Presidential Scholarship

Smart fabrics: Thermally adaptive materials with applications to outerwear

Case Study: Engineering Research

WHEN

In progress

Overview

Growing up as a cross country skier in Minnesota, where I raced in spandex suits so thin that your sweat would freeze seconds after the race finished, I knew that there had to be a better way to solve the problem of proper insulation. Similarly, if you have ever been downhill skiing, you know that you get sweaty going down the hill and then freeze on the chairlift.

What if we could design a jacket that could change its properties in order to keep you the right temperature at all times, regardless of the activity?

This has been a problem I have been passionate about solving since high school and was one of the things that first drew me into fashion and garment design. Through this interdisciplinary Presidential Scholarship, I have been able to begin researching potential solutions under the advisement of Professor Wernimont and with the guidance of Professor Frost.

***Please note: This project spans two (non-consecutive) ten-week terms. The first term, which I completed this summer, was set aside for reviewing existing literature, researching and evaluating existing/ emerging technology. The second term, which I have NOT YET COMPLETED, will be this coming spring and will focus on the application pf this knowledge and developing some initial prototypes. ***

Team

Josh Vorbrich – Researcher

Professor Jacqueline Wernimont – Advisor

Timeframe

Summer 2022, Spring 2023

Skills

User Centered Design

Biology of Human Comfort

User Research

Market Research

Clothing Design

Existing Technology Research

Patent Searching

Fabric Science

Thermodynamics

Materials Science

How might we design an adaptive garment that keeps the user at a comfortable temperature in varying conditions?

Establishing Parameters: Defining Comfort

Temperature Parameters:

Comfortable skin = 33.4°C
Variation of 1.5-3°C - body is unaware of change
Difference of ± 4.5°C → discomfort
Trapping infrared radiation keeps us warm
Infrared Radiation ≥ 40% of heat exchange between body and environment (even when indoors)

Moisture:

Comfort is dictated by feeling moisture accumulation and vapor resistance of clothing
During sports, thermal and overall comfort is strongly correlated to moisture accumulation and the sensation of moisture accumulation

Objectives and Success Criteria

Develop a product to help the user regulate their body temperature

Success Criteria: Maintain stable skin temperature between 31 - 35°C

Keep the inside of the garment dry

Learning about heat storage basics

Once I had defined my goals, I began working to understand heat transfer and insulation of garments. I learned about sensible, latent, and chemical heat storage before diving into existing technology.

Existing Technology

I began by reviewing existing technology used in most coats: waterproof breathable fabrics (WPB), like GoreTex, and durable water repellent (DWR) coatings and finishes. I learned about the the types of waterproof breathable fabrics: Waterproof and moisture penetrable high density fabrics, Microporous membrane fabrics, Nonporous membrane fabrics and Smart fabrics. I reviewed existing technology in order to determine the specific flaws with each type.

Emerging Technologies

The emerging technologies that I studied fall under 5 main categories: flaps and pores, infrared transparency, radiative cooling, phase change materials (PCMs) and shape memory materials. I evaluated each of these technologies, its feasibility, my ability to conduct research in the field, and how these technologies could be applied to manufactured garments.

1. Flaps and Pores

The basic process behind this technology is that sweat/ moisture actives flaps, causing them to open and create pores on teh surface of the fabric that allow heat to escape. These flaps do not require electricity and have been proven to effectively and quickly reduce temperature when activated. They use a bilayer construction with a hygroscopic (moisture absorbing) layer, commonly made of polyethylene glycol (PEG) and Cellulose acetate (CA) actuator, along with a hydrophobic polymer made of a type of polyester that does not expand or absorb water. However, the PEG is hydrophilic, which leads to an uncomfortable sticky sensation when it touches the skin. In order for this technology to work, the PEG would need to be dispersed within the CA in order to prevent contact with the skin

2. Infrared Transparency

Over 40% of the body's heat exchange with the environment is in the form of IR radiation. Through using a system with dynamic infrared transparency, such as by having distance dependent electromagnetic coupling between neighboring coated fibers in the yarn of the textile, it is possible that we could develop possibility for wearable TATs with localized thermal management systems. The electromagnetic field in one nanotube induces current in other tubes. This effectively tunes the nanotube similar to bending an antenna to change its wavelength or frequency. By manipulating the distance between the fibers, we can change how much infrared radiation and thus heat is allowed to pass through.

3. Radiative Cooling

This emerging technology uses photon heat flow to carry away energy. In doing such, it is able to cool objects to lower than the ambient air temperature without an external energy input. It uses micro or nano photonic structures that both reflect irradiation while emitting thermal infrared radiation with a different transparency. Recent developments in nano photonics have opened up a new field of possibilities and lots of research is currently being done in this field. However, it is notable that none of this radiative technology is responsive to its environment.

4. Shape Memory

Shape memory (SM) materials (such as shape memory alloys (SMAs) and shape memory polymers (SMPs) change shape when they receive a certain stimulus. Because SM is not an intrinsic property, but rather results from a process and combination of two materials (one with high elasticity and one that is inelastic and controls the stimulus under the conditions), it means that both the shape the SM material takes on and the triggering conditions can be customized.

Basics: Exceeding unique critical temperature → recovery deformation occurs in material → return to original shape

Further, it is possible to make these reactions reversible through specific cross linking, so that this transition could happen repeatedly as would be necessary in a commercial garment. Manufacturing SM fibers poses a surmountable challenge as it can, with certain variations, be spun either through dry spinning or wet spinning, with different properties in each.

5. Phase Change Materials (PCMs)

When these materials are exposed to a certain temperature, they experience a phase change such as melting or crystalizing that either absorbs or releases energy. These materials then lose their dynamic capabilities until they are heated/ cooled again. Thus, these short term solutions provide significant heating/ cooling effects that are generally limited to about 15 minutes. As a result, they would best be used in environments with constantly changing temperatures in order to reap maximum benefit from the thermal regulation effects of their phase transitions. As for manufacturing, the most promising solutions are to have hollow fibers be filled with PCMs, have a PCM coating on an existing fiber, or have PCM capsules can be mixed in with the fibers and spun into the yarn.

Moving Forward

The specific technologies that I am still actively considering are as follows:

Sweat activating pore flaps
1. Promising and feasible. Comparatively simple but lots to improve on especially architecturally. (PET-PEG construction)
Yarn/ polymer fibers with Carbon Nanotubes
1. More complicated than #1 as it incorporates IR radiation transmission and wavelength elements
2. Less focus on physical architecture/ layout of piece of textile
Shape Memory NiTi
1. Start with cold-worked nickel titanium alloy monofilaments (commercially available), spin, knit/ weave together, anneal at right temperature and ratio in order to select melting temperatures etc
2. Design physical structure/ architecture possibly including spirals for how to arrange new air pockets that are created
PCM
1. Pick between PET, PTMG, PET-PEG, Linear chain hydrocarbon, Polyhydric alcohol mixture
2. Use for short term temp change regulation
3. Manufacture as fiber filled with integral microcapsules or as hollow fiber
Further development of existing solutions (Such as WPB and DWR)
1. Not likely a good route. This tech is situated for small incremental improvements not large, interesting, or groundbreaking innovations and I would assume many of the companies currently using this technology already have people researching this.