10/20/2025
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation Proposal defense by Talya Scheff on: "Designing PFAS-free liquid-repellent surfaces through wetting state control and reentrant architecture."

Candidate Name: Talya Scheff
Degree: Doctoral
Defense Date: Tuesday, October 21, 2025
Time: 10 a.m.-noon
Location: ETIC-345

Committee:

  • Advisor: Joey Mead, Ph.D., University Professor, Plastics Engineering Department, UMass Lowell
  • Jinde Zhang, Ph.D., Assistant Research Professor, Plastics Engineering Department, UMass Lowell
  • Jay Park, Ph.D., Associate Professor, Plastic Engineering Department, UMass Lowell
  • Professor Hanna Dodiuk, Polymer Materials Engineering department, Shenkar College of Engineering and Design, Israel
  • Professor Samuel Kenig, Polymer Materials Engineering department, Shenkar College of Engineering and Design, Israel

Abstract:
PFAS were widely used to repel oils and applied as textile coatings. Since they are hazardous and environmentally persistent, new developments are required to achieve oil repellency through alternatives. This study explores the use of reentrant and other complex structures. These will serve as replacements for developing a deeper understanding of Cassie–Baxter wetting and the transition from Cassie-Baxter to Wenzel states. The overall goal is to achieve alternatives capable of repelling fluids with low surface tensions such as oils.

In the first chapter, the focus is on predicting the AATCC 118 standard for fabrics using flat-surface chemistry and fabrics geometry. The AATCC188 standard is widely used in industry to grade the oil repellency level using qualitative observation. Here, a model is constructed by studying different C6-coated (Fluorine chemistry) fabrics with varying geometries and comparing their performance to Young’s contact angles measured on flat surfaces with the same coating chemistry. Fabric geometry is revealed by using scanning electron microscopy and laser confocal microscopy. Then, the wetting state is observed by fluorescence imaging revealing the oil penetration depth. This predictive framework allows the design of desired repellency levels by controlling both fabric geometry and chemistry.

In the second chapter, the ability of reentrant structures in repelling decreasing surface-tension liquids is studied, ranging from water (72 mN/m) to ethanol (23 mN/m). The distance between silica re-entrant spheres was controlled through a novel inert spacer method. The inert spacer method uses polystyrene spheres as sacrificial spacer agents such that by removing the polystyrene spacers using hexane/toluene mixtures, different silica interparticle spacings were achieved. The performance of these structures provided a deeper understanding of the Cassie-to-Wenzel transition and identified optimal spacing conditions for repelling liquids across a wide range of surface tensions. This study further explains the geometry required for designing PFAS free coating capable of repelling various low surface tension fluids.

In the third chapter, double reentrant structures and their development on textiles will be explored. It was concluded from chapter 2 that a single re-entrant structure's ability to repel low surface tension fluids is limited. Therefore, exploring a double re-entrant structure is suggested to better encapsulate air pockets. Hierarchical reentrant structures on flat surfaces demonstrated some improvements in repellency across multiple liquid surface tensions. We will investigate the use of hierarchical re-entrant structures to delay the transition from Cassie-Baxter to Wenzel state, enabling a repellency of lower surface tension fluids on textiles.