Optically
transparent wood has emerged as a promising glazing material.
Thanks to the high optical transmittance, strong mechanical properties,
and excellent thermal insulation capability of transparent wood, it
offers a potential alternative to glass for window applications. Recently,
thermo-, electro-, and photochromic transparent woods that dynamically
modulate light transmittance have been investigated to improve building
energy efficiency. However, it remains challenging to widely replace
windows with transparent wood because of its poor weather resistance.
In this study, an environment-friendly thermochromic transparent wood
film (TTWF) with thermal switching of transmittance is proposed and
demonstrated. To achieve thermochromism, the bleached wood is impregnated
with the vanadium dioxide (VO2)/polyvinyl alcohol composite.
Due to the self-densification of cellulose microfibrils during the
evaporation of solvents, the transparent wood is in the form of thin
films, which can be attached on the inner face of a window to protect
it from severe weather conditions, making the installation convenient
and low-cost. Furthermore, the surface of VO2-TTWF is modified
by octadecyltrichlorosilane to enhance the waterproof ability and
achieve self-cleaning and antidust functions. The proposed VO2-TTWF shows great potential for application in energy-efficient
buildings using sustainable materials with advanced optical properties
(i.e., T
lum = 50.5%,
ΔT
sol = 3.4%, and haze = 70%) that
are mechanically robust (i.e., σ = 130.6 MPa
along the wood growth direction), have low-thermal conductivity (i.e., K = 0.29 W m–1 K–1 along the perpendicular direction to the wood fibers),
and demonstrate hydrophobic self-cleaning and antidust functions (i.e., contact angle: 121.9°). An experiment, using
a model house, showed that the VO2-TTWF attached on the
inner face of the window could significantly reduce the indoor air
temperature by 33.9 °C compared with a bare glass panel, proving
that VO2-TTWF has potential to be applied as a new-generation
energy-efficient material for smart windows.
A wearable textile that is engineered
to reflect incoming sunlight and allow the transmission of mid-infrared
radiation simultaneously would have a great impact on the human body’s
thermal regulation in an outdoor environment. However, developing
such a textile is a tough challenge. Using nanoparticle-doped polymer
(zinc oxide and polyethylene) materials and electrospinning technology,
we have developed a nanofabric with the desired optical properties
and good applicability. The nanofabric offers a cool fibrous structure
with outstanding solar reflectivity (91%) and mid-infrared transmissivity
(81%). In an outdoor field test under exposure of direct sunlight,
the nanofabric was demonstrated to reduce the simulated skin temperature
by 9 °C when compared to skin covered by a cotton textile. A
heat-transfer model is also established to numerically assess the
cooling performance of the nanofabric as a function of various climate
factors, including solar intensity, ambient air temperature, atmospheric
emission, wind speed, and parasitic heat loss rate. The results indicate
that the nanofabric can completely release the human body from unwanted
heat stress in most conditions, providing an additional cooling effect
as well as demonstrating worldwide feasibility. Even in some extreme
conditions, the nanofabric can also reduce the human body’s
cooling demand compared with traditional cotton textile, proving this
material as a feasible solution for better thermoregulation of the
human body. The facile fabrication of such textiles paves the way
for the mass adoption of energy-free personal cooling technology in
daily life, which meets the growing demand for healthcare, climate
change, and sustainability.
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