Material Characterization Of Fiber Reinforced Plastic Using Raman Spectroscopy/PL/AFM Techniques

Fundamentals of Material Characterization

Based on the ‘hot topic’ investigated in Assessment 1, students are now required to apply their new understanding of advanced characterisation techniques to critically evaluate the appropriateness of a particular characterisation technique or combination of techniques.

Material science is a broad discipline that involve studying and application of materials in different sectors of developments. This discipline has found applications in automotive sectors, construction sectors, textile and even medicine sectors. Material science for many years have advanced and nowadays different techniques are used to detect and analyzed material properties for different applications [15]. The future of material science lies on the foundations of the material characterizations. Material characterization is a field in material science that is committed to analysis of materials to understand the chemical, physical and mechanical properties of materials. Several techniques exist for material characterization. The choice of a particular method depends on the information needed and the nature of the material [16]. This paper core aim is to discuss the hot topic of material characterization of fiber reinforced plastic (FRP) using Raman spectroscopy/PL/AFM techniques. SWOT analysis is applied to paint out the clear perspectives of justification, strengths, limitations, usability and improvements of this technique in the FRP advanced characterization.

Fiber reinforced plastic consist of fiber mixed with polymer matrix made of carbon, asbestos, basalt, aramid and wood [12]. Any technique of choice should be able to address and analyze the properties of composite materials being analyzed.

Raman spectroscopy, Atomic Force Microscopy, and photoluminescence are light microscopy material characterization techniques that are used to probe both organic and inorganic materials. The information from these techniques is used to evaluate the chemical, molecular structure, bonding, stress/strain and environmental effects of the materials. These are the properties of interest in the FRP material [9].

The techniques are very useful in the wide range of samples including solids, liquids, and gases. Over the years the applications of these techniques has progressed because they are nondestructive and the scale at which the information is obtained varies to accommodate different needs. FRP is made up of composite materials that are chemically bounded together [3, 7, and 9]. To specifically understand the nature and strength of the molecular bonds in heterogeneous materials like FRP, correlative characterization techniques are the most suitable to be adopted.

AFM technique simultaneously acquire the topographical information. Raman and PL technique gives the chemical information of the FRP. Chemical bonding information provides the details on the effectiveness of the fabrications of the process. These provide many advantages compared to other techniques like SEM. These techniques does not need any special treatments to the sample and also provide very high resolution [1].

Properties and Applications of Fiber Reinforced Plastic

AFM has been widely used to provide high resolution 3D images of the surface both semiconductors and insulating materials at different scales. It has been used to indicate surface roughness, microstructural studies, defect/failure studies, surface polishing, and phase separation in polymers, critical dimension measurements, stiffness, adhesion and frictions in the materials. Atomic force microscopy offers precise advantages in excess of other microscopies for the reason that it provides mechanical interactions among the tip and sample [6].  All these are also the properties of interest in the FRP, hence justification for adopting this technique over the others.

Raman microscopy needs no sample preparation for analysis of fiber samples [6].  It is useful for chemical identifications, characterization of structures, effects of bonding, environment and stress on a sample. The technique has high sensitivity, low noise, signal linearity. This technique can also be used to analyze the very tiny quantity of material (less than 1 micrometer in dimension). Aramid and carbon shows a vibrational modes in Raman that indicate a change in frequency with applied stresses and strain. This is the same case in the polymers like polypropylene fibers. This form a justification why this technique is necessary for the fiber characterizations. When Raman/AFM/PL are combined, multiple roles can be performed easily [9].

Having this in mind, Confonical Raman/PL/AFM combination provide the best suitable technique to characterize Fiber reinforced plastics. The technique exploit all the angles necessary for the FRP properties and applications in the industry [17].

AFM gives three key abilities namely, measurement of force, imaging, and the manipulation.  AFM as it has been highlighted above allows for 3D characterization of material with sub nanometer resolution. A resolution of up to 500nm x 500nm phase image can be achieved using this technique.  This provide a number of advantages over the other methods. To start with, it is possible to characterize the material that are 0.5nm thickness and larger. In our case FRP, contains a thicker layer that can only be suitably analyzed using this technique [13]. Parameters analyzed in this case are surface roughness, microstructural studies, defect and failure studies, surface polishing, and phase separation in polymers, critical dimension measurements, stiffness, adhesion and frictions in the materials [4].

Secondly, the image produced are excellent for contrast where contrast is based on the material.  Technique provide an excellent contrast, sensitivity and discrimination based on material nature of polymers. It aids in the scrutiny of mechanical nature of materials such as adhesion and stiffness. Reinforcement of FRP depends on the stiffness of the boundaries between the composite materials [17]. This information is clearly indicated through the use of this technique of material characterization.

Techniques used for Material Characterization

Thirdly, this technique does not require any post processing of the results. The results are obtained in refined form and the only thing needed is the interpretation and analysis to understand the nature and properties of the material being analyzed. As highlighted previously, the technique does not needs any sample preparation aside from cryomicrotoming. No any staining is required as in the case of other techniques like SEM and TEM. Atomic Forced Microscopy apply sharp tip to analyze the material properties through scanning external topography through extremely extraordinary magnification powers of up to x1000000 compared to other microscopic techniques [12]. It gives this technique an upper hand in production of 3D images with higher resolution powers.

Combination of Raman with other techniques like PL has a number of benefits. No necessity of sample preparation before analysis is required.  There is no chemical or physical conditioning of sample is needed. The technique is nondestructive and provide a contactless measurements. This technique is very rapid and convenient in application of the FRP materials. Nondestructive properties of Raman enable the sample to be treated for another analysis after the Raman exposure. Non-contact of the sample during the analysis ensure very minimal contamination of the sample during the analysis unlike the other techniques [5].

Technique is very sensitive. The resolution are very high in the order of micrometers. Only very small amount of sample is needed in the analysis, hence this technique saves on the time and resources. The method is very rapid and the results are obtained inside a very short lapses of time in a matters of minutes.

Combination also is very ideal for both organic and inorganic material. This is a unique feature because FRP composite materials falls in this categories. The intensity of spectral features is scientifically proven to be directly proportional to particular concentration of species. Another benefit of this combination of techniques is the remote analysis realization. Fiber optic can be used to analyze material over a long distant of around 100meters far away from the Raman analyzer [11].

Photoluminescence in the form of terahertz radiation provides a number of advantages when used with other techniques like Raman and AFM in material characterization. To begin with, radiations penetrate through wide varieties of dielectric materials including fabric, paper, plastics leather and wood. FPR falls narrowly under this category hence this technique is applicable. This technique is also non-ionizing and has very minimal effects on the human body unlike the use of x-rays that are very detrimental to the health of the human beings and biological tissues [18]. These properties make photoluminescence suitable for the applications in the characterization of Fiber reinforced plastics.

Advantages of Raman/PL/AFM Combination

AFM tip model interactions frequently analysed in interaction mode is not clearly appropriate for detection of a lone atom, trivial molecules or faults laterally the surface of the characterization materials. Another drawback is provision of a single scan image size. The image is of the order of 150x150 micrometers [9]. When compared to other techniques, this image is of low quality and the technique can be enhanced by improving the quality of the image. Another disadvantages associated to this technique is the slow scanning time. Comparing this method to other techniques, measures has to be taken to enhance the time of scanning. Slow scanning time can leads to thermal drifts on the sample, hence giving false information on the properties of the material being analysed [14].  The method involve the use of very small amount of samples. This is a challenge for the use in the sample that degenerate with time. Measuring of corrosion in materials can also be very difficult since there is likeliness of increase in sizes hence limitations because the technique require only small amount of samples.

Raman technique on the other hand poses some limitations in the mode of applications. The spectroscopy technique is associated to sensitivity challenges. Technique capabilities are poor and an insufficiency of 10^-6 of preliminary photons is non-elastically dispersed. This means that other gadgets and equipment like detectors, lasers and filters have to be incorporated in the equipment for maximum results orientation [12]. This in other words leads to increase in the costs of performing the material characterizations.

Secondly, Raman is used together with fluorescence to generate the signals. This attracts other limitation linked to this application. During the analysis, there exist a competing process between the Raman scattering and fluorescence signals. This competing scenario in the process delay the efficiencies of the analysis. The solution to this problem is the selection of the appropriate wavelengths with lower photon energy.  As the wavelength excitation became shorter, Raman scattering intensity increases and fluorescence become less troublesome as the laser wavelength increases in the size [13]. The problem with fluorescence can also be overcome by adopting a spectroscopy with more than one or several lasers.

Another challenge of this method is the selectivity of the material. This technique can be used in a wide variety of materials. However, some metals and alloys are not Raman active hence cannot be characterized using this technique [8].

Limitations of AFM and Raman Techniques

PL has shown tremendous progress in its applications. However, a number of drawbacks are pulling this progress behind. To start with, detection of radiations is sometimes difficulty since blackbody radiation in the ambient temperatures is strong on the terahertz frequencies, hence posing a challenge in the applications. This calls for the improvements to the ratio terahertz images can be able to detect. This solution is however, applicable only for the static materials. The atmospheric attenuation of the radiation is much more lethal than in the spectral regions like infrared radiation and visible light regions. This technique has also the limitations of selection of particular optics in the imaging systems. Lens in PL are rarely applied extensively in the terahertz system for the reason that lack of suitable materials and anti-reflection coatings effective over extensive series of frequencies [1 and 3]. Complications in the construction of progressive lenses are related with one of the best important curbs of THz methods, which is measurement resolution.

The major improvements in the techniques used for FRP characterization are associated to the advancement of the technology. As we move deeper to the digital era, more sophisticated technology and gadgets are being incorporated to Raman, AFM and PL for better characterization of the materials. Recently, Raman has been made with capabilities to characterize material with little or no noise at all. Major drawbacks associated to Raman are the size of the sample, speed, cost and self-conflicting with the fluorescence signals [5].

Raman provides a very small space for sample hence holding only a very small amount of the sample. Improvement can be made by increasing the size of the probe to increase the amount of the sample holding. This is the same case to AFM technique [11].

Another improvement associated with the Raman/ AFM is the quality and size of the image. The scanning image is of the size 150 x 150 micrometer. This image is of low and poor quality and it is not compatible to the increasing adoption of the new technology and software. 

Speed enhancement is another improvement that ought to be done in Raman and AFM. The results of material characterization is obtained after some few minutes. This speed considering the era we are in should be enhanced to few seconds or even milliseconds [16].

Improvements can also be on the material characterization compatibilities. Some materials and alloys are not compatible with Raman, hence the limitations is based on some specific materials. The equipment should be made in such a way they can be changed depending with the material being analysed at a given time.  Generally, Raman and AFM can be enhanced by increasing the speed and capacity of the functionalities. We are in the world where speed is very important and this quality should be incorporated to all equipment’s to enhance the performance [18].

PL on the other hand can be enhanced by increasing its compatibilities with Raman technique and other techniques for provision of the images of high quality. This device should be able to measure the density and weight of the material. These qualities of materials are very essential and they should not be analyzed separately. An equipment should be designed to measure this properties simultaneously [12].

There are also other problems associated to the PL like complications in the construction of progressive lenses are related with one of the best important curbs of THz methods, which is measurement resolution. This should be improved by adopting alternative ways of constructing the progressive lenses rather than depending on one technique in the construction [13].

Conclusion

In the contemporary world, material science has been tremendously accepted and adopted by all walks of sectors of development. Material science contribute to the high GDP of any country because economy is driven by materials and everything including the clothes, vehicles, building, pharmaceutical products and even roads all involve handling and characterizing materials effectively. With all these applications of materials, proper characterization and investigation of material for the best qualities is an alarming call in the field of material science [16]. Different techniques as it has been discussed effectively exist for material characterization. The nature and information needed from the material are what dictate what method to use and what to avoid. Raman/PL/AFM are the suitable correlative techniques used in this report. The technique were chosen for their suitability in the characterization of the Fiber reinforced plastic [12]. Material characterization exist to avoid the challenges associated to the use of defects materials that later brings catastrophic problems in our society. The future of material science lies on the foundation of the material characterization. Materials of good qualities means the building will not fall, the roads will last for a long period without potholes, the vehicles will be durable, pharmaceutical field will be  able to produce good medicine and generally the world will move on well.

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