Life is full of science, scientists reveal why the towel to dry will harden?

We know that, in the absence of added wash softener and natural dry, cotton towels tend to harden. But have you ever thought about why that is?

生活处处是科学,科学家揭示毛巾晾干为什么会变硬?
Figure 1: after natural drying cotton beam hardening, as just stuck together (left), and dried in a forced water discharge washing machine remains soft cotton beam (right) by physical agitation

in previous studies, Kao\’s research team that bound water – a manifestation of the unique properties of the surface material in a special water – and sclerosis. The team presents a theoretical model, in this model, binding of water to remain in the cotton surface by capillary adhesion process between the single fibers cause crosslinking.

生活处处是科学,科学家揭示毛巾晾干为什么会变硬?
Figure 2: a schematic cross-linked hydrogen bond between water conditioning cotton monofilament.

Recently, by means of atomic force microscopy and atomic force microscopy – IR, Kao Corporation Takako Igarashi, Hokkaido University, Ken-ichiro Murata team observed directly under natural drying conditions, present on the surface of cotton single fibers bound water, and state is different from hydrogen bound water, free water. Since the air – water (hydrophobic) and water – effect of cellulose (hydrophilic) interface, two kinds of OH group stretching vibration mode apparently separated from each other. This study provides strong evidence for Kao\’s model, suggesting a possible link between the microscopic properties and macroscopic mechanical behavior of cotton fabric combined with water. Related work \”Direct Observation of Bound Water on Cotton Surfaces by Atomic Force Microscopy and Atomic Force Microscopy-Infrared Spectroscopy\” was published in the Journal of Physical Chemistry C.

First, the natural drying cotton beam hardening phenomenon

We compared the preparation of natural drying in the washing machine beam and cotton by physical stirring forced water discharge (e.g. shaking) drying the cotton beam, the former can be seen stiff seemed stuck together, while the latter is compliant. For bending force (B value) yarn prepared under natural drying conditions measurement tableNext, a bending force is applied as long as the cotton would decrease the stiffness of the beam, even if the force is repeatedly applied to the same level, will not change further. Interestingly, after waiting for some time no force will restore the stiffness, similar to the so-called random system self-healing phenomenon, which means that due to the combined presence of water, every separation due to bending of fiber will connect again.

生活处处是科学,科学家揭示毛巾晾干为什么会变硬?
FIG. 3: (a, b) changes in appearance (a) → washed natural drying, (b) washing → drying → dehydrating → drying. B change value (c) bending cotton sample properties KES-FB (2) a.

bis, AFM force curve of the outermost surface of the cotton confirmed the presence of water bound

at different humidity levels, and proximity AFM force curves away from cotton single fibers can clearly see close and away from the hysteresis process, which is characterized in capillary adhesion, cotton outermost surface show the presence of bound water. Further, the maximum separating force increases as the humidity increases, indicate the amount of bound water and humidity control probe helps adhesion. While no binding was observed with a crosslinked structure resulting from the water itself, these results support the hypothesis that the bound water plays the role of a crosslinking agent, plays a key role in the natural drying of cotton produced in the stiffness of remaining on the filament.

生活处处是科学,科学家揭示毛巾晾干为什么会变硬?
FIG 4: (a) at different humidity levels, close to the (blue line) and the force curve away from the (red) cotton single fibers. (B) a single fiber cotton surface of the silicon probe the relationship between the relative humidity maximum separation force.

three, ATR-IR spectra of the outermost surface further demonstrated the presence of water bound

In order to understand the microscopic properties of cotton fabric of the outermost layer of bound water, researchers studied using ATR-IR spectra of its hydrogen bond status. These two differences can be seen in cotton spectra, indicating the presence of bound water, but the difference was not significant. Difference spectra corresponding to the surface of the pure cotton bound water portion, characterized in that the spectrum is similar to the free liquid water, but due to the influence of the noise level difference spectrum of sufficient quality discussion microscopic properties of bound water, free water comprising a difference.

生活处处是科学,科学家揭示毛巾晾干为什么会变硬?
FIG. 5: ATR-IR spectra of cotton. (A) natural drying (50% relative humidity) and (b) completely dry. The illustration shows (a) subtracting (b) a difference spectrum obtained.

IV, AFM-IR showed the presence of water binding combination of two different ways

In order to extract the true binding information microscopic water, the researchers used another surface-sensitive methods AFM-IR, a spatial resolution can be obtained the infrared spectrum of 10nm. The image can be clearly seen in each point having a high reproducibility of the two peaks. After removal of residual water under vacuum and heat, to give two small peaks and Analysis calculated OH stretching vibration mode to match the cellulose. It can be seen, two characteristic peaks of AFM-IR binding water from the surface of the single fiber of cotton. Bound water exhibiting two OH stretching vibration mode of the group is clearly separated from each other, as opposed to the free liquid trapezoidal broad spectrum, shows the effect of hydrogen bonds with the cellulose surface-bound state by water interaction. If these two vibration modes reflect the state of hydrogen connection with different types of water, they can naturally be interpreted as corresponding to cotton fiber – water at the interface of water (higher wave number side, in combination with the hydroxyl group of cellulose) or water (lower wave number side, due to the hydrophobic effect of the strong hydrogen bonds are formed) air interface – water. This can also be supported through research Nihonyanagi et al.

生活处处是科学,科学家揭示毛巾晾干为什么会变硬?
Figure 5: Cotton single fiber image in (a) AFM. Five cross mark indicates the measurement point of the AFM-IR. (B) under natural drying conditions (50% RH) conditions and completely dry cotton AFM-IR spectra of single fibers. The inset shows an enlarged view of a completely dry conditions spectrum.

Summary:

corresponding author Ken-ichiro Murata said: \”experiments showed evident cotton surface bound water, which helps some dynamic properties, such as adhesion by the capillary the adjustment of the hardness] Further, the water itself also exhibit unique state different from the normal hydrogen water \”another Corresponding author adds Takako Igarashi:\”.. it is generally believed softener can reduce friction between the cotton fibers, however, our results show that the combination of water involved in the hardening process of cotton, which provides a new perspective for us to understand how softener and helps us develop better agents, formulations and systems. \”in addition, researchers in the article he pointed out that this study has not been directly observed cross-linked structure of bound water itself brings. Fill the knotThe gap between macroscopic mechanical behavior of microscopic properties of water combined with cotton fabric, is also an important problem to be solved recently. So, clever you, if my heart has long been answered? Source Reference: https: //pubs.acs.org/doi/10.1021/acs.jpcc.0c00423#

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