Wenjie Xia

Iowa State University | ISU · Department of Aerospace Engineering

We explore the structural and dynamic properties of bulk materials composed of graphene nanosheets using coarse-grained molecular dynamics simulations. Remarkably, our results show clear evidence that the bulk graphene materials exhibit fluid-like behaviors similar to linear polymer melts at elevated temperatures and that these materials transform...

Multiscale coarse-grained (CG) modeling of soft materials, such as polymers, is currently an art form because CG models normally have significantly altered dynamics and thermodynamic properties compared to their atomistic counterparts. We address this problem by exploiting concepts derived from the generalized entropy theory (GET), emphasizing the...

Understanding the mechanical properties of nanoconfined polymers is essential in the design of nanostructured soft materials. Here, we investigate the mechanical properties of free-standing polymer thin films by employing an atomistically based coarse-grained (CG) modeling approach. By examining three representative CG polymer models, i.e., polysty...

Understanding the mechanical behavior of glassy polymers at a fundamental molecular level is of critical importance in engineering and technological applications. Among various molecular parameters, cohesive interactions between polymer chains are found to play a key role in influencing the thermomechanical response of glass-forming polymers. Here,...

Semiconducting donor–acceptor (D–A) polymers have attracted considerable attention toward the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for a...

The conjugated polymer’s backbone conformation dictates the delocalization of electrons, ultimately affecting its optoelectronic properties. Most conjugated polymers can be viewed as semirigid rods with their backbone embedded among long alkyl side chains. Thus, it is challenging to experimentally quantify the conformation of a conjugated backbone....

This research introduces a novel method for evaluating the structural features of biomolecules, utilizing our innovative Elliptical Dichroism (ED) spectrometer specifically designed for stereochemical analysis. By integrating ED spectrometry with autocorrelation (AC) analysis, we investigate the conformational characteristics of biological molecule...

Thermoset materials often involve the addition of molecular and nanoparticle additives to alter various chemo-physical properties of importance in their ultimate applications. The resulting compositional heterogeneities can lead to either enhancement or degradation of thermoset properties, depending on the additive chemical structure and concentrat...

Conjugated polymers (CPs) have emerged as pivotal functional materials in the realm of flexible electronics and optoelectronic devices due to their unique blend of mechanical flexibility, solution processability, and tunable optoelectronic properties. This review synthesizes the latest molecular simulation-driven insights obtained from various mult...

Semiconducting conjugated polymers (CPs) are pivotal in advancing organic electronics, offering tunable properties for solar cells and field-effect transistors. Here, we carry out first-principle calculations to study individual cis-polyacetylene (cis-PA) oligomers and their ensembles. The ground electronic structures are obtained using density fun...

Understanding and predicting the mechanical and conformational properties of conjugated polymer (CP) thin films are a central focus in flexible electronic device research. Employing molecular dynamics simulations with an architecture-transferable chemistry-specific coarse-grained (CG) model of poly(3-alkylthiophene)s (P3ATs), developed by using an...

Pancreatic adenocarcinoma (PDAC) is one of the most deadly cancers, characterized by extremely limited therapeutic options and a poor prognosis, as it is often diagnosed during late disease stages. Innovative and selective treatments are urgently needed, since current therapies have limited efficacy and significant side effects. Through proteomics...

Polymer-grafted graphene (PgG) sheets are of interest in the development of functional nanocomposite materials for sensing, energy storage, and coatings. Although extensive studies have reported on various physical properties of PgG sheets, our understanding of the fundamental structural behavior of crumpled PgG sheets is still lacking. Here, we pe...

Conjugated polymers (CPs) are solution-processible for various electronic applications, where solution aggregation and dynamics could impact the morphology in the solid state. Various solvents and solvent mixtures have been used...

Graphene aerogel (GA), as a novel solid material, has shown great potential in engineering applications due to its unique mechanical properties. In this study, the mechanical performance of GA under high-velocity projectile impacts is thoroughly investigated using full-atomic molecular dynamics (MD) simulations. The study results show that the poro...

A temperature transferrable coarse-grained (CG) model of a silicone polymer has been developed to capture the thermomechanical behaviors using the energy-renormalization (ER) approach.

Conjugated polymers (CPs), characterized by rigid conjugation backbones and flexible peripheral side chains, hold significant promise in various organic optoelectronic applications. In this study, we employ coarse-grained molecular dynamics (CG-MD) simulations to investigate the intricate interplay of solvent quality, temperature, and chain archite...

The introduction of molecular additives into thermosets often results in changes in their dynamics and mechanical properties that can have significant ramifications for diverse applications of this broad class of materials such as coatings, high-performance composites, etc. Currently, there is limited fundamental understanding of how such additives...

Graphene-reinforced conjugated polymer (CP) nanocomposites are attractive for flexible and electronic devices, but their mechanical properties have been less explored at a fundamental level. Here, we present a predictive multiscale modeling framework for graphene-reinforced poly(3-alkylthiophene) (P3AT) nanocomposites via atomistically informed coa...

Carbon‐based nanoparticles are widely regarded as promising nanofillers in nanocomposites to pursue advanced properties. To date, there has been a lack of systematic investigation into the structural variations of nanofillers and their influences on dispersion characteristics, as well as the resulting mechanical properties of nanocomposites. In thi...

This special issue focuses on the optimization design and simulation of advanced polymer/metal matrix composites at various length scales, ranging from nano/molecular to full product/structure level. The research targets mechanical issues and performance of advanced composites and structures, with emphasis on the application and development of nove...

Wearable devices benefit from the use of stretchable conjugated polymers (CPs). Traditionally, the design of stretchable CPs is based on the assumption that a low elastic modulus (E) is crucial for achieving high stretchability. However, this research, which analyzes the mechanical properties of 65 CP thin films, challenges this notion. It is disco...

Sodium montmorillonite (Na-MMT) clay mineral is a common type of swelling clay that has potential applications for nuclear waste storage at high temperatures and pressures. However, there is a limited understanding of the mechanical properties, local molecular stiffness, and dynamic heterogeneity of this material at elevated temperatures and pressu...

Tuning the optoelectronic properties of donor-acceptor conjugated polymers (D-A CPs) is of great importance in designing various organic optoelectronic devices ranging from photovoltaics, photodetectors, light emitting diodes, and photoresistors. However, there remains a critical challenge in precisely control of bandgap through synthetic approach,...

This study employs all-atomistic (AA) molecular dynamics (MD) simulations to investigate the crystallization and melting behavior of polar and nonpolar polymer chains on monolayers of graphene and graphene oxide (GO). Polyvinyl alcohol (PVA) and polyethylene (PE) are used as representative polar and nonpolar polymers, respectively. A modified order...

Two model systems were investigated in order to gain a better knowledge of AX interaction with Na-MMT clay surface: (1) dry clay model and AX chains, (2) clay model and AX chains with a different percentage of water molecules. As for the in vitro component concerning AX, the breast cancer cells were cultured successfully, in 2D and 3D conditions. H...

Understanding the interfacial behavior of graphene-polymer nanocomposite is a long-standing endeavor to gain deep insight into the mechanical properties of engineered structural materials. In this study, we implement the 'hard' cutoff scheme to develop a 4-1 mapping coarse-grained graphene (CGGr) model and the corresponding CG potential TersoffCG(4...

Upon crumpling, graphene sheets yield intriguing hierarchical structures with high resistance to compression and aggregation, garnering a great deal of attention in recent years for their remarkable potential in a variety of applications. Here, we aim to understand the effect of Stone–Wales (SW) defects, i.e., a typical topological defect of graphe...

Controlling CNT dispersion has been the key challenge for CNT nanocomposites. This study investigated the dispersion, mechanical and piezoresistive properties of CNT reinforced cementitious composites using carboxymethyl cellulose (CMC) treatment by comparing with three other existing mixing methods, including direct mixing, surface treatments usin...

Cellulose nanocrystal (CNC) thin films are of increasing interest as sustainable materials due to their anisotropic mechanical properties. Previous computational work has shown that the fracture mechanisms of CNC films vary as a function of particle alignment with respect to the loading direction. However, it is challenging to experimentally measur...

When a thin sheet is confined to a volume much smaller than its length (or width), it forms a complex state of sharp bends, point-like developable cones (d-cones) and extended ridges known as crumpled matter. One interesting feature of this state, is its high resistance to compression given its light weight. While the origins of this strength still...

Atomistic modeling has significantly contributed to the establishment of computer simulations as the third pillar of science, together with experiments and theory. Atomistic modeling involves many disparate fields of science, ranging from classical and statistical mechanics to quantum chemistry, numerical methods, or algorithmic developments. The g...

In this chapter, the fundamental theoretical principles and application examples of density functional theory (DFT) are presented. Particularly, we not only discuss the history and theoretical framework of DFT, outlining some of its main advantages and disadvantages, but also address the application of DFT in calculating material properties such as...

The bottom-up prediction of complex behaviors of materials to serve the needs of materials design and prediction of their performance is a grand challenge due to the prohibitive computational times of atomistic simulations. Mesoscale modeling is thus necessary to bridge the spatiotemporal scales for making progress on this problem. This chapter pro...

In this chapter, the mechanical behavior of supramolecular assemblies of two-dimensional (2D) materials simulated using coarse-graining (CG) modeling approaches is discussed. Taking graphene as an exemplary system of 2D materials, four different CG models of graphene and graphene oxide with distinct mapping schemes and parameterizations are introdu...

Machine learning (ML) is an evolving scientific field of advanced statistical models and algorithms that are developed to imitate human intelligence by learning from data. In recent years, ML has successfully accelerated materials development and discovery in various engineering and technological applications. In this chapter, we provide a comprehe...

The chain conformation of donor-acceptor conjugated polymers (D-A CPs) is critical to their optical and electronic properties. However, probing the conformation of D-A CPs (e.g., persistence length, contour length) at...

Preventing ice formation and accumulation on solid surfaces has been a great challenge to address for various engineering and technological applications. Recently, the new development of zwitterionic polymer coatings attracted...

To develop structure-property relationships for cross-linked thermosetting polymers, it is crucial to better understand key factors that control their segmental dynamics and macroscopic properties. Here, we employ a coarse-grained (CG) polymer model to systematically explore the combined effect of varying the cohesive energy (ϵ) and cross-link dens...

Stereochemical analysis is essential for understanding the complex function of biomolecules. Various direct and indirect approaches can be used to explore the allosteric configuration. However, the size, cost, and delicate nature of these systems limit their biomedical usage. Here, we constructed elliptical dichroism (ED) spectrometer for biomedica...

Cross-linking is known to play a pivotal role in the relaxation dynamics and mechanical properties of thermoset polymers, which are commonly used in structural applications because of their light weight and inherently strong nature. Here, we employ a coarse-grained (CG) polymer model to systematically explore the effect of cross-link density on bas...

Semiconducting conjugated polymers (CPs) have shown great potential in organic solar cells and organic field-effect transistors (OFETs), due to their tunable electronic and optical properties. In this study, we compare computational predictions of electronic and optical properties of ensembles of cis-polyacetylene (cis-PA) multiple oligomers in two...

The morphological stability of an organic photovoltaic (OPV) device is greatly affected by the dynamics of donors and acceptors occurring near the device's high operational temperature. These dynamics can be quantified by the glass transition temperature (Tg) of conjugated polymers. Because flexible side chains possess much faster dynamics, the cle...

Transition metal oxide (TMO)-decorated TiO2 catalysts excel at low-temperature Hg⁰ oxidation. However, TMOs are typically found in large nanoparticles (NPs), resulting in a lower atom utilization efficiency. The current paper presents the design of an Au single atom (SA)-doped Ti⁴⁺ defected TiO2 (Au SAC-Ti1-xO2) and investigations concerning the in...

Organic conjugated polymers (CPs) are promising candidates for organic photovoltaic (OPV) devices due to their unique tunable mechanical and optoelectronic performance. Over the last decade, optoelectronic properties of narrow band gap CPs as a blend with acceptor units are largely optimized, which leads to noticeable progress in OPV technology. Ho...

Conjugated polymers (CPs) with the characteristics of relatively rigid conjugation backbone and peripheral flexible side-chain have drawn considerable attention in applications of organic optoelectronic devices. However, the “bottom-up” prediction of the thermomechanical behavior of CPs to serve the needs of devices design and prediction of their p...

Epoxy thermosets are often exposed to high humidity environments in various applications, undergoing reversible and irreversible degradation depending on the environment. This study presents a reactive molecular dynamics (MD) simulation framework to gain deeper insights into the hygrothermal aging process, which is essential to develop a targeted a...

As a thin sheet is crumpled up, it becomes more and more resistant to compression (making it a useful material system for packaging). Unfortunately, it is still unclear how to predict exactly how much compression a given crumple can hold, suggesting that basic physical processes might have been overlooked by current models. In this work, we examine...

A theoretical investigation is conducted to describe optoelectronic properties of Fe-doped montmorillonite nanoclay under spin states of low spin (LS), intermediate spin (IS), and high spin (HS). Ground state electronic properties are studied using spin-polarized density functional theory calculations. The nonradiative and radiative relaxation chan...

Predicting the glass transition temperature (Tg) is of critical importance as it governs the thermomechanical performance of conjugated polymers (CPs). Here, we report a predictive modeling framework to predict Tg of CPs through the integration of machine learning (ML), molecular dynamics (MD) simulations, and experiments. With 154 Tg data collecte...

Formaldehyde (CHOH), a common volatile organic compound, causes many adverse effects on human health. The highly exposed TiO2(001) facet possesses a high photodegradation efficiency of CHOH due to its excellent ability to trap photogenerated holes and high density of surface unsaturated Ti atoms (Ti5c) to bind CHOH. However, the rapid recombination...

Photoluminescence (PL) is one of the key experimental characterizations of optoelectronic materials, including conjugated polymers (CPs). In this study, a simplified model of an undoped cis-polyacetylene (cis-PA) oligomer was selected and used to explain the mechanism of photoluminescence (PL) of the CPs. Using a combination of the ab initio electr...

Elemental mercury (Hg⁰) is the most difficult mercury species to remove from the flue gas. Photocatalysts of transition metal oxide modified TiO2 can effectively remove Hg⁰. However, the metal oxide easily aggregates into large nanoparticles, reducing the atom utilization efficiency and photocatalytic activity. We presented a facile strategy of emp...

Inspired from natural materials, functionally graded materials (FGMs) with gradual variations in their compositions and microstructures have drawn considerable attention in structural materials design to achieve superior stiffness, strength, and toughness. Taking Cu-Ni alloy as a representative model system, herein, we systematically explore the me...

Tumor-derived extracellular vesicles (EVs) are under intensive study for their potential as noninvasive diagnosis biomarkers. Most EV-based cancer diagnostic assays trace supernumerary of a single cancer-associated marker or marker signatures. These types of biomarker assays are either subtype-specific or vulnerable to be masked by high background...

Understanding the influence of reconstructed single vacancies (SV) defects on the crumpling behavior of graphene sheets is crucial for successful implementation of graphene in advanced technologies. Here, we report the results of a systematic coarse-grained molecular dynamics (CG-MD) simulation study of the crumpling process of graphene sheets at v...

Cellulose nanocrystals (CNCs) thin films draw considerable interest in engineering and technological applications due to their excellent mechanical and physical properties associated with dynamic and microstructural features. Here, we employ coarse-grained molecular dynamics (CG-MD) simulations to investigate how the dynamics and microstructure cha...

TiO2-based photocatalysts are a potential technology for removing indoor formaldehyde (CHOH) owing to their strong photooxidation ability. However, their photooxidation performance is generally weakened when suffering from the competitive adsorption of H2O. In a method inspired by the oxygen evolution reaction (OER) to generate intermediates with h...