\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[ngerman,greek,english]{babel}



\usepackage{float}








\begin{document}

\title{Stretchable gas barrier films achieved by hydrogen-bond self-assembly of
nano-brick multilayers}



\author[1]{Kaiqiang Shi}%
\author[1]{Xiaozhi Xu}%
\author[1]{Siyuan Dong}%
\author[1]{Biao Li}%
\author[1]{Jingbin Han}%
\affil[1]{Beijing University of Chemical Technology}%


\vspace{-1em}



  
  \date{March 13, 2025}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
Stretchable gas barrier films achieved by hydrogen-bond self-assembly of
nano-brick multilayers%
\end{abstract}%



\sloppy


Stretchable gas barrier films achieved by hydrogen-bond self-assembly of
nano-brick multilayers

Kaiqiang Shi, Xiaozhi Xu, Siyuan Dong, Biao Li and Jingbin Han*

\emph{State Key Laboratory of Chemical Resource Engineering, Beijing
Advanced Innovation Center for Soft Matter Science and Engineering,
Beijing University of Chemical Technology, Beijing 100029, P. R. China}

\textbf{Author Information}

* Corresponding authors. Phone: +86-10-64412131. Fax: +86-10-64425385.
E-mail: hanjb@mail.buct.edu.cn.

\textbf{Abstract:} Stretchable gas barrier films hold great application
potentials in flexible electronics, sensors and food/drug packaging.
Inorganic-organic hybrid films containing two-dimensional nanosheets
have shown good gas barrier performance, but moderate tensile property,
because of the rigid characteristics of covalent or ionic bonds between
the assembly units. In this work, we used LDH nanosheets rich in
hydroxyl groups as building units, followed by modification of tannic
acid (TA), to assemble with polyethylene oxide (PEO) through hydrogen
bonds. Compared with previous work, the tensile property and oxygen
barrier performance of (TA@LDH/PEO)\emph{\textsubscript{n}} films have
been significantly improved. A fifty-bilayer TA@LDH/PEO film (865 nm
thick), deposited on a 1 mm thick natural rubber substrate, results in a
29\selectlanguage{ngerman}× reduction (contrast with bare substrate) in oxygen transmission rate
and maintains its good barrier property even under a large elongation of
120\%. The excellent tensile and gas barrier properties are attributed
to the ductility of hydrogen bond network among building blocks and the
significant prolongation of oxygen transmission path induced by LDH
nanosheets. This work provides a simple and cost-effective strategy for
the preparation of nanosheets-based hybrid materials, which are useful
in those fields requiring simultaneously high gas barrier and good
flexibility.

\textbf{KEYWORDS:} films, membrane materials, two-dimensional
nanosheets, gas barrier,

hydrogen bonds assembly

\textbf{1. Introduction}

Gas barrier films have a wide range of applications in food/drug
preservation and electronic device
encapsulation.\selectlanguage{english}\textsuperscript{1-5}The protection of flexible displays,
inflation/deflation of tires and football/basketball require
deformation. So the demand for flexible and stretchable gas barrier
films has greatly increased. Conventional alumina/zinc oxide coatings
display excellent barrier properties but are easy to break or crack when
the barrier films are stretched. Although pure polymer materials such as
ethylene/vinyl alcohol copolymer (EVOH), polyvinyl alcohol (PVA), and
polyvinylidene chloride (PVDC) can meet the requirement of general
packaging application, they cannot be applied to high barrier
fields.\selectlanguage{english}\textsuperscript{6-12} Besides, such polymer materials have
limited application range due to their humidity sensitivity and poor
mechanical strength. By hybridizing inorganic nanoplatelets (such as
hydrotalcite and montmorillonite) with polymers, multilayer
organic-inorganic films called ''nano-brick'' solve the problem of poor
gas barrier property of polymers and simultaneously improve the
mechanical property.\selectlanguage{english}\textsuperscript{13-18}

Layer-by-layer (LBL) assembly is an effective method to prepare gas
barrier coatings through nanoscale control of film
architecture.\selectlanguage{english}\textsuperscript{19-23} Electrostatic layer assembly
technology is the earliest and most common method for constructing
multilayer films.\textsuperscript{13, 24} This method is suitable for
assembly between oppositely charged elements, such as polymer
electrolytes, inorganic nanoparticles, two-dimensional (2D)
nanoplatelets, etc. Although the electrostatically assembled films have
good barrier properties, these nano-walls are usually very strong and
cracks upon stretching. Stretchable gas barrier films must be crack-free
because the cracks act as gas transmission highways. For example, a 10\%
strain resulted in cracking of PEI/montmorillonite nanocoating and thus
an increase in gas permeability by an order of
magnitude.\textsuperscript{25, 26} Hydrogen bonded multilayer films are
generally less rigid than ionically bonded
films.\selectlanguage{english}\textsuperscript{27-29}The weaker hydrogen bonds lead to a looser
film structure with a lighter crosslink density that produces greater
strain without damage. However, extensibility generally increases at the
expense of gas permeability because the barrier properties of LBL
deposited films are dependent on density and density is related to
hardness. One strategy to break through this limitation is to modify the
hydrogen bonding system to increase barrier properties while maintaining
its extensibility.

Hydrotalcite, referred to as layered double hydroxide (LDH), is an
important 2D layered material.\selectlanguage{english}\textsuperscript{30-34} The surface of the
LDH laminate contains a large number of hydroxyl groups, and the
presence of trivalent metal ions in metal-oxygen hexahedra makes the
laminate positively charged. Therefore, LDH can be incorporated into
hydroxyl group-containing or negatively-charged polymer matrix\emph{via}
hydrogen bond or electrostatic interaction, respectively. In our recent
work, we used LDH nanoplatelets to construct high-barrier film materials
through electrostatic force.\textsuperscript{5} However, the barrier
properties of such materials will decrease during long-term use or under
bending conditions, which restricts their application in the fields that
require good flexibility and stretchability.

In this work, we prepared single-layer LDH nanosheets followed by
surface modification with tannic acid (TA) (named as TA@LDH), which were
alternately assembled with polyethylene oxide (PEO) to prepare hybrid
films with stretchable gas barrier property. It is revealed that the
combination of TA@LDH into PEO prolongs the diffusion path of the gas
molecules, resulting in enhanced gas barrier properties. The ability to
prevent cracking and preserve the gas barrier up to 120\% elongation
provides a tremendous opportunity for improving the barrier of
elastomeric materials. After several times of stretching 100\%, the film
still has a high oxygen barrier property. The hydrogen bond results in
more loose film structure, lighter crosslinking density, and larger
strain without damage. Due to the abundant hydrogen bond sites on the
LDH surface, stretching may lead to the transfer of hydrogen bond from
one bonding site to another, rather than fracture. These highly
elastomeric assemblies are potentially useful for light-weighting
inflatable devices, tyres and wrapping.

\textbf{2. Experimental section}

\textbf{2.1 Reagents and Materials.} Analytically pure
Mg(NO\textsubscript{3})\textsubscript{2}*6H\textsubscript{2}O,
Al(NO\textsubscript{3})\textsubscript{3}*9H\textsubscript{2}O were
purchased from Beijing Chemical Plants. Urea and ammonia were obtained
from Xilong Scientific Co., Ltd. TA was purchased from Aladdin
Biotechnology Co., Ltd. PEO was obtained from Maclean Biochemical
Technology Co., Ltd. Natural rubber (NR) substrate was purchased from
ASONE (Shanghai) Trading Co., Ltd. All the reagents were used without
further purification. Deionized (DI) and decarbonated water was used in
all the experiments.

\textbf{2.2 Preparation of colloidal MgAl-LDH nanosheets
suspension.}MgAl(CO\textsubscript{3})-LDH was prepared by urea-assisted
hydrothermal method.\textsuperscript{14} Specifically, 25.64 g of
Mg(NO\textsubscript{3})\textsubscript{2}*6H\textsubscript{2}O, 18.70 g
of Al(NO\textsubscript{3})\textsubscript{3}*9H\textsubscript{2}O, and
30.03 g of urea were dissolved in 500 ml of water and placed in a
stainless steel autoclave lined with polytetrafluoroethylene. After
hydrothermal treatment at 110 degC for 24 h, it was then washed several
times with a centrifuge using deionized water and ethanol. After
cooling, the precipitate of MgAl(CO\textsubscript{3})-LDH nanoplatelets
was washed several times with deionized water and ethanol and dried at
room temperature.

Then the interlayered CO\textsubscript{3}\selectlanguage{english}\textsuperscript{2-} were
exchanged by NO\textsubscript{3}\selectlanguage{english}\textsuperscript{-} ions through the
salt-acid treatment of MgAl(CO\textsubscript{3})-LDH, to facilitate
delamination.\textsuperscript{35} The sample of 1 g
MgAl(CO\textsubscript{3})-LDH nanoplatelets was added into 1 L aqueous
salt-acid solution (311 \selectlanguage{greek}μ\selectlanguage{english}L of HNO\textsubscript{3}, 98 wt\% and 127 g of
NaNO\textsubscript{3}) and stirred for 24 h in a nitrogen atmosphere.
The MgAl(NO\textsubscript{3})-LDH nanoplatelets were collected by
centrifugation and washed with water and ethanol and dried in a vacuum
oven. Afterward, samples of 0.1 g MgAl(NO\textsubscript{3})-LDH
nanoplatelets were placed into 100 mL formamide for 48 h with stirring
to prepare single-layer nanosheets suspension.\textsuperscript{36}

\textbf{2.3 Preparation of TA@LDH suspension.} TA was put into formamide
and stirred at room temperature until complete dissolution. Under the
protection of N\textsubscript{2}, LDH nanosheet suspension was mixed
with formamide solution of TA and stirred at room temperature for 24
hours. TA@LDH suspension can be obtained through the above operations.
To study the effect of TA: LDH ratio on the gas resistance and tensile
properties of the films, different TA@LDH suspensions with various TA:
LDH ratios were prepared. To ensure that the total concentration of
TA@LDH suspension is 0.1 wt\% and pH is 8.0, four groups of experiments
were carried out according to TA: LDH = 1:1, 2:1, 3:1 and 4:1. Normally,
the expression of TA@LDH represents the sample with TA: LDH = 3:1,
unless specified.

\textbf{2.4 Fabrication of
(TA@LDH/PEO)\emph{\textsubscript{n}}multilayer films.} An aqueous
solution of PEO (0.1 wt\%) was stirred at 60 \selectlanguage{ngerman}°C for 2 h to achieve
homogeneity. The pH of each PEO solution and rinsing DI water was
altered to 8.0 using ammonia. Multilayer films of
(TA@LDH/PEO)\emph{\textsubscript{n}} were fabricated by applying the LBL
assembly procedure. Quartz glass, silicon wafer and NR film (thickness:
\textasciitilde{}1 mm) were chosen as substrates for various
characterizations and tests. Quartz glass substrate was used for UV-vis
absorption spectra characterization, and silicon wafer was applied for
SEM and AFM study. All the other measurements were based on the samples
on NR substrate. Before assembly, every NR film was rinsed with DI
water, soaked in n-propanol at 40 °C for 10 min, then treated with
n-propanol and deionized water by ultrasound at 40 °C, and dried
naturally. Quartz glass and silicon wafer were firstly washed in 30\%
H\textsubscript{2}O\textsubscript{2}/NH\textsubscript{3}·H\textsubscript{2}O
(v/v=3:7) and concentrated H\textsubscript{2}SO\textsubscript{4} for 30
min each to make the substrate surface hydrophilic and negatively
charged. The overall LBL process consists of a cyclic repetition of the
following steps: (a) dipping the pre-treated substrate into a colloidal
TA@LDH suspension for 10 min, followed by rinsing with DI water
thoroughly; (b) immersing into an aqueous solution of PEO for 10 min and
washed with DI water. Multilayer films of
(TA@LDH/PEO)\emph{\textsubscript{n}} were fabricated by alternate
deposition of TA@LDH suspension and PEO solution for \emph{n} cycles.
The resulting films were finally rinsed with water and dried at ambient
temperature. As for comparison samples, the
(TA/LDH)\emph{\textsubscript{n}} , (TA/PEO)\emph{\textsubscript{n}} and
(LDH/PEO)\emph{\textsubscript{n}} films were prepared by a similar
assembly procedure in a sequence of LDH nanosheets suspension, TA, PEO
aqueous solution. All films were prepared using an automatic dip-coating
machine (Figure S1, Supporting Information). A stretching instrument
(Figure S2, Supporting Information) was used to apply different strains
to the films with and without nanocoatings for 1 min.

\textbf{3. Results and discussion}

XRD pattern of the MgAl(CO\textsubscript{3})-LDH sample (Figure 1A)
shows clear diffraction peaks at 12.2°, 24.3°, 34.9°, 39.1°, 47.2°,
61.2° and 62.3°, which correspond to (003), (006), (009), (015), (018),
(110) and (113) diffractions of a hydrotalcite
phase.\textsuperscript{37} To delaminate LDH into monolayer, the
interlayered CO\textsubscript{3}\selectlanguage{english}\textsuperscript{2-} were replaced by
NO\textsubscript{3}\selectlanguage{english}\textsuperscript{-} ions. Figure 1B displays the
(003) characteristic peak shifts from 12.2deg to 10.2deg and the
corresponding layer spacing expands from 0.77 nm to 0.89 nm, which
confirms that the anions between the hydrotalcite layers have been
exchanged from carbonate to nitrate. Figure 1C and 1D are the scanning
electron microscopy (SEM) images of MgAl(CO\textsubscript{3})-LDH and
MgAl(NO\textsubscript{3})-LDH. It is found that they have similar
regular hexagonal shape, and their particle size distribution is around
1.7\selectlanguage{english}-2.5 \selectlanguage{greek}μ\selectlanguage{english}m.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1.} XRD patterns and SEM images of (A)/(C)
MgAl(CO\textsubscript{3})-LDH and (B)/(D) MgAl(NO\textsubscript{3})-LDH.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2.} (A) Schematic diagram of preparation process of
monolayer LDH nanosheets; (B) Schematic diagram of LDH modification by
TA; (C) FTIR spectra of LDH and TA@LDH; (D) Partial magnification of
FTIR spectra.

Single-layer LDH nanosheets rich in hydroxyl groups were obtained by
delaminating MgAl(NO\textsubscript{3})-LDH in formamide (Figure 2A).
Then, the surface of the monolayer LDH nanosheets was modified by TA
(Figure 2B). Upon irradiation by a red laser, the LDH and TA@LDH
suspensions both show clear Tyndall effect, indicating their homogeneity
(Figure S3 A and B, Supporting information). The interaction between TA
and LDH was investigated by FTIR spectra (Figure 2C). The LDH and TA@LDH
both display obvious absorption peaks at 3500 cm\textsuperscript{-1} and
1642 cm\textsuperscript{-1}, which are ascribed to stretching and
bending vibration absorption of O-H. For LDH sample, a strong sharp
absorption peak at 1384 cm\textsuperscript{-1} is attributed to the
antisymmetric stretching vibration of
NO\textsubscript{3}\textsuperscript{-}. Bending vibration of M-O-M
appears at 837 cm\textsuperscript{-1}, which shifts to 880
cm\textsuperscript{-1} after hybridization with TA. The blue shift of
M-O-M absorption band for the TA@LDH sample suggests the formation of
hydrogen bonds between TA and LDH.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3.} (A) Schematic illustration for the assembly of
(TA@LDH/PEO)\emph{\textsubscript{n}} films by LBL method; (B) UV-vis
absorption spectra of the (TA@LDH/PEO)\emph{\textsubscript{n}}
(\emph{n}=10-70) films on quartz glass substrates (inset: the linear
relationship between the absorbance at 213 nm and the bilayer number
\emph{n} ); (C) Top-view and (D) cross-sectional SEM images of a
(TA@LDH/PEO)\textsubscript{50} film.

(TA@LDH/PEO)\emph{\textsubscript{n}} multilayer films were fabricated
through layer-by-layer technique on pre-treated substrates (Figure 3A).
UV-vis spectra (Figure 3B) of the as-prepared
(TA@LDH/PEO)\emph{\textsubscript{n}} films show two intense absorption
bands at 213 nm and 338 nm, attributed to the characteristic absorption
of TA. The absorbance increases linearly (Figure 3B, inset) relative to
the number of deposition cycles, illustrating the well-proportioned and
gradual growth of the multilayer films. According to the molecular
structure of PEO (Figure S3 C, Supporting Information) and TA (Figure
2B), hydrogen bond network can be formed in the
(TA@LDH/PEO)\emph{\textsubscript{n}} films.

Top-view SEM image of a (TA@LDH/PEO)\textsubscript{50} film with a
continuous and smooth surface is shown in Figure 3C. Clay alignment in
the multilayer films is clearly observed using cross-sectional SEM
(Figure 3D) image of 50 bilayer film deposited on silicon wafer with a
thickness of ~865 nm. The image shows a clear layered structure with LDH
nanosheets shown in white lines, which illustrates good dispersity and
high orientation of the LDH nanosheets. The 2D nanosheets with a perfect
parallel orientation to the substrate will play the best role in the gas
barrier function.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 4.} (A) OTR of (TA@LDH/PEO)\emph{\textsubscript{n}}
(\emph{n} =10-70) films with different bilayer numbers; (B) Schematic
diagram of gas penetration in a barrier film.

The bare NR substrate displays an oxygen transmission rate (OTR) of 3190
cm\textsuperscript{3}/(m\textsuperscript{2}\selectlanguage{ngerman}·24h·0.1MPa), as shown in
Figure 4A. Upon deposition of
(TA@LDH/PEO)\emph{\textsubscript{n}}coatings, the OTR values undergo a
significant decrease. With an increase in the number of the assembly
layers, the permeability decreases because of the barrier effect caused
by horizontal LDH nanosheets. The improved oxygen barrier properties are
attributed to the good 2D ordering of LDH nanosheets, which increases
the diffusion path of oxygen molecules, commonly known as tortuous
pathway (Figure 4B). The best oxygen resistance performance can be
obtained when the composite film has 50 layers (OTR = 110
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa)). When the
number of (TA@LDH/PEO)\emph{\textsubscript{n}} film layers continues to
increase, the oxygen barrier performance begins to decline. This is
probably because when there are too many layers and the film is too
thick, the substrate will be hard to bear so that the composite film
will fall out or crack. Therefore, 50 layers are selected as the best
number of bilayers.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\par\null

\textbf{Figure 5.} OTR of (TA@LDH/PEO)\textsubscript{50} hybrid films
with different ratios of TA: LDH.

Hydrogen bonds are much weaker than electrostatic interactions but
stronger than van der Waals forces. Therefore, hydrogen-bonded films
have good tensile properties.\textsuperscript{27} Because hydrogen
bonding is very important for mechanical properties, we regulated the
ratio of TA to LDH. The OTR of four kinds of thin films with different
ratios and layers were measured. Besides the
(TA@LDH/PEO)\textsubscript{50} film with TA: LDH of 3: 1, the samples
with other proportions (1:1, 2:1 and 4:1) also exhibit the same change
trend for OTR with increasing the bilayer number (Figure S4, Support
Information).

No matter what the ratio of TA to LDH, the OTR of the films increased
slightly after stretching (Figure 5). The oxygen resistance of the film
is still good after stretching. However, with the decrease of LDH
content in TA@LDH, the attenuation of the oxygen barrier is slower upon
stretching. When the ratio of LDH nanosheets is 50\%, the OTR of 120\%
stretching is 79\% higher than that without stretching (from 99 to
177cm\textsuperscript{3}/(m\textsuperscript{2}\selectlanguage{ngerman}·24h·0.1MPa)). When the
ratio of LDH is 20\%, the OTR of 120\% stretching is only 23\% higher
than that without stretching (from 120 to 149
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa)). These results
show a higher content of TA is favorable to the film ductility due to
the presence of elastic hydrogen network, although the incorporation of
LDH nanosheet improves the barrier property.

Considering the balance between oxygen barrier and tensile properties,
the best ratio of LDH is 25\% (i.e. TA: LDH = 3:1). At 50-bilayer, the
OTR is 110 cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa), and
its oxygen barrier capacity is 28× higher than that of NR substrate.
When the stretch ratio was 25\%, the OTR increased by 12\% to 124
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa). The OTR is 128
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa) at 50\%
stretching, which is 17\% higher than that of the unstrained film. It
still has good oxygen resistance at 100\% stretching, with OTR increased
by 20\% to 133 cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa).

As shown in Table 1, the (TA@LDH/PEO)\textsubscript{50} hybrid film has
significant advantages over other films in published work. Although the
oxygen barrier property of (TA@LDH/PEO)\textsubscript{50} film is not
the best, its tensile deformation ratio reaches 120\%, which is not
achieved by other works. And after 120\% stretching, the permeability is
only 29\% higher than that without stretching. It can be found that
increasing the tensile capacity needs to sacrifice part of the oxygen
barrier capacity. Even so, our (TA@LDH/PEO)\textsubscript{50} film shows
simultaneously excellent tensile property and competitive oxygen barrier
capability.

\textbf{Table 1.} Comparative study on gas barrier performance after
stretching between our (TA@LDH/PEO)\textsubscript{50} film and reported
materials\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
Film Materials & Tensile Deformation & Permeability Reduce (relative to
the blank substrate) & Permeability Increase upon Stretching &
Ref.\tabularnewline
\midrule
\endhead
(TA@LDH/PEO)\textsubscript{50} & 120\% & 29\selectlanguage{ngerman}× & 29\% & This
work\tabularnewline
(PAA/PEO)\textsubscript{20} & 100\% & 10\selectlanguage{ngerman}× & 70\% & 26\tabularnewline
(PEI/PAA/PEO/PAA)\textsubscript{20} & 50\% & 15\selectlanguage{ngerman}× & 138\% &
40\tabularnewline
(PPM/PEO)\textsubscript{20} & 20\% & 80\selectlanguage{ngerman}× & 20\% & 29\tabularnewline
(C-PU/GO/A-PU)\textsubscript{40} & 15\% & 4\selectlanguage{ngerman}× & 18\% & 41\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

\textbf{Figure 6.} (A) OTR of four different composite films:
(TA@LDH/PEO)\textsubscript{50}, (TA/LDH)\textsubscript{50},
(LDH/PEO)\textsubscript{50} and (TA/PEO)\textsubscript{50}; (B) OTR of
these composite films after stretching.

Three films (TA/LDH)\textsubscript{50}, (LDH/PEO)\textsubscript{50} and
(TA/PEO)\textsubscript{50} were prepared as control samples and compared
with (TA@LDH/PEO)\textsubscript{50}. As shown in Figure 6A, we can find
that the (TA/PEO)\textsubscript{50}composite film shows the worst oxygen
barrier ability, which is only 10\selectlanguage{ngerman}× lower than that of NR substrate at
50-bilayer (OTR = 311
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa)). The reason why
(TA/PEO)\textsubscript{50} composite films have poor oxygen barrier
ability than other films is due to the absence of LDH.
(TA@LDH/PEO)\textsubscript{50} composite films have the best properties,
which might be because (TA@LDH/PEO)\textsubscript{50} has better
interfacial compatibility and richer hydrogen bond networks than
(TA/LDH)\textsubscript{50}(OTR = 124
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa)) and
(LDH/PEO)\textsubscript{50} (OTR = 128
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa)). Hydrogen
bonded films can increase the diffusion residence of oxygen molecules
and enhance the barrier ability of the films. The OTR of other films
with various assembly numbers also shows that
(TA@LDH/PEO)\emph{\textsubscript{n}} has the best performance (Figure
S5, Support Information).

The morphology of these samples under different tensile conditions was
studied. When the stretch ratio is 25\%, cracks appear in the
(LDH/PEO)\textsubscript{50} film (Figure 7B), and the OTR increases by
53\% (from 128 to 196
cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa)). At 120\%
stretching, OTR increased by 404\%. Similar to
(LDH/PEO)\textsubscript{50} film, the (TA/LDH)\textsubscript{50}film
also exhibits a disappointing oxygen barrier after stretching. However,
the stretch ratio of (TA/LDH)\textsubscript{50} film is better than that
of (LDH/PEO)\textsubscript{50}. Cracks appeared at 50\% tension (Figure
7E) and OTR reached
210.03cm\textsuperscript{3}/(m\textsuperscript{2}·24h·0.1MPa). Although
the oxygen resistance of (TA/PEO)\textsubscript{50} thin films is poor,
its tensile properties are excellent. Only when the stretch ratio
reaches 120\% (Figure 6J), the small cracks appear. At this time, its
OTR increased by 31\%. TA effectively acts as a small molecule
cross-linker between flexible PEO chains, posing very little restriction
to chain segment mobility within the TA/PEO assembly. The non-rigid
hydrogen bonding network between TA and PEO provides excellent tensile
properties. Similarly, the (TA@LDH/PEO)\textsubscript{50} film also has
small cracks when stretched by 120\%. The oxygen barrier ability of
(TA@LDH/PEO)\textsubscript{50} film is much higher than that of
(TA/PEO)\textsubscript{50} film, while these two films show similar
stretchability. The excellent properties of
(TA@LDH/PEO)\textsubscript{50} films are attributed to the bridging
effect of TA at the interface of LDH and PEO, which provide stretchable
elastic network to tolerate the external force.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

\textbf{Figure 7.} SEM images of four kinds of composite films after
stretching. (Green circles mark the aggregation of LDH nanosheets and
orange circles represent the fracture of the film.)

The cyclic stability under tensile condition was further investigated.
Because of the generation of small cracks in 120\% deformation, the
repeated tensile test was carried out under 100\% deformation. It can be
found that the OTR of (TA@LDH/PEO)\textsubscript{50} films does not
change much after stretching (Figure S6, Support Information). With the
increase of the recycle times, the gas blocking performance only slowly
decays, and after 10 recycle times, it decreases by only ~20\%. The
excellent performance after multiple stretching makes the
(TA@LDH/PEO)\textsubscript{50} film a promising candidate for
stretchable gas barrier material.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

\textbf{Figure 8.} (A) Schematic diagram of the hydrogen bond networks
in the (TA@LDH/PEO)\emph{\textsubscript{n}} films; (B) Reorientation of
LDH nanosheets to perfect parallel alignment after stretching.

Whether upon repeated stretching or at a high stretching ratio, the
(TA@LDH/PEO)\textsubscript{50} film keeps very good oxygen barrier
performance. Many factors make it have good oxygen resistance and
stretchable ability. LDH, TA and PEO all have plentiful hydrogen bonding
sites. When the film deformation is small, the H-bonding between TA@LDH
and PEO has much higher bond strength than van der Waals forces between
PEO chains, so the deformation is more likely to be a result of PEO
chain segment reorientation and extension rather than breaking hydrogen
bonds. In the process of further stretching, hydrogen bond damage and
regeneration of the film occur continuously (Figure 8A). In addition,
some LDH nanosheets that are not strictly parallel to the substrate will
reorient after stretching to improve the oxygen barrier capability of
the film (Figure 8B). Therefore, the (TA@LDH/PEO)\textsubscript{50} film
simultaneously shows good barrier property and excellent stretchability.

\textbf{4. Conclusions}

This work uses layers of self-assembly (based on hydrogen bonding) to
prepare stretchable gas barrier films. The combination of a high stretch
ratio is the most distinct feature in this work compared with other
inorganic platelet-reinforced polymers as gas barrier films. The LDH
nanosheets as well as the hydrogen bonding network in this work induce a
long diffusion length, thus suppressing the oxygen permeability. Based
on the extensibility of hydrogen bond, the composite film has good
oxygen resistance after large-deformation and repeated stretching, and
has strong competitiveness in terms of stretching ability and gas
barrier performance. The assembly strategy based on hydrogen bonding
could be expanded in the construction of barrier materials used in
flexible electronics, sensors and packing of devices.

\textbf{Supporting Information Available:}DipCoater image, Schematic
diagram of tensile film of tensile testing machine and OTR measurement.
This material is available free of charge \emph{via} the Internet at
XXX.

\textbf{Acknowledgements.} This work was supported by the National
Natural Science Foundation of China (21671015, 21521005) and the
Fundamental Research Funds for the Central Universities (XK1802-6,
BHYC1702B, and XK1803-05).

\textbf{References}

(1) Xu, X.; Wang, L.; Wang, J.; Yin, Q.; Dong, S..; Han, J.; Wei, M.,
Hydroxide--ion--conductive gas barrier films based on layered double
hydroxide/polysulfone multilayers. \emph{Chem. Comm.} 2018;54:7778-7781.

(2) Di Maio, L.; Marra, F.; Bedane, T. F.; Incarnato, L.; Saguy, S.,
Oxygen transfer in co-extruded multilayer active films for food
packaging. \emph{AlChE J.} 2017;63: 5215-5221.

(3) Yang, C.; Cussler, E. L., Oxygen barriers that use free radical
chemistry. \emph{AlChE J.} 2001; 47: 2725-2732.

(4) Adel, P.; Moran, E.; Efrat, E.; Hadar, N. N.; Albert, R.; Israel,
B., A novel hybrid solid dispersion film coat as a moisture barrier for
pharmaceutical applications. \emph{J. Drug Delivery Sci.
Technol.}2017;40:105-115

(5) Dou, Y.; Pan, T.; Xu, S.; Yan, H.; Han, J.; Wei, M.; Evans, D. G.;
Duan, X., Transparent, ultrahigh-gas-barrier films with a
brick-mortar-sand structure.\emph{Angew. Chem. Int. Ed.}
2015;54:9673-9678.

(6) Seethamraju, S.; Ramamurthy, P. C.; Madras, G., Performance of an
ionomer blend-nanocomposite as an effective gas barrier material for
organic devices. \emph{RSC Adv.} 2014;4:11176-11187.

(7) Lee, M. E.; Jin, H. J., Nanocomposite films of poly(vinyl
alcohol)-grafted graphene oxide/poly(vinyl alcohol) for gas barrier film
applications. \emph{J. Nanosci. Nanotechnol.} 2015;15:8348-8352.

(8) Gaume, J.; Taviot-Gueho, C.; Cros, S.; Rivaton, A.; Th\selectlanguage{ngerman}érias, S.;
Gardette, J. L., Optimization of PVA clay nanocomposite for
ultra-barrier multilayer encapsulation of organic solar cells.\emph{Sol.
Energy Mater. Sol. Cells} 2012;99:240\selectlanguage{english}-249.

(9) Layek, R. K.; Das, A. K.; Min, U. P.; Kim, N. H.; Lee, J. H.,
Layer-structured graphene oxide/polyvinyl alcohol nanocomposites:
dramatic enhancement of hydrogen gas barrier properties. \emph{J. Mater.
Chem. A} 2014;2:12158\selectlanguage{english}-12161.

(10) Zhang, J.; Lei, W.; Schutz, J.; Liu, D.; Tang, B.; Wang, C. H.;
Wang, X., Improving the gas barrier, mechanical and thermal properties
of poly(vinyl alcohol) with molybdenum disulfide nanosheets. \emph{J.
Polym. Sci., Part B: Polym. Phys.} 2019;57:406\selectlanguage{english}-414.

(11) Ham, M.; Kim, J. C.; Chang, J. H., Characterization of poly(vinyl
alcohol) nanocomposite films with various clays. \emph{Polym.
Korea}2013; 37:225--231.

(12) Inagaki, N.; Tasaka, S.; Nakajima, T., Preparation of oxygen gas
barrier polypropylene films by deposition of SiO\emph{x} films
plasma-polymerized from mixture of tetramethoxysilane and
oxygen.\emph{J. Appl. Polym. Sci.} 2000;78:2389\selectlanguage{english}-2397.

(13) Dou, Y.; Zhou, A.; Pan, T.; Han, J.; Wei, M.; Evans, D. G.; Duan,
X., Humidity-triggered self-healing films with excellent oxygen barrier
performance. \emph{Chem. Comm.} 2014;50:7136\selectlanguage{english}-7138.

(14) Wang, L.; Dou, Y.; Wang, J.; Han, J.; Liu, L.; Wei, M.,
Layer-by-layer assembly of layered double hydroxide/rubber multilayer
films with excellent gas barrier property. \emph{Compos. Part A Appl.
Sci. Manuf.} 2017;102:314\selectlanguage{english}-321.

(15) Pan, T.; Xu, S.; Dou, Y.; Liu, X.; Li, Z..; Han, J.; Yan, H.; Wei,
M., Remarkable oxygen barrier films based on layered double
hydroxide/chitosan hierarchical structure. \emph{J. Mater. Chem.
A}2015:3;12350\selectlanguage{english}-12356.

(16) Cui, Y.; Kundalwal, S. I.; Kumar, S., Gas barrier performance of
graphene/polymer nanocomposites. \emph{Carbon} 2015;98:313--333.

(17) Petersen, H.; Jakubowicz, I.; Enebro, J.; Yarahmadi, N.,
Development of nanocomposites based on organically modified
montmorillonite and plasticized PVC with improved barrier
properties.\emph{J. Appl. Polym. Sci.} 2015;133:189\selectlanguage{english}-196.

(18) Wang, P.; Wang, H.; Liu, J.; Wang, P.; Jiang, S.; Li, X.; Jiang,
S., Montmorillonite@chitosan-poly (ethylene oxide) nanofibrous membrane
enhancing poly (vinyl alcohol-co-ethylene) composite
film.\emph{Carbohydr. Polym.} 2018;181:885\selectlanguage{english}-892.

(19) Cao, P. F.; Li, B.; Hong, T.; Xing, K.; Voylov, D. N.; Cheng, S.;
Yin, P.; Kisliuk, A. M.; Mahurin, S. M.; Sokolov, A. P., A robust and
elastic polymer membrane with tunable properties for gas
separation.\emph{ACS Appl. Mater. Interfaces} 2017;9:26483\selectlanguage{english}-26491.

(20) Priolo, M. A.; Gamboa, D.; Grunlan, J. C., Transparent clay-polymer
nano brick wall assemblies with tailorable oxygen barrier. \emph{ACS
Appl. Mater. Interfaces} 2010;2:312\selectlanguage{english}-320.

(21) Hagen, D. A.; Lauren, S.; Grunlan, J. C., Controlling effective
aspect ratio and packing of clay with ph for improved gas barrier in
nanobrick wall thin films. \emph{ACS Appl. Mater.
Interfaces}2014;6:22914\selectlanguage{english}-22919.

(22) Song, Y.; Gerringer, J.; Shuang, Q.; Grunlan, J. C., High oxygen
barrier thin film from aqueous polymer/vlay slurry. \emph{Ind. Eng.
Chem. Res.} 2018;57:6904\selectlanguage{english}-6909.

(23) Zhai, X.; Li, Z.; Zhang, J.; Shi, J.; Zou, X.; Huang, X.; Zhang,
D.; Sun, Y.; Yang, Z.; Holmes, M.; Gong, Y.; Povey, M., Natural
biomaterial-based edible and ph-sensitive films combined with
electrochemical writing for intelligent food packaging. \emph{J. Agric.
Food. Chem.} 2018;66,12836\selectlanguage{english}-12846.

(24) Dou, Y.; Xu, S.; Liu, X.; Han, J.; Yan, H.; Wei, M.; Evans, D. G.;
Duan, X., Transparent, flexible films based on layered double
hydroxide/cellulose acetate with excellent oxygen barrier
property.\emph{Adv. Funct. Mater.} 2014;24:514\selectlanguage{english}-521.

(25) Holder, K. M.; Spears, B. R.; Huff, M. E.; Priolo, M. A.; Harth,
E.; Grunlan, J. C., Stretchable gas barrier achieved with partially
hydrogen-bonded multilayer nanocoating. \emph{Macromol. Rapid
Commun.}2014;35:960\selectlanguage{english}-964.

(26) Xiang, F.; Ward, S. M.; Givens, T. M.; Grunlan, J. C., Super
stretchy polymer multilayer thin film with high gas barrier. \emph{ACS
Macro Lett.} 2014;3:1055\selectlanguage{english}-1058.

(27) Xiang, F.; Givens, T. M.; Ward, S. M.; Grunlan, J. C., Elastomeric
polymer multilayer thin film with sustainable gas barrier at high
strain. \emph{ACS Appl. Mater. Interfaces} 2015;7:16148\selectlanguage{english}-16151.

(28) Shuang, Q.; Song, Y.; Floto, M.; Grunlan, J. C., Combined high
stretchability and gas barrier in hydrogen-bonded multilayer nanobrick
wall thin films. \emph{ACS Appl. Mater. Interfaces} 2017;9:7903\selectlanguage{english}-7907.

(29) Priolo, M. A.; Gamboa, D.; Holder, K. M.; Grunlan, J. C., Super gas
barrier of transparent polymer-clay multilayer ultrathin
films.\emph{Nano Lett.} 2010;10:4970\selectlanguage{english}-4974.

(30) Zhao, M. Q.; Zhang, Q.; Huang, J. Q.; Wei, F., Hierarchical
nanocomposites derived from nanocarbons and layered double
hydroxides-properties, synthesis, and applications. \emph{Adv. Funct.
Mater.} 2012;22:675\selectlanguage{english}-694.

(31) Guo, X.; Zhang, F.; Evans, D. G.; Duan, X., Layered double
hydroxide films: synthesis, properties and applications. \emph{Chem.
Commun.} 2010;46:5197\selectlanguage{english}-5210.

(32) He, S.; An, Z.; Wei, M.; Evans, D. G.; Duan, X., Layered double
hydroxide-based catalysts: nanostructure design and catalytic
performance. \emph{Chem.Commun.} 2013;44:5912\selectlanguage{english}-5920.

(33) Zi, G.; Atherton, J. J.; Zhi, P. X., Hierarchical layered double
hydroxide nanocomposites: structure, synthesis and
applications.\emph{Chem. Comm.} 2015;51:3024\selectlanguage{english}-3036.

(34) Wang, Q.; O'Hare, D., Recent advances in the synthesis and
application of layered double hydroxide (LDH) nanosheets. \emph{Chem.
Rev.} 2012;112:4124\selectlanguage{english}-4155.

(35) Dong, S.; Jia, Y.; Xu, X.; Luo, J.; Han, J., Crystallization and
properties of poly(ethylene terephthalate)/layered double hydroxide
nanocomposites. \emph{J. Colloid Interface Sci.} 2018;539:54\selectlanguage{english}-64.

(36) Wang, J.; Pan, T.; Zhang, J.; Xu, X.; Yin, Q.; Han, J.; Wei, M.,
Hybrid films with excellent oxygen and water vapor barrier properties as
efficient anticorrosive coatings. \emph{RSC Adv.} 2018;8:21651\selectlanguage{english}-21657.

(37) Wang, J.; Xu, X.; Zhang, J.; Chen, M.; Dong. S.; Han, J.; Wei, M.,
Moisture-permeable, humidity-enhanced gas barrier films based on
organic/inorganic multilayers. \emph{ACS Appl. Mater.
Interfaces}2018;33:28130\selectlanguage{english}-28138.

(38) Stockton, W. B.; Rubner, M. F., Molecular-level processing of
conjugated polymers.4.layer-by-layer manipulation of polyaniline via
hydrogen-bonding interactions. \emph{Macromolecules} 1997;30:2717\selectlanguage{english}-2725.

(39) Yang, S. Y.; Rubner, M. F., Micropatterning of polymer thin films
with ph-sensitive and cross-linkable hydrogen-bonded polyelectrolyte
multilayers. \emph{J. Am. Chem. Soc.} 2002;124:2100\selectlanguage{english}-2101.

(40) Cho, C.; Xiang, F.; Wallace, K. L.; Grunlan, J. C., Combined ionic
and hydrogen bonding in polymer multilayer thin film for high gas
barrier and stretchiness. \emph{Macromolecules} 2015;48:5723\selectlanguage{english}-5729.

(41) Ji, N. M.; Jun, O. M.; Ho, C. J.; Yu, J. C.; Woo-Jae, K.; Juhyun,
P.; Chang, Y. W.; Yoo, P. J., Layer-by-layer assembled multilayers of
charged polyurethane and graphene oxide platelets for flexible and
stretchable gas barrier films. \emph{Soft Matter.} 2018;35:960\selectlanguage{english}-964.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/1/1}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/2/2}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/3/3}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/4/4}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/5/5}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/6/6}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/7/7}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/8/8}

\end{center}
\end{figure}

\selectlanguage{english}
\FloatBarrier
\end{document}

