Faculty and Research

ChME department’s research

PI: Yanwei Wang, Associate Professor

School of Engineering – Chemical & Materials Engineering

Email: yanwei.wang@nu.edu.kz               Office: Block 3, Room 3e319

 

Project 1:  Polymer Physics and Modeling of Polycarboxylate-based Superplasticizers

This is a Pre-Research Project for a proposal submitted to the Faculty Development Competitive Research Grants Program.

Fig. 1. Schematic illustrations of (A) the comb-shaped architecture (Kjeldsen 2006) and (B) typical chemical structure of PCEs; (C) Schematic illustrations of (a) flocculation between PAA-coated ceramic particles due to ion-bridging and (b) steric stabilization provided by the PEO side chains (Kirby 2004).

Polycarboxylate-based Superplasticizers (hereafter abbreviated as PCE SPs, where SP is for superplasticizer and PCE is for polycarboxylate ester or polycarboxylate ether) are comb-shaped copolymers, possessing a linear anionic backbone and charge-neutral side chains. PCEs can offered far better suspension stability relative to simple polyelectrolytes species, such as polyacrylate acid and polymethacrylate acid, particularly in a high ionic strength environment where electrostatic screening strongly penalizes electrostatic stabilization (Kirby 2004). Nowadays, PCE SPs are widely used in high performance and self-consolidating concretes as well as in many other particulate or colloidal suspensions, such as silica (Whitby 2003), BaTiO3 suspensions (Kirby 2004), TiO2 nanoparticles (Koch 2016), carbon nanotubes (Liebscher 2017), graphene oxide in alkaline cementitious solutions (Lu 2017), to name a few. However, despite the important and widespread applications of PCE SPs, there are still debates on very basic understandings of (1) PCE adsorption on like-charged surfaces, (2) contributions of non-adsorbed PCEs to inter-particle dispersion forces, and (3) adsorption conformations of PCEs close to surface saturation. The purpose of this pre-research project is to develop the computational a computational box for simulation and modeling of the structural and adsorption properties of PCE SPs in high-salt aqueous solution and at liquid/solid interfaces. Our primary goal is to make such computational models accessible to ourselves and to experimentalists and R&D researchers interested in the structure-property relationships of PCE SPs.

 

Project 2:  Polymer Physics and Modeling of Thermo-Viscosifying Polymers (TVPs)

This is a Pre-Research Project for a proposal submitted to the NU Collaborative Research Program for 2020-2022.

Fig. 2. Apparent viscosity plotted as a function of temperature and polymer concentration for (A) PAM and (B) TVP in different salinity conditions (Li 2017); (C) Design concept of TVPs.

Thermo-viscosifying polymers (TVPs) are a novel class of functional polymers developed for enhanced oil recovery (EOR) applications in high-temperature and high-salinity (HTHS) oil reservoirs (Kamal 2005). A particularly attractive property of TVPs is that their solution viscosity increases upon increasing temperature and salinity. In such polymers, some grafted side-chains with the characteristics of a lower critical solution temperature (LCST) were incorporated onto the hydrosoluble polymer skeleton. These grafts will change their characters from being hydrophilic to hydrophobic over this transition temperature. The final copolymer is well-dissolved in water and behaved as conventional HAPM at room temperature, but the thermo-responsive “grafts” self-assemble into hydrophobic micro-domains when heating to a critical associating temperature. In the semi-dilute solution region, physical cross-links will be formed by the hydrophobic association of LCST grafts from different water-soluble backbones above the critical associating temperature, giving rise to a thermo-thickening response macroscopically, in contrast to the usual “thermo-thinning” behaviors observed in traditional water-soluble polymers (Li 2017).

The purpose of this pre-research project is to develop a meso-scale simulation model that can capture this peculiar “thermo-thickening” behavior. This is an important first step towards a theory and understanding of how intra- and inter-molecular interactions affect conformational organizations, polymer dynamics, and rheological properties of semi-dilute solutions of TVPs.

 

Project 3:  Polymer Physics and Modeling of Polymer Electrolyte-based Electrical Double-Layer Capacitors (EDLC)

This is a research project submitted in accordance with the NU Social Policy Grant.

Fig. 3. Schematic illustrations of (A) the linear, ring-shaped and star-shaped polyelectrolytes to be compared in this project, (B) the image charge method for handling dielectric discontinuities across liquid-solid interfaces, (C) an electric double-layer capacitor (EDLC) using simple electrolytes.

A recent study (Bagchi et al., June 2019. arXiv:1906.01106v1) has shown that surface polarization enhances energy storage and leads to the emergence of negative differential capacitance in confined linear polymer electrolyte (PE) solutions. Our goal is to illustrate how the polyelectrolyte architecture may play a role. We want to examine for the same molecular weight whether the electrostatic energy stored in the electrical double-layer (EDL) can be further increased by changing the topological structure of the polymer electrolytes.

Currently, exciting development is coming up in the area of interfacial electrostatics and dynamics. With ever increasing computational power, “new physics” such as like-charge attraction, charge reversal, and negative differential capacitance is being reported and gradually understood, and will eventually help us design better devices such as super-capacitors (also known as electric double-layer capacitors, EDLC) and micro-/nano-fluidic systems for bio-applications.