1. Introduction
With the advancement of net-zero carbon emission targets, the effective
utilization of renewable resources has attracted widespread attention
[1, 2]. Photothermal materials can capture near-infrared light
dissipated in the atmosphere and convert it into thermal energy to be
utilized, which is highly promising for wearable outdoor devices,
disease-assisted therapy, seawater evaporation, catalysis and so on
[3-6]. Flexible electrospun-based photothermal membranes (such as
Poly (L-lactic acid) (PLLA) and nylon) can offer high comfort, large
specific surface area, and wide applicability, so have great potential
in the field of wearable photothermal applications [7]; however,
durability, excellent photothermal conversion and simplicity of
fabrication of flexible photothermal membranes are still key challenges.
The photothermal performance of membranes is directly related to surface
micromorphology. Functional micro/nanostructures can exchange or promote
the engineering characteristics of materials [8]. Organisms in
nature often evolve special microstructures to better adapt to their
environment [9]. The wrinkles of the cerebral cortex enhance
intelligence [10]; the wrinkles of the guts enhance nutrient
absorption [11]; and the wrinkled membranes of leukocytes ensure a
higher specific surface area and enhance deformability [12, 13].
Inspired by this, scientists have tried to explore thin membranes with
wrinkled microstructures through various methods to enhance the specific
surface area and absorption capacity, however, the current imitation of
wrinkled sizes still remains at the micrometer scale [9]. The usual
methods for obtaining wrinkle microstructures, such as mechanical force
[9], photopolymerization [14], infrared induction [15], and
post-polymerization [16], have been able to achieve the desired
wrinkle morphology. 3D printing allows for the generation of
controllable nanowrinkles [17], but its high preparation cost limits
the preparation of large-area nanowrinkles. Mechanical force and
photopolymerization, etc. enable fast batch preparation, but it is
difficult to form nanoscale wrinkles. Post-polymerization enables
low-cost preparation of nanowrinkles, but the long cross-linking
reaction time and instability limit the enhancement. The realization of
low-cost, large-area and durable nanowrinkle membranes remains a
challenge. Also, ultra-thin electrospun membranes are often easily
damaged [18]. Therefore, an effective treatment procedure based on
electrospun membranes is urgently needed to develop the durability of
the material while realizing high specific surface area photothermal
films.
Here, a solvent-induced recrystallization approach is developed firstly
to obtain high-strength CS/MWCNTs/PLLA photothermal membranes with
nanowrinkled structures. The adhesive polydimethylsiloxane (PDMS)
dissolved in the solvent will residue on the fiber membrane after the
solvent evaporates, which not only tightly connects the photo-thermal
particles, but also forms an adhesive network to facilitate the
intensive cross-linking between the fibrils, so significantly enhancing
the membrane strength. The membranes also show two-sided heterochromatic
features or transparency because of the gradient photothermal particle
concentration, which considerably extends the fashionability and
customizability. Remarkably, the membrane also has excellent response
sensitivity and can heat up immediately after exposure to light. The
ultrathin nanowrinkled photothermal membrane by solvent-induced
recrystallization enables rapid batch preparation of enhanced functional
composite membranes, showing broad prospects in snow clothing, Winter
Olympics garments, and so on.