Abdur Rashid, Honorable Head, Department of Chemistry, BUET, for giving me his wonderful support in moving through the academic processes during this M.Sc. I am thankful to all other respected teachers of Chemistry Department of BUET for their support from time to time. I would also like to thank all the clerks and fellows of the Chemistry Department of BUET for their constant help throughout my studies.
I am very grateful to all members of the examiners for their valuable suggestions and insightful comments. But here, composites of polymers prepared with a very small weight percentage of GOBC overcome the disadvantages of the traditionally cross-linked counterparts by improving the mechanical and thermal stability of the polymer composites.
Introduction
Composite
A composite material is a material made from two or more constituent materials with significantly different physical or chemical properties, which in combination give a material with properties that are different from the individual components. The individual components remain separate and distinct in the finished structure, distinguishing composites from mixtures and solid solutions.
Polymer
Full synthetic polymers were developed in the twentieth century, most in the period 1950-1970s driven by chemical industry expansion. The feedstock for polymerization processes is petrochemical, and environmental concerns have led to more recent developments of polymers from renewable resources. Polymeric materials dominate packaging applications and environmental pressures will ensure that recycling and reuse of waste materials will continue to be an important area of development.
Healthcare equipment, medical devices, and drug delivery systems have seen significant use and development of polymeric materials, particularly bioabsorbable systems. Development of biomimetic polymers and analysis of structured molecular architectures has grown as the understanding of natural polymers has increased.
Cross- linked Polymer
Crosslinks can be formed by chemical reactions initiated by heat, pressure, change in pH or radiation.
Hydrogel
- Synthesis of Hydrogel
- Chemically Cross-linked Hydrogel
- Physically Cross-linked Hydrogel
- Properties of Hydrogel
- Swelling Property
- Mechanical Property
- Biocompatibility
- Applications of Hydrogel
Addition and condensation polymerization involves the gradual addition of polyfunctional crosslinking agents with monomeric functional groups. This cross-linking process does not require the presence of ionic groups in the polymer. PVA hydrogels can be formed by physical cross-linking using repeated freeze/thaw methods or chemical cross-linking with glutaraldehyde or epichlorohydrin.
Changing the degree of cross-linking of the desired mechanical property of the hydrogel could be achieved. Therefore, there is an optimal degree of cross-linking to achieve a relatively strong and yet elastic hydrogel.
Graphene
- Applications of Graphene
Reservoirs in the current distribution of drugs; especially ionic drugs, delivered by iontophoresis (see ion exchange resin). Materials that mimic animal mucosal tissue to be used for testing the mucoadhesive properties of drug delivery systems. Graphene's stability is due to its tightly packed carbon atoms and an sp2 orbital hybridization—a combination of the s, px, and pyt orbitals that make up the σ bond.
These bands are responsible for most of graphene's remarkable electronic properties, via the half-filled band that allows electrons to move freely. Ever since its discovery in 2004, graphene has made a profound impact on many fields of science and technology due to its remarkable physicochemical properties.
Graphene Oxide (GO)
- Application of Graphene Oxide
- Electronics Devices
- Energy Devices
- Biosensors
- Biomedical Application
- Water Purification
- Coating Technology
- GO Composite & Paper-like Materials
- Simple Solution Mixing
- Freezing-Thawing Method
- Shaking and Sonication
- In-situ Polymerization
- Addition of Chemical Cross- linkers
- Addition of Metal- ion
- Properties & Application of Graphene Containing Polymer Hydrogels…. 20
- Self- Healing Property
- Stimuli- Responsive Properties
- Shape Memory Properties
- Other Properties
The detailed structure is still not understood due to the strong disorder and irregular packing of the layers. One of the advantages of GO is its easy dispersibility in water and other organic solvents, as well as in various matrices, due to the presence of oxygen functionalities. One of the main areas where GO can be expected to be used is in the production of transparent conductive films after being deposited on any substrate.
The water permeability rate of the membrane is 0.1 mg/min/cm2, and the water diffusion rate is 1 cm/h. Finally, hydrogels are obtained by directed freeze-thaw of mixed solutions after several cycles. Recently, in order to obtain good mechanical properties of hydrogels, the addition of a chemical cross-linker was also used during the synthesis of hydrogels.
Compared to hydrogel with physical interaction, the mechanical strength of chemically cross-linked hydrogels is greatly increased. GO with multiple functional groups on the surface (including carboxyl, oxyhydryl, carbonyl, epoxy group, etc.) can increase the tensile strength of polymer hydrogels to some extent. With the growth of the crack, the entire mesh structure of the hydrogel can be destroyed, which deteriorates its mechanical properties and shortens its lifetime.
In terms of the healing mechanism, self-healing hydrogel can be classified into physical and chemical self-healing hydrogel. This kind of reversible physical cross-linking enables the realization of the self-healing property of polymer-GO nanocomposite hydrogel. Graphene can greatly contribute to improving the mechanical properties, self-healing properties, stimuli-response properties and absorbability of polymer-graphene nanocomposite hydrogel.
Literature Review
- Aims of Current Research
Ji et al., “Bottom-up synthesis of large-scale graphene oxide nanosheets,” Journal of Materials Chemistry, Vol. Prakash et al., “Folding and Cracking of Graphene Oxide Sheets During Deposition,” Surface Science, Vol. Tang et al., “Tough and highly stretchable graphene oxide/polyacrylamide nanocomposite hydrogels,” Journal of Materials Chemistry, Vol.
Tong et al., ―Preparation and characterization of oxidized konjac glucomannan/carboxymethyl chitosan/graphene oxide hydrogel,‖. Sim et al., “Graphene oxide/poly(acrylic acid) hydrogel by γ-ray pre-irradiation on graphene oxide surface,” Macromolecular Research, Vol. Karimi et al., ―Fabrication and mechanical characterization of poly(acrylic acid)/gelatin composite hydrogels reinforced with graphene oxide,‖ Journal of Applied Physics, Vol.
Qi et al., "Synthesis of a graphene oxide-polyacrylic acid nanocomposite hydrogel and its swelling and electroresponsive properties,". Li et al., “Mechanical, thermal and swelling properties of poly(acrylic acid)-graphene oxide composite hydrogels”, Soft Matter, Vol. Karthikeyan et al., "Graphene Oxide/Carbon Nanotube Composite Hydrogels—Versatile Materials for Microbial Fuel Cell Applications", Macromolecular Rapid Communications, Vol.
Hong et al., ―Infrared activation based on bilayer graphene oxide-poly(N-isopropylacrylamide) nanocomposite hydrogels,‖ Journal of Materials Chemistry A, Vol. El-Kady et al., ―Freestanding Composite Hydrogel Films for Superior Volumetric Capacitance,‖ Journal of Materials Chemistry A, Vol. Zhang et al., “One-Step Synthesis of Polyhydroquinone-Graphene Hydrogel Composites for High-Performance Supercapacitors,” Journal of Materials Chemistry A, Vol.
![Table 1.1: Comparison of the tensile mechanical properties of various hydrogels[61]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10877758.0/36.893.327.629.136.338/table-comparison-tensile-mechanical-properties-various-hydrogels-61.webp)
Experimental
Materials and Instruments
- Chemicals & Reagents
- Instruments
Method of Preparation
- Preparation of Oxidized Graphene Oxide (OGO)
- Preparation of GO Based Crosslinker
- Preparation of 2D Crosslinked Poly(acrylic Acid)
Oxidized graphene oxide (OGO) was synthesized from synthetic graphite powder according to Hummers' modified method. After cooling to room temperature, the mixture was diluted with 0.5L of deionized (DI) water and washed overnight. The mixture is then filtered and washed with DI water using to remove residual acid.
Then, 4.5 g of KMnO4 was slowly added with stirring and the temperature of the mixture was kept below 20°C for 2 hours. After further vigorous stirring for 2 days at room temperature, the reaction was quenched by the addition of DI water (140 mL) and 30% H2O2 solution (2.5 mL). The mixture is filtered and washed by repeated centrifugation and filtration, first with aqueous 1M HCl and then with DI water.
Finally, the resulting solid was air-dried and diluted to make an OGO dispersion (0.1 mg/mL). The resulting homogeneous yellow-brown dispersion was tested to be stable for several months and used for further functionalization. The preparation of GO-based 2D cross-linker (GOBC) which is named as acrylic functionalized graphene oxide (AFGO) was similar to that used in some previous studies of the amidation method.
Crosslinked poly(acrylic acid) (PAA) hydrogels were prepared using starting solutions consisting of monomer (AA), crosslinker (GOBC/BIS) and initiator (KPS). PAA-GOBC hydrogels with different GOBC contents (0.025 wt.% and 0.01 wt.%) were also prepared for various characterizations and analyses. In addition, PAA hydrogels crosslinked with N,N'-methylenebis(acrylamide) (BIS) of the same crosslinker concentration (0.05 wt.%, 0.025 wt.%, and 0.01 wt.%) were also prepared to compare the physical and thermal properties with PAA-GOBC.
Sample Characterization
- Fourier Transform Infrared (FTIR) Analysis
- UV/Vis Absorption Analysis
- Field Emission Scanning Electron Microscopy (SEM) &
- Thermogravimetric Analysis (TGA)
- Mechanical Properties Analysis
X-ray energy dispersive spectroscopy (EDS) of GOBC and PAA-GOBC (0.05 wt %) was also performed by the same instrument at that time. The thermal stability of PAA-GOBC (0.05 wt%) and PAA-BIS (0.05 wt%) were studied by a thermo-gravimetric analyzer (TGA) in a nitrogen atmosphere. The image shows the presence of small sheets of GOBC uniformly distributed in the polymer matrix of PAA-GOBC.
A thermogravimetric analysis of the PAA-GOBC-0.05% hydrogel and PAA-BIS-0.05% hydrogel was performed and provides useful information on thermal properties of these materials. But DSC heating thermograms of PAA-GOBC-0.05% and PAA-BIS-0.05% are summarized in the figure. The curve of PAA-GOBC hydrogel exhibits higher Tg and Tm than PAA-BIS which is attributed to the presence of greater intermolecular force and crosslinking in PAA-GOBC hydrogel.
So the DSC graphics clearly illustrate better thermal stability of PAA-GOBC than PAA-BIS. PAA-GOBC gels and PAA-BIS gels differ significantly in their mechanical properties. As can be clearly seen, the tensile strength and modulus of PAA-GOBC are very low compared to the mechanically hardened PAA-BIS.
PAA-BIS hydrogels show a brittle fraction, on the other hand, PAA-GOBC hydrogel behaves like a rubber. The elongations of PAA-GOBC hydrogels are much higher (1492% to 1919%) than those of PAA-BIS hydrogels. The surface morphology of the prepared PAA-GOBC hydrogel is studied by SEM analysis, and the presence of a nitrogen-containing functional group is confirmed by EDS analysis.
The thermal stability of PAA-GOBC and PAA-BIS hydrogels was studied by TGA and DSC analysis, which confirmed the better thermal stability of PAA-GOBC compared to PAA-BIS. In the study of mechanical properties using UTM, remarkable elongation, ductility and toughness of PAA-GOBC hydrogel were found.
Synthesis of GO Based 2D Cross-linker (GOBC )
- Functional Group Investigation by Fourier Transform Infrared
- UV/Vis Absorption Spectra Analysis
- Study of Surface Morphology of GOBC Using Field Emission
- Energy-Dispersive X-ray Spectroscopy (EDS/EDX) Analysis of GOBC … 47
- Study of Surface Morphology of PAA-GOBC Using Field Emission
- Energy-Dispersive X-Ray Spectroscopy (EDS/EDX)
- Thermogravimetric Analysis (TGA) of PAA-GOBC Hydrogel
- Differential Scanning Calorimetric Analysis of PAA-GOBC
- Study of Swelling Kinetics of PAA-GOBC Hydrogel
- Mechanical Properties of PAA Hydrogels
Conclusion
