13 - Polymer nanocomposites for biomedical applications

Carbon nanotubes (CNTs) based polymer composites have variety of engineering applications (electromagnetic shielding, antistatic coatings, high-strength low-density corrosion-resistant components, lightweight energy storage and many more); due to their excellent mechanical, electrical, chemical, magnetic, etc. properties. In the polymer nanocomposites CNTs are dispersed in the polymeric matrix. However the dispersion may be uniform or may not be uniform. The biggest challenge is the effective dispersion of individual CNTs in the polymer matrices, as CNTs tends to form clusters and bundles due to strong van der Waals’ forces of attraction. The aggregated structure continue until physical (Mechanical) or chemical modification (Encapsulation/surface modification) of CNTs. Few modification methods such as vigorous mixing of the polymers damages CNTs structure, and may hinder their properties. But these problems can be overcome by mechanical or chemical modification of CNTs surfaces. In the chemical modification, the modifier or the long tail surfactant may encapsulate and/or partially wrap the CNTs surfaces. In this review, recent work on CNTs based polymer nanocomposite is carried out with few modifiers/encapsulating agents. Incorporation of CNTs in polymer matrix changes the performance properties such as tensile strength, tensile modulus, elongation at break, toughness, Dynamic mechanical thermal analysis (DMTA), etc. The phase morphology of the composite materials throws light on the properties of CNTs based polymer nanocomposite. Moreover phase morphology may be directly correlated with the behavior of the material, hence reviewed here through transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Furthermore review is also carried out on the non-isothermal crystallization (DSC) and rheology of CNTs polymer nanocomposite.

The average pull-out force and interaction energy of polyethylene (PE) cross-linked functionalized carbon nanotubes (cfCNTs) embedded in polymer matrices (PE-cfCNTs@polymers) was studied using molecular dynamics (MD) simulations. Accordingly, the pull-out process of PE-cfCNTs from inside polymer matrices, i.e., Aramid and PE, was performed under displacement control. The results obtained were compared with those of pure carbon nanotube (CNT) incorporated into polymer matrices (pure CNT@polymers). The influence on the pull-out force and interaction energy between the CNT and polymer of the structure of polymer matrices, the weight percentage and two types of distribution patterns of cross-linked PE chains, namely mapped and wrapped, was investigated. The results indicate that the structure of the polymers and distribution patterns of cross-linked PE chains strongly affect important parameters related to interfacial properties. The average pull-out force of mapped and wrapped PE-cfCNTs@polymers increases as the weight of attached PE chains on the CNT surface increases. The effect of wrapped structures on increasing the pull-out force is greater than that of the mapped configurations. Also, the PE-cfCNTs@polymers show higher average pull-out forces than those of their pure counterparts. As the CNT pulls out from the polymer matrix, an approximately linear reduction in the absolute value of interaction energy with the pull-out displacement is observed. However, this trend is changed to some extent by imposing instability through the wrapped PE-cfCNTs.

BASF forecasts colour trends

Directional alignment of carbon nanotubes in polymer matrices: Contemporary approaches and future advances

PSS)/nanographite nanocomposite (NC) films prepared by the solution blending method were irradiated with SHI (Ni ion beam, 80 MeV) at a fluence range of 1 × 10(10) to 1 × 10(12) ions/cm(2). XRD studies revealed that ion irradiation results in delamination and better dispersion of NGPs in the irradiated nanocomposite films compared to unirradiated films, which is also depicted through SEM, AFM, TEM, and Raman studies. In the irradiated polymer nanocomposite films, the conformation of PEDOT chains changes from coiled to extended coiled structure, which, along with homogeneously dispersed NGPs in irradiated NCs, shows an excellent synergistic effect facilitating charge transport. The remarkable improvement in conductivity from 1.9 × 10(-2) in unirradiated NCs to 0.45 S/cm in irradiated NCs is observed with marked improvement in sensing the response toward nitroaromatic vapors at room temperature. The temperature induced conductivity studies have been carried out for PSS/nanographite NCs to comprehend the charge transport mechanism in NC films using the 3D Mott variable range hopping model also. The study reveals SHI as a novel method, addressing the challenge associated with the dispersion of NGPs within the polymer matrix for their enhanced performance toward various applications.

Controlling the spatial morphology of the nanorods (NRs) in a polymer matrix and understanding the structure-property relationship are crucial for fabricating high-performance polymer nanocomposites (PNCs). By employing molecular dynamics simulations, we systematically studied the structural and mechanical properties of NR filled PNCs. The simulated results showed that the NRs gradually self-assembled into a three-dimensional (3D) network upon increasing the NR-NR interaction strength. The generated 3D NR network transferred loads along the NR backbone, differing from the well dispersed system which transfers loads between NRs and nearby polymer chains. Increase of the nanorod diameter or NR content further enhanced the PNCs by improving the NR network integrity. These findings provide insights into the reinforcement mechanism of NRs toward polymer matrices and provide guidance for designing PNCs with excellent mechanical performance.

Structure and Drug Release in a Crosslinked Poly(Ethylene Oxide) Hydrogel

Polymer nanocomposites with carbon nanotubes (CNTs) have become very attractive class of materials for numerous engineering applications since carbon nanotubes exhibit a high aspect ration, unique electrical, mechanical and structural properties. Functionalization of CNTs offer new potentials for other technical challenges of the polymer based nanocomposites associated with their specific interactions. A biocompatible polymer matrices PMMA and PCL were used to provide good interfacial bonding between carbon nanotubes. MWCNT (d=30-50 nm, purity>95%) were used for preparation of polymer based nanocomposites with 0.2, 0.5 and 1.0 % w/w MWCNTs content. PMMA-based nanocomposites were prepared via the mixing of the MWCNT and polymer in a dichloromethane solution for 24 h, while for the PCL-based nanocomposites as a solvent tetrahyrofurane was used. Functionalization of the CNTs was performed in acid (HNO3) and alkali (NH4OH+H2O2) medium as well as by additional thermal oxidation at 490°C. Characterization of the nanocomposite films was performed by DSC, TGA, WAX, FTIR and SEM. The obtained results have shown that introducing MWCNT into polymer matrix significantly changes have been found in the properties of the obtained nanocomposites.

Nowadays special attention is given to the so-called "smart-materials" or "intellectual" materials, which have the ability to purposefully change their physical and physical-chemical properties depending on changing external conditions. Сonductive conjugated polymers - polyaniline (РАNi) and its derivatives may alter their properties in response to external action - exhibit sensory sensitivity, electrochromic, thermochromic and solvachromic effects. When creating РАNi composites with industrial polymer matrices, an important issue is to determine the physical and mechanical properties, in particular, of microhardness as a material strength characteristic. Composite samples were obtained by the method of thermal pressing of highly dispersed powders of conductive polymers dispersed in polymer matrices. The mechanical properties of the composites were studied by the method of measuring microhardness and boundary microhardness on a Heppler consistometer. The determination of the electrical conductivity of the composites in the molded samples was determined by the standard 2-contact method at a temperature T = 293 K. The influence of the acid doped polyaniline (РАNi) as an conductive polymer filler оn on the microhardness of composites with polymer matrices of different structure (polyvinyl alcohol (PVA), polymethylmethacrylate (PMMA), polybuthylmethacrylate (PBMA), epoxy resin ED-20) was studied. It is found that the nature of the interaction between the polymer matrix and the conductive polymer filler depends on its content and the structure of the matrix, which is manifested in the growth of microhardness for composites PBMA – РАNi and ED-20 - РАNi and its reduction for composites PVA– РАNi at the contents of the filler 5-20 %. The dielectric polymer matrix preserves the properties inherent in both high polymers (high elasticity, thermoplasticity) and the semiconductor nature of the electrical conductivity inherent in the conjugated polymers. The value of the specific conductivity of the composites obtained well correlated with changes in microhardness, which is a confirmation of the enhancing or loosening nature of the interaction between the polymer matrix and the conductive polymeric filler.

Magnetoactive polymer compositesЁ— polymer matrices with embedded magnetic micro- and/or nanoparticlesЁ— belong to the class of «smart» materials and currently attract significant fundamental and practical interest. This article focuses primarily on magnetoactive elastomers (MAEs) based on chemically crosslinked polymer systems, research on which has been conducted at the Physics Faculty of Moscow State University since the late 1990s. A definition of MAEs is provided, and the properties of their main components — the polymer matrix and magnetic particles — are described. An overview is given of the physical phenomena observed in these materials when an external magnetic field is applied. The influence of the material composition on its magnetic response is discussed in detail, with an emphasis on magnetomechanical properties, which are most critical for practical applications. The results of recent studies related to the synthesis of new matrices for MAEs, the influence of the shape and distribution of magnetic particles in the polymer matrix, as well as contemporary theoretical approaches to describing the behaviour of MAEs in an external magnetic field are analyzed. Finally, the prospects for further advancement in the development of magnetoactive polymer materials and their practical applications are discussed.

We highlight the significance of capillary pressure in the directed assembly of nanorods in ordered arrays of colloidal particles. Specifically, we discuss mechanisms for the assembly of carbon nanotubes at the interstitial sites between latex polymer particles during composite film formation. Our study points to general design rules to be considered to optimize the ordering of nanostructures within such polymer matrices. In particular, gaining an understanding of the role of capillary forces is critical. Using a combination of electron microscopy and atomic force microscopy, we show that the capillary forces acting on the latex particles during the drying process are sufficient to bend carbon nanotubes. The extent of bending depends on the flexural rigidity of the carbon nanotubes and whether or not they are present as bundled ensembles. We also show that in order to achieve long-range ordering of the nanotubes templated by the polymer matrix, it is necessary for the polymer to be sufficiently mobile to ensure that the nanotubes are frozen into the ordered network when the film is formed and the capillary forces are no longer dominant. In our system, the polymer is plasticized by the addition of surfactant, so that it is sufficiently mobile at room temperature. Interestingly, the carbon nanotubes effectively act as localized pressure sensors, and as such, the study agrees well with previous theoretical predictions calculating the magnitude of capillary forces during latex film formation.

This paper reports the effect of three different polymer matrices (PVP, PMMA and PVK) and Ag doping on the photo-sensitivity of CdSe polymer nanocomposites. The results reveal that the photoconductivity is high for linear chain polymer nanocomposites as compared to aromatic ones with decreasing trend as: CdSe-PMMA > CdSe-PVP > CdSe-PVK. The large substituents or branches along the polymer backbone hinder the stacking sequences in CdSe-PVK nanocomposites resulting in lowest photoconductivity. On contrary, CdSe-PVK nanocomposite exhibit highest photosensitivity. The reason behind it is the low value of dark conductivity in CdSe-PVK nanocomposite and photoconductive PVK matrix. With Ag doping, no considerable effect on the value of photosensitivity has been observed. The obtained results indicate that the photo-conducting properties of these polymer nanocomposites can be tuned by using different polymer matrices.

Polymer nanocomposites for optical applications require high optical transparency at high filling ratios of nanoparticles. The nanoparticles provide optical functionality but unfortunately have a strong tendency to aggregate in polymer matrices leading to strong turbidity and reduced optical transmission, particularly at high filling ratios. We report a general route to nonaggregated highly filled, optically transparent polymer nanocomposites. It is based on using nanoparticles that have been coated with polymers forming spherical brushlike layers providing thermodynamic miscibility with the polymer matrix over the complete range of nanoparticle volume fractions. The polymers are attached via a versatile ligand exchange procedure which enables to prepare a wide range of optically transparent polymer nanocomposites up to weight fractions of 45%. This is demonstrated for a broad range of metal and semiconductor nanoparticles in optically transparent polymer matrices relevant for selective light/UV absorptio...

Carbon nanotubes (CNTs) are increasingly attracting scientific and industrial interest because of their outstanding characteristics, such as high Young’s modulus and tensile strength, low density, and excellent electrical and thermal properties, which make them ideal fillers for polymer composites. The incorporation of CNTs into polymer matrices greatly improves the electrical, thermal, and mechanical properties of the materials. Surface modification of CNTs can be carried out in order to improve their processibility and dispersion within the composites. Homogeneous dispersion of CNTs in a polymer matrix plays a crucial role in the preparation of polymer composites based on interfacial interactions between CNTs and the polymer matrix. This chapter aims to review the surface modification of CNTs, the processing technology, and improvement of properties of CNT-reinforced polymer composites.

The potential of nanocomposite-based coatings for corrosion protection of metals: A review