Latest News

August 2017:
Morris et al. perspective is a top 20 read for August

August 2017:
Congrats to Priyanka for passing quals

August 2017:
The Epps group welcomes Seung as a new post-doc

July 2017:
Dr. Epps is appointed as the new CMET Director

June 2017:
The Epps group welcomes Shelby and Grace, as summer REU students

May 2017:
Congratulations to Chad for successfully defending his thesis

May 2017:
Congratulations to Cameron for successfully defending his thesis

May 2017:
Chad is an ACS/ESBES International Graduate Student Design Challenge Finalist

April 2017:
Dr. Epps Delivers the Lindsay Lecture at Texas A&M University

April 2017:
Kaleigh wins the Richard Wool Award for Women in Green Engineering

March 2017:
The Epps groups is featured in UDaily Tuning Block-polymers

March 2017:
Cameron wins best DPOLY poster at APS 2017 March Meeting

October 2016:
Dr. Epps Delivers the Thiele Lecture at the University of Notre Dame

August 2016:
UD Hosts the 2016 Future Faculty Workshop

June 2016:
Announcing the 2016 Future Faculty Workshop to be held at UD

June 2016:
The Epps group welcomes Spencer, a summer REU student

June 2016:
Epps group collaboration with DuPont Performance Materials announced

May 2016:
Congratulations to Ming for successfully defending his thesis

May 2016:
Congratulations to Dr. Epps for his promotion to professor

May 2016:
Congratulations to Chad for receiving the Saurabh A. Palkar Graduate Award for Mentoring

April 2016:
Congratulations to Melody for receiving the Robert L. Pigford Teaching Assistant Award

April 2016:
Congratulations to Kai for successfully defending his thesis

March 2016:
Congratulations to Victoria for being named a 2016 Barry Goldwater Scholar

March 2016:
Victoria receives 2nd Place in the ACS Undergraduate Research in Polymer Science Symposium

December 2015:
Congratulations to Angela for successfully defending her thesis

October 2015:
Congratulations to Dr. Epps for receiving the 2016 American Physical Society Dillon Medal

June 2015:
Congratulations to Dr. Epps for receiving the 2015 AIChE Owens Corning Early Career Award

May 2015:
Angela is selected to speak at the AIChE 08A Excellence in Graduate Polymer Research Award Symposium

May 2015:
Tom is awarded the Paul H. Schipper Fellowship

April 2015:
Angela is awarded a UD Dissertation Fellowship

April 2015:
The Epps’ group battery membrane research was featured in the UDaily

March 2015:
Tom is awarded NSF GRFP Honorable Mention

March 2015:
Congratulations to Angela for being selected to speak at the 2015 Polymers Gordon Research Seminar!

March 2015:
Kaleigh is selected to attend the 65th Lindau Nobel Laureate Meeting

February 2015:
Chad's work on light-sensitive polymers for controlled gene silencing is featured on materialsviews.com

January 2015:
Ming and Cameron’s work on XPS depth profiling highlighted at Nanotechweb.org

January 2015:
Rashida is awarded a NSF Systems Biology of Cells in Engineered Environments IGERT Fellowship

Epps Research Group Highlighted Projects

Tapered Block Polymers

Tapered block polymers are block polymers with interfacial regions that taper from one polymer block to another polymer block (in a well-defined fashion over a well-defined region of the copolymer). The incorporation of a tapered region between the blocks offers an opportunity to manipulate block polymer segregation strength independent of molecular weight and chemical constituents, which allows the design of materials with improved mechanical properties while retaining the desired phase separated structures in the vicinity of the order-disorder transition temperature.

SAXS tapered

Therefore, tapered block polymers allow for experimental control of the interfacial interactions in order to overcome greater block incompatibilities with increased molecular weight. Recently, our group has successfully synthesized and reported on the self-assembly of tapered block copolymers, using a poly(isoprene-b-styrene) [P(I-S)] based system. Interestingly, for the first time, we show that our normal-tapered poly(isoprene-b-isoprene/styrene-b-styrene) [P(I-IS-S)] and inverse-tapered poly(isoprene-b-styrene/isoprene-b-styrene) [P(I-SI-S)] diblock copolymers self-assemble into double-gyroid network structures. Both synchrotron small-angle X-ray scattering (above) and transmission electron microscopy corroboratively show that the incorporation of tapered regions up to 30% of the total copolymer volume does not extinguish the double-gyroid network. Subsequently, dynamic mechanical analysis (below) indicates that the normal and inverse tapered regions allow us to manipulate the order-disorder transition temperatures (TODT) of our materials while preserving network morphologies that are ideally suited for membrane and ion-conducting applications.

DMA tapered


Block Polymer Electrolytes for Lithium Battery Applications

Lithium batteries are considered promising candidates for next generation energy storage devices. In order to improve battery performance and safety, significant effort has been put towards creating new lithium ion-conducting membranes. These new membranes require high ionic conductivities to decrease the internal potential losses and adequate mechanical strength to reduce dendrite formation and prevent short-circuiting between electrodes. Block polymers with network structures offer the opportunity to create 3-dimensional conducting paths for lithium ions to transport between electrodes and a sturdy matrix to prohibit dendrite formation. Additionally, the lithium salt dissolved in the conducting domain modifies the interactions between different blocks which potentially alters the domain sizes and/or morphologies of the resulting material.

salt_doping


Polymers from Renewable Waste Streams

Renewable polymers are needed to help reduce global dependence on petrochemicals. Many renewable polymers are also biodegradable, biocompatible, and beneficial for a variety of applications, such as compostable cups and cutlery, elastomeric shoe soles and car tires, sturdy machine parts and electronics casings, and compatibilizing agents. Lignin and fatty acids are two of the most abundant renewable waste streams that can contribute to the collection of renewable (biobased) polymers already available. Lignin is a byproduct from pulp and paper mill manufacturing and typically is burned for energy. Fatty acids can come from waste cooking oils and sometimes are fed to livestock or converted to biofuels. Alternatively, these renewable resources can provide lignin model compounds (LMCs) shown structurally in the figure and n-alkyl (“fatty”) alcohols of varying aliphatic chain-length and degree of saturation. We can incorporate such LMCs and fatty alcohols into materials through functionalization and subsequently polymerization. The functional handles and structural diversity in these biobased monomers provide means for adjusting properties to our needs. Thus, we are interested in de novo design of practical lignin- and fatty acid-based polymers, such as polycarbonate resins and block copolymer thermoplastic elastomers, to create next-generation plastics.

bio-polymers


Polymer Thin Films

thermally_responsive_AFM

Many applications and devices require controlled distribution of material functionality in multiple dimensions. At the nanometer length scale, attempts to meet this challenge have included template-mediated materials chemistry. Interest in block copolymers has evolved because of their potential use in numerous nanotechnologies including nanotemplating, filtration membranes, and organic optoelectronics (LEDs and photovoltaics). Self-assembly of block copolymers in thin films is a complex phenomenon. A large parameter space, including film thickness, annealing conditions (thermal or solvent), molecular mass, and surface energy, governs the film morphology. Surface energetics and interface interactions also direct morphology orientation.

The behavior of thermally-responsive block copolymers compounds this complexity. When a thermally-responsive block copolymer undergoes a thermal transition resulting in a mass loss, the parameter space expands to include volume fraction shift, thickness decrease, surface energetic shifts of the relative blocks, and a change in substrate and free surface energetics. The resulting phenomenon is impacted by the complexity of multiple and often co-dependent variables. Control in chemically amplified transformations such as in thermal deprotection reactions can prove extremely useful especially when the self-assembly of the block copolymer is affected. Current investigations include controlling the final self-assembled morphology and orientation of thermally-responsive block copolymers using different surface chemistries and fabrication techniques as well as high-throughput methods for rapid characterization and identification of critical parameters.

An important aspect of exploiting high-throughput methods has been the development of novel gradient fabrication devices to efficiently probe the effects of substrate surface energy/chemistry and annealing conditions on block copolymer thin film morphology. These gradient approaches are becoming increasingly important for mapping the phase behavior of new materials for specific applications. In the following example, we used controlled vapor deposition to generate a gradient in substrate surface energy/chemistry and we show how the orientation of a cylinder-forming PS-b-PMMA thin film evolves with changes in substrate surface chemistry from a pure benzyl silane monolayer on silicon (left) to a pure methacryl silane monolayer on silicon (right), with gradient compositions and morphologies shown in between.

thin film

We have also designed a solvent resistant microfluidic mixing device that produces discrete gradients in solvent vapor composition and/or concentration to quickly and easily examine the use of solvent mixtures (versus a single solvent) for controlling thin film self-assembly. The image below shows a schematic of our solvent vapor annealing setup with the microfluidic device and its use as a screening tool to locate phase transformations in a poly(styrene-b-isoprene-b-styrene) triblock copolymer as a function of solvent composition and swollen film thickness.

microfluidic mixing device


Solution Assembly of Stimuli-Responsive Polymeric Nanomaterials

Polymeric nanomaterial assemblies have several attractive features including tunability, control over the size and structure of the assemblies, and enhanced stability. Furthermore, the chemical versatility of polymers enables the incorporation of various stimuli-responsive moieties. Our group is interested in exploiting these valuable properties to develop polymer assemblies for novel shape-changing nanomaterials, which could be utilized in a broad range of applications.

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We are currently focusing on biomedical aspects such as nucleic acid and small molecule drug delivery. Controlled release of these therapeutic molecules is widely recognized as one of the most significant challenges hindering clinical success. To this end, our lab has designed and synthesized novel photo-responsive block copolymers to bind and encapsulate nucleic acids and mediate efficient release upon application of the photo-stimulus. We are continuing to investigate the nanocarrier self-assembly process and developing methods to spatiotemporally control the release of the cargo. From a precision medicine standpoint, we are also working on the development of bio-responsive amphiphilic micelles for theranostic applications.

conf_cells2-r11svn

Thomas

Thomas H. Epps, III

Thomas and Kipp Gutshall Professor
Chemical & Biomolecular Engineering
Materials Science & Engineering
Center for Molecular & Engineering Thermodynamics Director
University of Delaware

Phone: 302.831.0215
Fax: 302.831.1048
Email: thepps@udel.edu
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Recent Honors & Awards

-APS John H. Dillon Medal, 2016
-AIChE Owens Corning Early Career Award, 2015
-Sigma Xi Young Investigator Award, 2014
-Thomas & Kipp Gutshall Professorship, 2012
-Martin Luther King, Jr. Visiting Professor Award, 2012
-UD Gerard J. Mangone Best Young Scholar Award (Alison Young Professor), 2011
-DuPont Young Professor Award, 2010