to create magnetic, paramagnetic, or oxide containing carbon fibers is reported by Martin Thuo et al. in their Research Article (e202308822).

Morphing

Carbon fibers

Surface Modification

10.1002/ange.202384461

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