A novel soft matter composite material for energy-saving smart windows: From preparation to device application

Article abstract of DOI:10.1039/c4ta06347c

Nowadays, with the increasing energy consumption of buildings and the continuous improvement of human living standards, use of architectural glass with multi-functional features of large-scale manufacturing, safety and energy saving has become the mainstr

Full text of DOI:10.1039/c4ta06347c

Volume 3 Number 20 28 May 2015 Pages 10613–11138
Journal of
Materials Chemistry A
Materials for energy and sustainability
www.rsc.org/MaterialsA
ISSN 2050-7488
PAPER
Lanying Zhang, Huai Yang et al.
A novel soft matter composite material for energy-saving smart windows:
from preparation to device application

Journal of
Materials Chemistry A
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PAPER
A novel soft matter composite material for energy-
saving smart windows: from preparation to device
application†
Cite this: J. Mater. Chem. A, 2015, 3,
10738
Yanzi Gao,‡a Wenhuan Yao,‡b Jian Sun,b Huimin Zhang,b Zhendong Wang,a
b
c
a
a
*
*
Ling Wang, Dengke Yang, Lanying Zhang and Huai Yang
Nowadays, with the increasing energy consumption of buildings and the continuous improvement of
human living standards, use of architectural glass with multi-functional features of large-scale
manufacturing, safety and energy saving has become the mainstream trend. In this paper, a series of
cholesteric side-chain liquid crystal polymers (ChSCLCPs) are designed and synthesized to composite
with a widely used laminating material for safety glasses, ethylene-vinyl acetate (EVA), to endow the
windows with IR light shielding property. The synthesized ChSCLCPs have the desired reflection
wavelengths and thermal stability. Preparation methods of EVA/ChSCLCP composite materials are
investigated and different ratios of the contents and various film treatment conditions are attempted.
Interestingly, when the contents of EVA and ChSCLCP are equal, “sky-blue” areas are found under
polarized optical microscopy (POM) and the film exhibits stronger light scattering and selective reflection
properties. Taking advantages of this phenomenon, a new type of IR shielding film is manufactured by
the powder blending method and it not only performs broadband reflection, but also exhibits a strong
light scattering. Then, model buildings equipped with and without the film are set up and an energy
conservation efficiency of up to 40.4% is obtained, which proves the film's practical applications in
energy-saving smart windows.
Received 21st November 2014
Accepted 18th March 2015
DOI: 10.1039/c4ta06347c
www.rsc.org/MaterialsA
buildings be equipped with that type of “skin” to reduce the
power supply for the air-cooling system?
Introduction
Because of the unique helical supra-molecular structure,
cholesteric liquid crystals (ChLC) exhibit a selective light
reection property and reect the circularly polarized incident
light whose handedness is identical to the helical axis.8 The
reection wavelength is given by eqn (1),
Possessing a variety of forms such as liquid crystals (LCs), gels,
membranes and other polymeric materials, so matter or so
materials are also called structured uids.1,2 Their distin-
guished properties, especially being able to respond to external
stimuli, endow them with wide applications in sensors,
controllers and electric devices.3–5 Material scientists have
found that the cuticle of the crab Carcinus mænas performs the
cholesteric structure with a pitch gradient,6,7 which equips the
creatures who spend plenty of time on beach with a reector to
prevent themselves from over-heating by the sun, which is
instructive for energy-saving of buildings. Why cannot the
l ¼ nP
(1)
where n is the average of the ordinary (no) and extraordinary (ne)
refractive indices of the ChLC, P is the cholesteric pitch corre-
sponding to the length of a 2p molecular rotation. The reected
bandwidth (Dl) is given by eqn (2),
Dl ¼ (ne ꢀ no)P ¼ DnP
(2)
aDepartment of Materials Science and Engineering, College of Engineering, Peking
University, Beijing 100871, People's Republic of China. E-mail: yanghuai@pku.edu.
cn; zhanglanying@pku.edu.cn
bDepartment of Materials Physics and Chemistry, School of Materials Science and
Engineering, University of Science and Technology Beijing, Beijing 100083, People's
Republic of China
where Dn is the birefringence of the LC. Because Dn is typically
limited to 0.5, the bandwidth of a single-pitch ChLC is usually
less than a hundred nanometers, which is insufficient for
applications such as brightness enhancement lms, wide-band
reective polarizers, and smart reective windows. To broaden
the bandwidth, different methods have been employed such as
forming a pitch gradient9,10 or creating a non-uniform pitch
distribution.11,12 In recent years, many theoretical studies13–15
cLiquid Crystal Institute and Department of Physics, Kent State University, Kent, Ohio
44242, USA
† Electronic supplementary information (ESI) available: Synthetic routes, FT-IR,
1H-NMR of the polymers. See DOI: 10.1039/c4ta06347c
‡ Joint rst authors, these authors contributed equally.
10738 | J. Mater. Chem. A, 2015, 3, 10738–10746
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and experimental methods16–18 have been developed to achieve a applications in photonic crystal materials,46 self-organization
broadband reection. The rst example was introduced by D. J. functional materials,47 and wide-band reective devices.48,49 With
Broer in 1995, and he obtained a broadband reection of the the rational design and efficient synthesis of novel cholesteric
entire visible spectrum by introducing a pitch gradient in the SCLCPs (ChSCLCPs), numerous advanced functional materials
cholesteric polymer network via UV-induced polymerization of have been obtained.50–52
chiral LC diacrylate/nematic monoacrylate/photoinitiator
Due to the excellent properties such as optical transparency,
blends.19,20 M. Mitov and colleagues employed two layers of high exibility and cohesiveness, and other good mechanical
polymer-stabilized ChLCs (PSChLCs)21,22 or glassy cholesteric properties, the ethylene-vinyl acetate (EVA) copolymer is widely
polysiloxane LC oligomers23,24 to prepare a wide-band reection used in laminated safety-glasses of building and vehicle
lm with a pitch gradient by a simple thermal diffusion windows. The combination of EVA and ChSCLCPs could not
method. Results showed that the optical properties of the only endow the materials with good adhesion properties, which
bilayer system were not the sum of the individual properties. ensure the safety, but also make the composite lms reect or
Moreover, wavelengths greater than 300 nm, covering visible shield the light of the IR region to lower the transmittance of IR
and near-IR areas, were successfully obtained, which provided light, in order to achieve the purpose of energy conservation.
potential applications for the manufacture of white-or-black However, which ratio between EVA and ChSCLCPs could endow
polarizer-free screens with high brightness and smart windows the composite lm with the best comprehensive performance is
for buildings. L. Li et al. created a non-linear pitch gradient by a very interesting and meaningful issue to study.
the exploitation of ChLC materials by polymerization-induced
Furthermore, smart windows have various applications in
molecular re-distribution, which contained one polymeric LC controllable reectance mirrors and in energy saving windows,
component and other non-reactive LCs.25,26 The obtained due to their transmittance modulation range in the visible and
polarizing lms exhibited an excellent thermal stability and an entire solar spectrum.53 Several methods have been investigated
adjustable spectral bandwidth of about 2000 nm covering from to functionalize the traditional ones such as employing the
the UV to the entire visible spectrum and up to near-IR. electrochromic54–56 and thermochromic57,58 compositions.
Numerous immediate applications such as brightness However, for smart windows to serve on the windows of
enhanced liquid crystal displays (LCDs), switchable energy- skyscrapers, large scale manufacturing and safety of the
saving/privacy windows, and energy saving IR reective paints windows are essential. Moreover, one of the best methods is to
and coatings were also discussed. Based on the properties of the composite EVA and ChSCLCP, with the aid of the performances
polymer dispersed liquid crystal (PDLC) and PSChLC, Prof. H. of the original laminating glass and the new materials, and to
Yang also conducted a lot of research. A composite of a polymer achieve the purpose of energy saving without weakening the
network, nematic liquid crystal, and chiral dopant exhibiting a mechanical properties. In this paper, we report the synthesis
chiral nematic (N*) phase at room temperature has been and characterization of a series of ChSCLCPs with different
developed and the bandwidth of the selective reection spec- reection wavelengths covering the IR region. Composite lms
trum could become wider and narrower reversibly with with different EVA/ChSCLCPs ratios were rst prepared with
increasing and decreasing temperature.27 Moreover, consider- heating and pressure under vacuum conditions, and the
able effort was focused on the broadband reection of ChLC by optimum conditions of proportion and the preparation method
the formation of a pitch gradient or non-uniform pitch distri- were determined. Different from a work reported previously, the
bution and several methods were invented: (1) in a PSChLC IR shielding lm for smart windows was successfully prepared
system containing non-reactive LC, a nematic diacrylate and by “stacking” of the EVA/ChSCLCP lm powders with different
cholesteryl compounds of different functionality, the concen- center reection wavelengths in the IR region. Therefore, the
tration of chiral centers near or away from the backbone were resultant composite lm is a model system to investigate the
non-uniform and this resulted in different pitch lengths;28,29 (2) effect of the phase transition of the ChSCLCPs and the ratio of
due to the increasing pitch of the CLC composite caused by EVA to ChSCLCPs on the optical properties of the lm that is
rising temperature, a single layer CLC lm with non-uniform designed to be used in smart windows.
pitch distribution was achieved by regulating the tempera-
ture;30–32 and (3) employing the UV curable LC monomers/chiral
dopants/bulk LC system, a PSChLC lm with a pitch gradient
can be fabricated by UV induced polymerization of the photo-
polymerizable acrylate monomers.33–35
Results and discussion
Mesomorphic and optical properties of the polymers
From our previous studies, we have found that the center
Side-chain liquid crystalline polymers (SCLCPs), which reection wavelength of chiral compounds was mainly depen-
combine the ordered structures of liquid crystals and the excellent dent on temperature and the content of the chiral compo-
properties, such as good thermal stability and processability, have nent.59–61 With increasing content of the chiral groups, the
been focused on in recent years due to their extensive applications center reection wavelength blue shied. According to this rule,
in actuators, sensors, engineering plastics and other functional we designed these polymers with selective reective wavelength
materials.36,37 When the side groups (at least partially) are chiral, a centers covering different IR regions. As shown in ESI Schemes
helically twisted structure (also called cholesteric structure) can be S1 and S2,† the polymers were obtained via conventional free
obtained. Owing to the special optical,38,39 thermal,40,41 elec- radical polymerization of nematic and cholesteric liquid crys-
trical,42,43 and mechanical44,45 properties, ChLC are of potential talline monomers (M1 and M2) of different ratios.
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Table 1 Synthetic and characterization data of ChSCLCPs
M2a [mol%]
Yield [%]
Mn,GPC [ꢂ 103]
PDIb
Tid [ꢁC]
l [nm]
b
c
Td [ꢁC]
d
Tg [ꢁC]
Sample
P1
P2
P3
20
15
10
86
83
84
2.69
2.70
2.68
1.24
1.18
1.11
309.5
317.3
315.8
59.0
58.4
57.6
252.7
253.7
254.4
990
1420
1870
a
b
The molar fractions of M2 were based on (M1 + M2). The number-average molecular weight (Mn,GPC) and polydispersity indices (PDI) were
c
measured by GPC with THF as the eluent and PS as standarꢀd1s. The temperatures at 5% weight loss of the samples under nitrogen were
d
measured by TGA heating experiments at a rate of 10 ꢁC min
.
The glass transition temperatures (Tg) and clearing temperatures (Ti) were
determined by DSC under nitrogen at a scanning rate of 20 ꢁC minꢀ1
.
The chemical structures of the monomers and polymers degradation, all the characterizations were conducted at temper-
were veried by the combination of 1H-NMR and FTIR (see ESI atures well below Td. As shown in Fig. 1A, two endothermic peaks
Fig. S1 and S2†). The molecular characteristics of the polymers at about 60 ꢁC and about 250 ꢁC, which may be related to the glass
are summarized in Table 1. By adjusting the proportion transition and the isotropization of the polymers from a possible
between M1 and M2, three polymers with high yield were LC phase, were detected in each of the DSC curves for all the
successfully prepared. Thermogravimetric analysis (TGA) synthesized polymers during the heating process.
results showed that all the polymers performed good thermal
To further conrm the phase behaviours and structures of all
stabilities under a nitrogen atmosphere and their 5% weight the polymers, the POM technique was utilized. The polymers
ꢁ
loss temperatures (Td's) were all above 300 C.
were lled into the cells whose inner surfaces had been planar
The phase transition behaviours of all the polymers were orientated by capillary action. Fig. 1B shows the typical LC
examined by a combination of differential scanning calorimetry textures of all the polymers at different temperatures obtained
(DSC) and POM measurement. In order to avoid thermal from the isotropic state. At ambient temperature, the entire
Fig. 1 (A) Differential scanning calorimetry curves of the polymers P1, P2, and P3 during the first cooling and second heating scans at a rate of
20 ꢁC minꢀ1. (B) Typical polarized optical microscopic images of P1, P2, and P3 at different temperatures cooled from isotropic states: (a) P1 at
263.6 ꢁC; (b) P1 at 53.8 ꢁC; (c) P2 at 257.2 ꢁC; (d) P2 at 54.9 ꢁC; (e) P3 at 255.1 ꢁC (f) P3 at 55.3 ꢁC.
10740 | J. Mater. Chem. A, 2015, 3, 10738–10746
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when the EVA content reached over 50%. Interestingly, when
the ratios of EVA and P1 were almost the same (as can be seen in
Fig. 3f), no black area was detected under POM instead “sky-
blue” colour lled the entire region. This was unbelievable
because the amount of EVA was still considerable. In order to
elucidate whether the phenomenon occurred occasionally, we
also tried long annealing time and different heating and cooling
rates for several times, “sky-blue” areas could be still observed.
To further investigate the optical properties of the composite
lms with different EVA contents and what interesting charac-
teristics could the “sky-blue” appearance represent, UV/VIS/IR
spectra and diffuse reectance studies were conducted, as
shown in Fig. 4 and S3 (ESI†). It can be clearly seen that when
the EVA ratio was similar to that of P1, which corresponded to
the “sky-blue” phenomenon under POM, the composite lm
exhibited optimal selective reection properties and the light
scattering was also very strong, which is desirable for the
preparation of IR shielding lms for the application in smart
windows. When EVA content was in minority in composite
lms, the light scattering gradually decreased with the decrease
in EVA content, probably due to the reduction in specic surface
areas in the lms originating from the phase separation of EVA
and P1, while the selective light reectance was not weakened
obviously. However, when EVA proportion was higher than
50%, the light scattering of the composite lms deceased
gradually because the surface areas became fewer and the
selective reection also became less obvious due to the lower
amount of P1. Moreover, a phenomenon similar to that
observed for EVA/P1 was seen for both EVA/P2 and EVA/P3.
Fig. 2 The chemical structures and the transmission spectra of P1, P2,
and P3 (the molar ratios between x and y were 80 : 20, 85 : 15, and
90 : 10, respectively).
eld of view was black and almost no birefringence was
observed. Upon heating, the polymers immediately developed
the LC phase aer the glass transition temperatures and it
disappeared slowly aer the isotropic temperatures. While
cooling from the isotropic state, the oily streak texture, a char-
acteristic of the Ch phase, developed again. Interestingly,
further cooling to the temperatures below Tg, the oily streak
textures could be maintained to a very low temperature. Upon
combining the results of DSC and POM, we concluded that all
the polymers developed a wide Ch phase structure during the
heating and cooling process, which was useful for the applica-
tions of smart windows with wideband reective lms.
Fig. 2 shows the typical prole of the transmission spectra of
all the polymers under normal incidence. As expected, the
center reection wavelengths of the polymers were red shied
with the decreasing ratio of the cholesteric liquid crystalline
monomer M2 and they covered almost the entire IR region. This
was because the smaller amount of M2 provided fewer chiral
centers, which weakened the helical twisting power and resul-
ted in the lm with a longer reection wavelength. When the
molar ratios of M2 were 20%, 10% and 5%, the center reection
wavelengths of the polymer lms were located at about 1000,
1400 and 1800 nm, respectively (as shown in Table 1).
Device application of the composite lms as IR shielding lms
in smart windows
According to the results described above, when EVA and ChSCLCP
contents were similar, the composite lm exhibited the optimal
properties, which were favorable to the application in smart
windows. Thus, an IR shielding lm was prepared by the stacking
of the EVA/ChSCLCP composite lm powders with different
center reection wavelengths, as shown in Fig. 5a. POM results
showed that the planar texture of the cholesteric phase with
visibly different morphology formed and a “sky-blue” appearance
developed aer heating-compression action (as can be seen in
Fig. 5c). Then, UV/VIS/IR experiment was conducted and results
illustrated that the obtained wide-band reective lm not only
Optical properties of the EVA/ChSCLCP composite lms
EVA/ChSCLCP composite lms with different weight ratios were maintained the reection properties of the original single
prepared and characterized in order to nd out the optimal composite lms (P-I, P-II and P-III), but also new center reection
proportion. Fig. 3 represents the typical POM images of the EVA/ wavelengths, which were probably corresponding to the new pitch
P1 composite lms with EVA ratios ranging from 5% to 95%. lengths arising from two adjacent different powders (B-I and B-II),
When EVA ratios were below 20%, they aggregated and formed were detected and the reection bandwidth was also signicantly
“droplet” shape domains (as shown in Fig. 3a–c). As EVA ratios broadened. We assumed that there may be thermal-diffusion
ascended to 40%, EVA and ChSCLCP aggregated and formed between neighboring composite lm powders. Scanning electron
separately amorphous domains. Moreover, when EVA content microscopy (SEM) demonstrated our assumption; Fig. 5d shows
was relatively low, severe shrinkage occurred aer the annealing the SEM image of the fractured surface of the lm. The dimension
process. The boundaries of the shrinkage areas are noted to of the three bands in the ne structure on the fractured plane is P,
have milky-blue curves in Fig. 3a–e. However, with the further corresponding to a 2p cholesteric molecular rotation. It can be
increasing content of EVA, the severity of shrinkage was grad- clearly seen that non-uniform pitch lengths, changing from about
ually relieved, and no obvious shrinkage could be observed 510 nm to about 930 nm, distributed in different domains in the
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Fig. 3 Typical polarized optical microscope images of the EVA/P1 composite films with different EVA ratios cooled to room temperature: (a) 5%;
(b) 10%; (c) 20%, (d) 30%; (e) 40%; (f) 50%; (g) 60%; (h) 70%; (i) 80%; (j) 90%; (k) 95%. The boundaries of the shrinkage areas are marked out with
milky-blue curves in (a–e).
fracture plane. Additionally, new pitch lengths at about 590 nm efficiency (h), which is dened as the ratio of the IR energy
and about 810 nm were observed in the neighboring areas obstructed by the lm was calculated according to eqn (3),
between different powders and P1 < P4 < P2 < P5 < P3. By
DQ
QCTRL ꢀ QISF CairmDTCTRL ꢀ CairmDTISF
h ¼
¼
¼
adjusting the composition of M1 and M2, the IR light broadband
reective lms can be obtained.
Then, the lm was attached on the window of a model house to
investigate its energy conservation effect. The energy conservation
QCTRL
QCTRL
CairmDTCTRL
DTCTRL ꢀ DTISF
DTCTRL
¼
(3)
10742 | J. Mater. Chem. A, 2015, 3, 10738–10746
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respectively. As shown in Fig. 6a, DTCTRL and DTISF are calculated
ꢁ
as being 4.95 ꢁC and 2.95 C, QCTRL and QISF are calculated as
being 20.68 J and 12.32 J, respectively. The indoor temperature of
the model building equipped with the EVA/ChSCLCP composite
lm was signicantly restrained and an energy conservation effi-
ciency of 40.4% was obtained.
Furthermore, to make sure that the EVA/ChSCLCP
composite lm could serve for the windows in huge buildings,
the safety characteristics were tested and the peeling strength
was obtained. As can be seen in Fig. 6b, compared with the
control group of the pure EVA laminated lm, the EVA/
ChSCLCP composite lm presented almost the same peeling
strength. Combined with the result of energy conservation
efficiency, the composite lm exhibited relatively excellent
comprehensive performance, and proved to have practical
application in energy conservation smart windows.
Fig. 4 The transmission spectra of the EVA/P1 composite films with
different ratios.
where QCTRL and QISF represent the absorbed energy of the model
buildings with and without the EVA/ChSCLCP composite lm,
DTCTRL and DTISF represent the indoor temperature changes of
the corresponding model buildings over a period of time, cair and
m represent the specic heat capacity of air and the mass of air,
Experimental section
Materials
The ChSCLCP were obtained via conventional free radical
polymerization of nematic and cholesteric liquid crystalline
Fig. 5 (a) Schematic drawing of the preparation of the IR shielding film. (b) The transmission spectra of the IR shielding film in different areas. (c) A
polarized optical microscope photograph of the IR shielding film. (d) A scanning electron microscope image of the cross-section of the IR
shielding film.
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Fig. 6 (a) The temperature changes of the module house during exposure under sunlight. ISF: the house with the IR shielding film attached to its
window, CTRL: the house with two layers of PET film laminated with EVA attached to its window (inset picture is the photo of the model houses).
(b) Peeling strength results of the corresponding samples.
monomers and detailed synthetic routes were elaborated in the 90.0 ꢁC for 1 h, and then rubbed with a textile cloth under a
ESI.† EVA (TPC, Singapore, MA-10) were commercially available pressure of 2.0 g cmꢀ2 along the same direction. Polyethylene
and used without further purication.
terephthalate (PET) lms of 20 mm thickness were used as cell
spacers. The polymers were lled into the cells by capillary
action at 180 C, and these samples lled with P1, P2 and P3
ꢁ
Measurements
only were named Sample P1-0, P2-0, and P3-0, respectively.
The molecular weights and molecular weight distributions of
the polymers were determined by a GPC equipped with a Waters
2410 instrument equipped with a Waters 2410 RI detector and
Preparation of the EVA/ChSCLCP composite lms
˚
three Waters m-Styragel columns (103, 104, and 105 A), using
To investigate the inuence of EVA and ChSCLCP compositions
on the optical and mechanical properties of the composite lms
and to search the optimal proportion between them, different
ratios of EVA and ChSCLCP were attempted, as shown in Table
2. A series of composite lms Pn-x (where n represents the
polymer, x represents the weight percentage of the EVA
component) were prepared by a solution evaporation method.
Take the preparation of sample P1-5 as an example, a mixture of
THF as the eluent at a ow rate of 1.0 mL minꢀ1 at 35 C. The
ꢁ
calibration curve was obtained using polystyrene (PS) as stan-
dards. TGA was performed on a TA Q50 instrument under
nitrogen at a heating rate of 10 C minꢀ1. DSC was utilized to
ꢁ
study the phase transitions of the polymers using a Perkin-
Elmer DSC 8000 calorimeter under nitrogen owꢀ1(30.0 mL
minꢀ1) and the heating/cooling rate was 10 C min under a
ꢁ
dry nitrogen purge. POM (Carl Zeiss AxioVision SE64) was used
to observe the LC textures of the samples with a Linkam LTS420
hot stage calibrated to an accuracy of ꢃ0.1 ꢁC and a digital
camera (AxioCam MRc 5). Spectral characterization was con-
ducted by an unpolarized UV/VIS/IR spectrophotometer (JASCO
V-570) in transmission mode at normal incidence. A diffuse
reectance (DR) study was conducted using an UV/VIS/IR
spectrophotometer (Perkin-Elmer Lambda 950) with a DR
attachment with an integrating sphere coated by BaSO4. SEM
was used to observe the morphology of the cross-sections of the
samples on a HITACHI S-4800 instrument. The peeling strength
experiment was practiced on a universal tensile test machine
(Instron 5969).
Table 2 Compositions and weight ratios of the EVA/P1 composite
films
Sample
EVA [mg]
ChSCLCP [mg]
EVAa [wt%]
CH2Cl2 [mL]
P1-5
1.8
3.5
7.0
33.2
31.5
28.0
24.5
21.0
17.5
14.0
10.5
7.0
5
10
20
30
40
50
60
70
80
90
95
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
P1-10
P1-20
P1-30
P1-40
P1-50
P1-60
P1-70
P1-80
P1-90
P1-95
10.5
14.0
17.5
21.0
24.5
28.0
31.5
33.2
3.5
1.8
Preparation of the cells lled with ChSCLCPs
To induce planar orientation of ChSCLCP molecules, the inner
surfaces of the glass cells were coated with a 3.0 wt% polyvinyl
alcohol (PVA) aqueous solution. The deposited lm was dried at
a
The weight fractions of EVA were based on the total weights of EVA
and ChSCLCP.
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EVA (1.8 mg) and P1 (33.2 mg) was dissolved in CH2Cl2 under Ministry of Education (Grant 20120001130005), the Fok Ying
magnetic stirring at room temperature for 4 h, the micropearls Tung Education Foundation (Grant no. 142009), the Major Project
of 12 mm were added to control the thickness of the composite of Beijing Science and Technology Program (Grant no.
lm. About 0.2 mL of the homogeneous solution was dropped Z121100006512002,
on a clean glass substrate of 1 cm2 and maintained for 6 h at acknowledged.
room temperature to slowly evaporate the solvent, and then the
Z141100003814011)
are
gratefully
lm was coated with another glass substrate. Aerwards, the
Notes and references
composite device was treated in a vacuum oven at 120 ꢁC for 5 h
under a pressure of 200.0 g cmꢀ2
.
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Aer the determination of the optimal proportion between EVA
and ChSCLCPs, the IR shielding lm for smart windows was
prepared by the “stacking” of the EVA/ChSCLCP composite lm
powders with different center reection wavelengths in the IR
region. The three composite lms with appropriate composi-
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h under a pressure of 200.0 g cmꢀ2. Finally, the lm was
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been equipped with thermal insulation materials. Aer the
indoor temperature was regulated to 26 ꢁC, it was exposed
under sunshine (environment temperature: 32 ꢁC) for 20
minutes and the temperature change was recorded. Moreover, a
control group was set-up with two layers of a PET lm laminated
with EVA attached on the window.
Conclusion
In summary, employing the selective light reection charac-
teristic of ChSCLCP, by “stacking” of the EVA/ChSCLCP
composite lm powders with different reection wavelengths, a
novel so matter composite material for laminated glass has
been successfully developed with an energy conservation effi-
ciency of 40.4% and relatively strong bonding performance, for
the rst time. The energy conservation mechanism was attrib-
uted to the broadband reection of the ChSCLCP in the IR
region as well as the light scattering because of the formation of
“sky-blue” areas, which was conrmed by the results of POM,
transmission and reectance spectra, and SEM experiments. It
is believed that the composite so material with relatively high
energy conservation efficiency and strong bonding features has
great potential application in large-scale laminating glass
windows with the dynamic control of solar light. Future work
will be focused on the mechanism of formation of the “sky-
blue” area and the further enhancement of the energy saving
efficiency of the lm.
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Acknowledgements
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