“Soft materials from block copolymer self-assembly: from bioinspired membranes to hierarchically-structured hydrogels” and “Nanoscale 4D Microstructural Characterization of Corrosion in High Performance Light Metal Alloys using Correlative Microscopy”

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Thursday, December 3, 2020 -
2:00pm to 3:15pm
Chao Lang, Ph.D., Postdoctoral Researcher, Penn State and Sridhar Niverty, Ph.D., Postdoctoral Scholar, Purdue University

IMSE presents the North American Materials Colloquium Series:


Two presentations will be given in today’s seminar slot:

For the link to the synchronous presentation and live Q&A session (12/3 2-3:15PM or 12/4 3-4:15PM):  RSVP Here

Asynchronously view the presentation ONLY here:  Asynchronous Presentation (link not live yet)

 

“Soft materials from block copolymer self-assembly: from bioinspired membranes to hierarchically-structured hydrogels”

Chao Lang, Ph.D.,

Postdoctoral Researcher,

Penn State

Due to advancements in theoretical understanding and synthetic methods, block copolymers have found widespread applications ranging from uses in commodity products to highly-engineered devices. In this presentation, I will talk about innovative strategies for preparing bioinspired soft materials based on block copolymer self-assembly. In the first part, I will introduce a biomimetic strategy to construct channel-based membranes inspired by nature. In living systems, cell membranes control mass, energy, and information flow to and from the cell with extremely high selectivity and efficiency, a feat unmatched by current synthetic membranes. 

To fabricate channel-based membranes, ABA triblock copolymer lamellae were used as a scalable and robust replacement of lipid bilayers for aligning the channel molecules while maintaining their molecular-level transport functions. By coassembly of block copolymers with either artificial channels or natural channels, we were able to synthesize nanofiltration membranes with sharp selectivity profiles as well as uncharged ion exchange membranes exhibiting ion selectivity. The strategy reported here could promote the construction of a range of channel-based membranes and sensors with desired properties, such as ion separations, stimuli responsiveness, and high sensitivity. In the second half of the presentation, I will talk about a universal and quantitative method, named rapid-injection, for fabricating and controlling physically crosslinked block copolymer hierarchically-ordered hydrogels. Plasmonic nanocomposite hydrogels containing gold nanoparticles and hierarchically-ordered hydrogels exhibiting structural colors were assembled within one minute using this rapid-injection technique. 

Surprisingly, the rapid-injection hydrogels display superior mechanical properties and can be further processed into shape-memory materials. These works provide new inspirations for applying block copolymer materials in technologically relevant areas such as water filtration, drug delivery, tissue engineering, and soft robotics. 

Chao Lang received his B.S. in chemistry (minor in biotechnology) in 2011 and doctorate in polymer chemistry and physics in 2016 at Jilin University. His Ph.D. conducted under the guidance of Professor Junqiu Liu on biomimetic channels and transporters resulted in the first report on synthetic transmembrane channels made from helical polymers. 

As a postdoctoral researcher, he worked in the labs of professors Manish Kumar and Robert Hickey at Penn State. At Penn State, he has developed a block copolymer thin-film platform for fabricating channel-based membranes, which can be used for incorporating both artificial and biological channels. Focusing on block copolymer self-assembly, he has also established a universal and quantitative method, rapid-injection, for preparing different colloidal block copolymer hierarchical structures (micelles, microgels, and hydrogels) during non-equilibrium processing conditions. He is now working on light-weight artificial muscles based on polymer crystallization. 

“Nanoscale 4D Microstructural Characterization of Corrosion in High Performance Light Metal Alloys using Correlative Microscopy”

Sridhar Niverty, Ph.D.,

Postdoctoral Scholar,

Purdue University

AA 7XXX alloys are used extensively in aircraft and naval structures due to their excellent strength to weight ratio. These alloys are often exposed to harsh corrosive environments and mechanical stresses that can compromise their reliability in service. Furthermore, they are comprised of constituent particles of different chemical compositions that determine their performance. Of interest in this study are nanoscale precipitates that are designed to improve the mechanical performance of AA 7XXX alloys.

Precipitate location, size, and composition also play a pivotal role in determining the initiation and propagation of corrosion damage in these alloys. Visualizing the effect of precipitates on a local as well as global length scale can be challenging due to the small length scales involved. In this study, x-ray nanotomography using Transmission X-ray microscopy (TXM) has been employed to non-destructively study localized corrosion in AA 7075 exposed to 3.5 wt.% NaCl solution. Four-dimensional (4D) ex situ experiments conducted on peak and highly overaged AA 7075 yielded extremely interesting insights into the complex interplay between precipitates, grain boundaries, and other second phase particles. The time dependent tomography yielded valuable informationpertaining the preferred sites of intergranular corrosion initiation, and propagation at the nanoscale. Coupling this with serial sectioning EBSD provided insight into the role of grain boundary character on precipitate distribution and propensity for intergranular corrosion. The use of a correlative microscopy-based approach yielded multimodal characterization results that have provided a unique and seminal insight into corrosion mechanisms in AA 7075.

Sridhar Niverty is a postdoctoral scholar at the School of Materials Engineering at Purdue University. He has a doctorate in materials science and engineering from Arizona State University where he studied the effects of environmentally assisted damage in light metal alloy systems under the guidance of Professor Nikhilesh Chawla.

Prior to joining Arizona State University, Sridhar spent two years as a junior manager at JSW Steels Ltd., India, where heled a team of engineers and technicians responsible for the production of a variety of grades of steel using a continuous slab caster.Sridhar is very interested in pursuing a career in academia wherein he intends on implementing correlative microscopy-based workflows to study microstructural evolution during processing and damage evolution in-service.

He is also passionate about materials science education and teaching and is a recipient of the Outstanding Teaching Assistantship award from Arizona State University

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