Introduction
X-ray diffraction has an important role in the study of the particles present in cosmetics as their properties attain the anticipated cosmetic features and also their uptake by the skin (XRD.co). Because cosmetic products are under the regulation of the US Food and Drug Administration, these products are considered safe. On the other hand, the cosmetic industry is self-regulated, and there are many established international cosmetic brands that practice strict quality control during manufacturing. There are also fake products that are not produced under any worth-mentioning controls, and their use can be harmful.
Cosmetics come in many forms, such as lipsticks, face wash soaps, face powders, nail polishes, face creams and anti-ageing creams, sunshades, moisturizers, shampoos, etc. The formulations are in the form of lotions, gels, powders, creams and liquid suspensions, which contain various undissolved solids.
Experimental Detail
XRD provides important information about the components which show the semi-crystalline or crystalline properties. This is a less expensive technique. However, the role of expensive tools and instrumentation cannot be underestimated and must be restored when precise details about the constituents of the sample are required.
X-ray Diffraction is a technique used to study the physical properties, structure and chemical composition of the materials based on the pattern of the diffraction of the sample compounds. It is a non-destructive technique which reveals the amorphous and crystalline proportion of the content. This technique uses an irradiated X-ray beam and does not need dilutions or pretreatment of the sample. The beam is directed to the sample holder or a glass slide containing the powder.
Steps
The faces of the crystal planes of the sample scatter the beams due to constructive interference and give the diffraction pattern. The sample is scanned by the X-ray incident beam over a range of degrees. This takes place by spinning the sample stage at a programmed angular scan rate.
Single crystal diffraction and powder diffraction are the two ways to carry out this technique. In the former, the crystal is used, while in the latter, the amassed of fine crystalline particles is used to get the diffraction pattern by the incident of the x-ray beam (Hideo).
In many fields, including foods, material science, pharmaceuticals, electronics and cosmetics, nanotechnology has brought about a revolution. Nanoparticles are being progressively used to develop the anticipated features in cosmetic products, including lotions, sunscreens, and conditioners.
Theories
Many concepts and theories are used in the X-ray Diffraction technique. One such concept is Bragg’s law, according to which the scattering is concerted at distinct points, and away from these points, the mutual interference results in no remarkable scattering.
X-ray powder diffraction is a theory established by Debye & Scherrer and is an important technique for the characterization of the phases of materials, evaluation of microstructure, and determination of the molecular structure of materials and their quantitative proportion.
For each crystalline plane, scattering according to the Bragg condition is the base for the conventional theory of X-ray powder diffraction. According to this concept, there are enough crystallites in the right orientation to make the pattern observed. This makes it practical in the beginning, using standard instrumentation, and there could be millions of illuminated crystallites at any one time. The orientation distribution of crystallite and the geometry of the instrument will give an idea of the intensities for the scattering peaks.
There are many remarkable differences in the estimated intensities when kinematical and dynamical theories are used, depending on the material. The conventional theory generally does not include the effects of refractive index for powders. However, according to the researchers, the dynamical theory includes them naturally (Fewstera).
References
Fewstera, Paul F. “A new theory for X-ray diffraction.” Acta Crystallogr A Found Adv 70 (2014): 257–282. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4011009/#bb45>.
Hideo, Toraya. “Introduction to X-ray analysis using the diffraction method.” Rigaku Journal 32.2 (2016).
xrd.co. “http://xrd.co/applications-xrd-cosmetics/.” n.d. Applications of XRD-Cosmetics. <http://xrd.co/applications-xrd-cosmetics/>.
