While heat acts as an essential component of various hair care processes, the thermal properties of hair are little studied and these properties dictate how heat is spread and stored in hair. Here, the infrared microscopy enhanced Ångström's method is introduced for accurate measurement of thermal diffusivity of hair. Three factors that could influence the thermal diffusivity were statistically tested in vacuum: (1) hair type, (2) the specific fiber from the same hair type, and (3) the specific locations along the same hair fiber (i.e., near the root vs. near the tip). The average thermal diffusivity of hair across the types measured in vacuum is 0.15 mm2/s, which is in good agreement with the published data. Hair type, fiber, and location had no statistically significant impact on the thermal diffusivity. Hair is particularly sensitive to moisture content and while absolute measurements of thermal diffusivity in air are not reported here, we show that increasing humidity level reduced the apparent thermal diffusivity of the samples. Understanding the variations in thermal properties with humidity is crucial to understanding how treatment processes impact hair health.

Ångström's method has been used to quantify thermal diffusivity of materials for over 150 years via measurement of thermal waves propagating through a long, thin sample. However, the traditional Ångström's method has some limitations. First, the traditional method is insensitive to potential variability in thermal diffusivity along the length of a sample because only two sensors are used. Second, conventional contact-based sensing techniques such as thermocouples limit the method to samples that are sufficiently large so as to be unaffected by heat loss through the sensors. Here, we develop and validate the infrared microscopy enhanced Ångström's method that overcomes these limitations and enables measurement of microscale samples. This work demonstrates the accuracy and applicability of the technique through measurement of several commercially available polymer monofilaments and films and comparison of the data to published values. This method is particularly robust to uncertainty in emissivity making it attractive for characterization of semitransparent samples.

Although the hair care industry is a multi-billion dollar industry, there still remains a dearth in the available technologies and research methods to answer one simple question: What temperature and frequency of use will lead to permanent structural damage (i.e. heat damage) to curly hair? Currently, trained professionals in the hair industry cannot predict when heat damage will occur and often rely on heuristics and intuition in their hair care approaches. In addition, scientists that have conducted studies with heat and hair have often used European hair types, which cannot be generalized to all ethnic groups; they have also conducted experiments that are not ecologically consistent with individuals' use context. As a result, a number of lay scientists have emerged whose use contexts are ecologically valid, but are lacking the experimental and quantitative rigor that engineers can provide. In this work, we discuss an interdisciplinary approach to integrating customer needs, design methodology, and thermal sciences for application to the hair care industry. We discuss the formulation of a predictive model, the design of an experimental test-bed for collecting data, and present initial results.

Lead users play an integral part in helping engineers to identify latent needs of customers, and this approach has been used in a variety of ways within the design community. However, despite their close resemblance to lead users, do-it-yourself (DIY) practitioners have not been directly examined by the design community. A seven-step framework is presented where the first four steps resemble a typical design process and the remaining steps are relevant for the approach of identifying DIY practitioners as lead users. A case study from the hair care industry is presented to illustrate this framework. This paper establishes a connection between these two groups of customers and demonstrates how the insights of DIY practitioners, which manifest as latent needs for knowledge, can inspire research for the development of new technologies.