Research Article www.acsami.org
Facile Fabrication of Multifunctional Hybrid Silk Fabrics with Controllable Surface Wettability and Laundering Durability Fengxiang Chen,†,‡ Huiyu Yang,‡ Xin Liu,‡ Dongzhi Chen,‡ Xingfang Xiao,‡ Keshuai Liu,‡ Jing Li,† Fan Cheng,† Binhai Dong,† Yingshan Zhou,‡ Zhiguang Guo,† Yong Qin,§ Shimin Wang,*,† and Weilin Xu*,‡ †
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, and Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062, PR China ‡ State Key Laboratory of New Textile Materials and Advanced Processing Technologies, Wuhan Textile University, Wuhan 430200, PR China § State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, PR China S Supporting Information *
ABSTRACT: To obtain a hydrophobic surface, TiO2 coatings are deposited on the surface of silk fabric using atomic layer deposition (ALD) to realize a hierarchical roughness structure. The surface morphology and topography, structure, and wettability properties of bare silk fabric and TiO2-coated silk fabrics thus prepared are evaluated using scanning electron microscopy (SEM), field-emission scanning electron microscopy (FESEM), scanning probe microscope (SPM), X-ray diffraction (XRD), static water contact angles (WCAs), and roll-off angles, respectively. The surfaces of the silk fabrics with the TiO2 coatings exhibit higher surface roughnesses compared with those of the bare silk fabric. Importantly, the hydrophobic and laundering durability properties of the TiO2-coated silk fabrics are largely improved by increasing the thickness of the ALD TiO2 coating. Meanwhile, the ALD process has a litter effect on the service performance of silk fabric. Overall, TiO2 coating using an ALD process is recognized as a promising approach to produce hydrophobic surfaces for elastic materials. KEYWORDS: atomic layer deposition, TiO2, hydrophobic, durable, service performance
1. INTRODUCTION
which are greatly appreciated by a more nitpicking and demanding consumer market. Inspired by the lotus leaf, scientists have made impressive efforts to explore the physical and chemical mechanisms of superhydrophobicity in nature and fabricate primary superhydrophobic productions, such as oil/water separators, waterproof textiles, and microfluidic channels.2−7 Superhydrophobic surfaces are those on which the water contact angles (WCAs) are greater than 150° and the roll-off angles are lower than 10° or those on which water on the hydrophobic surfaces either does not adhere or only weakly adheres.8,9 It is well-known that superhydrophobic surfaces are governed by a low surface-freeenergy chemical structure combined with a particular surface roughness because surface roughening contributes to superhydrophobicity by trapping air below water droplets.10 Therefore, modification of the surface chemistry to achieve superhydrophobic surfaces is always needed in conjunction
With the deepening of research on superhydrophobic surfaces, flexible substrates such as textiles have recently attracted great interest because of their high surface areas as well as the abundance and inexpensiveness of the raw materials, easy largescale-area production, and primary potential application. Of all of the principal clothing fabrics, silk fibers and fabrics are the most favored high-quality textile materials because of their elegant appearance, softness, superior wear comfort, warmth, biodegradability, skin-friendliness, renewability, and promoted use in sustainable design compared with conventional chemical fibers.1 However, the abundant hydrophilic groups, such as hydroxyl, carboxyl, and amino groups, on the surface of silk fibers and fabrics make the fabrics absorbent and easily stained by dirt, rainwater, and debris. Moreover, silk fabrics inherently exhibit certain deficiencies such low thermal stability, weak UV protection capability, and high flammability. These defects greatly contribute to the limited application of silk fibers and fabrics. Therefore, great efforts have been made to develop high-value-added textiles, such as hydrophobic silk fabrics, © XXXX American Chemical Society
Received: November 25, 2015 Accepted: February 2, 2016
A
DOI: 10.1021/acsami.5b11420 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces
Figure 1. Schematic illustration of the fabrication of durable and robust hydrophobic silk fabrics using ALD process.
nately, it is extremely difficult to form good interfaces between flexible substrates and inorganic coatings, resulting in poor adhesion force and poor durability.28 Therefore, there is a high demand to find a simple route for preparing inorganic coatings on complex textile topologies to enhance effectively the hydrophobicity under moderate operation conditions. One promising approach to overcome these restrictions imposed on the flexible substrate is the use of atomic layer deposition (ALD), which has been demonstrated to produce superhydrophobic surfaces with exceptional properties.10,29−34 Atomic layer deposition (ALD) is a surface-controlled LBL coating method for atomic-layer control and conformal deposition based on sequential, self-limiting gas−solid reactions, which is suited to produce conformal and uniform coatings of inorganic or inorganic−organic thin films with low impurity content for surface modification or replicas of those structures on flexible substrates.33,35 The ALD process consists of two time-separated half reactions. In the first half reaction, the substrate is exposed to a precursor vapor that forms a monolayer or submonolayer of the precursor on the surface of the substrate, followed by the use of a purge gas to remove the excess precursor from the vapor phase. In the second half reaction, the reactant gas is subsequently pulsed onto the substrate, where it reacts with the adsorbed precursor layer to form a layer of the target film-forming compound. During such a completed cycle, only one molecular layer is deposited on the surface of the substrate, and these cycles are repeated until a
with surface roughness, which can significantly expand the range of potential applications.11−13 Feng et al. reported that inorganic metal oxides exhibit better mechanical durability than organic materials.14 Therefore, inorganic coatings on fibers and fabrics are capable of meeting some of these objectives.15 In all the inorganic metal oxides, titanium dioxide (TiO2), as an important photofunctional material, has recently received attention. TiO2 is a type of distinguished photocatalytic and is widely utilized as a self-disinfecting, biocompatible, corrosion resistant, and self-cleaning material16,17 because of its excellent photochemical stability, low cost, and nontoxicity.18 Most importantly, superhydrophobicity in TiO2 coatings can also be achieved by forming a special morphology such as a lotus-leaf morphology. Therefore, TiO2 might be an ideal material for fabricating hydrophobic silk fabrics. Currently, various inorganic coating methods and techniques, such as lithography, layer-by-layer (LBL) assembly, solution immersion, and sol−gel methods19−27 have been adopted to prepare superhydrophobic surfaces by forming hydrophobic coatings. However, in many cases, the approaches mentioned above are not appropriate for textiles because of the high reaction temperature involved, weak chemical bond adhesion strength between the particles and fabrics, and poor mechanical durability and thermal stability. In addition, the uniformity of conventional coating processes on fiber and fabric surfaces is often not ideal, resulting in detrimental variations in material performance, which can severely limit applications.20 UnfortuB
DOI: 10.1021/acsami.5b11420 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces Table 1. Structure and Performance Parameters of the Bare Silk Fabric and TiO2-Coated Silk Fabrics
sample bare silk fabric TiO2-400 TiO2-800 TiO2-1200
add-on amount (%)
thickness (mm)
weight (g/m2)
whiteness index
0.148
63.3
57.0
0
0.150 0.154 0.156
70.7 76.5 81.2
59.3 62.5 64.2
3.52 5.67 7.72
drop absorption time (s)
handle properties
mechanical properties
bending length (cm)
rigidity
tensile strength (N)
elongation at break (%)
air permeability (mm/s)
WCRA (°)
DCRA (°)
UPF
1.95
0.469
174
22.3
138.19
109.8
74.7
11.6
1.98 2.05 2.09
0.548 0.659 0.741
177 201 248
14.8 17.1 18.2
128.69 125.53 121.84
108.5 105.2 99.7
74.6 69.2 65.0
47.1 51.8 56.9
0.28 5964 6768 7752
the fabrication of durable and robust hydrophobic silk fabrics is exhibited in Figure 1. As can be seen from Figure 1, the ALD process for TiO2 deposition with TIP and H2O can be separated into two half reactions: (1) TIP is introduced on the silk fabric surface and reacts with the −OH that forms a −OCH(CH3)2 surface; (2) water is introduced and reacts with the −OCH(CH3)2 that forms a −OH surface.40−43 Details are described as follows:
layer with a specific thickness is achieved. Because no gas-phase reaction occurs, the target film is grown layer by layer on the substrate, such that the thickness of the deposited film can be accurately controlled by the number of times the process is repeated.35−38 Using this technique, a dense inorganic or inorganic−organic layer can be grown on a wide variety of flexible substrates at relatively low temperatures (
