Preparation and characterization of covalently bonded PVA/Laponite/HAPI nanocomposite multilayer freestanding films by layer‐by‐layer assembly

Abstract

The layer-by-layer (LBL) assembly technique is an attractive method to make functional multilayer thin films and has been applied to fabricate a wide range of materials. LBL materials could improve optical transmittance and mechanical properties if the film components were covalently bonded. Covalently bonded nanocomposite multilayer films were prepared by employing hydrophilic aliphatic polyisocyanate (HAPI) as the reactive component, to react with Laponite and polyvinyl alcohol (PVA). FT-IR spectra suggested that HAPI reacted with Laponite and PVA at ambient temperature rapidly. Ellipsometry measurement showed that the film thickness was in linear growth. The influences of HAPI on the optical, mechanical and thermal properties of the films were investigated by UV-Vis spectroscopy, tensile stress measurement, DSC and TGA. The obtained results showed that the optical transmittance and mechanical strength were enhanced when the film components were covalently bonded by HAPI. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 00, 000-000 KEYWORDS: covalently bonded; layer-by-layer; nanocomposites; self-assembly; thin films INTRODUCTION The layer-by-layer (LBL) assembly technique is an attractive method to make functional multilayer thin films and has been applied in the fabrication of nanodevice, drug release, and biomimetic materials.1-4 LBL multilayer films are more versatile in many aspects than bulk materials because they have more precisely controlled composition and structure at nanoscale dimensions. 5 Many researchers have investigated freestanding LBL films.6-8 However, the LBL ultrathin film breaks or decomposes easily during the application, which is one of the main shortages that hampers the application of the materials.9 Covalent assembly is an effective strategy for improving the physical or chemical properties of the LBL films.10-12 Another approach is achieved by introducing inorganic materials such as Laponite, montmorillonite and carbon nanotube into the LBL multilayer films. [13][14][15][16] Researchers have employed hydrogen bond, dipolar bond, or electrostatic attraction between polymer and inorganic particles to fabricate nanocomposite LBL multilayer films. 17,18 This type of physical interaction, however, often leads to unstable multilayer films in strong acid, strong alkali or high humidity conditions.

Influence of graphene oxide incorporation and chemical cross-linking on structure and mechanical properties of layer-by-layer assembled poly(Vinyl alcohol)-Laponite free-standing films

“…The role of GO in cross‐linking may be explained using the schematic illustration given in Figure . As shown therein, similar reaction may also occur in case of PVA/Laponite LBL films, since Laponite has also hydroxyl groups in its structure, which can also take part in cross‐linking reaction . However, from the results, it appears that the cross‐linking reaction is more effective when both GO and Laponite are present.…”

“…However, Kotov and coworkers have actually shown the outstanding mechanical performance and potentiality of these films for the first time . Since then numerous attempts have been made in fabricating LBL films using various nanoparticles, carbon nanotubes (CNTs), clays, few layers of graphenes, and graphene oxide (GO) on polymer or polyelectrolyte surfaces with a goal of preparing strong and tough multilayered films. These films generally consist of building blocks of rigid and stiff nanofillers tightly bound with a few nanometre‐thick polymer layers in between, which makes them truly bio‐inspired structure as mentioned earlier.…”

Functional modification of poly(vinyl alcohol) by copolymerizing with a hydrophobic cationic double alkyl‐substituted monomer

“…The peaks at 3067 cm −1 , 1647 cm −1 , and 988 cm −1 correspond to the stretching vibration of unsaturated CH, the stretching vibration of CC, and the bending vibration of CH 2 , respectively, due to the presence of the double bond (CH 2 C). Moreover, the absorption peaks at 3303 cm −1 , 1647 cm −1 , and 1543 cm −1 are ascribed to the stretching vibration of the NH group, the stretching vibration of CO, and the bending vibration of the NH group, respectively, confirming the existence of the amide bond …”

“…Moreover, the absorption peaks at 3303 cm 21 , 1647 cm 21 , and 1543 cm 21 are ascribed to the stretching vibration of the NAH group, the stretching vibration of C@O, and the bending vibration of the NAH group, respectively, confirming the existence of the amide bond. 24 The structures of the HM are further confirmed by 1 H-NMR analysis. The 1 H-NMR spectrum ( Figure 2) exhibits several characteristic peaks, such as the NAH protons (H g ) at 8.6ppm, the CH 2 @CHA region (H k , H l , H j ) at 5.5-6.3 ppm, and the methylene (H h ) attached to the urethane groups at 4.4ppm.…”

Organic Thermoelectric Multilayers with High Stretchiness

“…Functionalized multilayers can be created with a variety of combinations of materials such as quantum dots, biological molecules, dendrimers, and carbon nanomaterials [31][32][33][34]. LbL assembly is mainly a result of electrostatic interaction in most cases, but other molecular interactions between the LbL materials, including hydrogen bonds, coordination bonds, charge transfer, hydrophobic interactions, and the combined interaction of the above forces have been shown to be driving forces to build up multilayer films [35][36][37]. LbL films have been engineered in a diverse range of applications, such as drug delivery, sensing, self-cleaning, super hydrophobic surfaces, separation membranes, and energy storage [38][39][40][41].…”